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Effect of Benazepril on Survival and Cardiac Events in Dogs with Asymptomatic Mitral Valve Disease: A Retrospective Study of 141 Cases

Authors


Corresponding author: Valérie Chetboul, DVM, PhD, Dipl. ECVIM-CA (Cardiology), Unité de Cardiologie, Ecole Nationale Vétérinaire d'Alfort, 7 avenue du Général de Gaulle, 94 704 Maisons-Alfort, cedex, France; e-mail: vchetboul@vet-alfort.fr.

Abstract

Background: Angiotensin-converting enzyme inhibitors (ACEIs) improve quality of life and extend the life span of dogs with naturally acquired ISACHC class II-III congestive heart failure (CHF). However, their effects on asymptomatic heart disease remain controversial.

Hypothesis: Benazepril (BNZ), an ACEI, could have beneficial effects at the asymptomatic stage of degenerative mitral valve disease (MVD).

Animals: Dogs with ISACHC class Ia MVD and moderate-to-severe mitral regurgitation (MR) assessed by the color Doppler mapping technique at entry (Day 0) were retrospectively included.

Methods: Dogs were assigned to the treated group (BNZ group) if they received BNZ (and no other cardiac medication) from Day 0 or to the untreated group (UT group) if they did not receive any cardioactive treatment until occurrence of CHF.

Results: A total of 141 dogs were included in the study, 66 in the BNZ group (dosage: 0.30 ± 0.13 mg/kg) and 75 in the UT group. In the population (n = 93) including all breeds except Cavalier (CKC) and King Charles Spaniels (KC), median survival time to all causes of death in the BNZ group (n = 34, 3.3 years) was significantly longer than in the UT group (n = 59, 1.9 years) as was time to cardiac event (P < .05). Conversely, no effect of the BNZ treatment was observed in the CKC and KC population.

Conclusions and Clinical Relevance: BNZ had beneficial effects in asymptomatic dogs other than CKC and KC affected by MVD with moderate-to-severe MR. Breed distribution should be taken into account for interpretation of clinical trials performed in dogs with cardiac disease.

Angiotensin-converting enzyme inhibitors (ACEIs) represent one of the most commonly used categories of drugs in humans and dogs with cardiac disease. Over the last 10 years, the efficacy and long-term tolerability of ACEIs have been demonstrated in dogs through clinical trials involving large numbers of animals.

Several prospective, double-blinded, multicenter, and randomized studies have shown that ACEIs improve quality of life, increase exercise tolerance, and extend life expectancy in dogs with naturally acquired congestive heart failure (CHF) because of degenerative mitral valve disease (MVD) and dilated cardiomyopathy, which are the 2 most common causes of canine CHF1–6 (see Lefebvre et al7 for review). However, very few studies have focused on the effects of ACEIs on patients with asymptomatic heart disease.8–12 One of the most documented and agreed upon aspects of ACEIs obtained from these studies is their short- and long-term tolerability in asymptomatic canine MVD. For example, Atkins et al8 demonstrated that long-term (up to 26 months) administration of enalapril to dogs with severe compensated mitral regurgitation (MR) did not have any adverse effects on renal function. In this multicenter, prospective, randomized, controlled study, no differences were observed between the enalapril and placebo groups with regard to serum creatinine and urea nitrogen concentrations at any time, and also with regard to change from baseline concentration or the proportion of dogs that had a ≥35% increase in serum creatinine or urea nitrogen concentrations.8

Similarly, another prospective, randomized, double-blinded, placebo-controlled multicenter trial (Scandinavian Veterinary Enalapril Prevention, or SVEP, trial),10 which was conducted over a 4.5-year period, demonstrated that long-term treatment with enalapril in asymptomatic Cavalier (CKC) and King Charles Spaniels (KC) with MVD was well tolerated.

However, unlike tolerability, conflicting results have been obtained regarding ACEIs efficacy on asymptomatic canine MVD. In the SVEP trial,10 the number of CKC developing CHF was similar in the treatment and placebo group, and treatment with enalapril did not delay the onset of CHF regardless of whether or not cardiomegaly was present at initiation of the study. Conversely, the follow-up of dogs recruited from the VETPROOF study (Veterinary Enalapril Trial to Prove Reduction in Onset Of heart Failure) demonstrated that chronic enalapril therapy was effective in delaying the onset of CHF and had a benefit on the combined endpoint of CHF–all-cause death.9

Benazepril (BNZ) is an ACEI whose effective metabolite benazeprilat is cleared by both renal (45%) and hepatic (55%) routes.7,13 Benazeprilat has been shown to potently inhibit canine ACE activity with an IC50 value, ie, the free plasma concentration required to produce 50% of the total inhibition, 1.4- and 4-fold lower than that of ramiprilat and enalaprilat, respectively.7,13 BNZ has been demonstrated to improve quality of life and extend the life span of dogs with naturally acquired ISACHC II-III HF class with good tolerability.3,4 However, its efficacy to delay the onset of CHF and to increase survival time of dogs with asymptomatic MVD remains unknown.

