Importance of initiation pattern of polymorphic ventricular tachycardia in patients with implantable cardioverter defibrillators

Mechanism of spontaneous initiation of ventricular fibrillation in patients with implantable defibrillators

INTRODUCTION

To improve the mechanistic understanding of spontaneous initiation of ventricular fibrillation (VF), we characterized the patterns of premature ventricular complex (PVC) preceding spontaneous VF in primary and secondary implantable cardioverter-defibrillator (ICD) recipients.

METHODS AND RESULTS

A single-center, cross-sectional analysis of 1209 patients with primary and secondary prevention ICD identified 190 patients who received ICD therapy (firing or antitachycardia pacing) for VF or monomorphic ventricular tachycardia (MMVT). Initiation was quantified by the coupling interval (CI), the cycle length immediately preceding the CI (CL(-1)), the CI corrected by CL(-1) using Fridericia's formula (CIc), and the prematurity index (PI). In both VF (n = 44; 23%) and MMVT (n = 134; 71%), the most common pattern of initiation was late-coupled PVC, followed by the short-long-short pattern. The parameters such as pre-initiation median CL, CL(-1), CI, and PI were not significantly different between VF and MMVT for any patterns. At least some events (45% of VF and 63% of MMVT) had extremely long CIs beyond the QTc cut-off estimated from the CL(-1), suggestive of initiation by a train of multiple PVCs or nonsustained VT instead of a single PVC.

CONCLUSION

Some spontaneous VF events in ICD recipients appear to be initiated by a train of multiple PVC or nonsustained VT rather than a single PVC. This finding indicates that patterns of a single PVC are not an important determinant of VF initiation and thus account for conflicting results in previous studies.

Mode of onset of polymorphic ventricular tachycardia in acute myocardial infarction

BACKGROUND

Polymorphic ventricular tachycardia (PVT) can occur during acute myocardial infarction (MI). In the past, studies investigated the initiation pattern of ventricular tachycardias in different patient populations; however, the mode of onset of PVT in acute MI patients has not been investigated previously.

OBJECTIVE

To retrospectively investigate the electrophysiological features of PVT with different initiation patterns in acute MI patients to assess whether there is a relationship of the initiation patterns of PVT with clinical and electrophysiological characteristics.

METHODS

Sixty-two rhythm strips defined as PVT from 53 patients (mean [± SD] age 63±8 years) with acute ST elevation MI were analyzed. All patients were monitored while they were hospitalized in the coronary care unit, and the electrocardiogram strips were obtained from continuous monitoring. PVT was defined as sudden-onset tachycardia if it was not preceded by ventricular ectopic beats. PVT that was preceded by single or multiple ectopic beats was defined as nonsudden-onset tachycardia.

RESULTS

Nonsudden-onset episodes were more common than suddenonset episodes (40 episodes [64.5%] versus 22 episodes [35.5%]). In the nonsudden-onset group, 25 episodes (62.5%) were initiated after a single ectopic beat, while 15 episodes (37.5%) were initiated after multiple complexes. The mean (± SD) left ventricular ejection fraction of patients with nonsudden-onset PVT was decreased (53±6% versus 65±7%, P<0.01). Nonsudden-onset tachycardias had lower coupling intervals than suddenonset tachycardias. Similarly, the PVT cycle length was shorter in the presence of nonsudden-onset initiation. When nonsudden-onset PVT episodes were further subclassified based on the morphology of the first beat of tachycardia, 26 PVTs (65%) had a first beat of tachycardia similar to the subsequent PVT beats and 14 (35%) did not.

CONCLUSIONS

These results demonstrate that PVT is often preceded by ventricular ectopy in acute MI patients. Nonsudden-onset PVT is usually characterized by a lower coupling interval, shorter PVT cycle length and an associated lower ejection fraction.

Clinical importance of short-long-short sequences: analysing the mode of onset of ventricular tachycardias and atrial fibrillation

Clinical importance of atrial and ventricular ectopic beats are investigated in some experimental and clinical trials. They are common and occur in a broad spectrum of the population. This includes patients without structural heart disease and those with any form of cardiac disease, independent of severity. Although we know something about the mechanisms and etiology of serious ventricular arrhythmias and atrial fibrillation, we don't know a lot about mode of onset of those arrhythmias. Can short-long-short sequences, related ectopic beats predict AF and ventricular tachycardias in some selected groups of patients? In this paper we will try to answer this important question.

Mechanisms of ventricular fibrillation initiation in MADIT II patients with implantable cardioverter defibrillators

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.