Modification and abolition of re-entry within the His-Purkinje system in man by diphenylhydantoin

Efficacy of phenytoin in suppressing inducible ventricular tachyarrhythmias

We examined the efficacy of phenytoin in 69 of 87 consecutive patients undergoing serial electrophysiologic studies for inducible sustained ventricular tachycardia or fibrillation (VT/VF). In general, during the initial session lidocaine and procainamide were tested immediately after baseline electrophysiologic evaluation, followed by phenytoin and quinidine during the next two sessions, and then by additional drugs as needed. Once a successful drug was identified, all testing was stopped. Drugs that had failed in prior empiric trials were not tested. Twenty-five of the 87 patients (28.7%) had success in 258 serial drug tests. Sixty-nine patients were tested on phenytoin (mean serum level 13.4 +/- 5.0 mg/L), 52 after oral loading, and 17 after intravenous loading; the remaining 18 had either had prior successful testing with other drugs (9 patients) or had prior empiric failures with phenytoin (9 patients) or had prior empiric failures with phenytoin (9 patients). Nine of the 69 phenytoin trials were successful (13.0%), compared to 8 of 57 trials (14.0%) with procainamide, 4 of 37 trials (10.8%) with quinidine, and 0 of 41 trials (0%) with lidocaine. All nine patients who had successful phenytoin trials tolerated chronic doses adequate to maintain serum phenytoin levels equivalent to those measured during successful drug testing. For the 25 patients with successful drug trials, the mean follow-up was 14.5 +/- 9.8 months, and the actuarial incidence or recurrent VT/VF was 7 +/- 5% at 12 months. For the nine patients who had success with phenytoin the mean follow-up was 18.4 +/- 11.7 months, and the 12-month actuarial recurrence was 0%. Phenytoin is a well tolerated drug whose efficacy appears similar to most standard antiarrhythmic agents. If our results are confirmed in a larger, randomized study, routine testing with phenytoin should be considered.

Rapid ventricular tachycardia due to His-Purkinje reentry

Two patients developed rapid His-Purkinje reentrant tachycardia during programmed ventricular stimulation for evaluation of recurrent ventricular tachycardia. In Patient 1, His-Purkinje reentry induced a morphologically distinct ventricular tachycardia which may have been a reentrant circuit operating independently for several cardiac cycles. His-Purkinje reentry was not inducible in Patient 2 until lidocaine was given. Following lidocaine administration, sustained His-Purkinje reentrant tachycardia was initiated by 2 premature ventricular stimuli. The tachycardia was rapid (240 beats per minute) and required cardioversion.

Clinical electrophysiology of intravenous sotalol, a beta-blocking drug with class III antiarrhythmic properties

The electrophysiologic changes produced by the intravenous administration of 0.6 mg/kg of sotalol were studied in 12 patients aged 45 to 85 years (mean 68 years). Effects upon atrioventricular (AV) nodal conduction time (AH interval) and His-Purkinje conduction time (HV interval) were assessed at identical rates. The Wenckebach cycle length was determined by rapid atrial stimulation. Refractory periods before and after the drug were compared at the same cycle length. Retrograde conduction was studied, with special reference to reentry phenomena within the His-Purkinje system. Sinoatrial function was evaluated using sinus node recovery time and sinoatrial conduction time. The following changes were noted: (1) decrease in sinus rate, (2) prolongation of QT interval, (3) depression of AV nodal conduction (prolonged AH interval) and increase in effective and functional refractory periods of the AV node, (4) increase in relative refractory period of the His-Purkinje system with no associated change in HV interval, (5) prolongation of effective refractory period in the atrium and ventricle, and (6) increase in retrograde refractory period of specialized ventricular tissue and depressed conduction of premature ventricular responses. Reentry phenomena in the His-Purkinje system were not significantly affected by the drug. Thus certain of the electrophysiologic effects of sotalol in humans were found to be in favor of a class III antiarrhythmic mechanism of action. These results justify further studies to evaluate the usefulness of this drug as an antiarrhythmic agent.

Mechanism of the repetitive ventricular response in man

The electrophysiologic characteristics of the repetitive ventricular response that followed an electrically induced single premature ventricular complex were evaluated to determine its mechanism during atrial pacing or sinus rhythm in 30 patients. Seven patients had preexisting bundle branch block. His bundle or right bundle branch deflections did not precede the repetitive complex in 29 of the 30 patients, which implies that the proximal His-Purkinje system was not involved in the reentry circuit. In 24 of 30 patients the QRS axis ot the repetitive complex was divergent 45 degrees or more from the stimulated complex. In 22 of 30 patients the reprtitive complex had a right bundle branch block configuration. In 14 of 18 patients with two or more repetitive complexes, the QRS pattern changed from beat to beat, which implies that either the reentry pathway or conduction was changing. Thus, the repetitive ventricular response, which can be associated with clinically important ventricular arrhythmias, probably represents intraventricular rather than proximal His-Purkinje system reentry.