The aims of the present study were therefore (1) to retrospectively determine the effect of BNZ as a monotherapy on survival of asymptomatic dogs from various breeds affected by MVD with moderate-to-severe MR, and (2) to analyze the ability of BNZ to postpone cardiac events, including CHF and cardiac death, in the same canine population.

Materials and Methods

Animals

The case records of asymptomatic small-breed dogs (body weight ≤ 13 kg) subjected to echocardiographic and Doppler examinations leading to the diagnosis of MVD between 1995 and 2006 at the Cardiology Unit of Alfort were reviewed retrospectively.

The diagnosis of MVD was established by experienced cardiologists (Dipl. ECVIM, resident, or practitioner with at least 3 years of experience with echocardiography at our unit: V.C., V.G., F.S., C.C.S., M.C.) and was based on the following signs: (1) left systolic apical heart murmur of late appearance (age >1 year old), (2) no history of known infectious disease, and (3) echocardiographic and Doppler signs of MVD, including irregular and thickened mitral valve leaflets observed on the right parasternal 4-chamber view and a color-flow jet of systolic mitral insufficiency in the left atrium on the left parasternal 4-chamber view.

The inclusion criteria were as follows: (1) left atrial diameter within the reference range by a 2-dimensional (2D) method (ie, left atrium/aorta ratio [LA/Ao] ≤ 1.214), which corresponds to ISACHC stage 1a (ISACHC)15; (2) moderate or severe MR assessed by the color mapping method16,17 (ie, maximal area of the regurgitant jet signal/left atrial area ratio [ARJ/LAA] between 20 and 70% or > 70%, respectively); (3) dogs either treated from the time of the initial echo-Doppler examination (Day 0) with BNZ (BNZ group) or left untreated (untreated group, UT group); (4) dogs with a follow-up available from Day 0 for morbidity-mortality Kaplan-Meier analysis.

Information obtained from the medical records included signalment (breed, sex, and age), heart murmur grade, and main echo-Doppler findings at Day 0.

Exclusion Criteria. The exclusion criteria were dogs with eccentric MR or with mitral regurgitant jets that did not last throughout systole, dogs with other heart diseases, dogs with known extracardiac diseases (eg, cancer, diabetes mellitus, hyperadrenocorticism, hypoadrenocorticism, epilepsy), dogs already receiving cardioactive treatment at Day 0 and within the month before, and dogs treated from Day 0 with the combination of BNZ and any other cardiac medication.

Follow-Up. Entry time into the study was considered as the time of the first echocardiographic examination confirming the MVD diagnosis with the above inclusion criteria (Day 0). The follow-up evaluation, including the status at the time of the last available information (survivor or nonsurvivor; occurrence or not of cardiac events), was retrospectively assessed. One investigator (N.J.) was responsible for calling each owner at the time of the retrospective recording to obtain maximum details about the outcome of their animals. The cause of death was recorded as either related (ie, CHF, sudden death) or unrelated to the heart disease. Cardiac events included cardiac death and signs of CHF such as cough and dyspnea because of pulmonary edema with associated cardiomegaly confirmed by thoracic radiographs. The diagnosis of CHF was accepted only when the data from the case history, physical examination, and thoracic radiographs were available. The whole canine population, including dogs from all breeds, was first studied, and then 2 distinct subpopulations were analyzed: (1) a population (CKC-KC population) including only CKC and KC and (2) a population including dogs from all breeds except CKC and KC (other breed or OB population). The subgroup analysis of CKC and KC dogs was justified from the known faster progression of CHF in these breeds compared with other breeds in addition to the fact that only CKC dogs were studied in the SVEP trial.10 For each of these 3 populations, the effects of therapy on death from all causes, cardiac death, and cardiac events were studied.

Echocardiographic and Doppler Examinations

Echocardiographic and Doppler examinations were carried out in standing awake animals with continuous ECG monitoring with ultrasound unitsa,b equipped with 7.5–10 MHz, 5–7.5 MHz, and 2–5 MHz transducers, as previously described and validated at our unit.18

Echocardiography. Ventricular measurements were taken from the right parasternal location with the 2D-guided M-mode19 and the fractional shortening (FS%) was then calculated. The aortic and left atrial diameters were measured by a 2D method as previously described and LA/Ao was calculated.14

Doppler Examination. The left apical 4-chamber view was used to assess MR semiquantitatively by measuring the size of the systolic color-flow jet originating from the mitral valve and spreading into the LA. At the time of examination, the images were carefully analyzed frame by frame to compute the ARJ as previously described.17,20 The LAA was measured by computerized planimetry in the same frame in which the maximal ARJ had been determined. The ARJ/LAA ratio then was calculated. Doppler-derived evidence of systolic and diastolic pulmonary arterial hypertension (PAH) was obtained as previously described.21 A color flow Doppler examination was used to identify diastolic pulmonic and tricuspid regurgitant flows, which then were quantitatively assessed by continuous-wave Doppler examination. A telediastolic peak pulmonic insufficiency velocity ≥2 m/s and peak tricuspid insufficiency velocity ≥2.5 m/s were considered indicative of diastolic and systolic PAH. The modified Bernoulli equation (ΔP= 4 × velocity2) was applied to the maximal velocity of telediastolic pulmonic and tricuspid insufficiency to calculate the diastolic and systolic gradients across the pulmonic and tricuspid valves, respectively. Systolic pulmonary arterial pressure then was calculated by adding the estimated right atrial pressure to the systolic RV-to-RA pressure gradient. The estimated right atrial pressure was 5 mmHg in patients with a nondilated right atrium, 10 mmHg in those with an enlarged right atrium but no right-sided HF, and 15 mmHg in those with right-sided HF.22

