Case report: adenosine induced ventricular fibrillation in a patient with stable ventricular tachycardia.

Adenosine is frequently used in emergency departments and intensive care units for the termination of narrow complex tachycardias. Recently its utility in terminating wide complex tachycardias has been reported in the literature. Adenosine is generally felt to be a safe medication even though its proarrhythmic effects in the setting of narrow complex or supraventricular tachycardias have been well documented. Herein, we describe the first case to our knowledge of adenosine inducing ventricular fibrillation in a patient with a stable wide complex tachycardia that was subsequently proven to be ventricular tachycardia at electrophysiologic study.

Treatment of refractory ventricular fibrillation by combined internal (epicardial) and external (transthoracic) defibrillation.

This report describes a modified defibrillation technique used successfully in a patient with an implanted epicardial cardioverter defibrillator who developed refractory ventricular fibrillation. During operative testing at the time of generator replacement, two episodes of intractable ventricular fibrillation were terminated by using a combined internal (epicardial)-external (transthoracic) defibrillation system that delivered a 360-J shock between the anterior epicardial patch and a large posterior skin electrode.

Pure atrial-based lower rate timing of dual chamber pacemakers: implications for upper rate limitation.

The release of dual chamber pulse generators with atrial-based lower rate timing has added a new dimension to the complexity of pacemaker function and electrocardiography. This discussion focuses on the concept that in pulse generators with pure atrial-based lower rate timing, preservation of the atrial lower rate interval takes hierarchical precedence over all other timing intervals including the ventricular-based upper rate interval. Under certain circumstances whenever upper rate limitation requires extension of the programmed AV interval, a DDD pulse generator with pure atrial-based lower rate timing can violate its atrial-driven upper rate interval to provide constancy of the lower rate interval. Such behavior also has important implications for upper rate control in devices that function in the DDI (DDIR) or DDDR mode with pure atrial-based lower rate timing.

Unusual Wenckebach upper rate response of an atrial-based DDD pacemaker.

We describe in this report an unusual form of Wenckebach upper rate response produced by a DDD pulse generator with atrial-based lower rate timing. The pacemaker maintained the programmed upper and lower rate intervals at the expense of a prolonged atrial paced-ventricular paced AV interval. This form of upper rate behavior eliminated the longer cycle (containing the unsensed P wave) that occurs at the end of the pacemaker Wenckebach sequence during traditional DDD pacing with ventricular-based lower rate timing.

Electrophysiologic and antiarrhythmic effects of magnesium in patients with inducible ventricular tachyarrhythmia.

Intravenous magnesium is reported to be effective in the treatment of ventricular arrhythmias associated with hypomagnesemia, digitalis toxicity, or prolongation of the QT interval. In most previous reports, magnesium was added to conventional antiarrhythmic drugs that had failed. There are few data on the antiarrhythmic efficacy of magnesium as monotherapy in patients without these associated abnormalities. Ten patients with life-threatening ventricular arrhythmia and inducible ventricular tachyarrhythmia by programmed electrophysiologic testing were treated with intravenous magnesium. Following magnesium infusion, all patients still had inducible ventricular tachyarrhythmia. Moreover, magnesium therapy was not associated with significant changes in ventricular refractory period or in the morphology, cycle length, or hemodynamic response to induced ventricular tachycardia. These data suggest that intravenous magnesium has no significant electrophysiologic or antiarrhythmic effects in patients with life-threatening ventricular arrhythmia and inducible ventricular tachyarrhythmia.

Comparison of hemodynamic pressure half-time method and Gorlin formula with Doppler and echocardiographic determinations of mitral valve area in patients with combined mitral stenosis and regurgitation.

Mitral valve area determined by the Gorlin formula in patients with combined mitral stenosis and regurgitation underestimates the true orifice size. Recent data suggest Doppler ultrasound and two-dimensional echocardiography more accurately estimate the mitral valve area in patients with mixed mitral valvular disease. This study assessed the accuracy of an alternate method, the hemodynamic pressure half-time method, for mitral valve area determination in such patients. In 22 patients, 28 separate mitral valve areas were calculated by the hemodynamic pressure half-time method, the Gorlin formula, and the Gorlin formula corrected for mitral regurgitation, and were compared with results calculated by the Doppler pressure half-time method. Six patients were studied both before and after balloon mitral valvuloplasty. In addition, mitral valve areas calculated by all four methods were compared with results obtained by planimetry in 15 patients with technically optimal echocardiograms. The mitral valve areas determined by hemodynamic pressure half-time corretated closely with the valve areas determined by Doppler (r = 0.90), whereas mitral valve areas determined by the Gorlin formula (both without and with correction for mitral regurgitation) did not correlate as well with the Doppler-estimated valve areas (r = 0.47 and r = 0.56, respectively). Correlation between the Doppler-derived mitral valve areas and the planimetered valve areas was also good (r = 0.84), as was that between the mitral valve areas calculated by hemodynamic pressure half-time and those calculated by planimetry (r = 0.78).(ABSTRACT TRUNCATED AT 250 WORDS)