Ambulatory electrocardiographic markers predict serious cardiac events in patients with chronic kidney disease: The Japanese Noninvasive Electrocardiographic Risk Stratification of Sudden Cardiac Death in Chronic Kidney Disease (JANIES‐CKD) study

Abstract Background Noninvasive electrocardiographic markers (NIEMs) are promising arrhythmic risk stratification tools for assessing the risk of sudden cardiac death. However, little is known about their utility in patients with chronic kidney disease (CKD) and organic heart disease. This study aimed to determine whether NIEMs can predict cardiac events in patients with CKD and structural heart disease (CKD‐SHD). Methods We prospectively analyzed 183 CKD‐SHD patients (median age, 69 years [interquartile range, 61−77 years]) who underwent 24‐h ambulatory electrocardiographic monitoring and assessed the worst values for ambulatory‐based late potentials (w‐LPs), heart rate turbulence, and nonsustained ventricular tachycardia (NSVT). The primary endpoint was the occurrence of documented lethal ventricular tachyarrhythmias (ventricular fibrillation or sustained ventricular tachycardia) or cardiac death. The secondary endpoint was admission for cardiovascular causes. Results Thirteen patients reached the primary endpoint during a follow‐up period of 24 ± 11 months. Cox univariate regression analysis showed that existence of w‐LPs (hazard ratio [HR] = 6.04, 95% confidence interval [CI]: 1.4−22.3, p = .007) and NSVT [HR = 8.72, 95% CI: 2.8−26.5: p < .001] was significantly associated with the primary endpoint. Kaplan–Meier analysis demonstrated that the combination of w‐LPs and NSVT resulted in a lower event‐free survival rate than did other NIEMs (p < .0001). No NIEM was useful in predicting the secondary endpoint, although the left ventricular mass index was correlated with the secondary endpoint. Conclusion The combination of w‐LPs and NSVT was a significant risk factor for lethal ventricular tachyarrhythmias and cardiac death in CKD‐SHD patients.


| INTRODUC TI ON
Patients with chronic kidney disease (CKD), which number more than 20 million in the United States (Pun, 2014), have a 4-to 20-fold higher risk of sudden cardiac death (SCD) than does the general population.
Cardiovascular disease (CVD) and CKD are closely related, with the former having a significant impact on CKD mortality (Go et al., 2004;Roncoetal.,2008).Alargecohortstudyhasshownthatwhile only 3.1% of stage 2-4 CKD patients progress to renal replacement therapy, 24.9% die (Keith et al., 2004), and that a higher cumulative cardiovascular comorbidity was associated with the risk of death regardless of CKD severity (Jesky et al., 2013). Therefore, in CKD management, clinicians should pay attention not only to renal function deterioration but also to CVD. Identifying CKD patients at high risk, particularly those with structural heart disease (SHD), is of great importance. However, few studies have addressed this issue to date.
It has been reported that noninvasive electrocardiographic markers (NIEMs), including late potentials (LPs) (Gatzoulis et al., 2018),heartrateturbulence(HRT) (Baueretal.,2008),andnonsustained ventricular tachycardia (NSVT) , are useful predictors of lethal arrhythmic events and SCD in patients with SHD. We have recently demonstrated that a combined assessment of NIEMs obtained from high-resolution digital electrocardiogram (ECG) systems accurately predicts the occurrence of lethal arrhythmias and SCD in patients with SHD Kinoshita et al., 2020). Although LPs have been associated with mortality and SCD in patients with end-stage renal disease (Morales etal.,1998),littleisknownabouttheusefulnessofotherNIEMsin predicting lethal arrhythmias or cardiac mortality in patients with CKD, regardless of disease severity or the presence of concurrent SHD.
This study aimed to investigate whether noninvasive ECG parameters assessed using new ambulatory ECG systems could predict cardiac death, lethal arrhythmic events, and nonfatal cardiovascular events in CKD patients with SHD.

| Study design and population
This study was a sub-study of the Japanese Noninvasive

