Effect of procainamide on reentry within the His-Purkinje system in man

Ventricular tachycardia in valvular heart disease: facilitation of sustained bundle-branch reentry by valve surgery

BACKGROUND

The clinical characteristics of sustained monomorphic ventricular tachycardia (SMVT), when it develops after valve surgery, have not been described.

METHODS AND RESULTS

Between 1985 and 1996, 31 patients (30 men and 1 woman) who had undergone valve surgery were found to have inducible SMVT. Nine patients (29%) had sustained VT due to bundle-branch reentry (BBR) (group 1). Four of these patients had normal left ventricular function, and VT with a right bundle-branch morphology was inducible in 4 patients. Group 2 included 20 patients with inducible myocardial (ie, non-BBR) VT. Coronary artery disease was present in 15 group 2 patients (75%) due to atherosclerotic (n=12) and nonatherosclerotic (n=3) causes. Two patients had both inducible sustained BBR and myocardial VT (group 3). Sustained BBR VT occurred significantly earlier after valve surgery (median, 10 days) than the onset of postoperative myocardial VT (median, 72 months; P<.005).

CONCLUSIONS

Myocardial VT was the most common type of inducible SMVT in patients with valvular heart disease. The majority of these patients had underlying coronary artery disease and significant left ventricular dysfunction. However, in almost one third of the patients, sustained BBR VT was the only type of inducible SMVT. This type of VT was facilitated by the valve procedure occurring within 4 weeks after surgery in most patients. In these patients, left ventricular function was relatively well preserved, and the right bundle-branch block type of BBR was frequently induced. Because a curative therapy can be offered to these patients (ie, bundle-branch ablation), BBR should be seriously considered as the mechanism of VT in patients with valvular heart disease, particularly if the arrhythmia occurs soon after valve surgery.

Bundle branch reentry: a mechanism of ventricular tachycardia in the absence of myocardial or valvular dysfunction

OBJECTIVES

The aim of this study was to present bundle branch reentry as the mechanism of sustained ventricular tachycardia in the absence of myocardial or valvular dysfunction.

BACKGROUND

Previous reports have documented the relation between structural heart disease and bundle branch reentrant ventricular tachycardia. Myocardial or valvular dysfunction has thus far been recognized as the only anatomic substrate for the development of this tachycardia.

METHODS

Three patients with a wide QRS complex tachycardia underwent noninvasive and invasive cardiac evaluation and electrophysiologic studies to identify the substrate and mechanism of tachycardia. Catheter ablation of the right bundle branch using radiofrequency current was performed in each patient.

RESULTS

The patients were all men (aged 54, 34 and 72 years) who presented with presyncope, palpitation and cardiac arrest, respectively. Electrocardiography during sinus rhythm revealed nonspecific intraventricular conduction delay in all three patients. Cardiac evaluation revealed no evidence of myocardial or valvular dysfunction in any patient. The baseline HV interval was prolonged in each patient (90, 100 and 75 ms, respectively). Programmed right ventricular stimulation initiated bundle branch reentrant tachycardia with typical left (three patients) and right (one patient) bundle branch block pattern. Catheter ablation of the right bundle branch using radiofrequency current abolished bundle branch reentry in all three patients. After 26-, 13- and 8-month follow-up periods, complete right bundle branch block persisted, and all three patients remained asymptomatic without antiarrhythmic drugs.

CONCLUSIONS

Sustained bundle branch reentry can be a clinical arrhythmia in patients with no identifiable myocardial or valvular dysfunction except for isolated conduction abnormalities in the His-Purkinje system. This mechanism of tachycardia should be recognized during electrophysiologic evaluation, given the seriousness of this arrhythmia and the availability of the effective treatment.

Polymorphic ventricular tachycardia induced by programmed stimulation: response to procainamide

OBJECTIVES

This study was designed to evaluate the effects of procainamide on polymorphic ventricular tachycardia induced by programmed stimulation and to correlate the responses with heart disease, left ventricular endocardial activation abnormalities and the signal-averaged electrocardiogram (ECG).

