Intermittent parasystole with exit block

A 53-year-old patient had a complex ventricular arrhythmia, which most likely was an intermittent pure (nonmodulated) parasystole, due to protection limited to the first part of the cycle coexisting with exit block. However, other interpretations of the observations were possible. Foremost among these was modulated parasystole with partial protection or with an attenuated or nondetectable early delaying phase, with exit block. Interestingly, the parasystole appeared to have fulfilled the dynamic rules regarding the number of sinus beats interposed between manifest parasystolic beats, as has been reported for pure or weakly modulated parasystole. This case corroborates unusual manifestations of an arrhythmia, which because of its newly found complexities and various possible interpretations seems to be discussed with decreasing frequency in most textbooks on general cardiology.     

Electrophysiologic correlate of exit block

Electrophysiologic studies using canine and human tissue confirm, by direct recordings at the cellular level, the existence of exit block produced by artificial pacemakers and shed some light on the mechanism of the exit block. Both human ventricular and canine Purkinje or ventricular tissue, or both, demonstrated Wenckebach structure from the stimulus electrode to the recorded action potentials. This conduction depression was induced by hypoxia, digitalis or infusion of 4 times the normal concentration of potassium (10.8 mEq/liter). Both the exit block and the Wenckebach structure of the block recorded in these experiments are analogous to those seen in clinical situations. In addition, electrophysiologic evidence for unidirectional block is presented.     

Parasystolic ventricular tachycardia with exit block

A rare case of parasystolic ventricular tachycardia with variable exit block concurring with runs of reentrant ventricular tachycardia is described. The reentrant ventricular tachycardia or isolated ventricular extrabeats modified the exit block patterns of the parasystolic tachycardia.     

Atrial flutter with exit block.

The mechanism of atrial flutter is controversial. A 76-year-old woman with rheumatic heart disease was referred to our clinic with an unusual rhythm disturbance which initially appeared to be classic atrial flutter at a rate of 300 beats/min. Later tracings, however, demonstrated a rate exactly one-half that of the earlier ECGs, with an identical p-wave morphology and vector. This latter rhythm also behaved in a manner expected for a flutter mechanism in that both spontaneously and with carotid pressure high-degree atrioventricular block occurred without alteration of the underlying atrial mechanism. Finally, the two rates interchanged spontaneously over several days without any significant interval changes in medical therapy. These findings were initially explained as probable digoxin toxicity. The underlying mechanism, however, was more likely atrial flutter with exit block and in this patient may have represented another facet of her sick sinus syndrome. This unusual phenomenon is discussed in terms of previous reports and possible implications for the mechanism of atrial flutter.     

Parasystolic ventricular tachycardia with variable exit block

This case is an example of ventricular parasystolic tachycardia associated with variable expressions of ectopic-ventricular (E-V) exit block. The exit block manif estated with 2:1, 3:2,4:3 and higher ratios of E-V conductions, interspaced with periods of 1:1 conduction. Concealed E-V conduction of the ectopic impulse could also be deduced.     

Non-sustained ventricular tachycardia with Wenckebach exit block

A case of non-sustained, recurrent ventricular tachycardia, manifesting with irregular R-R intervals, is described. Analysis of a long electrocardiographic recording reveals that the arrhythmia is generated by a regularly discharging ectopic ventricular focus, the R-R interval variations being due to a Wenckebach form of exit block.     

Ectopic atrial rhythm with progressively increasing exit block

A case of ectopic atrial rhythm with progressively increasing exit block is reported in a case of ischemic heart disease. Such a rhythm suggests significantly diseased atria which are unable to sustain a regular rhythm for a long period. This arrhythmia should warn the clinician of impending atrial arrest.     

Bigeminal ventricular tachycardia with Wenckebach exit block.

A patient is presented in whom repeated attacks of ventricular tachycardia occurred. His last and fatal attack revealed an alternation or coupling of the cycle lengths of the ventricular beats. A large left ventricular wall aneurysm was found, which probably accounted for the unusual arrhythmias.     

Rapid ventricular parasystole with possible multilevel exit block

A case of ventricular parasystole firing at the extremely rapid rate of 214 beats per minute in a 73 year old woman is described. Manifest cycle lengths of parasystolic complexes varied widely due to variable degrees of exit block, which could be best interpreted by the concept of multilevel block or alternating Wenckebach periodicity in the ventriculo-ectopic junction. Discontinuation of digoxin reduced the degree of exit block and unmasked parasystolic tachycardia.     

Chronic rate dependent exit block after pulmonary vein isolation

Rate dependent exit block across the pulmonary veins has been previously described immediately following catheter ablation. We report a case of rate dependent pulmonary vein exit block seen at repeat ablation 7 years after the index procedure. To our knowledge, this is the first report of chronic rate dependent exit block discovered years after circumferential pulmonary vein antral isolation.