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Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

Background:

Enhanced external counterpulsation (EECP) has been reported to reduce blood pressure (BP) using clinic BP readings. The aim of this study was to assess the effect of a course of EECP on BP using ambulatory BP (ABP) measurements.

Hypothesis:

EECP has a lasting BP lowering effect.

Methods:

Patients referred for EECP due to refractory angina pectoris were consecutively included in the study. The ABPs were measured for 24 hours using a Spacelabs Ultralite 90217 device at 5 time points during the study period: 2 months before the EECP course, just before the EECP course, just after the EECP course, and at 3 and 12 months after EECP. Antihypertensive medication was held constant during the study period. Changes in BP were tested by repeated measures analysis.

Results:

Fifty patients were included in the study. The mean age was 63 years, and 72% were male. The Canadian Cardiovascular Society Angina Grading Scale class improved from a mean of 2.6 to 1.5. The mean daytime ABPs were 114/69, 114/70, 115/71, 114/70, and 116/71 mm Hg and the mean nighttime ABPs were 107/63, 108/63, 106/62, 108/63, and 107/62 mm Hg at 2 months before the EECP course, just before the EECP course, just after the EECP course, and at 3 and 12 months after EECP, respectively (all P > 0.10). Further, when controlling for quartiles of baseline ABP level, no significant change in ABP was found.

Conclusions:

Enhanced external counterpulsation treatment has no lasting effect on ABP.

The study was supported by a grant from the Danish Heart Foundation (grant no. 06-10-B551-A1204-22346) and from “Ringkøbing Amts Sundhedsvidenskabelige Forskningsfond.” The authors have no other funding, financial relationships, or conflicts of interest to disclose.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

Enhanced external counterpulsation (EECP) is a therapy offered to patients with angina pectoris resistant to medical treatment who are not amenable to coronary interventions. Enhanced external counterpulsation is usually given for 1 hour, 5 days a week, over 7 weeks. During each treatment, 3 sets of cuffs wrapped around the lower extremities are inflated to 260 to 300 mm Hg in diastole, augmenting the central blood pressure (BP) and increasing the coronary blood flow.1 Enhanced external counterpulsation is known to reduce the level of chest pain2 and increase quality of life.3

During EECP, shear stress is increased in the coronary arteries.1 Several studies have indicated that the endothelial function is improved,4–7 and it is well known that systolic BP falls during an EECP session.1,8 It is thus reasonable to hypothesize that the BP may also be reduced in the time following a course of EECP; indeed, some articles have reported a fall in the clinic BP after a course of EECP8–13 and 2 studies also using clinic BP readings have concluded that an EECP course has a more lasting BP-lowering effect.8,9 Yet, it is widely recognized that clinic BP readings have several sources of error, making ambulatory BP (ABP) readings more reliable.14,15

The purpose of the present study was to assess the effect of EECP on BP in the patient group normally offered EECP using ABP recordings.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

Patient Characteristics

Fifty consecutive patients undergoing EECP in our department were consecutively included in the study. The inclusion criteria were angina pectoris of Canadian Cardiovascular Society (CCS) class II to IV despite appropriate medical therapy, no treatable stenoses on coronary angiography, sinus rhythm, and reversible ischemia on myocardial scintigraphy. Exclusion criteria were pacemaker, known severe aortic aneurysm, or aortic regurgitation.

Blood Pressure Measurement

The ABP was measured using a Spacelabs Ultralite 90217 (Spacelabs Healthcare, Issaquah, WA), approved according to the British Hypertension Society criteria.16 The ABP was measured every 30 minutes starting in the afternoon, and only readings within the first 24 hours were used in the analyses. Readings were divided into daytime and nighttime values according to individual waking and bedtimes.17 Ambulatory blood pressure recordings were taken 2 months before and just before the EECP course, on the first workday after the EECP course, and 3 months and 12 months later.

At baseline, 2 months before EECP, a clinic BP (UA-852 digital; A&D Medical, Abingdon, UK) was measured at the left upper arm after ≥5 minutes of rest in the sitting position.

The patients were instructed that their medication should be kept unchanged during the study period, and at each visit the patients were asked about medication.

The study complies with the Declaration of Helsinki II, and the project was approved by the local ethics committee as well as the Danish Data Protection Agency. Written informed consent was obtained from each participant after verbal and written information was given.

Enhanced External Counterpulsation

All patients had a standard EECP course consisting of 35 1-hour sessions over 7 weeks. In diastole the cuffs were inflated to 260 mm Hg and the timing of the inflation was individually adjusted according to the electrocardiogram to give the highest diastolic/systolic BP ratio during treatment. The EECP equipment from Vasomedical (Westbury, NY) was used.

