Factors predisposing to ventricular tachyarrhythmia leading to appropriate ICD intervention in patients with coronary artery disease or non-ischaemic dilated cardiomyopathy.

Background: In order to achieve optimal outcomes when treating ventricular tachyarrhythmias with implantable devices, it is extremely important to identify parameters predisposing to arrhythmia. In view of current restrictions in healthcare funding, there is a growing demand for additional predictors of arrhythmia that would allow better patient selection for implantable cardioverter-defibrillator (ICD) use for primary prevention of sudden cardiac death (SCD).

Aim: To identify parameters predisposing to ventricular tachyarrhythmia/appropriate ICD intervention in ICD recipients.

Methods: We analysed 376 patients (56 women, 320 men, mean age 66.1 ± 11.2 [range 22-89] years) who underwent ICD implantation between January 2008 and December 2010. Of these, 275 patients underwent ICD implantation for primary prevention of SCD and 101 for secondary prevention. Operative protocols and in-hospital and outpatient records were analysed retrospectively. Mean QRS width and heart rate (HR) were calculated in resting surface electrocardiograms (25 mm/s, 10 mm/1 mV). Intracardiac electrograms stored in ICD memory were used to evaluate appropriateness of anti-arrhythmic interventions and analyse the number of ventricular tachyarrhythmia events, ICD interventions and their type. We analysed the following clinical and procedural variables: age, gender, left ventricular ejection fraction (LVEF), type of SCD prevention (primary or secondary), ICD type (single chamber--VR, dual chamber--DR), performing defibrillation threshold testing to establish defibrillation safety margin at ICD implantation, ventricular lead location (right ventricular outflow tract region, right ventricular apex), mean HR, QRS width, New York Heart Association (NYHA) functional class, occurrence of ventricular tachyarrhythmia/appropriate ICD intervention after implantation, ICD interventions, history of cardiovascular disease and arrhythmia (myocardial infarction, ischaemic and non-ischaemic dilated cardiomyopathy, arterial hypertension, ventricular fibrillation, ventricular tachycardia, permanent atrial fibrillation, percutaneous coronary intervention, and/or coronary artery bypass grafting), and medications (amiodarone, sotalol, beta-blockers, angiotensin-converting enzyme inhibitors [ACEI]/angiotensin receptor blockers [ARB], statins, loop diuretics, aldosterone antagonists).

Results: During the mean follow-up period of 387 ± 300 (range 5-1400) days, appropriate ICD intervention due to ventricular tachyarrhythmia occurred in 68 of 376 ICD patients (61 men, 7 women, mean age 64.7 ± 12.3 [range 22-89] years). Mean time interval from ICD implantation to the occurrence of arrhythmia was 281 ± 229 (range 5-972) days (p 〈 0.001). To optimize sensitivity and specificity when analysing ventricular tachyarrhythmia/appropriate ICD intervention vs. no ventricular tachyarrhythmia/appropriate ICD intervention, cutoff values were established using ROC curves (cutoff for LVEF = 31%, HR = 79 bpm). Using these cutoff values, patients with ventricular tachyarrhythmia/appropriate ICD intervention were compared to those without ventricular tachyarrhythmia/appropriate ICD intervention. Significant differences were observed in LVEF (p< 0.001), HR (p< 0.022), ACEI/ARB use (p< 0.034), and NYHA class (p< 0.001). By Kaplan-Meier univariate analysis, patients with LVEF> 31% (log-rank test p< 0.001), HR ≤ 79 bpm (log-rank test p< 0.022), QRS width ≤ 114 ms (log-rank test p < 0.045), and NYHA class II (log-rank test p< 0.001) were more likely to be free from ventricular tachyarrhythmia/appropriate ICD intervention. Cox multivariate analysis showed that reduced LVEF (≤ 31%) was the only independent predictor of arrhythmia/intervention. LVEF values below 31% are associated with a significant 20-fold increase (p< 0.02) in the risk of arrhythmia during the first 3 years after ICD implantation. Among 68 patients with ventricular tachyarrhythmia/appropriate ICD intervention, mean 4.1 interventions per person occurred during the follow-up period. In the overall study population, the number of interventions was 0.28 per person per year. Overall, 92 inappropriate ICD interventions were observed, all resulting from atrial fibrillation with rapid ventricular rate. Interventions had no effect on total mortality. Higher numbers of appropriate interventions were observed in patients who died due to heart failure.

Conclusions: Factors associated with a significantly increased risk of ventricular tachyarrhythmia/appropriate ICD intervention included reduced LVEF, increased resting HR, NYHA class II or higher heart failure, and wide QRS. Patients with low LVEF (< 31%) are at particular risk of SCD due to ventricular arrhythmia and this parameter alone can influence the decision regarding ICD implantation. No effect of ICD interventions on total mortality was observed, although more ICD interventions were observed in patients who died due to heart failure.