Electrocardiographic Risk Stratification for Prediction of Sudden
Cardiac Death (JANIES) study . The JANIES study was a multicenter, observational, prospective cohort study. It assessed the role of noninvasive ECG markers, obtained simultaneously using a 24-h high-resolution digital ambulatory ECG system, in predicting severe cardiac events, such as lethal arrhythmias and cardiac mortality in high-risk patients. Recruitment was performed between April 2012 and March 2015. The inclusion and exclusion criteria used have been reported previously .
Briefly, the JANIES study included patients with structural or idiopathic cardiac disorders who underwent 24-h high-resolution digital ambulatory monitoring ( Figure 1). The exclusion criteria were as follows: hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, persistent atrial fibrillation or flutter, right or left bundle branch block and intraventricular conduction delay, permanent pacing, second-or third-degree atrioventricular block, nonsimultaneous measurement of ECG markers, and patient dropout (missing follow-up data or unknown cause).
In this study, we exclusively selected patients with CKD for analysis. CKD was defined according to the Kidney Disease: Improving Global Outcomes (KDIGO) 2012 classification (Levey etal.,2005). Overall,183patients(meanage70years,127men) were eligible for analysis. Patient characteristics are presented in NSVT resulted in a lower event-free survival rate than did other NIEMs (p < .0001).
No NIEM was useful in predicting the secondary endpoint, although the left ventricular mass index was correlated with the secondary endpoint.

Conclusion:
The combination of w-LPs and NSVT was a significant risk factor for lethal ventricular tachyarrhythmias and cardiac death in CKD-SHD patients.

K E Y W O R D S
ambulatory electrocardiography, chronic kidney disease, late potentials, nonsustained ventricular tachycardia, sudden cardiac death, ventricular tachycardia characteristics, including the prevalence of hypertension, dyslipidemia, diabetes mellitus, serum brain natriuretic peptide levels, New York Heart Association (NYHA) functional class, and medication use, are detailed in Table 1.
The study was conducted in accordance with the Declaration of
The presence of NSVT was defined as more than three consecutive ventricular premature contractions (VPCs) at >100 beats/min, as previously reported (Lin et al., 2016). All participants underwent 24-h ECG assessment during their ordinary daily activities.
Additionally, ECGs were obtained to assess cardiac structure and function; the left ventricular ejection fraction (LVEF), left ventricular end-diastolic diameter, left ventricular mass (LVM), and LVMI were measured.

| Measurement of ambulatory-based LPs
Electrocardiogram data for measurement of ambulatory-based LPs were obtained at a sampling rate of 1000 Hz and amplitude resolu-tionusinga20-bitanalogtodigitalconverter.Athree-pole(18dB/ octave) corrected bidirectional filter (infinite pulse response method) was used, with a bandpass ranging from 40 to 200 Hz. ECG data were filtered and ranged from 40 to 250 Hz. Orthogonal X, Y, and Z bipolar leads with silver-silver chloride electrodes (Magnerode ® ; Fukuda

| HRT measurements
Heart rate turbulence was measured according to a previously established protocol (Bauer et al., 2008) and recorded when more than one VPC occurred. HRT is characterized by two parameters, turbulence onset (TO) and turbulence slope (TS). TO captures the early-phase sinus rhythm acceleration after VPC, followed by TS, which captures the compensatory deceleration phase. TO was calculated as the shortening ratio of RR intervals immediately after the compensatory pause of the VPC. TS was calculated as the steepest regression over any five consecutive sinus rhythm RR intervals after VPCandwithin15sinusrhythmbeats(Baueretal.,2008).TO≥0% andTS≤2.5ms/RRintervalswereconsideredabnormal.HRTwas identified when both TO and TS were abnormal. Isolated TO and TS abnormalities were not regarded as HRT, nor was the inability to calculateHRTduetotheabsenceofVPC(Baueretal.,2008).

| Study endpoints and follow-up
The primary endpoint was the occurrence of lethal ventricular tachyarrhythmias, such as ventricular fibrillation (VF) or sustained ventricular tachycardia (SVT) and cardiac death. Shock delivery using an implantable cardioverter-defibrillator (ICD) and anti-tachycardia pacing for sustained VT were included as lethal ventricular tachyarrhythmias. The secondary endpoint was a composite of hospital admission due to heart failure, percutaneous coronary intervention(PCI),coronaryarterybypasssurgery(CABG),peripheralartery disease intervention, or aortic dissection. Causes of death were retrieved from medical or autopsy records and testimonies of the primary doctors or witnesses. The occurrence of lethal ventricular tachyarrhythmias was verified through ECG monitoring performed in the hospital or by 24-h Holter ECG recorded during hospitalization or inferred using an ICD. Follow-up data were collected at 6-month intervals until September 2015.