BACKGROUND

Polymorphic ventricular tachycardia is induced frequently during electrophysiologic studies. In many patients this response is an artifact of programmed stimulation; in others, it appears to be clinically relevant. Previous observations have suggested that in some patients type IA antiarrhythmic agents can change the response to programmed stimulation from polymorphic to uniform ventricular tachycardia.

METHODS

Programmed right ventricular stimulation was performed in the absence of antiarrhythmic drugs and after procainamide. Signal-averaged ECGs and left ventricular maps were performed during sinus rhythm in the absence of antiarrhythmic drugs.

RESULTS

We evaluated 79 consecutive patients undergoing clinical electrophysiologic studies, in whom polymorphic ventricular tachycardia was the only arrhythmia induced in the absence of antiarrhythmic drugs. After procainamide administration, uniform monomorphic ventricular tachycardia was induced in 24 patients (Group 1), inducible polymorphic ventricular tachycardia persisted in 30 patients (Group 2) and no ventricular tachycardia could be induced in the remaining 25 patients (Group 3). Twenty-three (96%) of 24 patients developing uniform ventricular tachycardia after procainamide administration had coronary artery disease compared with 63% of Group 2 and 48% of Group 3 patients (p = 0.003). Left ventricular aneurysms were also found more frequently (46%) in the patients developing uniform ventricular tachycardia after procainamide than in either Group 2 or Group 3 (13% and 0%, respectively, p < 0.008). Abnormalities of the signal-averaged ECG typically seen in patients with spontaneous reentrant sustained ventricular tachycardia were significantly more frequent in patients who developed inducible uniform ventricular tachycardia after procainamide than in those who did not. Similarly, patients developing uniform ventricular tachycardia after procainamide had more extensive abnormalities of left ventricular endocardial activation revealed by catheter maps during sinus rhythm.

CONCLUSIONS

The conversion of inducible polymorphic ventricular tachycardia to uniform ventricular tachycardia after procainamide administration occurs almost exclusively in patients with coronary disease, previous myocardial infarction and abnormal left ventricular function. This response may permit activation mapping of tachycardias, allowing the application of surgical or catheter ablation techniques that would otherwise not be possible in such patients.

Are antiarrhythmic drugs safe?

The indications for antiarrhythmic therapy are far from clearly defined and the choice of treatment is usually based on empiric strategies. Antiarrhythmic agents can have serious side effects. Systemic adverse effects are usually use-related and reversible with withdrawal of the drug. Impairment of left ventricular function is considerable in patients with heart failure. The most important, life-threatening side effect of antiarrhythmic drugs is their proarrhythmic tendency which gives rise to certain concern about their clinical use. Aggravation of arrhythmia often occurs without symptoms, goes unrecognized by the patient, and is exposed only by monitoring, exercise testing, or invasive electrophysiological testing. Patient monitoring with electrolyte measurement, Holter recording, and electrophysiological reassessment can reveal or reduce the proarrhythmic risk but cannot eliminate the problem completely. The institution of antiarrhythmic therapy should be considered in highly symptomatic or life-threatening arrhythmias after careful consideration of the benefit-risk ratio.

Atrial sensing to augment ventricular tachycardia detection by the automatic implantable cardioverter defibrillator: a utility study