Statistical Analysis

Data are expressed as mean ± standard deviation. Basic statistical analyses were performed by the statistical software StatView,c and for survival analyses (log rank test and Cox proportional hazards) SASd was used. Age, body weight, and echo-Doppler variables (LA/Ao, ARJ/LAA, FS%, pulmonary arterial pressure) in the BNZ and UT groups at Day 0 were compared by means of an unpaired Student t-test. The same test was used to compare the dosage of BNZ used in BNZ groups from the OB and CKC-KC populations. Heart murmur grades in the BNZ and UT groups at Day 0 were compared using a Mann-Whitney test. The prevalence of males and females between BNZ and the UT groups from each population was compared using a χ2 test. The same test was used to compare the prevalence of dogs with moderate or severe MR between the BNZ and UT groups of each population. Survival analyses were performed considering as events either all death causes, cardiac deaths, or cardiac events as previously defined. Median survival times or median time to cardiac events was calculated for each group (BNZ and UT groups) and compared using the Kaplan-Meier method and log rank test followed by the Cox proportional hazards model.d Dogs without further follow-up after a known time were censored from that time. Dogs that died as a result of noncardiac diseases were censored at the date of death from the Kaplan-Meier analysis of both cardiac death and cardiac events. The selected level of significance was P < .05.

Results

A total of 141 dogs were enrolled in the study (66 in the BNZ group and 75 in the UT group). The daily oral dosage of BNZ was 0.30 ± 0.13 mg/kg (range, 0.10–0.59 mg/kg) and was comparable between BNZ groups from the OB (0.32 ± 0.12 mg/kg; range, 0.10–0.59 mg/kg) and CKC-KC populations (0.27 ± 0.14 mg/kg; range, 0.10–0.58 mg/kg). The median follow-up duration was 1.8 years for the overall study (ie, 2.2 and 1.4 years in the BNZ and UT groups, respectively). In the OB population, the median follow-up duration was 1.4 years (ie, 2.2 and 1.3 years in the BNZ and UT groups, respectively). Lastly, in the CKC-KC population, the median follow-up duration was 2.2 years (ie, 2.2 and 1.9 years in the BNZ and UT groups, respectively).

Epidemiologic Characteristics of the Canine Populations at Day 0

The main epidemiologic characteristics of the 3 canine populations (whole study population, OB, and CKC-KC populations) are presented in Table 1. As expected, the recruited dogs mainly consisted of male (n = 89, 63%), aged adult dogs (9.4 ± 3.4 years; range, 1.5–16.0 years). The proportion of males and females was similar in the BNZ and UT groups for all 3 populations (whole, OB, and CKC-KC populations).

Table 1.   Epidemiological characteristics of the study population at Day 0.
 All Breeds (n = 141)Cavalier King Charles and King
Charles Spaniels (n = 48)
Other Canine
Breeds (n = 93)
Treated
(n = 66)
Untreated
(n = 75)
Treated
(n = 32)
Untreated
(n = 16)
Treated
(n = 34)
Untreated
(n = 59)
  • *

    P < .05 versus the untreated group.

  • n, number of dogs; treated, dogs received benazepril but no other cardioactive drug; untreated, no cardioactive drug used.

Sex (% and n/group)
 Male63.6% (42/66)62.7% (47/75)65.6% (21/32)50.0% (8/16)61.8% (21/34)66.1% (39/59)
 Female36.4% (24/66)37.3% (28/75)34.4% (11/32)50.0% (8/16)38.2% (13/34)33.9% (20/59)
Age
 Mean ± SD (years)8.6 ± 3.4*10.0 ± 3.26.2 ± 2.35.7 ± 2.610.8 ± 2.611.2 ± 2.2
 Minimum–maximum (years)c1.5–162–141.5–102–116–163.5–14
Body weight
 Mean ± SD (kg)8.0 ± 2.58.4 ± 2.89.6 ± 1.79.0 ± 2.06.8 ± 2.5*8.2 ± 3.0
 Minimum–maximum (kg)2.8–132.6–136.5–136.0–12.52.8–122.6–13

