Nonsustained ventricular tachycardias (NSVTs) are frequently observed in patients with left ventricular (LV) dysfunction. The prognostic implications of such NSVTs are conflicting. Our objective was to determine the relation between the burden of NSVT occurring early (within the first 6 months after ICD implant) and prognosis among ICD patients with LV dysfunction. We followed 416 ICD patients (age: 65 ± 11 years; LV ejection fraction: 30 ± 8; ischemic origin: 62%; primary prevention: 63%) with LV dysfunction for 41 ± 27 months. ICD programming was standardized. NSVT was defined as any VT of ≥5 beats at ≥150 beats/min which did not meet the detection criteria occurring within the first 6 months after ICD implant. A total of 250 patients (60%) presented at least one NSVT (median = 2; interquartile range 0 to 7). We classified the patients into 3 groups according to the number of NSVTs: no NSVT (n = 166); 1 to 5 NSVTs (n = 130); and >5 NSVTs (n = 120). The incidence of cardiac mortality (7.2% vs 17.7% vs 31.7%; p = 0.003), hospitalizations for heart failure (10.6% vs 24.4% vs 44.7%; p <0.001), and appropriate shock (15.7% vs 24.8% vs 43.8%; p <0.001) increased significantly with the number of NSVTs. By multivariate analysis, >5 NSVTs were found to be an independent predictor of cardiac mortality (hazard ratio [HR] 1.75; p = 0.03), hospitalization due to heart failure (HR 1.72; p = 0.001), and appropriate shock (HR 1.89; p <0.001) but not of inappropriate therapy (HR 0.9; p = 0.6). In conclusion, among ICD patients with LV dysfunction, NSVT episodes occurring in the first 6 months after implant are independently associated with a poor prognosis. Subjects with >5 NSVTs are at the highest risk.
Nonsustained ventricular tachycardia (NSVT) is a frequent phenomenon in patients with structural heart disease, particularly with left ventricular (LV) dysfunction and heart failure. Some studies using the occurrence of NSVTs in ambulatory outpatient patients have shown that NSVTs increase mortality or appropriate implantable cardioverter-defibrillator (ICD) therapies, whereas others have shown that NSVTs do not offer additional information regarding prognosis. Since modern ICDs permit the detection of arrhythmic events, they provide an excellent opportunity to determine the incidence and clinical impact of NSVT. However, very little data are available regarding the prognostic impact of NSVT detected by ICDs. Although Chen et al reported that fast NSVTs are associated with a higher mortality and arrhythmic events among ICD primary prevention patients, whether such findings can be extrapolated to slow NSVT and to secondary prevention patients is unknown. The present study evaluates the incidence and prognostic impact of NSVT (≥150 beats/min) burden identified upon ICD interrogation during the first 6 months after implant in a nonselected population of primary and secondary prevention patients with LV dysfunction.
Methods
A total of 416 patients (age: 65 ± 11 years; LV ejection fraction (EF): 30 ± 8; ischemic origin: 62%; primary prevention: 63%; functional class >1: 63%) with LV dysfunction–(LVEF) <45%–an ICD implanted according to the standard indications and without cardiac resynchronization therapy were studied. Subjects were consecutively enrolled from January 2006 to December 2013 and were followed up until June 2014. Vital status was available for 100% of the subjects at the end of the follow-up period. Patient recruitment was carried out at ICD implantation. Mean follow-up after implant was 41 ± 27 months. Doses of medical treatments were carefully optimized following current guidelines.
All patients underwent implantation of pectoral devices with a transvenous endocardial lead positioned at the right ventricular apex. Upon discharge from the hospital, patients were seen at 1 week, 1, 3, and at 6 months after implantation, including clinical visits, symptom monitoring, and ICD interrogation. Thereafter, checkups took place every 6 months. The study complied with the Declaration of Helsinki. Enrollment of the patients followed the acceptance by the institutional review board of the protocol, and informed consent was obtained from all patients.
Detection and therapy programming were standardized and included 3 zones : Ventricular fibrillation (cycle length <250 ms), fast VT (cycle length from 250 to 320 ms), and slow VT (cycle length from 321 to 400 ms). First antitachycardia pacing therapy in the fast VT zone was a single 5-pulse–burst pacing train at 84% of the VT cycle length. Therapies for slow VT included 3 consecutive bursts of 15 pulses at 91% of the VT cycle length, with no decrement. Failed antitachycardia pacing therapies were followed by a sequence of shocks. Additional criteria (onset, stability, and morphology) were programmed in the slow VT zone. In the Medtronic devices the “smart mode” was programmed to “off.”
All tip-to-ring– and far-field–stored electrograms from spontaneous episodes were classified using predetermined criteria based on visual inspection and comparison with sinus rhythm electrograms. Exclusion of supraventricular tachycardias and the classification of ventricular tachyarrhythmias were performed by 2 independent investigators. In case of lack of consensus, a third investigator was consulted.
NSVT was defined as any ventricular tachyarrhythmia with >5 beats at ≥150 beats/min terminating spontaneously before therapy that occurred within the first 6 months after ICD implant Figure 1 . Cardiac death was considered as any death occurring due to myocardial ischemia, heart failure, or arrhythmias. Hospitalization due to heart failure was defined as an admission for heart failure with 24 or more hours of intravenous administration of inotropic or vasoactive drugs.