The triggering of automatic implantable cardioverter defibrillator (AICD) discharges by supraventricular tachycardias, despite the presence of a probability density function algorithm, remains a limitation of an otherwise highly effective device. We systematically investigated the diagnostic utility which theroretically could derive form the addition of atrial sensing capability to the AICD in 25 patients with 30 inducible sustained monomorphic ventricular tachycardias (VTs) at clinically relevant rates (greater than or equal to 150 beats/min). Patients were included only if they were not taking medication capable of depressing ventriculoatrial (VA) conduction for at least 5 half-lives prior to electrophysiological testing. We tested the simple criterion for VT that ventricular cycle length (CL) be shorter than the atrial CL (not met in sinus or most other supraventricular tachycardias). Mean VT CL was 283 +/- 47 ms (range 210 to 370). In 25 (83%) VTs, the VT criterion was consistently satisfied. Of the five cases in which the criterion was not met, 1:1 VA conduction during VT was present in four, three of which initially manifested 2:1 VA conduction lasting from 14 to 28 s and therefore would have transiently fulfilled the VT criterion. The remaining patient who failed to satisfy the VT criterion had ongoing atrial flutter during a relatively slower sustained VT, but this circumstance could be recognized because of the varying AV interval. The absence of 1:1 VA conduction at CLS less than or equal to 400 ms during ventricular pacing accurately predicted the absence of 1:1 VA conduction during VT in 95% of patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Bundle branch reentrant tachycardia treated by electrical ablation of the right bundle branch

A 66 year old man presented with multiple episodes of tachycardia. Some had QRS complexes with a right bundle branch block configuration identical to those of sinus beats. The onset of the tachycardia was preceded by premature His bundle depolarizations. There was a His potential before each QRS complex of the tachycardia. Atrial activity was dissociated. Occasionally the appearance of sinus beats with a left bundle branch block pattern announced a tachycardia with an identical configuration and atrioventricular dissociation. His bundle activity occurred before the QRS complex and was followed by a right bundle branch deflection. A reentrant mechanism within the bundle branch system was invoked. One 200 J shock was delivered through an electrode catheter to the site of the right bundle branch. The postprocedure course was uneventful (follow-up 10 months).

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.

Facilitation of ventricular tachycardia induction with abrupt changes in ventricular cycle length

The effect of abrupt short-to-long changes in cycle length (CL) on the postulated reentrant circuit of ventricular tachycardia (VT) was evaluated. This was performed using single and double ventricular extrastimuli in a group of 21 patients clinically suspected of having VT in whom VT could not be induced at comparable or shorter constant CLs. A second group of 10 patients without suspected VT was similarly studied. Compared with constant CLs of equal or shorter duration preceding the single or double ventricular extrastimuli, abrupt short-to-long CL changes resulted in (1) initiation of sustained VT in 13 of 21 patients in whom VT could not be induced at constant CLs despite the use of shorter S1S3 by 66 +/- 17 ms; (2) increased incidence of initiation of sustained VT after the V3 phenomenon resulting from macroreentry within the His-Purkinje system (Re-HPS); (3) a small but higher incidence of sustained VT due to sustained Re-HPS; and (4) no induction of sustained or nonsustained VT with either method in the second group of patients. These results provide additional support for reentry as the basis for sustained ventricular tachyarrhythmias. Abrupt short-to-long CL changes may be effective for initiating sustained VT in patients at risk for these arrhythmias.

Differentiation of septal from free wall accessory pathway location: observations during bundle branch block in reciprocating tachycardia in the presence of type I antiarrhythmic drugs

In patients with Wolff-Parkinson-White syndrome, observations during bundle branch block (BBB) in reciprocating tachycardia are of value in accessory pathway localization. Most importantly, an increase in the ventriculoatrial (VA) interval of greater than or equal to 35 ms has indicated an ipsilateral free wall location and excluded a septal location. The present study examined whether data collected in the presence of type I antiarrhythmic drugs retained localizing value. Review of retrospective data showed that observations in the drug-free state were precluded by the need to suppress atrial arrhythmia during electrophysiologic study in 20% of patients with Wolff-Parkinson-White syndrome who underwent preoperative workup. Prospectively, in 15 patients with left free wall or posteroseptal pathways, we observed transient left BBB during tachycardia before and after administration of procainamide, disopyramide or quinidine. Serum drug levels ranged from 4.6 to 6.9 mg/liter, except in 1 patient with a serum procainamide level of 18 mg/liter. Drugs increased the VA interval during narrow QRS tachycardia by 17% (p less than 0.01). However, the change in the VA interval with left BBB was not significantly affected. The baseline and drug values averaged 73 ms (range 39 to 94) and 70 ms (range 39 to 90), respectively, for left free wall pathways (n = 8), and 19 ms (range 0 to 28) and 21 ms (range 2 to 35), respectively, for posteroseptal pathways (n = 7). Among the latter, the interval increased less than 30 ms during left BBB except in the patient with the high serum procainamide level, in whom the increase was 35 ms. Thus, the VA interval change that accompanied left BBB remained of localizing value with moderate blood levels of type I drugs, and an increase greater than or equal to 35 ms indicated a left free wall rather than posteroseptal pathway.