The whole population was composed of 48 CKC and KC (32 treated with BNZ and 16 untreated) and 93 dogs from other canine breeds (34 treated with BNZ and 59 untreated), including 24 Poodles, 12 Yorkshire Terriers, 8 Dachshunds, 4 Bichons, 4 Shih-tzus, 3 Pekingeses, 3 Cocker Spaniels, 3 Tibetan Terriers, 2 Cairn Terriers, 20 cross breeds, and 10 other small-breed dogs, ie, Pinscher, West Highland White Terrier, Fox Terrier, Whippet, Shiba Inu, Vastgotaspet, Brittany Spaniel, Belgian Griffon, Butterfly Spaniel, Chinese crested dog (n = 1 for each). The CKC-KC population included mostly CKC (42/48, 87.5%), which was also the most commonly represented breed in the whole population (29.8%). Most of the CKC (30/42, 71.4%) were treated with BNZ after Day 0, representing 45.5% of all treated dogs in the study (versus only 16% of the untreated). This unequal proportion of CKC between the 2 groups explains why treated dogs from the whole study population were significantly younger (P < .05) than untreated dogs, whereas treated and untreated dogs from the OB population were age-matched.

Clinical and Echo-Doppler Characteristics at Day 0

The main clinical and echo-Doppler characteristics are shown in Table 2. Heart murmur grade was significantly higher in the BNZ than in the UT group (P < .05) in both the whole and CKC-KC populations. In these 2 populations, the proportion of dogs with severe MR (ARJ/LAA > 70%) was significantly higher in the BNZ than in the UT group (P < .05) and the ARJ/LAA value was also significantly higher (P < .01). The latter difference was also observed in the OB population (P < .05), although the proportion of dogs with severe MR was comparable in both groups. No statistical difference between treated and untreated dogs was observed with regard to LA/Ao and FS% for the 3 populations. Lastly, chordae tendinae rupture, mitral valve prolapse, and PAH were detected with an overall prevalence of 4.3% (6/141), 5% (7/141), and 10% (14/141), respectively.

Table 2.   Main clinical and echo-Doppler characteristics of the study population at Day 0 (n= 141).
 All Breeds
(n = 141)
Cavalier King Charles
and King Charles
Spaniels (n = 48)
Other Breeds
(n = 93)
Treated
(n = 66)
Untreated
(n = 75)
Treated
(n = 32)
Untreated
(n = 16)
Treated
(n = 34)
Untreated
(n = 59)
  • Variables values are presented as mean ± SD and minimum-maximum.

  • *

    P < .05 versus the untreated group.

  • **

    P < .01 versus the untreated group

  • ARJ/LAA ratio, maximal mitral regurgitant jet area/left atrial area ratio; MR, mitral regurgitation; n, number of dogs.

Heart murmur grade3.5 ± 0.8*3.1 ± 0.93.4 ± 0.8*2.8 ± 0.83.5 ± 0.73.2 ± 0.9
[2–5][2–5][2–5][2–4][2–5][2–5]
Echocardiography
 Left atrium/aorta ratio0.90 ± 0.140.90 ± 0.110.87 ± 0.130.82 ± 0.070.93 ± 0.170.92 ± 0.11
[0.62–1.16][0.68–1.19][0.63–1.10][0.71–0.91][0.62–1.16][0.68–1.19]
 Fractional shortening (%)43 ± 742 ± 741 ± 540 ± 544 ± 943 ± 8
[30–67][28–57][32–50][29–49][30–67][28–57]
 Chordae tendinae rupture (n)6.1% (4/66)2.7% (2/75)3.1% (1/32)0.0% (0/16)8.8% (3/34)3.4% (2/59)
 Mitral valve prolapse (n)4.6% (3/66)5.3% (4/75)6.2% (2/32)0.0% (0/16)3.0% (1/34)6.8% (4/59)
Doppler examination
 ARJ/LAA (%)72.8 ± 25.2**54.4 ± 27.274.5 ± 22.0**48.3 ± 22.671.3 ± 27.9*56.1 ± 28.2
[21–100][20–100][28–100][20–100][21–100][20–100]
  Moderate MR (20%≤ ARJ/LAA ≤ 70%) (n)42.4% (28/66)**70.7% (53/75)34.4% (11/32)*75.0% (12/16)50.0% (17/34)69.5% (41/59)
  Severe MR (ARJ/LAA > 70%) (n)57.6% (38/66)**29.3% (22/75)65.6% (21/32)*25.0% (4/16)50.0% (17/34)30.5% (18/59)
 Pulmonary arterial hypertension (PAH)
  Dogs with Doppler evidence of systolic PAH (n)10.6% (7/66)9.3% (7/75)9.4% (3/32)6.3% (1/16)11.8% (4/34)10.2% (6/59)
  Systolic pulmonary arterial pressure of hypertensive dogs (mmHg)54.0 ± 26.343.9 ± 19.475.7 ± 26.144.037.7 ± 10.643.8 ± 21.2
[30–95][30–86][46–95][30–53][30–86]