Statistical Analysis

Comparisons of mean BP measurements at the 5 time points were conducted by repeated measures analysis. To account for empty cells, the type IV sum of squares was used. Differences were taken to be significant if the P value was <0.05. The analyses were carried out using PASW Statistics 18. Model assumptions for the multivariate analyses were tested by Mauchly's test of sphericity, and if the test indicated that sphericity could not be assumed, the P value calculated according to Greenhouse-Geisser was used. The change in CCS class and medication was tested by the Friedman test for related samples.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

Fifty patients were included in the study; 36 (72%) were males and the mean age was 63.0 years (standard deviation [SD] 8.0 years). (See Table 1 for further patient characteristics.) Ambulatory blood pressures with heart rates were obtained from all 50 patients 2 months before, just before, and just after EECP. For the measurement 3 months after EECP, 3 ABP readings were missing (1 technical error, 1 patient died, and 1 patient did not attend the examination), and for the measurement 12 months after EECP, 10 readings were missing (1 patient died and 9 did not attend the examination). The mean daytime and nighttime systolic and diastolic BP as well as heart rates at the 5 time points are listed in Table 2. Repeated measures analysis showed no significant within-subject variation for any of the readings, whether daytime/nighttime/dip, systolic/diastolic values, or heart rates (P > 0.05).

Table 1. Baseline Characteristics of Study Participants
CharacteristicsAll Patients (N = 50)
  1. Abbreviations: ACEI, angiotensin-converting enzyme inhibitor; ARB, angiotensin II receptor blocker; BMI, body mass index; BP, blood pressure; CABG, coronary artery bypass graft; CCB, calcium channel blocker; CCS, Canadian Cardiovascular Society; DM, diabetes mellitus; MI, myocardial infarction; NTG, nitroglycerin; OHA, oral hypoglycemic agents; PCI, percutaneous coronary intervention; SD, standard deviation.

  2. Data are given as n (%) unless otherwise indicated.

Clinical characteristics 
 Male sex36 (72)
 Age, y, mean (SD)63.0 (8.0)
 BMI, kg/m2, mean (SD)29.7 (4.2)
 Previous MI29 (58)
 Previous CABG24 (48)
 Previous PCI29 (58)
 Hypertension32 (64)
 Systolic clinic BP at baseline, mm Hg, mean (SD)118 (16.8)
 Diastolic clinic BP at baseline, mm Hg, mean (SD)75 (11.8)
 DM12 (24)
 Current smoker9 (18)
 CCS class II26 (52)
 CCS class III–IV24 (48)
Medication 
 ACEI/ARB26 (52)
 β-Blocker45 (90)
 CCB34 (68)
 Long-acting NTG41 (82)
 Diuretics23 (46)
 Nicorandil19 (38)
 Morphine8 (16)
 Statins47 (94)
 Insulin5 (10)
 OHA6 (12)
Table 2. Ambulatory Blood Pressure, Heart Rate, and Antihypertensive Medication
 2 Months Before EECP Course (N = 50)Just Before EECP Course (N = 50)Just After EECP Course (N = 50)3 Months After EECP Course (N = 47)12 Months After EECP Course (N = 40)P Value
  1. Abbreviations: ACEI, angiotensin-converting enzyme inhibitor; ARB, angiotensin II receptor blocker; BPd, diastolic blood pressure; BPs, systolic blood pressure; CCB, calcium channel blocker; dip, daytime value − nighttime value; EECP, enhanced external counterpulsation; HR, heart rate; NTG, nitroglycerin; SD, standard deviation.

Readings, mean (SD)      
 BPs, day, mm Hg113.7 (11.9)113.7 (10.4)114.4 (11.7)114.4 (12.4)115.9 (11.4)0.078
 BPs, night, mm Hg106.8 (13.2)107.6 (12.5)106.2 (13.4)107.8 (12.2)106.6 (11.4)0.861
 BPs, dip, mm Hg6.9 (7.6)6.4 (8.7)8.0 (9.7)6.6 (9.9)9.5 (9.6)0.188
 BPd, day, mm Hg69.0 (7.2)69.5 (6.7)70.6 (8.1)69.9 (8.2)71.1 (9.0)0.078
 BPd, night, mm Hg62.6 (6.2)62.6 (6.0)61.9 (6.6)63.1 (7.1)62.4 (6.1)0.936
 BPd dip, mm Hg6.4 (4.4)7.1 (5.9)8.5 (5.8)6.8 (6.6)8.6 (6.1)0.068
 HR, day, min−166.0 (9.5)67.3 (9.4)66.7 (9.6)67.4 (9.3)67.7 (9.3)0.312
 HR, night, min−160.7 (8.7)61.9 (8.3)60.4 (8.2)61.9 (7.9)61.1 (8.5)0.205
 HR, dip, min−15.3 (6.0)5.5 (6.0)5.5 (6.3)6.8 (5.9)6.2 (5.6)0.188
Medication, n (%)      
 ACEI/ARB26 (52)26 (52)26 (52)25 (53)19 (48)0.406
 β-Blocker45 (90)46 (92)46 (92)42 (89)36 (90)0.406
 CCB34 (68)34 (68)34 (68)33 (70)28 (70)0.406
 Diuretics23 (46)23 (46)23 (46)20 (43)17 (43)0.806
 Long-acting NTG41 (82)40 (80)40 (80)38 (81)32 (80)1.000

