Abstract
Background
Left ventricular ejection fraction (LVEF) ≤35% is the cutoff value used to identify patients at high risk of sudden cardiac death. However, whether patients who have moderate left ventricular dysfunction and left ventricular enlargement (LVE) have a high risk of ventricular arrhythmias (VAs) and cardiac death is unclear.
Hypothesis
Patients with moderate left ventricular dysfunction and LVE may have a high risk of VAs.
Methods
This study retrospectively analyzed the data of 853 patients who have an implantable cardioverter‐defibrillator/cardiac resynchronization therapy cardioverter‐defibrillator equipped with home monitoring. The patients were divided into 4 groups: group A, 35% < LVEF ≤ 45% and left ventricular end‐diastolic dimension (LVEDD) ≥60 mm; group B, LVEF ≤35% and LVEDD <60 mm; group C, 35% < LVEF ≤ 45% and LVEDD <60 mm; and group D, LVEF ≤35% and LVEDD ≥60 mm.
Results
During a mean follow‐up period of 30 ± 13 months, 324 patients (38%) experienced VAs and 125 patients (14.7%) experienced cardiac death. Based on multivariate Cox regression modeling, group A had an increased risk of VAs (A vs B, hazard ratio [HR]: 1.563, 95% confidence interval [CI]: 1.029‐2.375, P = 0.036; A vs C, HR: 1.661, 95% CI: 1.204‐2.294, P = 0.002) and cardiac death (A vs B, HR: 1.845, 95% CI: 1.013‐3.356; A vs C, HR: 2.041, 95% CI: 1.136‐3.731, P = 0.021).
Conclusions
Patients with moderate left ventricular dysfunction and LVE have a high risk of VAs and cardiac death.
Keywords: ventricular arrhythmias, left ventricular end‐diastolic dimension, implantable cardioverter defibrillator, left ventricular ejection fraction
1. INTRODUCTION
Sudden cardiac death (SCD) is the leading cause of cardiovascular death worldwide. Arrhythmic events account for approximately 85% to 90% of SCDs.1 The use of an implantable cardioverter‐defibrillator (ICD) as the first‐line treatment for patients at high risk for SCD has been confirmed by multiple clinical trials.2, 3, 4 However, only one‐fifth of SCDs meet current guideline recommendations for ICD implantation.5
A low left ventricular ejection fraction (LVEF; <35%) was used to guide ICD/cardiac resynchronization therapy cardioverter‐defibrillator (CRT‐D) implantation.6 An increased heart size, as measured by the left ventricular end‐diastolic dimension (LVEDD), has also been identified as a strong risk factor for ventricular arrhythmias (VAs).7, 8, 9, 10 However, left ventricular enlargement (LVE) does not always occur with low LVEF. Thus, questions arise as to whether patients with moderate left ventricular dysfunction and LVE have high risk of VAs and cardiac death.
We aimed to elucidate whether the presence of moderate left ventricular dysfunction (35% < LVEF ≤ 45%)11 and LVE in patients predicts the occurrence of clinical events such as VAs and cardiac death.
2. METHODS
We retrospectively analyzed archived data from the Study of Home Monitoring System Safety and Efficacy in Cardiac Implantable Electronic Device–implanted patients (SUMMIT) registry in China. The protocols were approved by the hospital ethics committees, and all patients provided written informed consent prior to study entry.
2.1. Subjects and device settings
Eight hundred fifty‐three patients who underwent ICD/CRT‐D implantation between February 2009 and August 2014 and met the selection criteria were enrolled. There were 458 patients in the present study having a device for secondary prevention of SCD. Among these patients, 289 (63%) having a history of documented sustained ventricular tachycardia, 120 (26%) having documented ventricular fibrillation and resuscitated SCD, and 48 (11%) having syncope history underwent electrophysiological study, during which ventricular tachycardia or ventricular fibrillation was induced. The demographic characteristics included patient age and sex. Baseline clinical characteristics were obtained from the patients’ medical records prior to ICD implantation and included comorbidities and baseline medication use. The programmed settings were as follows: ventricular tachycardia was detected at rates ≥140 bpm, and ventricular fibrillation was detected at rates ≥200 bpm. VAs were identified from the stored home monitoring (HM) data and confirmed by intracardiac electrograms. Inappropriate events were excluded.
2.2. Selection criteria
The inclusion criteria were (1) patients with an ICD/CRT‐D device (Biotronik, Berlin, Germany) equipped with HM that could process daily HM transmissions, and (2) patients with echocardiographic evaluations in the previous 2 months prior to implantation.