Effect of Therapy on Survival and Cardiac Events

Table 3 shows the number of dogs that were still alive and followed up at several time intervals. Out of the 141 dogs enrolled in the study, 91 (64.5%) were still alive at the end of their follow-up, whereas 50 (35.5%) died either from noncardiac-related causes (35/50, 70%) or for reasons related to the heart disease (ie, sudden death or CHF [15/50, 30%]). Only 5 sudden deaths (10% of all-cause deaths) were recorded, and all of them were observed in dogs belonging to the UT group. The 5 owners confirmed an absence of clinical signs before death, and four of these animals were examined by a veterinarian within the previous months (mean time between veterinary examination and death, 4.5 months); no abnormality other than the systolic heart murmur related to MVD was detected. Noncardiac-related causes of death included cancer (n = 14), renal insufficiency (n = 7), neurological diseases (n = 4), surgery (for intestinal obstruction, perineal hernia, pyometra; n = 3), diabetes mellitus (n = 1), trauma (n = 1), and euthanasia because of age-related problems (severe arthrosis, blindness, or urinary incontinence; n = 5) in animals of advanced age (≥13 years).

Table 3.   Number of dogs still alive and followed up in the Kaplan-Meier studies at different time points.
Time of
Follow-Up
(Years)
All Breeds (n = 141)Cavalier King Charles and
King Charles Spaniels (n = 48)
Other Canine Breeds (n = 93)
Treated
(n = 66)
Untreated
(n = 75)
Treated
(n = 32)
Untreated
(n = 16)
Treated
(n = 34)
Untreated
(n = 59)
  1. n, number of dogs; treated, dogs received benazepril but no other cardioactive drug; untreated, no cardioactive drug used.

0667532163459
0.5626631163150
1525327142539
1.5433723122025
237221971815
2.52814157137
>316119675

With regard to death from all causes in the whole study population (Fig 1A, Table 4), the survival time in the BNZ group was significantly longer (P= .014) than in the UT group, with a relative risk of 0.48. Similar results were obtained in the OB population (Fig 1B, Table 4), with a relative risk of 0.44 and P= .024. Conversely (Fig 1C, Table 4), in the CKC-KC population, there was no difference in survival between the BNZ and UT groups (P= .59).

Figure 1.

 Death from all causes. Kaplan-Meier survival curves of dogs treated with benazepril (solid line) or untreated (dotted line) after the initial diagnosis of ISACHC class Ia mitral valve disease and moderate-to-severe mitral regurgitation in the whole study population (A, n = 141), in the OB population (B, n = 93), and in the CKC-KC population (C, n = 48). CKC-KC population, population including Cavalier King Charles and King Charles Spaniels only; OB population, population including dogs from breeds other than Cavalier King Charles and King Charles Spaniels. P values calculated by log rank test. NS, not significant.

Table 4.   Survival data for dogs with an initial diagnosis of ISACHC class 1a mitral valve disease and moderate-to-severe mitral regurgitation treated with benazepril (treated group) or no cardiac medication (untreated group).
Endpoint and Subgroup of DogsMedian (Interquartile Range)
Time to Event (Years)
and Number of Dogs
Cox Proportional
Hazards Model
P Value
(Log Rank Test)
TreatedUntreatedRisk Ratio Treated/Untreated95% Confidence Interval
  1. CKC, Cavalier King Charles; KC, King Charles; NA, not available; CHF, congestive heart failure. Bold numerals correspond to statistically significant variables.

Death from all causes
 Whole population4.5 (2.6–8.0)662.9 (1.3–4.8)750.480.26–0.87.014
 Other breeds (not CKC or KC)3.3 (2.3–8.9)341.9 (1.2–3.7)590.440.22–0.92.024
 CKC and KC5.8 (2.8–8.0)324.8 (4.8–4.8)161.550.31–7.8.590
Cardiac death
 Whole populationNA (5.8–NA)664.8 (3.7–4.8)750.410.13–1.2.100
 Other breeds (not CKC or KC)NA343.7 (3.7–3.7)590.130.014–1.2.041
 CKC and KC5.8 (5.8–NA)324.8 (4.8–4.8)160.930.17–5.1.930
Cardiac event
 Whole population6.4 (3.0–NA)664.8 (2.0–4.8)750.610.29–1.3.190
 Other breeds (not CKC or KC)6.4 (3.3–6.4)343.7 (3.7–3.7)590.280.075–1.1.047
 CKC and KC3.6 (2.2–NA)324.8 (2.0–4.8)161.10.34–3.6.860

Similar results regarding cardiac death were obtained in the OB population, with a significantly higher survival rate (P= .041) in the BNZ group than in the UT group with a relative risk of 0.13 (Fig 2, Table 4). Median survival could not be calculated for that analysis because only 1 dog died from heart disease in the BNZ group. Unlike the OB population, no statistical difference regarding cardiac death was observed between the BNZ and UT groups for the whole population (P= .1), with a relative risk of 0.41. For cardiac death in the CKC-KC population, there was no difference between the BNZ and UT groups (P= .93).

Figure 2.

 Cardiac death. Kaplan-Meier survival curves of dogs treated with benazepril (solid line) or untreated (dotted line) after the initial diagnosis of ISACHC class Ia mitral valve disease and moderate-to-severe mitral regurgitation in the whole study population (A, n = 141), in the OB population (B, n = 93), and in the CKC-KC population (C, n = 48). CKC-KC population, population including Cavalier King Charles and King Charles Spaniels only; OB population, population including dogs from breeds other than Cavalier King Charles and King Charles Spaniels. P values calculated by log rank test. NS, not significant.