| Statistical analyses
Data are presented as mean ± standard deviation for normally distributed continuous variables and as medians (interquartile range: 25th-75th percentile) for nonnormally distributed variables. The normality of the distribution was tested using the Shapiro-Wilk method.
Patient characteristics were compared using the χ 2 test for categorical variables, the Student's t-test for continuous and parametric data, and the Mann-Whitney test for nonparametric data. Cox univariate and multivariate regression analyses were performed to investigate associations between the endpoints and clinical parameters. Cardiac event-free survival rates were calculated for each NIEM using the Kaplan-Meier method, and differences in cardiac event-free survival rates were calculated using the log-rank test. Statistical analyses were conductedusingSPSSsoftwareversion25(IBMCorp).Alltestswere two-sided, and a p-value of .05 was considered significant.

| Cardiac events during follow-up
During the mean follow-up period of 20.7 ± 11.1 months, 13 patients reached the primary endpoint of the study. Their characteristics are shown in Tables 2 and 3.

| Primaryendpoint
Univariate analysis (     (Table S1). Kaplan-Meier analysis revealed that the concurrence of w-LPs and NSVT positivity was associated with a significantly lower event-free survival rate than was the presence of either variable alone (log-rank, p < .0001) (Figure 2).

| DISCUSS ION
The main findings of this study were as follows. In patients with CKD and SHD, the combination of w-LPs and NSVT was a strong predictor of lethal ventricular tachyarrhythmia or cardiac death, even after adjusting for factors, such as age, sex, eGFR, and LVEF. The combined positivity of w-LP and NSVT was associated with a significantly lower event-free survival rate than was the positivity of either variable alone, and no independent factor was useful for predicting the secondary endpoint.

| Combined ECG markers for primary endpoint prediction
To the best of our knowledge, this is the first study to evaluate the usefulness of w-LPs, HRT, and NSVT in patients with CKD.
Furthermore, we evaluated the utility of w-LPs recorded using a new and highly versatile high-resolution ambulatory ECG system.
Individually, w-LPs, HRT, and NSVT had high negative predictive values for predicting lethal ventricular tachyarrhythmias and cardiacdeath(90%−95%),withPPVsof10%-20%.Webelievethatthe strong point of our study is the finding that LPs and NSVT combined haveasuperiorPPVthandoeseithervariablealone.Ameta-analysis by Fu et al. (2017) reported that ICD implantation improved the survival rate in patients with CKD stage 3 but was not beneficial in patients with stage 4 or 5 disease. They suggested that this may be because as CKD progresses, sympathetic nervous system activity increases and is modified by heart failure, making the ICD less effective. Therefore, ICD implantation should be considered, especially in patients with CKD stage 3 who are NSVT and w-LP positive and have not had ICD implantation. In our study, all four patients who developed SVT/VF had stage 3 CKD, and the presence of NSVT and w-LP was a useful risk marker in 50% (2/4) of these patients (Table 3). These two patients may have survived due to ICD implan-

tation.Inaddition,onlyoneofthe183patientsinourstudyresulted
in death without any NIEM (Table 3, no 12). Therefore, if a CKD patient with cardiac disease has no NIEMs, it is highly improbable that a fatal event such as SVT/VF or heart failure death will occur in the near future.

| Pathophysiology of lethal ventricular tachyarrhythmias and heart failure death in CKD patients and its relationship with ECG markers
The pathophysiology of lethal ventricular arrhythmias in CKD patients has not been fully elucidated. In the general population, electrophysiological abnormalities due to SHD and modifying factors, such as electrolyte imbalance or heart failure, facilitate the progression of transient arrhythmic triggers (e.g., extrasystoles) into lethal arrhythmias (Ikeda et al., 2007). It is speculated that the interaction between CKD and SHD accelerates these root causes, increasing the risk of sudden arrhythmic death. It is well known that LPs reflect an abnormal electrophysiological condition in patients with SHD (Ikeda etal.,2007;Zimmermannetal.,1997).Additionally,NSVTcouldbea trigger of lethal arrhythmias, such as VT and VF (Ikeda et al., 2007). Because w-LPs and NSVT are expressions of underlying arrhythmic mechanisms, they were predictive of the primary endpoint in this study.