Statistical analysis was performed using the 11.5 version for Windows (SPSS Inc., Chicago, Illinois). Normal and continuous variables were described by means and SDs, whereas categorical variables were summarized by the number of patients and percentages. Comparison of the categorical variables was performed with the chi-square test (or Fisher’s exact test if n <5). Comparison of 2 normal variables (determined by the Kolgomorov–Smirnov test), and continuous variables was done with the Student t test. Comparison of >2 continuous variables was performed using the analysis of variance test. To determine the individual antitachycardia pacing effectiveness and both the mean cycle length and duration of NSVT episodes, adjusted per multiple episode per patient, the generalized estimating equations method was used in the calculations and comparisons. To analyze the correlation between NSVT burden and prognostic variables, the C coefficient was established in the receiver-operating characteristic curve. Furthermore, the cut-off point of NSVT burden with the best sensitivity and specificity was carried out. Event-free survival is depicted graphically according to the method of Kaplan and Meier, with comparisons of cumulative incidences by the log-rank test. Univariate and multivariate Cox proportional hazards regression analysis was used to evaluate the contribution of baseline clinical factors–age, gender, diabetes, LVEF, functional class (New York Heart Association), origin (ischemic vs nonischemic), indication (primary vs secondary prevention), QRS duration (ms), atrial fibrillation, body mass index, serum creatinine (mg/dl), number of shocks, medical treatments, mean cycle length of NSVT episodes (ms), mean duration of NSVT episodes (ms) and >5 NSVT–to the occurrence of clinical events. Univariate variables with a p <0.1 were included in a multivariate Cox regression model.
Results
A total of 2,335 episodes of NSVT were recorded by devices. After excluding 134 which did not have stored electrograms, we analyzed 2,201 NSVTs occurring in 250 of the 416 patients. The mean length and the mean cycle length of NSVT were 10 ± 7 beats (3.3 ± 2.7 seconds) and 323 ± 32 ms, respectively. Fifty-five percent of such events had a cycle length >320 ms. Cycle length of NSVT was lower when occurring in primary prevention patients: 320 ± 31 versus 327 ± 32 ms (p = 0.008) with similar results being observed in ischemic and nonischemic patients: 323 ± 35 versus 324 ± 26 ms (p = 0.7). The median of NSVT episodes per patient was 2 (interquartile range 0 to 7). Five percent of patients had 25 or more NSVT. All NSVTs with no stored electrograms occurred in patients with >5 episodes.
We further classified the patients according to the tertiles of NSVT burden: 0 (n = 166), 1 to 5 (n = 130), and >5 episodes (n = 120). The baseline clinical characteristics of ICD patients according to the NSVT burden are displayed in Table 1 . We found significant differences in patients with more NSVT episodes, including older age, higher functional class, more atrial fibrillation, higher levels of serum creatinine, higher prevalence of previous episodes of NSVT. In addition, they were more likely to be receiving treatment with both digoxin and amiodarone. Patients with >5 NSVTs had a wider QRS complex and were less likely to be on β blockers.
| Variable | All patients n=416 | Patients without episodes n=166 (40) | Patients with 1-5 episodes n=130 (31) | Patients with > 5 episodes n=120 (29) | p value |
|---|---|---|---|---|---|
| Age, years | 65±11 | 63±12 | 65±12 | 69±9 | <0.001 ∗ |
| Male gender | 87% | 87% | 88% | 87% | 0.9 † |
| Body mass index (kg/m 2 ) | 28±3 | 27±2 | 29±3 | 29±3 | <0.001 ‡ |
| Ischemic etiology | 62% | 63 % | 62% | 63% | 0.8 † |
| Secondary prevention | 37% | 35% | 38% | 37% | 0.8 † |
| Atrial fibrillation | 15% | 20% | 32% | 0.002 † | |
| New York Heart Association Functional Class >1 | 63% | 56% | 64% | 71% | 0.036 † |
| Diabetes Mellitus | 25% | 28% | 22% | 24% | 0.5 ∗ |
| Left Ventricular Ejection Fraction (%) | 30±8 | 30±8 | 30±9 | 30±7 | 0.8 ∗ |
| QRS duration (ms) | 118±24 | 114±23 | 120±22 | 121±26 | 0.018 ‡ |
| Serum creatinine (mg/dl) | 1.22±0.48 | 1.15±0.33 | 1.22±0.37 | 1.32±0.7 | 0.012 ∗ |
| Previous clinical non-sustained ventricular tachycardias | 36% | 11% | 39% | 51% | <0.001 † |
| Statins | 62% | 63% | 61% | 59% | 0.7 † |
| Beta-blockers | 76% | 83% | 82% | 70% | 0.011 § |
| Angiotensin Converting Enzyme Inhibitors or Angiotensin II Receptor Blockers | 86% | 86% | 85% | 89% | 0.7 † |
| Amiodarone | 13% | 8% | 15% | 20% | 0.011 † |
| Digoxin | 18% | 9% | 22% | 25% | 0.001 ¶ |
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