What does this research mean for the field?

In the MADIT II patient population, ventricular fibrillation is predominantly initiated by a single ventricular premature complex rather than a short-long-short sequence, suggesting that pause-prevention pacing modes are unlikely to reduce the incidence of these episodes. Novelty: ClaimNovelty.INCREMENTAL. Consensus alignment: ConsensusAlignment.NEUTRAL.

January 24, 2008

Mechanisms of Ventricular Fibrillation Initiation in MADIT II Patients with Implantable Cardioverter Defibrillators

Structured PICO

What are the patterns of initiation of ventricular fibrillation in MADIT II patients with implantable cardioverter defibrillators?

Population

29 patients from the MADIT II trial with 60 episodes of ventricular fibrillation (mean age 64.4 +/- 2.5 years)

Intervention

Evaluation of stored intracardiac electrograms from implantable cardioverter defibrillators (ICDs)

Outcome

Patterns of initiation of ventricular fibrillation (VF) and associated intracardiac ECG parameterssurrogate

Ventricular fibrillation in MADIT II patients is more commonly initiated by a single ventricular premature complex than by a short-long-short sequence, suggesting that pacing modes designed to prevent bradycardia and pause-dependent arrhythmias are unlikely to decrease the incidence of most VF episodes.

Abstract

BACKGROUND: The availability of stored intracardiac electrograms from implantable defibrillators (ICDs) has facilitated the study of the mechanisms of ventricular tachyarrhythmia onset. This study aimed to determine the patterns of initiation of ventricular fibrillation (VF) in Multicenter Automatic Defibrillator Implantation Trial (MADIT) II patients along with associated electrocardiogram (ECG) parameters and clinical characteristics. METHODS: Examination of stored electrograms enabled us to evaluate the rhythm preceding each episode of VF and to calculate (intracardiac) ECG parameters including QT, QT peak (QTp), coupling interval, and prematurity index. RESULTS: Sixty episodes of VF among 29 patients (mean age 64.4 +/- 2.5 years) were identified. A single ventricular premature complex (VPC) initiated 46 (77%) episodes whereas a short-long-short (SLS) sequence accounted for 14 (23%) episodes. Of the 29 patients studied, 23 patients had VF episodes preceded by a VPC only, two patients with SLS only, and four patients with both VPC and SLS-initiated episodes. There were no significant differences between initiation patterns in regards to the measured ECG parameters; a faster heart rate with SLS initiation (mean RR prior to VF of 655 +/- 104 ms for SLS and 744 +/- 222 ms for VPC) approached significance (P = 0.06). The two patients with SLS only were not on beta-blockers compared to 83% of the VPC patients. CONCLUSION: Ventricular fibrillation is more commonly initiated by a VPC than by a SLS sequence among the MADIT II population. Current pacing modes designed to prevent bradycardia and pause-dependent arrhythmias are unlikely to decrease the incidence of VPC-initiated episodes of VF.

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