Electrophysiologic properties and antiarrhythmic mechanisms of intravenous N-acetylprocainamide in patients with ventricular dysrhythmias

To define electrophysiologic properties and antiarrhythmic mechanisms of N-acetylprocainamide (NAPA), we studied 16 patients with symptomatic ventricular dysrhythmias. Electrophysiologic studies were performed before and after intravenous infusion of NAPA at 20 mg/kg over 20 minutes, achieving plasma concentrations of 24 +/- 3.2 to 35.5 +/- 4.5 micrograms/ml. NAPA did not significantly change sinus cycle length or atrioventricular (AV) conduction times (PA, AH, HV, and QRS), but it lengthened the QTc interval (p less than 0.001) during sinus rhythm. Programmed atrial stimulation revealed that NAPA had no discernible effects on AV nodal conduction; however, it exerted depressive effects on the His-Purkinje system in 9 of 16 patients. In 7 of 16 patients who manifested frequent ventricular premature beats (VPBs), NAPA abolished VPBs in only three of them; NAPA induced progressive prolongation of the premature coupling interval before complete abolition of VPBs. In 8 of 16 patients who had inducible repetitive ventricular response (RVR) because of reentry within the His-Purkinje system, NAPA narrowed or abolished the RVR zone in 3 patients and slowed the RVR rate with widening of the RVR zone in the remaining 5 patients. In 2 of 16 patients with slow ventricular tachycardia (VT), NAPA had no antiarrhythmic effects. By contrast, in the other 2 of 16 patients in whom sustained VT could be reproducibly elicited with programmed ventricular stimulation, NAPA slowed the rate of VT and suppressed VT inducibility. We conclude that electrophysiologic properties of NAPA are slightly different from those of procainamide and that NAPA is not uniformly effective for suppressing ventricular dysrhythmias, but its antiarrhythmic mechanisms are similar to those of procainamide.

Electrophysiological effects of intravenous disopyramide phosphate on the Wolff-Parkinson-White syndrome

The effects of a single intravenous infusion of 2mg/kg body weight disopyramide phosphate (DP) on the mode of initiation of reentrant supraventricular tachycardia were assessed in seven patients with Wolff-Parkinson-White (WPW) syndrome using bundle of His electrograms and the ventricular extrastimulus method. The delta wave disappeared in three patients after DP. However, retrograde conduction via the accessory pathway persisted even after DP administration in all patients. These effects contributed to the induction of reciprocating tachycardia after DP. The retrograde functional refractory period of the His-Purkinje system (HPS) and the effective refractory period of the accessory pathway were increased in all cases and contributed to the development of reentry HPS. After DP, the zone of reentry HPS widened in four cases (including a newly developed case) and remained unchanged in three cases. Reentrant supraventricular tachycardia zones widened in three cases; these widened reentrant supraventricular tachycardia zones were induced by the widened reentry HPS, that is, reentry HPS was followed by the reentrant supraventricular tachycardia. This study demonstrates that persistence of retrograde accessory pathway conduction and widened reentry HPS which might be dose-related after DP could be the retrograde determinants affecting the reentrant supraventricular tachycardia zone.