2.3. Echocardiography and groups
If >1 echocardiograms were available, the closest was used. LVE was defined as LVEDD >60 mm.8 Patients enrolled were divided into 4 groups: group A (n = 134), 35% < LVEF ≤ 45% and LVEDD ≥60 mm; group B (n = 120), LVEF ≤35% and LVEDD <60 mm; group C (n = 289), 35% < LVEF ≤ 45% and LVEDD <60 mm; and group D (n = 310), LVEF ≤35% and LVEDD ≥60 mm. Patients with 35% < LVEF ≤ 45% in group A and group C were enrolled according to the guidelines at that time.12, 13
2.4. Endpoints
The primary endpoint was the treatment of VAs by the device. Routine follow‐ups were conducted if the patient's transmission was disrupted. Then, the status of the patient was confirmed by telephone. If a patient died, the date and cause of death were confirmed by contacting the family. The secondary endpoint was cardiac death.
2.5. Statistical analysis
Continuous variables are presented as mean ± SD, and categorical variables are expressed as numbers (percentages). Data comparison among the 4 groups were performed via χ2 test or Fisher exact test for continuous variables and 1‐way analysis of variance with Bonferroni post‐hoc testing for categorical variables. Statistical significance was established as P < 0.05. Kaplan‐Meier curves were plotted to evaluate the association between group A and each of the other 3 groups regarding clinical outcomes. Cox proportional hazard models were conducted for VAs and cardiac death. Hazard ratios (HR) and 95% confidence intervals (CIs) were calculated for each variable for the different endpoints. All variables that had a statistically significant effect at the 0.05 level were introduced into a multivariate Cox proportional hazards model (forced‐entry method). All statistical analysis was performed using SPSS Statistics version 22.0 (IBM Corp., Armonk, New York) and GraphPad Prism software version 6.0 (GraphPad Software, La Jolla, California).
3. RESULTS
3.1. Patient characteristics
A total of 853 patients were included. The median follow‐up period was 30 ± 13 months (range, 1–61 months). Patient characteristics according to the LVEF and LVEDD are detailed in Table 1.
Table 1.
Baseline demographic and clinical characteristics
| All Patients (n = 853) | Group A (n = 134) 35% < LVEF ≤ 45%, LVEDD ≥ 60 mm | Group B (n = 120) LVEF ≤ 35%, LVEDD < 60 mm | Group C (n = 289) 35% < LVEF ≤ 45%, LVEDD < 60 mm | Group D (n = 310) LVEF ≤ 35%, LVEDD ≥ 60 mm | P Value | |
|---|---|---|---|---|---|---|
| Demographics | ||||||
| Age at implantation, y | 60.7 ± 14.4 | 61.0 ± 12.6 | 61.1 ± 15.7 | 59.7 ± 16.3 | 61.3 ± 12.5 | 0.536 |
| Male sex, % | 73.2 | 80.6 | 62.5 | 67.5 | 79.4 | <0.001 |
| NYHA class III–IV, % | 69.3 | 68.9 | 77.3 | 41.5 | 76.1 | <0.001 |
| CRT‐D, % | 43.4 | 36.1 | 35.5 | 16 | 58.4 | <0.001 |
| Primary prevention, % | 46.3 | 36.6 | 78.3 | 6.9 | 74.8 | <0.001 |
| Comorbidities, % | ||||||
| Ischemic cardiomyopathy | 34.9 | 41.8 | 51.3 | 27 | 32.9 | <0.001 |
| HTN | 34.3 | 36.6 | 41.7 | 29.4 | 35.2 | 0.095 |
| DM | 10.8 | 11.9 | 11.7 | 9.3 | 11.3 | 0.804 |
| AF | 11.7 | 10.4 | 20.8 | 6.9 | 13.2 | 0.001 |
| Stroke | 1.8 | 2.2 | 0.8 | 2.4 | 1.3 | 0.593 |
| Pre‐implant syncope | 21 | 16.4 | 20.8 | 28.4 | 16.1 | 0.001 |
| Valvular heart disease | 2.2 | 3.7 | 5 | 1 | 1.6 | 0.045 |
| Echocardiography | ||||||
| LVEF, % | 32.8 ± 7.9 | 38.7 ± 3.5 | 28.7 ± 4.4 | 41.9 ± 5.1 | 28.2 ± 5.0 | <0.001 |
| LVEDD, mm | 65.2 ± 11.9 | 68.8 ± 8.2 | 53.4 ± 7.6 | 54.7 ± 4.8 | 71.8 ± 8.2 | <0.001 |
| Medications, % | ||||||
| β‐Blocker | 64.7 | 66.4 | 61.7 | 56.1 | 67.7 | 0.022 |
| Amiodarone | 30.4 | 37.3 | 25.8 | 36.7 | 23.2 | 0.001 |
| ACEI or ARB | 42.6 | 44.8 | 49.2 | 33.2 | 47.7 | 0.001 |
| Loop diuretic | 55.5 | 44.5 | 49.1 | 34.9 | 69 | <0.001 |
Abbreviations: ACEI, angiotensin‐converting enzyme inhibitor; AF, atrial fibrillation; ARB, angiotensin receptor blocker; CRT‐D, cardiac resynchronization therapy cardioverter‐defibrillator; DM, diabetes mellitus; HTN, hypertension; LVEDD, left ventricular end‐diastolic dimension; LVEF, left ventricular ejection fraction; NYHA, New York Heart Association.
