Journal of electrocardiology
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In a patient with the Wolff-Parkinson-White Syndrome we observed atrial fibrillation and three distinct paroxysmal re-entrant tachycardias. Intracardiac electrograms obtained during the tachycardias showed the mechanisms to be A-V nodal, accessory pathway and sinus node re-entry. When P wave morphology, R-P relationship and QRS configuration are considered, it is illustrated how these four tachyarrhythmias may be successfully diagnosed on the surface electrocardiogram. The therapeutic implications of multiple arrhythmias with different mechanisms in the Wolff-Parkinson-White Syndrome are discussed.
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The effect of intravenous verapamil on the termination of supraventricular tachycardia (SVT) was studied by continuous electrocardiographic monitoring of 27 episodes of SVT. Progressive increase of the cycle length heralded conversion in eight episodes while cycle-length alternation preceded cessation of the arrhythmia in 13 episodes. In five patients the arrhythmia was either stopped or closely followed by a ventricular premature beat (VPB), followed by further VPBs in three. ⋯ The first post SVT beats had an aberrant QRS configuration with a normal P-R interval in four cases and an aberrant QRS complex with a short P-R interval, resembling Wolff-Parkinson-White complexes, in a further seven patients. The possible mechanisms causing this variability of pre- and post-conversion period are discussed. It is suggested that some aspects of verapamil action may be explained by a parasympaticomimetic effect on the myocardium.
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The effect of the autonomic blockade on the automaticity of the A-V junctional pacemaker was evaluated in 15 awake dogs with experimentally induced A-V junctional rhythm. The duration of asystole after overdrive (D. A. ⋯ A. O. in the five dogs with sinus rhythm. Thus, it is suggested that (1) the sympathetic nerve might play a more important role in regulating the automaticity of the A-V junctional pacemaker than the vagus and (2) it physiologically might take over 5.0 seconds for the A-V junctional pacemaker to initiate an escape beat during longstanding sinus arrest, if a marked dysfunction of the A-V junctional pacemaker occurs due to a decrease in tension of the sympathetic nerve.