Procainamide in the induction and perpetuation of ventricular tachycardia in man

The effects of a single intravenous infusion of 750 mg of procainamide was studied in 12 patients with symptomatic chronic recurrent ventricular tachycardia in whom arrhythmias could reproducibly be initiated and terminated by programmed electrical stimulation of the heart. Sustained ventricular tachycardia was induced in 6 patients and non-sustained tachycardia was induced in the remaining 6 patients during control studies. Following procainamide (plasma level 10.3 +/- 3.7 mcg/ml), ventricular tachycardia could be induced in 10/12 patients, sustained in 4 patients and non-sustained in the remaining 6 patients. In 8/12 patients (66%), induction of ventricular tachycardia was facilitated as demonstrated by: (1) tachycardia zone was widened in 4 patients and was unchanged in another 3 patients; (2) non-sustained ventricular tachycardia was sustained ventricular tachycardia in one patient. the ventricular tachycardia had a faster rate and a different QRS morphology; (3) in 4 patients tachycardia was inducible with a lesser number of extrastimuli and/or by spontaneously occurring ventricular premature depolarization and; (4) increase of the number of induced ventricular responses of non-sustained ventricular tachycardia. In 4/12 patients (33%), procainamide abolished or modified the induction of ventricular tachycardia as demonstrated by: (1) inability to induce ventricular tachycardia in 2 patients; (2) narrowing of the tachycardia zone and conversion from sustained into non-sustained ventricular tachycardia (one patient) and; (3) decrease in the number of induced ventricular responses in one patient. The response to procainamide could not be predicted from rates of spontaneous ventricular tachycardia, induced ventricular tachycardia during control studies, degree of slowing of ventricular tachycardia or from prolongation of the coupling interval after procainamide. These results suggest that instead of abolishing the arrhythmia, procainamide in frequently employed doses in patients with chronic recurrent ventricular tachycardia can facilitate its initiation sometimes at even faster rates. Patients not responsive to the usual doses of procainamide should undergo acute drug trials to determine the optimal dose/drug levels.

Procainamide and retrograde atrioventricular nodal conduction in man

Recent studies that show a depressant effect of procainamide (PA) on retrograde conduction in patients with atrioventricular (AV) nodal reentrant tachycardia (RT) have suggested possible incorporation of AV nodal bypass tracts. Electrophysiologic effects of i.v. PA, 10 mg/kg, on retrograde AV nodal conduction were examined in 13 patients without RT, demonstrable AV nodal refractory period curves, or accessory pathways. Ventriculoatrial (VA) conduction was recorded before and after PA using intracardiac electrograms, incremental ventricular pacing and extrastimulation. With incremental pacing during the control, VA block occurred at a mean cycle length (CL) of 364.6 +/- 87.9 msec. After PA, VA conduction was abolished in five of 13 patients due to onset of retrograde block in the AV node; in seven of 13, VA block occurred at a longer paced CL after PA (344.2 +/- 51.2 msec vs 477.1 +/- 93.2 msec). In one patient, PA did not affect VA conduction. PA invariably produced prolongation in the VA interval at comparable CL of pacing. With ventricular premature stimulation, the retrograde H2A2 intervals during the control period were short (less than 50 msec) in seven of 13, intermediate (60-100 msec) in three of 13 and long (greater than 100 msec) in three of 13 cases. PA either abolished H2A2 conduction (H2 but no A2) or prolonged the H2A2 intervals by 5-20 msec in most cases in this series. The data suggest that i.v. PA almost uniformly depresses retrograde AV nodal conduction in the intact human heart. This depressant response to PA is not indicative of presence of partial or complete AV nodal bypass tracts.

Electrophysiologic effects of disopyramide phosphate on reentrant ventricular arrhythmia in conscious dogs after myocardial infarction