Of the 141 dogs, all of which were asymptomatic at Day 0, 24 (17%) developed CHF during the study period and 11 of these (45.8%) were still alive at the end of the study period.

No differences in the time to onset of CHF were found between the BNZ and UT groups in the whole study population or in the OB and CKC populations. Because the number of cases developing CHF was relatively low (n = 24), we considered the end-point “cardiac event,” which takes into account the time to onset of CHF or cardiac death if the latter was not preceded by CHF (ie, sudden death). Cardiac events were therefore 24 CHF and 5 sudden deaths. No significant difference in the time to cardiac events was found between BNZ and UT groups in the whole population (P= .19), with a relative risk of 0.61 (Fig 3A, Table 4). Conversely, in the OB population, the time to cardiac event was significantly longer (P= .047) in the BNZ group than in the UT group, with a relative risk of 0.28 (Fig 3B, Table 4). At Day 0 + 1.5 years (Fig 3), 100% of dogs from the BNZ group were still alive and asymptomatic (ISACHC I), whereas 25% of the untreated dogs had undergone at least 1 cardiac event by this time. There were no differences (P= .86) in time to cardiac event between the BNZ and UT groups in the CKC-KC population (Fig 3C, Table 4).

Figure 3.

 Time to cardiac events (cardiac death and congestive heart failure). Kaplan-Meier curves of dogs treated with benazepril (solid line) or untreated (dotted line) after the initial diagnosis of ISACHC class Ia mitral valve disease and moderate-to-severe mitral regurgitation, in the whole study population (A, n = 141), in the OB population (B, n = 93), and in the CKC-KC population (C, n = 48). CKC-KC population, population including Cavalier King Charles and King Charles Spaniels only; OB population, population including dogs from breeds other than Cavalier King Charles and King Charles Spaniels. P values calculated by log rank test. NS, not significant.

The effect of baseline covariates was studied by the Cox proportional hazards model using the whole population and all-cause death as the endpoint (Table 5). For all variables, the risk ratio was <1, suggesting a beneficial effect of BNZ in delaying the time to death regardless of baseline variables. However, differences were significant (P < .05) only for certain subgroups, namely heart murmurs of grade > 3 and ARJ/LAA > 50%.

Table 5.   Cox proportional hazards model analysis of the effect of baseline covariates on survival time for dogs with an initial diagnosis of ISACHC class 1a mitral valve disease and moderate-to-severe mitral regurgitation treated with benazepril (treated) or no cardiac medication (untreated).
Endpoint and
Subgroup of Dogs
Risk Ratio
Treated/
Untreated
95% Confidence
Interval
P Value
  1. The population tested was the whole dog population and the endpoint was all cause death. Bold numerals correspond to statistically significant variables.

Heart murmur
 Grade ≤ 30.680.28–1.6.38
 Grade > 30.380.15–0.96.041
Fractional shortening (%)
 ≤ 500.570.30–1.1.094
 > 500.210.026–1.7.14
Maximal area of the regurgitant jet signal/left atrial area ratio (%)
 ≤ 500.220.049–1.00.051
 > 500.440.21–0.91.027

Discussion

The results of this retrospective study show that BNZ had beneficial effects in asymptomatic dogs other than CKC and KC affected by MVD with moderate-to-severe MR. These beneficial effects included decreased risk of both death from all causes and cardiac death and also decreased risk of cardiac events. In OB dogs treated with BNZ, the median time to reach decompensation or cardiac death was delayed by a factor of 1.7 as compared with the UT group (6.4 versus 3.7 years, respectively). In other words, this suggests that BNZ increases quality of life in dogs with ISACHC class I MVD because it contributes to significantly prolong the asymptomatic period.

To the best of our knowledge, this study is the first to focus on the efficacy of BNZ to delay the onset of CHF and increase survival time of dogs with asymptomatic MVD. So far, most data regarding this drug have been obtained from dogs with CHF. In a large, multicentric, well-controlled clinical trial involving dogs with ISACHC class II and III CHF caused by either MVD or dilated cardiomyopathy (BENCH study),3 the efficacy of BNZ on both quality of life and life expectancy was demonstrated. BNZ, given alone or in combination with other drugs (eg, diuretics, digoxin, anti-arrhythmic drugs), increased survival times by a factor of 2.7 in comparison with the placebo group with mean survival times of 428 and 158 days, respectively. In the BENCH study, the long-term tolerability of BNZ in dogs with ISACHC class II and III CHF was also demonstrated, without any significant deleterious effects of BNZ on serum potassium concentration or renal or hepatic function.3,4 Moreover, in contrast to humans, BNZ pharmacokinetics and pharmacodynamics are not altered in dogs with renal impairment.23,24 The good tolerance of BNZ was also recently demonstrated in asymptomatic dogs affected by mild MVD (ISACHC class 1a) in a prospective, randomized, and blinded study performed by our group.12 Administration of BNZ to those dogs for more than 1 year did not lead to any alteration of renal function as assessed by plasma creatinine and urea concentrations and glomerular filtration rate, and did not lead to any adverse cardiac effects. Additionally, in contrast to pimobendan, long-term treatment with BNZ was not associated with any worsening of the valvular disease confirmed by echo-Doppler examination.12 However, in this last study,12 the absence of a placebo group precluded a definitive conclusion regarding the potential beneficial effect of BNZ in delaying natural disease progression. Thus, to our knowledge, whether or not asymptomatic dogs affected by MVD would benefit from early BNZ treatment has not been demonstrated before the present report.