A baseline systolic and diastolic ABP as well as heart rate were calculated as the mean of the 2 measurements before EECP. The increase in ABP just after the EECP course compared with baseline was for daytime systolic BP 0.7 (95% confidence interval [CI]: −1.3 to 2.7, P = 0.49) mm Hg, for nighttime systolic BP −1.2 (95% CI: −3.4 to 0.9, P = 0.26) mm Hg, for daytime diastolic BP 1.4 (95% CI: 0.14 to 2.7, P = 0.042) mm Hg, and for nighttime diastolic BP −0.7 (95% CI: −1.8 to 0.5, P = 0.26) mm Hg. So for daytime diastolic BP there was a small but statistically significant increase in the ABP after EECP compared with the baseline value.

For heart rate, the increase just after the EECP course compared with baseline was 0.0 (95% CI: −1.4 to 1.5, P = 0.96) min−1 in daytime and −0.9 (95% CI: −2.2 to 0.4, P = 0.20) min−1 for nighttime values.

To assess the effect of EECP on ABP according to the level of baseline ABP, we analyzed the ABP readings according to quartiles of baseline ABP using multivariate repeated measures analysis. No interaction was found between quartiles of baseline ABP and change in ABP, whether systolic/diastolic or daytime/nighttime were assessed (P > 0.10).

We also assessed the change in ABP according to baseline level of the clinic BP. A categorical variable was computed according to a systolic clinic BP value > (n = 14) or < (n = 36) 130 mm Hg, and no interaction was found between this variable and change in daytime systolic ABP (P > 0.10) in the multiple repeated measures analysis. Likewise, a categorical variable was created according to a diastolic clinic BP level > (n = 16) or < (n = 34) 80 mm Hg, and similarly no interaction was found between this variable and possible change in daytime diastolic ABP (P > 0.10).

Further, we divided the patients into 2 groups according to an increase (n = 26) or a fall (n = 24) in systolic ABP just after EECP compared with baseline values. No difference between these 2 groups was found concerning each of the baseline characteristics variables shown in Table 1 (P > 0.05).

The CCS class improved from mean 2.6 (SD 0.54) before EECP to 1.5 (SD 0.7) after EECP (P < 0.001).

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

The present study showed that an EECP course did not reduce the ABP level, whether systolic/diastolic or daytime/nighttime readings were analyzed. Just after the EECP course, a small but statistically significant change was found for the daytime diastolic ABP, but this was an increase and the finding is probably due to a type 1 error. Further, the ABP was constant in all baseline quartiles. The antihypertensive medication was held constant during the study period (Table 2). The lack of fall in the BP readings could therefore not be explained by a reduced effect of the antihypertensive medical therapy.

Our finding is contrary to previous reports. In a study from 2008 by Campbell et al, the clinic BP was measured before and after each EECP session as well as 6 weeks after the EECP course.8 They found no effect on diastolic BP, but the overall systolic BP was reduced by 6.4 mm Hg after a course of EECP. This fall in systolic BP over time could, however, have been anticipated, as it is well known that the white-coat effect is reduced when a clinic BP is repeatedly measured by a nurse.18 The amount of antihypertensive medications taken was not given in this article.

In a study from Kristianstad, Sweden, published in 2009, it was concluded that EECP reduced BP compared with a control group.9 This study included 153 patients with refractory angina pectoris. One hundred patients were treated with EECP and 53 were followed as a control group. The study was not randomized and the participants accepted as controls had contraindications to EECP or were not willing to undergo EECP treatment. The 2 groups were not well matched, as the patients in the control group had a significantly higher baseline systolic BP and fewer were treated with β-blockers. In this study also, clinic BP was used. The patients in the EECP group had more contacts with the nurse measuring their BP, as they visited the clinic 35 times for EECP treatment. It is thus reasonable to think that the fall in BP could be explained as a reduction in the white-coat effect as the patients in the EECP group became accustomed to the nurses working in the EECP unit. The change in BP was not controlled for change in antihypertensive medication. Like our patient group, the majority of their patients were treated with antihypertensive medication (β-blockers 79%, calcium channel blockers 44%, long-acting nitroglycerin 78%, renin-angiotensin-aldosterone system blockers 54%, and diuretics 36%).