The electrophysiologic actions of disopyramide phosphate on reentrant ventricular tachycardia induced by premature ventricular stimuli were evaluated in conscious dogs 2 to 4 days after myocardial infarction. Disopyramide was administered as a series of intravenous infusions to obtain successive steady state plasma disopyramide concentrations of 1.02 +/- 0.02, 2.05 +/- 0.08, 3.94 +/- 0.09 and 7.69 +/- +/- 0.18 micrograms/ml (mean values +/- standard error of the mean). Disopyramide plasma concentrations of 1.02 +/- 0.02 micrograms/ml produced an increase in the rate and duration of ventricular tachycardia as well as in the interval during which premature ventricular stimuli produced ventricular tachycardia. The effective refractory period of normal myocardium was decreased and conduction (activation time) was improved in ischemic myocardium. Increasing steady state plasma disopyramide concentrations slowed the rate of ventricular tachycardia without decreasing its duration. Slowing of the rate of tachycardia occurred simultaneously with a depression of conduction in normal and ischemic myocardium and an increase in ventricular refractoriness. Induction of ventricular tachycardia was prevented only at steady state plasma disopyramide concentrations of 7.69 +/- 0.18 micrograms/ml. The results of this study suggest that subtherapeutic plasma concentrations of disopyramide may facilitate the development of reentrant ventricular arrhythmia in the electrically unstable heart. Ventricular tachycardia or fibrillation, or both, may be prevented only by plasma disopyramide concentrations that are in excess of the normal therapeutic range of 2 to 4 micrograms/ml.

The effect of lidocaine on reentry within the His-Purkinje system in man

The effects of intravenous lidocaine were assessed in 11 patients with normal intraventricular conduction in whom reentry within the His-Purkinje system (RE-HPS) occurred consistently over a narrow range of ventricular (S1S2) coupling intervals. RE-HPS was characterized by a spontaneous beat (V3) inducible by critically timed premature stimuli (S2) during constant ventricular drive (S1S1), and was dependent upon critical retrograde conduction delay within the HPS (S2H2 interval). Lidocaine abolished RE-HPS in six of 11 patients (group 1) and shortened the zone of RE-HPS in five of 11 patients (group 2). In group 1 after lidocaine, critical S2H2 intervals for RE-HPS were not attained at any S1S2 in four patients and critical S2H2 intervals were equaled but not exceeded in two patients without resulting in RE-HPS. In group 2 after lidocaine. RE-HPS was present in all patients at S2H2 intervals comparable to control values; however, significantly closer S1S2 intervals were necessary to achieve these requisite S2H2 delays (p < 0.005). The longest S2H2 intervals at comparable S1S2 intervals were significantly shortened by lidocaine in 11 of 11 patients (p < 0.001). Thus, lidocaine causes a significant decrease in retrograde refractoriness within the HPS in patients with normal intraventricular conduction.

Intraventricular reentry with narrow QRS complex

Reentry within the His-Purkinje System (V3 phenomenon) where the reentry pathway incorporates both bundle branches and the bundle of His is a frequent phenomenon during ventricular refractory period studies. In this form of reentry, both divisions of the left bundle branch function as a single limb and the reentrant beats (V3) have either left bundle branch block or right bundle branch block pattern. In this report, we describe in three patients the occurrence of a new type of reentrant beat (V3) whose characteristics suggested reentry within a circuit in which the retrograde limb of the reentrant circuit was constituted by one of the two divisions of the left bundle branch and the antegrade limb(s) by right bundle branch and the remaining division of the left bundle branch; i.e., the two divisions of the left bundle branch functioned as two separate limbs. We reached this conclusion because 1) reentry occurred within a narrow range of V1V2 intervals and was dependent upon critical retrograde His-Purkinje conduction (V2H2) delays; 2) reentry did not occur when the V2 impulse blocked retrogradely within the His-Purkinje system below the site of His bundle recording; 3) the QRS duration of V3 was less than 90 msec; and 4) in two-thirds of the patients, the HV interval of V3 was the same as that of sinus beats.