The clinical outcome of MVD-affected dogs without overt clinical signs is still poorly defined, and criteria for identification of dogs in HF class I that are at a higher risk of early decompensation still have not been determined. However, several recent studies have demonstrated that ISACHC class I MVD is a very heterogeneous stage and may include more severely affected animals than clinically suspected and previously supposed.20,25,26 For example, in 1 study performed on dogs with MVD and chordae tendinae rupture,25 although most animals presented with moderate to severe signs of HF (75% were in ISACHC class II or III), chordae tendinae rupture was also identified in numerous asymptomatic dogs. All of these dogs were characterized by marked MR (ARJ/LAA > 50%), and several of them (7%) had normal LA/Ao ratio (ISACHC class Ia). Similarly, in the present study, 4% of the recruited dogs had echocardiographic signs of chordae tendinae rupture. In another study performed by our group in dogs with MVD, out of the 86 animals diagnosed with Doppler-derived evidence of PAH, 25 were recruited from a population of 450 dogs with asymptomatic MVD (thus representing 6% of all the dogs in ISACHC class I), and again, all of them showed moderate to severe MR as confirmed by ARJ/LAA.26 Similarly, in the present study, 10% of the recruited dogs had Doppler-derived evidence of PAH. Lastly, in 1 study dedicated to the quantification of MR in dogs with MVD by the PISA method,20 dogs without clinical signs had a wide range of regurgitation fractions (0.6–77.6%) and approximately one third of them had a regurgitation fraction > 50%. This dispersion of regurgitation fraction values at the asymptomatic stage is well known in humans with MR.27,28 Thus, use of the PISA method is now routinely recommended at this stage for the quantitative grading of mitral valve incompetence, which has been shown to be a powerful predictor of the clinical outcome of asymptomatic MR together with the echo-Doppler evaluation of cardiac adaptation to the volume overload and of pulmonary pressure.27–30 In humans, conventional echo-Doppler examination therefore has much improved the definition of high-risk patients that might benefit from early medical or surgical treatment.27–33 For example, ACEI therapy has been shown to have some beneficial effects on MR in asymptomatic human patients with moderate to severe MR.34,35 Similarly, the recent prospective study by Atkins et al9 demonstrated a benefit (ie, increased time to CHF–all-cause death and delayed onset of CHF) of early treatment with enalapril. Although in the latter study MR was not assessed using a Doppler method, we can hypothesize that all the recruited dogs had severe (although compensated) MR, because left atrial enlargement on M-mode or 2D echocardiography was one of the inclusion criteria.9 Interestingly, in the SVEP trial, although MR severity was not assessed (because dogs were evaluated at entry only by physical examination, ECG, and thoracic radiographs), CKC with an initial heart murmur of moderate intensity showed a markedly shorter time to CHF than in dogs with low-intensity murmurs.10 This may also be related to MR severity because a significant correlation has been demonstrated in the CKC breed between heart murmur grade and MR severity as assessed by ARJ/LAA.36 All of these data obtained from both dogs and humans in the asymptomatic stage led us to include only dogs in the present study for which MR severity had been assessed and in which MR was moderate to severe. Dogs with mild MR characterized by an ARJ/LAA < 20% as well as dogs with mitral regurgitant jets that did not last throughout systole were not enrolled in the protocol. Similarly, dogs with eccentric mitral regurgitant jets were not included in the study because eccentric wall-impinging jets have been demonstrated to appear significantly smaller than centrally directed jets of similar hemodynamic severity, thus leading to an underestimation of MR severity.20 Whether or not all the latter animals also would benefit from early BNZ treatment remains unknown.

In the present study, 3 separate canine populations were studied (ie, the whole study population including dogs from all breeds, the CKC-KC population including only CKC and KC, and the OB population including dogs from all breeds except CKC and KC). This separate analysis was conducted because the CKC breed is considered to have an accelerated form of the disease compared with MVD in other small breed dogs, with a higher prevalence and earlier onset of disease.37,38 In addition, only CKC dogs were studied in the SVEP study.10 As in the SVEP trial, BNZ treatment in the present study did not delay the onset of cardiac events and did not prolong survival in the CKC-KC population with regards to death from all causes and cardiac death, whereas such an effect was observed in the OB population. However, in this CKC-KC population, ARJ/LAA was 1.5-fold higher in the BNZ group than in the UT group (P < .01), and two thirds of the BNZ treated dogs (versus only a quarter of the UT group) showed severe MR characterized by ARJ/LAA > 70%. It may therefore be hypothesized that a substantially longer survival time would have been observed in the BNZ group from the CKC-KC population if the BNZ and UT groups had been comparable for MR severity at baseline.

