The clinical significance of polymorphic ventricular tachycardia provoked at electrophysiologic testing

Stability: an ICD detection criterion for discriminating atrial fibrillation from ventricular tachycardia

INTRODUCTION

The purpose of this study was to review a new implantable cardioverter defibrillator (ICD) detection criterion, stability, to determine if it can effectively discriminate rapid rhythms of atrial fibrillation from ventricular tachycardia. Inappropriate shocks for rapid atrial fibrillation limit the acceptance of ICDs. The advent of an additional detection criterion, stability, has been postulated to be of value in discriminating rapid atrial fibrillation, which may not warrant treatment, from ventricular tachycardia, which obviously does warrant therapy deliver.

METHODS AND RESULTS

Twenty-six patients were studied during 32 episodes of rapid atrial fibrillation and 24 episodes of monomorphic ventricular tachycardia below 220 beats/min. Each rhythm was repeatedly evaluated by the device at each of the seven stability values available (8, 16, 23, 31, 39, 47, and 55 msec) and then classified as stable or unstable. Upon completion of this acute study, 32 ICD patients had the stability feature activated and were followed for proper arrhythmia treatment by the device. Using stability windows from 8 to 47 msec, all atrial fibrillation rhythms were appropriately classified as unstable. Three of 6 were classified correctly for the 55-msec window. All ventricular tachycardia rhythms were appropriately classified as stable from all stability windows from 8 to 55 msec. Clinical follow-up confirmed appropriate therapy delivery when coupled with sustained rate duration (SRD). Thirty-two patients followed for 292 patient-months had no episodes of untreated ventricular tachycardia with 428 successfully classified as stable and treated. Only three episodes of suspected atrial fibrillation resulted in therapy delivery as the rhythm duration exceeded the SRD of 30 seconds.

CONCLUSIONS

The CPI Ventak PRx ICD is highly reliable in appropriately classifying atrial fibrillation as unstable and monomorphic ventricular tachycardia as stable for most stability windows evaluation tachycardias below 220 beats/min. As a result, when testing of atrial fibrillation is not possible, we recommend the routing programming of this stability feature at the 31-msec window with an SRD of 30 seconds. The reliability of this device in discriminating atrial fibrillation from monomorphic ventricular tachycardia may have important clinical implications for other tiered therapy ICDs with this feature as well as for future ICDs in development.

Clinical significance of rapid ventricular tachycardia (> 270 beats per minute) provoked at programmed stimulation in patients without confirmed rapid ventricular arrhythmias

Rapid uniform ventricular tachycardia (VT) (> 270 beats/min) or ventricular flutter induced during electrophysiological studies is thought not to be clinically significant in patients without cardiac arrest or documented rapid VT. The purpose of the study was to follow up 73 patients with inducible ventricular flutter but without confirmed rapid spontaneous VT. A long follow up (mean 3.5 years) identified two groups of patients. The first group had an excellent outcome and was characterised by a normal 24 hour Holter monitoring. In the second group, however, the risk of cardiac mortality was high (35%) and spontaneous VT was < 270 beats/min (26%) and was characterised by couplets or salvos of extrasystoles on Holter monitoring. In this group the history of syncope and decreased left ejection fraction increased the risk of mortality and VT. The presence of late potentials increased the risk of spontaneous VT. Electrophysiologically guided antiarrhythmic therapy reduced the risk of VT. Ventricular flutter was a non-specific finding in patients with normal Holter monitoring. In contrast, in patients with salvos of extrasystoles, ventricular flutter was associated with a high risk of cardiac mortality and VT.

Programmed electrical stimulation of the ventricle: an efficient, sensitive, and specific protocol

A relatively simple and efficient ventricular programmed electrical stimulation (PES) protocol was developed, capable of achieving high degrees of sensitivity and specificity. In a series of 481 subjects, 1, 2, and 3 extrastimuli (ES) were used successively during sinus rhythm and ventricular pacing at two drive cycle lengths, at one or more ventricular sites, together with rapid ventricular pacing, and other maneuvers such as isoproterenol infusion. Three ES were used immediately after two ES at each drive rate, rather than returning after completion of the protocol with two ES. Using the protocol, appropriate arrhythmias could be induced in 88% of all patients with ventricular fibrillation, 84% of all patients with sustained ventricular tachycardia (91% with underlying coronary disease), and 58% of patients with severe nonsustained ventricular tachycardia. There were significant differences in inducibility between patients whose ventricular arrhythmias were due to coronary artery disease and other causes. In contrast, sustained ventricular arrhythmias (all ventricular fibrillation) could be induced in only 5% of a control group of control patients, for a specificity of 95%. The protocol described is simpler and more efficient than those that use exhaustive testing of two ES before going to three ES. Three ES during sinus rhythm proved to be the most productive step, with a higher yield ratio (true: false-positives) than two ES or three ES during pacing, especially at faster rates. Greater efficiency is also achieved by leaving the timing of an extrastimulus just beyond its effective refractory period when an additional extrastimulus is to be added, compared to protocols in which the extrastimulus is moved later in the cycle and then decremented in tandem with the additional extrastimulus. Coupling intervals less than 200 msec produced some false-positives, but fewer overall than intervals greater than or equal to 200 msec, and with yield ratios comparable to other protocol steps. The protocol described meets NASPE standards for ventricular programmed stimulation protocols, and with its demonstrated specificity and relative simplicity and efficiency may be useful as a model for groups not yet committed to an alternative protocol.

