Atrioventricular block response to exercise and intraventricular conduction at rest

Pathological bradyarrhythmia in horses

Pathological bradyarrhythmia is rare in horses but should be especially considered when presented with a horse that has signs consistent with episodic weakness or collapse. This paper reviews the literature describing our current knowledge of, and possible mechanisms causing, clinically significant bradyarrhythmia in horses.

Fatal delayed hemodynamic depression after carotid artery stenting

Refractory and fatal hemodynamic depression remarkably occurred eight hours after left carotid artery stenting in a 62-year-old male who had no hemodynamic instability till then; possible contributory factors were pre-existing moderate left ventricular systolic dysfunction and new-onset complete heart block caused by vasopressor-induced sympathetic stimulation in the presence of covert distal conduction system disease.

[Exercise-induced atrioventricular block. Significance of the ischemic component. Report of 4 new cases]

We report four new cases of exercise-induced atrio-ventricular block (appearing during treadmill exercise testing). The mechanism was ischemia in two patients and the conduction disturbance disappeared after coronary artery bypass grafting. The literature on this matter is reviewed. Also the etiology, the natural history and management are discussed in these cases.

Exercise-induced complete heart block in a patient with chronic bifascicular block

Heart block induced by exercise or associated with symptomatic, chronic bifascicular block can progress to high-grade atrioventricular (AV) block and sudden death. The authors describe a case of exercise-induced AV block in a patient with chronic bifascicular block. Thirty seconds of ventricular asystole were observed during exercise treadmill testing. Myocardial ischemia was ruled out, and the cause was determined to be distal AV nodal block. The pathophysiology, diagnosis, and treatment of distal AV nodal block are reviewed. The role of exercise treadmill testing and electrophysiologic studies in distal AV block are outlined in a diagnostic and therapeutic strategy.

Tachycardia-dependent second degree AV-block in a patient with right bundle branch block

A 55-year old male patient, with dizzy spells during everyday activity and a complete right bundle branch block as the sole electrocardiographic abnormality, reproducibly demonstrated tachycardia-dependent Mobitz Type II- and 2:1 second degree atrioventricular block. An electrophysiologic study revealed a provocable block within the distal portion of the bundle of His without evidence of a split His potential. Because of the truly tachycardia-dependent AV-block, beta-blocker medication was initiated to prevent high sinus rates during everyday activity. This therapy abolished symptoms totally.

Exercise induced "Mobitz type II" second degree AV block in a patient with chronic bifascicular block (right bundle branch block and left anterior hemiblock)

A 55 year old healthy man with chronic bifascicular block (right bundle branch block and left anterior hemiblock) had a near syncopal episode. A treadmill test showed exercise induced Mobitz type II AV block manifested clinically by paradoxical slowing of the heart rate and decreased blood pressure. True His Purkinje block and pseudo AV block due to His extrasystoles were documented by an electrophysiological study.

Exercise-induced distal atrioventricular block

Three patients with 1:1 atrioventricular (AV) conduction at rest developed fixed 2:1 or 3:1 AV block during treadmill exercise testing. Electrophysiologic study documented block distal to the AV node in all three patients, and suggested that the exercise-induced block occurred because of increased atrial rate and abnormal refractoriness of the His-Purkinje conduction system. The findings in these three patients suggest that high grade AV block appearing during exercise reflects conduction disease of the His-Purkinje system rather than of the AV node, even in the absence of bundle branch block. Patients with this diagnosis should be considered for permanent cardiac pacing.

Mechanism of escape, extrasystolic, and parasystolic arrhythmias. Study on an electrical analogue

A simple analogue of the heart consisting of a system of neon relaxation oscillators is presented. The analogue may display rhythm patterns similar to sinus rhythm, escape rhythm, isorrhythmic dissociation with synchronization, atrial extrasystoles, ventricular extrasystoles, and parasystole. The strict rules followed by these arrhythmias, as well as the deviations from the rules commonly followed by the equivalent heart arrhythmias, may be easily reproduced on the analogue. Such features are the Treppe phenomenon and captured beats in escape rhythm, fixed coupling intervals in extrasystoles, partial or complete atrioventricular block in very premature atrial extrasystoles, prolongation of the period following an atrial extrasystole, interpolated premature beats, complete compensatory pause and the rule of bigeminy in ventricular extrasystoles, slight instability of the parasystolic period, multiple length parasystolic periods slightly different from the exact multiples of the parasystolic idioperiod, preference of the parasystoles for certain phase in the sinus cycle, synchronization at a phase difference and fluctuation repeatedly and without interruption from a parasystolic to an extrasystolic rhythm and synchronization in escape rhythm with isorrhythmic dissociation. The mechanisms involved in these phenomena are discussed in detail. The striking similarity between the properties of the cardiac pacemakers and those of the relaxation oscillators on the one hand and betwen the rhythm patterns of the heart and those of the analogue on the other may permit the hypothesis that the mechanisms operating in the analogue may be used in analyzing and understanding heart arrhythmias.