3.2. Prevalence of VAs and cardiac death in the 4 groups
The clinical outcomes of the patients in the 4 groups are presented in Table 2. During the follow‐up, 324 patients (38%) experienced VAs and 125 patients (14.7%) experienced cardiac death. Estimated Kaplan‐Meier survival curves were plotted to determine VAs and cardiac death among patients based on the 4 groups (Figure 1). We used unadjusted and multivariate Cox regression models to estimate the HRs of VAs and cardiac death with group A as the reference group. Figure 2 depicts the multivariate Cox proportional analysis results for the clinical outcomes.
Table 2.
Clinical outcomes of patients in the 4 groups
| Clinical Outcomes | Overall | Group A | Group B | Group C | Group D |
|---|---|---|---|---|---|
| VAs | 324 (38) | 67 (50) | 41 (34.2) | 104 (36) | 112 (36.1) |
| Cardiac death | 125 (14.7) | 28 (21.1) | 18 (15) | 20 (6.9) | 59 (19) |
Abbreviations: VAs, ventricular arrhythmias.
Data are presented as n (%).
Figure 1.
Kaplan‐Meier estimates of the cumulative incidence of the outcomes: (A) VAs, (B) cardiac death. Abbreviations: VA, ventricular arrhythmia.
Figure 2.
Fully adjusted HRs with 95% CIs for VAs and cardiac death, respectively, with group A as a reference. The y‐axis refers to the HR between 2 groups. *P < 0.05. Abbreviations: CI, confidence interval; HR, hazard ratio; VA, ventricular arrhythmia.
3.2.1. The prevalence of VAs in the 4 groups
During the follow‐up, 324 patients experienced VAs with 67 (50%) patients in group A, 41 (34.2%) patients in group B, 104 (36%) patients in group C, and 112 (36.1%) patients in group D. In an unadjusted model (Figure 1A), group A had an increased risk of VAs compared with the other 3 groups. However, following adjustment in a multivariate model, group A continued to have an increased risk of VAs compared with group B (HR: 1.563, 95% CI: 1.029‐2.375, P = 0.036) and group C (HR: 1.661, 95% CI: 1.204‐2.294, P = 0.002), but not group D. The covariates included for adjustment were patients with CRT‐D implantation, the presence of syncope and atrial fibrillation, amiodarone use, and treatment for primary prevention.
3.2.2. The prevalence of cardiac death in the 4 groups
In group A, 28 (21.1%) patients experienced cardiac death, along with 18 (15%) patients in group B, 20 (6.9%) patients in group C, and 59 (19%) patients in group D. In an unadjusted model (Figure 1B), group A had an increased risk of cardiac death compared with group B and group C. However, there was no statistical difference between group A and group D. Group C had decreased risk of cardiac death compared with all 3 other groups. When adjusted in a multivariate model, group A continued to have an increased risk of cardiac death compared with group B (HR: 1.845, 95% CI: 1.013‐3.356, P = 0.045) and group C (HR: 2.041, 95% CI: 1.136‐3.731, P = 0.021). There was no significant difference between group A and group D in both the univariate and multivariate Cox regression model. The covariates included for adjustment were age, β‐blocker and diuretic use, the presence of CRT‐D, the presence of hypertension and ischemic heart disease, previous myocardial infarction (MI), treatment for primary prevention, and New York Heart Association classification.
3.2.3. Prevalence of VAs and cardiac death according to type of cardiopathy
We further analyzed the data based on ischemic cardiomyopathy and nonischemic cardiomyopathy. Group A had increased risk of VAs and cardiac death in patients with nonischemic cardiomyopathy compared with group B and C, no matter in the univariate or multivariate Cox regression model (Table 3). However, in patients with ischemic cardiomyopathy, group A only had increased risk of cardiac death compared with group C, no matter in the univariate or multivariate Cox regression model (Table 3).
Table 3.