Incidence, determinants and significance of fixed retrograde conduction in the region of the atrioventricular node. Evidence for retrograde atrioventricular nodal bypass tracts

Of 104 consecutive patients studied in our laboratory with His bundle electrograms, atrial and ventricular pacing and the atrial and ventricular extrastimulus techniques, 18 patients in whom the existence and utilization of ventriculoatrial (V-A) bypass tracts were excluded demonstrated evidence for fixed and rapid retrograde conduction in the region of the atrioventricular node (A-V) as suggested by the following: (1) short (36 +/- 2 msec [mean +/- standard error of mean]) and constant retrograde H2-A2 intervals during retrograde refractory period studies; (2) significantly (P less than 0.025) better V-A than A-V conduction; (3) significantly (P less than 0.025) shorter retrograde functional refractory period of the V-A conducting system than of the A-V conduction system; and (4) the retrograde effective refractory period of the A=V nodal region was not attainable in any of the 18 patients. Fourteen of the 18 patients (77 percent) had a history of palpitations and 10 (51 percent) had documented paroxysmal supraventricular tachycardia; in 13 (72 percent) single echoes or sustained reentrant supraventricular tachycardia, or both, could be induced during atrial pacing or atrial premature stimulation studies, or both. During tachycardia all these 13 patients had a short (37 +/- 2.4 msec) and constant conduction time in the retrograde limb (H-Ae interval) of the reentrant circuit that was identical to the H2-A2 interval. In conclusion, fixed and rapid retrograde conduction in the region of the A-V node (1) is seen in approximately 17 percent of patients, (2) is associated with a large incidence of reentrant paroxysmal supraventricular tachycardia, and (3) suggests the presence of A-V nodal bypass tracts (intranodal or extranodal functioning in retrograde manner).

Gap phenomenon in "the right and left bundle branch systems" during retrograde conduction in man

Gap phenomenon in right and left bundle branch systems during retrograde conduction is described in two patients with manifest reentry within the His-Purkinje System (V3 phenomenon). In this form of gap the premature impulse (S2) initially blocked in the right bundle branch system and conducted retrogradely via the left bundle branch system as manifested by sudden prolongation of S2H2 interval and appearance of V3. At close coupling intervals S2 impulse encountered retrograde block in the left bundle branch system and resumed retrograde conduction via the right bundle branch system with S2H2 intervals shorter than critical value and was not followed by V3. However, on further shortening the S1S2 intervals S2 impulse blocked again in right bundle branch system and resumed conduction via the left bundle branch system with S2H2 intervals longer than critical values and V3 reappeared. The mechanism of these gaps is not clear but we believe is similar to the one proposed in Types I and II gaps in antegrade bundle branch conduction and involves proximal delay allowing distal recovery. The similarities and differences between the gap phenomenon in bundle branches during antegrade and retrograde conduction are discussed.

Effects of digitalis on ventricular myocardial and His-Purkinje refractoriness and reentry in man

The effects of digitalis on retrograde conduction and refractoriness of the His-Purkinje system, ventricular myocardium and reentry within the His-Purkinje system were studied in 17 patients using the ventricular extrastimulus (V2) technique. Studies were performed, before and 30 minutes after intravenous administration of ouabain, 0.01 mg/kg. After treatment with ouabain, there was a significant decrease in the functional refractory period (266 +/- 19 to 254 +/- 18 msec, P less than 0.001), relative refractory period (253 +/- 17 to 240 +/- 16 msec, P less than 0.001) and effective refractory period (242 +/- 23 to 231 +/- 24 msec, P less than 0.005) of the ventricular muscle. In contrast, there was no significant change in retrograde His-Purkinje conduction and refractoriness. The phenomenon of reentry within the His-Purkinje system characterized by the reentrant beat (V3) at critical retrograde conduction delays in the His-Purkinje system (V2-H2) within a narrow range of V1-V2 intervals was seen in 10 of 17 patients. Ouabain increased and shifted to the left the zone of reentry within the His-Purkinje system in 7 of 10 patients (36 +/- 23 to 55 +/- 23 msec, P less than 0.001) and decreased it by 10 to 30 msec in the remaining 3 patients. The critical V2-H2 (186 +/- 29 to 193 +/- 27 msec, difference not significant [NS]) and V1-V2 (299 +/- 30 to 294 +/- 36 msec, NS) intervals for reentry did not significantly change after ouabain. However, the minimal V1-V2 intervals (266 +/- 26 to 253 +/- 25 msec, P less than 0.025) decreased significantly, whereas the maximal V2-H2 intervals (266 +/- 40 to 239 +/- 37 msec, P less than 0.01) increased significantly. Thus, in the intact human heart, digitalis (1) significantly decreased all measures of ventricular myocardial refractoriness, (2) had no significant effect on retrograde conduction and refractoriness of the His-Purkinje system, and (3) widened the zone of reentry within the His-Purkinje system due to shortening of the functional refractory period of the ventricular muscle with attainment of longer V2-H2 delays.

The repetitive ventricular response in man. A predictor of sudden death

We examined the value of cardiac pacing for assessing ventricular electrical instability and for predicting ventricular tachycardia and sudden death in 50 patients with refractory symptomatic ventricular tachycardia, 12 normal patients, and 48 survivors of a recent myocardial infarction. The repetitive ventricular response (two or more ventricular premature beats produced by a single ventricular pacing stimulus during control of heart rate with atrial pacing) was absent in all 12 normal patients but was present in 44 of the 50 patients (88 per cent) with recurrent ventricular tachycardia (P less than 0.001). Of the 48 survivors of myocardial infarction, 19 had repetitive ventricular responses. During the next 12 months 15 of these patients (79 per cent) had symptomatic ventricular tachycardia or sudden death, or both, as compared with four of 29 patients (14 per cent) who did not have repetitive ventricular responses (P less than 0.001). The repetitive ventricular response identifies patients with life-threatening ventricular instability, but it is still an investigational technic that should be used only with due precautions.