The results obtained in the present study for the OB population, characterized by age-matched BNZ and UT groups, were relatively similar to those recently published by Atkins et al,9 with however a better cardiac benefit (2.7 years of cardiac event-free benefit versus 5.1 months of CHF-free benefit, respectively, in our study and in the Atkins et al9 trial). Moreover, in our study, survival time with regard to cardiac death was significantly longer in the BNZ group than in the UT group, whereas such a benefit was not described in the Atkins et al9 study. This difference between the 2 studies may at least partially be explained by the fact that Atkins et al9 included more severely affected dogs than ours. All dogs in the former study were characterized by an LA enlargement confirmed by echocardiography with LA/Ao > 1.6, whereas all the dogs in our study had normal LA diameter with LA/Ao < 1.2.

Interestingly, the present study shows that, similar to enalapril,9 BNZ had a significant effect on all-cause death in both the whole and OB populations (whereas the effect on cardiac death was observed only in the OB population). Several possible mechanisms may explain these noncardiac beneficial effects. First, renal dysfunction was recently identified in dogs with MVD,39 and ACEIs have been shown to exert a renoprotective action owing to decreases in systemic arterial pressure, glomerular capillary pressure, and glomerular volume together with an increase in glomerular filtration rate.7,40 Moreover, ACEIs may also have some benefit on the central nervous system as demonstrated in humans, exerting vascular protection in the case of brain ischemia and slowing cognitive dysfunction in elderly patients.41,42 The possible action of BNZ in improving overall survival time merits further investigation because none of these beneficial renal and cerebral effects could be confirmed in this retrospective study.

This study had several limitations that must be clearly defined. First and importantly, this was a retrospective study, not a prospective, randomized, or double-blinded one. Retrospective studies in principle provide weaker evidence than well-designed prospective studies, but can nevertheless provide a useful contribution to knowledge, especially when prospective studies are missing or difficult to organize, as in this case. A well-designed prospective study comparing ACEI with placebo to test the hypotheses in this study would take many years to conduct.

Second, for the 3 populations (whole, OB, and CKC-KC populations), MR severity in the BNZ and UT groups was not comparable, with more severely affected dogs in the BNZ than in the UT group. This difference may be explained by the fact that veterinarians and owners were more likely to start medical treatment with BNZ when their dogs were more severely affected at Day 0. This finding may have had an effect on the subsequent analyses and may explain at least in part the lack of observed effect of BNZ to delay the onset of cardiac events and prolong survival in the CKC-KC population. Nevertheless, the fact that OB dogs receiving BNZ had significantly better outcomes than nontreated dogs despite worse severity of disease at baseline provides strong evidence for a benefit of ACEI.

Third, in the present study, only one third of the dogs died either for reasons related to the heart disease or from noncardiac-related causes, and this low mortality rate represents another limitation of the present report. The relatively short follow-up period for the Kaplan-Meier analysis (median of about 2 years in the overall study population) is again a limitation. Moreover, because no postmortem examination was obtained in dogs that underwent sudden death, it cannot be ascertained with certainty that MVD was the actual cause of death. However, this does not change the results for all-cause death.

Lastly, the impact of pre-existing azotemia at Day 0 was not assessed in the present report. One recent study performed on dogs with MVD has shown that renal function assessed by glomerular filtration rate decreases with HF severity and that it may also already be altered at early stages of the disease.39 In humans, a decline in glomerular filtration rate has been shown to be an independent risk factor for the development or worsening of cardiovascular diseases.43 Whether or not renal function influenced survival time and time to cardiac events in the present report should be investigated in further future studies.

In conclusion, in this retrospective study BNZ had beneficial effects (ie, prevented the development of cardiac event or cardiac death and had a life-prolonging effect in asymptomatic dogs other than CKC and KC affected by MVD with moderate-to-severe MR). Prospective studies should be carried out to confirm these results in well-controlled conditions and to determine the underlying factors and mechanisms explaining the global beneficial effect of BNZ illustrated by the significant decrease in death from all causes. Lastly, this study also clearly demonstrates that data obtained in one breed cannot be extrapolated without reservation to other breeds. Breed distribution is a factor that should be taken into account for interpretation of canine heart failure clinical trials.

Footnotes

aVingmed System 5, Vivid 5, Vivid 3, and Vivid 7, General Electric Medical System, Waukesha, WI and Horten, Norway

bAU3 Partner and Challenge Sim 7000 CFM, Esaote, Italy

cStatview, SAS Institute, Cary, NC

dProcedure Lifetest, SAS Version 9, 2002–2004, SAS Institute Inc

Acknowledgment

One of the Vivid 7 ultrasound systems was sponsored by Novartis Animal Health (Rueil Malmaison, France).

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