The finding in our study that EECP does not have a lasting effect on BP is not necessarily in contradiction to the improvement in endothelial function shown in several studies.4–7 A better endothelial function indicates a more responsive muscle layer in the vessel but does not automatically mean that the average degree of contraction in the muscle layer is reduced.

Further, it is well known that ABP is a more reliable measure of BP compared with clinic BP.14,15

Study Limitations

We studied the group of patients routinely offered EECP, patients with angina pectoris despite optimal anti-ischemic medication. The average BP in the group was low, so a blood pressure-lowering effect of EECP in persons with higher BP levels cannot be excluded from this study.

Conclusion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

This study indicates that an EECP course does not have a lasting effect on BP.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References
  • 1
    Michaels AD, Accad M, Ports TA, et al. Left ventricular systolic unloading and augmentation of intraventricular pressure and Doppler flow during enhanced external counterpulsation. Circulation. 2002;106:12371242.
  • 2
    Lawson WE, Kennard ED, Hui JC, et al. Analysis of baseline factors associated with reduction in chest pain in patients with angina pectoris treated by enhanced external counterpulsation. Am J Cardiol. 2003;92:439443.
  • 3
    Michaels AD, Linnemeier G, Soran O, et al. Two-year outcomes after enhanced external counterpulsation for stable angina pectoris (from the International EECP Patient Registry [IEPR]). Am J Cardiol. 2004;93:461464.
  • 4
    Garlichs CD, Zhang H, Werner D, et al. Reduction of serum endothelin-1 levels by pneumatic external counterpulsation. Can J Cardiol. 1998;14:87F.
  • 5
    Masuda D, Nohara R, Hirai T, et al. Enhanced external counterpulsation improved myocardial perfusion and coronary flow reserve in patients with chronic stable angina. Eur Heart J. 2001;22:14511458.
  • 6
    Shechter M, Matetzky S, Feinberg MS, et al. External counterpulsation therapy improves endothelial function in patients with refractory angina pectoris. J Am Coll Cardiol. 2003;42:20902095.
  • 7
    Bonetti PO, Barsness GW, Keelan PC, et al. Enhanced external counterpulsation improves endothelial function in patients with symptomatic coronary artery disease. J Am Coll Cardiol. 2003;41:17611768.
  • 8
    Campbell AR, Satran D, Zenovich AG, et al. Enhanced external counterpulsation improves systolic blood pressure in patients with refractory angina. Am Heart J. 2008;156:12171222.
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    Bondesson S, Pettersson T, Ohlsson O, et al. Effects on blood pressure in patients with refractory angina pectoris after enhanced external counterpulsation. Blood Press. 2010;19:287294.
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    Casey DP, Beck DT, Nichols WW, et al. Effects of enhanced external counterpulsation on arterial stiffness and myocardial oxygen demand in patients with chronic angina pectoris. Am J Cardiol. 2011;107:14661472.
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    Dockery F, Rajkumar C, Bulpitt CJ, et al. Enhanced external counterpulsation does not alter arterial stiffness in patients with angina. Clin Cardiol. 2004;27:689692.
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    Braith RW, Conti CR, Nichols WW, et al. Enhanced external counterpulsation improves peripheral artery flow-mediated dilation in patients with chronic angina: a randomized sham-controlled study. Circulation. 2010;122:16121620.
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    Nichols WW, Estrada JC, Braith RW, et al. Enhanced external counterpulsation treatment improves arterial wall properties and wave reflection characteristics in patients with refractory angina. J Am Coll Cardiol. 2006;48:12081214.
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    Mancia G, Zanchetti A, Agebiti-Rosei E, et al. Ambulatory blood pressure is superior to clinic blood pressure in predicting treatment-induced regression of left ventricular hypertrophy. Circulation. 1997;95:14641470.
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    Mancia G, De BG, Dominiczak A, et al. 2007 Guidelines for the management of arterial hypertension: the Task Force for the Management of Arterial Hypertension of the European Society of Hypertension (ESH) and of the European Society of Cardiology (ESC). Eur Heart J. 2007;28:14621536.
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    O'Brien E, Petrie J, Littler W, et al. The British Hypertension Society protocol for the evaluation of automated and semi-automated blood pressure measuring devices with special reference to ambulatory systems. J Hypertens. 1990;8:607619.
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    May O, Arildsen H, Damsgaard EM. The diurnal variation in blood pressure should be calculated from individually defined day and night times. Blood Press. 1998;7:103108.
  • 18
    Mancia G, Parati G, Pomidossi G, et al. Alerting reaction and rise in blood pressure during measurement by physician and nurse. Hypertension. 1987;9:209215.