Univariate and multivariate Cox proportional hazard models according to type of cardiopathy
| Between Groups | HR | 95% CI | P Value | |
|---|---|---|---|---|
| Ischemic cardiomyopathy | ||||
| Univariate | ||||
| Cardiac death | Group A vs C | 2.747 | 1.214‐6.211 | 0.015 |
| Multivariate | ||||
| Cardiac death | Group A vs C | 2.193 | 1.11‐5.05 | 0.046 |
| Nonischemic cardiomyopathy | ||||
| Univariate | ||||
| VAs | Group A vs B | 1.37 | 1.02‐1.84 | 0.036 |
| Group A vs C | 1.59 | 1.08‐2.35 | 0.018 | |
| Cardiac death | Group A vs B | 2.39 | 1.04‐5.52 | 0.04 |
| Group A vs C | 2.99 | 1.32‐6.76 | 0.009 | |
| Multivariate | ||||
| VAs | Group A vs B | 1.23 | 1.01‐1.5 | 0.045 |
| Group A vs C | 1.52 | 1.04‐2.24 | 0.032 | |
| Cardiac death | Group A vs B | 1.908 | 1.01‐3.60 | 0.046 |
| Group A vs C | 2.40 | 1.04‐5.52 | 0.04 | |
Abbreviations: CI, confidence interval; HR, hazard ratio; VA, ventricular arrhythmia.
4. DISCUSSION
The most significant finding of the present study is that patients with ICD/CRT‐D implantation who had 35% < LVEF ≤ 45% and LVEDD ≥60 mm exhibited increased incidence of VAs and cardiac death compared with patients with 35% < LVEF ≤ 45% and LVEDD <60 mm and patients with LVEF ≤35% and LVEDD <60 mm.
Compared with group B and group C, patients in group A had larger LVEDD. LVE often results from a scar derived from MI or disordered ventricular excitation from cardiomyopathy infiltration. LVE can create a favourable milieu for re‐entrant ventricular arrhythmias.10 LVEDD as a strong risk factor for VAs in the present study is consistent with previous studies.7, 8, 10, 14 Shen et al demonstrated that LVEDD is a predictor of VAs and SCD.7 These authors also reported that LVEDD was a risk marker of SCD in heart failure patients.15 However, it is unclear whether the patients with LVE in these studies had moderate LVEF as well. In contrast to previous studies, we investigated LVEF and LVEDD in ICD/CRT‐D patients with HM, which allowed accurate identification of VAs. Moreover, we grouped patients with LVEDD and LVEF to determine whether patients who had LVE with moderate LVEF had increased risk of VAs and cardiac death.8
Compared with group B, patients in group A have moderate LVEF and LVE. Given its demonstrated association with increased mortality risk,2, 4 an LVEF ≤35% is the cutoff used to identify patients at high risk of SCD according to current guidelines.16 However, the presence of low LVEF has limited predictive accuracy for VAs.17, 18 The insufficient sensitivity of low ejection fractions in the prediction of SCD has also been supported by several studies.19, 20 In a study by La Rovere et al,19 only 44% of the patients who died of SCD had an LVEF ≤35%. Low ejection fractions have a high power to predict death but low specificity in predicting SCD.21, 22
In the present study, patients in group A exhibited no increased risks of VAs and cardiac death compared with group D. Patients with moderate LVEF and LVE may be at a special stage of the disease. Some studies found recovery of LVEF but no change in LVEDD.14, 23 Under the standard heart failure therapy, LVEFs of patients with severe LVEF may undergo recovery, whereas those with larger LVEDDs are less likely to recover.24 Moderate LVEF also has frequently been reported in post‐MI patients; after reperfusion therapy, >85% of survivors of MI have only mild or moderate reduction of LVEF in the recovery phase.25 A previous study also demonstrated that most SCD occurs in patients with mild or moderate left ventricular dysfunction.26
4.1. Study Limitations
This study was retrospective; thus, a prospective one is necessary to validate these results. Some patients with 35% < LVEF ≤ 40% were enrolled by the standards of the time. Whether the positive electrophysiological study was the risk factor that prompted the implantation of ICD is unknown. We were not able to obtain the timing of ICD implantation after MI and adjust for it as a risk factor.
5. CONCLUSION
In the present study, 35% < LVEF ≤ 45% and LVEDD ≥60 mm was an independent risk factor of VAs and cardiac death. These results will be helpful for doctors to make proper clinical decisions.
Conflicts of Interest
The authors have no other funding, financial relationships, or conflicts of interest to disclose.
Acknowledgments
The authors thank Hui Li (Beijing Hui Kang Xin Technology Co., Ltd.) and his group for data processing and monitoring.
Zhao S, Chen K, Su Y, Hua W, Yang J, Chen S, Liang Z, Xu W and Zhang S. High incidence of ventricular arrhythmias in patients with left ventricular enlargement and moderate left ventricular dysfunction, Clin Cardiol 2016;39(12):703–708.
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