Rapid self-terminating ventricular tachycardia induced during electrophysiologic study: a prospective evaluation

The clinical significance of rapid self-terminating ventricular tachycardia induced during electrophysiologic study was prospectively evaluated in three patient groups with clinical ventricular arrhythmias. Group A (11 patients) had inducible rapid self-terminating ventricular tachycardia only (mean cycle length less than or equal to 250 ms and greater than or equal to 10 beats in duration). In Group B (22 patients) induction of this arrhythmia was followed by the induction of sustained ventricular tachycardia. In Group C (82 patients) sustained ventricular tachycardia was induced without preceding rapid self-terminating ventricular tachycardia. All clinical characteristics of Group B patients were similar to those of Group C patients but differed markedly from those of Group A patients. Compared with Group A patients, Group B patients had a lower left ventricular ejection fraction (32 +/- 13% versus 52 +/- 17%, p = 0.004) and a greater prevalence of coronary artery disease (82% versus 0%, p less than 0.0001), structural heart disease and a history of clinical sustained ventrical arrhythmias. Similarly, the induced self-terminating ventricular tachycardia differed in Group A and Group B patients. The arrhythmias in Group B patients were more often monomorphic, were more often induced with one or two extrastimuli and had a longer cycle length than those in Group A patients. In Group B patients, the electrophysiologic characteristics of the self-terminating and the sustained induced ventricular tachycardias were similar. Cardioversion was required in 50% of Group B patients compared with 27% of Group C patients (p = 0.038).(ABSTRACT TRUNCATED AT 250 WORDS)

Programmed ventricular stimulation in coronary artery disease and dilated cardiomyopathy: influence of the underlying heart disease on the results of electrophysiologic testing

In order to evaluate the clinical and prognostic significance of programmed ventricular stimulation (PVS), 100 patients were investigated. Twenty-four of 51 patients with coronary artery disease and 22 out of 49 with dilated cardiomyopathy had clinical ventricular tachycardia (VT). The study protocol included 24-h Holter ECG, cardiac catheterization and angiography, and PVS employing 1 and 2 premature extrastimuli and incremental pacing. In patients with coronary artery disease, VT was induced in 67% with prior VT and in 18% without such episodes (p less than 0.01). In dilated cardiomyopathy, however, patients with and without clinical VT did not differ with regard to VT inducibility (18% vs. 15%, NS). The inducibility of monomorphic sustained VT--most frequently induced in VT patients--was significantly higher in patients with coronary artery disease (p less than 0.05). Polymorphic nonsustained VT (in both coronary artery disease and dilated cardiomyopathy) was only initiated in patients without clinical VT. In patients with coronary artery disease, left ventricular ejection fraction could be correlated to clinical arrhythmia (p less than 0.001), while induced VT could only be correlated to depressed left ventricular function in patients with left ventricular aneurysm. Neither clinical nor induced VT could be correlated to left ventricular ejection fraction in patients with dilated cardiomyopathy. During a mean follow-up of 21 months, 7 patients died from sudden cardiac death. Six of them had clinical VT, but in only 1 patient with coronary artery disease was VT initiated. There was no apparent difference in the antiarrhythmic therapy of the patients with sudden death with respect to the surviving population. In conclusion, the response to PVS with the stimulation protocol applied is different in patients with coronary artery disease and dilated cardiomyopathy. The prognostic significance of the results obtained from PVS remains uncertain.

Clinical types of proarrhythmic response to antiarrhythmic drugs

The problem of drug-induced or drug-aggravated cardiac arrhythmias has been recognized for many years. Digitalis glycosides and class I, II, III, or IV antiarrhythmic drugs can cause severe sinus node dysfunction or atrioventricular block. Digitalis can cause a variety of supraventricular arrhythmias; atrial tachycardia with block and nonparoxysmal atrioventricular junctional tachycardia are the most characteristic. Recognition that class IA and class III antiarrhythmic drugs can aggravate arrhythmias or cause new arrhythmias in patients being treated for potentially malignant or malignant ventricular arrhythmias has intensified the interest in proarrhythmia in recent years. Several characteristic types of proarrhythmic response have been described. Torsades de pointes (multiform) ventricular tachycardia (VT) accompanied by prolongation of the QT interval can be caused by class IA and class III antiarrhythmic drugs as well as other drugs that bind to the membrane sodium channels of ventricular cells, for example, tricyclic antidepressants. Uniform VT in patients with malignant ventricular arrhythmias and poor left ventricular function is a characteristic proarrhythmic response to class IC antiarrhythmic drugs. Bidirectional VT or accelerated idioventricular rhythm are characteristic of digitalis toxicity. More difficult to establish as proarrhythmic responses are increased frequency of ventricular premature depolarizations and increased ease of inducing VT with programmed ventricular stimulation.