Electrophysiological effects of disopyramide in patients with bundle branch block

Electrophysiological studies were performed in 22 patients with intraventricular conduction delay before and after intravenous infusion of disopyramide (Norpace), 2 mg/kg. Mean control maximal sinus node recovery time (1039 +/- 187 msec), atrioventricular nodal conduction time (113 +/- 28 msec), and atrioventricular nodal effective refractory periods (349 +/- 67 msec) did not change significantly after administration of disopyramide (1073 +/- 284 msec, 112 +/- 31 msec, and 342 +/- 42 msec, respectively). Mean spontaneous cycle length (756 +/- 146 msec) decreased significantly 5 minutes after disopyramide (717 +/- 124 msec) (p less than 0.05), but not after 30 minutes (734 +/- 142 msec). A small but statistically significant (p less than 0.05) increase occurred after disopyramide in the mean atrial effective refractory period (259 +/- 51 to 280 +/- 53 msec), ventricular effective refractory period (253 +/- 23 to 275 +/- 33 msec), as well as the relative refractory period of the ventricular specialized conduction system (six patients) 433 +/- 78 to 479 +/- 62 msec). Although mean control infranodal conduction time (67 +/- 35 msec) increased 5 minutes after disopyramide (79 +/- 41 msec) (p less than 0.001) (18%), no spontaneous episodes of second-degree or third-degree atrioventricular block were observed. In six patients with premature ventricular depolarizations (greater than or equal to 1/min), the arrhythmia was totally abolished in four, markedly reduced in one, and remained unchanged in one. Disopyramide resulted in significant prolongation of infranodal conduction time as well as in atrial and ventricular refractoriness, but nevertheless appears to be safe in patients with bundle branch block.

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.

Abolition and modification of reentry within the His-Purkinje system by procainamide in man

The effects of intravenous procainamide infusion of 10--14 mg/kg body weight (i.e., 750 mg) of procainamide (PA) on reentry within the His-Purkinje system (HPS) were studied in 13 patients using His bundle electrograms and ventricular extrastimulus method. PA abolished reentry in eight patients (group 1) and decreased the width of reentry zone in the remaining five (group 2). At comparable S1S2 intervals, the S2H2 intervals after PA were longer than control in all patients. In group 1 patients, after PA, reentry did not occur even at S2H2 intervals that were significantly longer than control critical S2H2 intervals. In two of eight patients in group 1, PA abolished reentry by converting unidirectional block into bidirectional block in the antegrade limb (right bundle) of the reentry circuit. In the remaining six patients reentry was abolished because of consistent retrograde block of S2 impulse at some point between the site of stimulation and the His bundle recording site. In group 2, reentry was initiated after PA at approximately the same S1S2 intervals as in control, but required significantly longer S2H2 intervals; in these patients the zone of reentry was shortened due to increase in effective refractory period of the ventricular muscle. PA significantly increased the functional refractory period of HPS and the effective refractory period of ventricular muscle. The results of this study differ from the previously reported effects of lower concentrations of PA which facilitated reentry within the same circuit. We conclude that the effects of PA on reentry are dose-related and can both facilitate and suppress reentry, depending on critical changes in conduction and refractoriness of the HPS.

Reentry within the His-Purkinje system. Elucidation of reentrant circuit using right bundle branch and His bundle recordings

Routes of impulse propagation during reentry in the His-Purkinje system (Re-HPS) in 13 patients were studied using the right ventricular extra stimulus (V2) method and right bundle branch (RBB) recordings in addition to the conventional His (H) bundle recordings. The H-V and RB-V intervals during sinus rhythm averaged 44.2 and 27.6 msec respectively, with the average antegrade H-RB interval 16.6 msec. All 13 patients demonstrated Re-HPS in the form of V3 showing a left bundle branch block (LBBB) pattern, and two of the 13 patients also manifested V3 with a right bundle branch block (RBBB) pattern. During Re-HPS showing a LBBB pattern, the retrograde activation of the His bundle (H2) in response to V2 occurred via the left bundle branch (LBB), as indicated by inscription of retrograde H2 prior to RB2 in nine of 13 cases (average H2-RB2 = 9.4 msec), and simultaneous incription of retrograde H2 and RB2 in the remaining four. When V3 showed a RBBB pattern the retrograde RB2 preceded H2, suggesting H2 activation via the RBB. These findings suggest that circuit of Re-HPS incorporates both bundle branches and the bundle of His. The H-RB recordings were also useful in distinguishing sustained Re-HPS from atrioventricular nodal reentry when in both instances the QRS complex showed a LBBB pattern.