TA B L E 4 Associationandprognosticabilityofambulatoryelectrocardiographicparameterswithrespecttotheprimaryendpoint
Nine of the 13 patients who reached the primary endpoint died of heart failure, and more than four developed fatal arrhythmias.
CKD patients are likely to suffer from ischemic heart disease and LVH, which lead to myocardial electrophysiological abnormalities, especially ventricular conduction delay (Morales et al., 1998).
Moralesetal (Moralesetal.,1998)foundthatinpatientswithCKD, LVH could prolong the fQRS duration in LPs due to a longer depolarizationtime.Additionally,pumpfailureiscommoninCKDpatients due to neurohormonal abnormalities, left diastolic dysfunction, inflammation due to decreased coronary perfusion, and coronary tissue calcification (Ronco et al., 2008). In CKD patients, complex ventricular arrhythmias such as NSVT were significantly associated with a lower LVEF, a higher LVMI, and an increased calcium score (Bonato et al., 2016). Additionally, it has been reported that documented NSVT is associated with increased mortality in CKD patients with SHD (Bonato et al., 2016). Because w-LPs and NSVT reflect the severity of heart failure due to LVH, they were predictive of death due to heart failure in this study. However, there were no significant differences in LVMI between the primary endpoint and event-free groups (Table 2). Cox univariate analysis showed that neither LVM nor LVMI could predict the primary endpoint. Therefore, the combination of w-LPs and NSVT was a superior surrogate marker to predict the progression of heart failure leading to death.

| Noninvasive ECG markers and the secondary endpoint
In this study, NIEMs were not useful for predicting cardiac events requiring hospital admission (secondary endpoint). Expectations in this regard were low because these markers have ordinarily been associated with severe events, such as SCD or lethal arrhythmias Kinoshita et al., 2020;Morales et al., 1998). In our study, there was a significant association between LVMI and the secondary endpoint (Table 4), which is consistent with the results from several other studies that showed a positive correlation between an increased LVMI and complications, such as heartfailure,myocardialinfarction,anginarequiringPCIorCABG, and stroke (Dubin et al., 2017;Lee et al., 2020;Sundström et al., 2001).

| Limitations
Our study has some limitations. First, although the JANIES study included a large population (n = 1829), our sample size was small becausewefocusedsolelyonCKDpatients.Additionally,sinceall subjects had SHD, our results cannot be extrapolated to CKD patients without cardiac disease. Finally, because of the limited scope of our study, T-wave alternans were not included for analysis. This recognized repolarization abnormality increases the risk for lethal F I G U R E 2 Kaplan-Meierevent-freesurvivalcurvesofNIEMsforcardiacdeathandlethalarrhythmias(primaryendpoint).The combination of a-LP and NSVT was associated with a significantly lower event-free survival rate than was any other combination. NIEMs, noninvasive electrocardiographic markers; NSVT, nonsustained ventricular tachycardia; w-LPs, worst values of ambulatory-based late potentials ventricular tachyarrhythmias or SCD and may be a useful predictive parameter in CKD patients.

| CON CLUS ION
In patients with CKD and SHD, the combined assessment of w-LPs and NSVT was a strong predictor of lethal ventricular tachyarrhythmia and cardiac death. Additionally, the presence of combined w-LPs and NSVT was associated with a significantly lower event-free survival rate. However, NIEMs were not useful in predicting cardiovascular events requiring hospital admission. Our results suggest that these parameters may be clinically useful for risk assessment in patients with CKD and SHD. Patients with positive w-LP and documented NSVT should be considered for ICD implantation, particularly those with stage 3 CKD. Future studies, including larger populations of CVD and CKD patients, are needed to confirm our results and explore further applications of these robust risk markers.

ACK N OWLED G M ENTS
The first author (K.H.) would like to express his gratitude and appreciation for his advisor, Hiroaki Shimabukuro, who has been an exceptional mentor, encouraging the author throughout this study. The

CO N FLI C T O F I NTE R E S T
The authors have stated explicitly that there are no conflicts of interest in connection with this article.

E TH I C A L A PPROVA L
The study was conducted in accordance with the Declaration of

DATA AVA I L A B I L I T Y S TAT E M E N T
The data used in this report are available from the corresponding author on reasonable request.