Chronic longterm electrophysiologic study of paroxysmal ventricular tachycardia

Nine patients with recurrent paroxysmal ventricular tachycardia underwent chronic electrophysiologic studies to delineate effective drug therapy for prevention of recurrence of this arrhythmia. The frequency of attacks of ventricular tachycardia necessitating hospitalization ranged from 2 to 12 (mean 5 +/- 4) attacks per year. Pacing induction of ventricular tachycardia was performed prior to and following intravenous or oral administration of procainamide (eight patients), disopyramide phosphate (nine patients), aprindine (five patients) and propranolol (four patients). Successful drug response (prevention of ventricular tachycardia induction or induction of nonsustained episodes of tachycardia) was noted in six of nine patients (66 percent). Lack of drug effect on the ability to sustain ventricular tachycardia was noted in three patients (34 percent). In addition, a deleterious drug response, manifested by potentiation of ventricular flutter or fibrillation, was observed in two of the three patients who failed to respond to drugs. Chronic drug therapy based on successful response in six patients resulted in cure of ventricular tachycardia in five of six patients (83 percent), one patient having one attack necessitating hospitalization. Of the three patients who demonstrated lack of drug effect during chronic electrophysiologic studies, one died suddenly and two had recurrent episodes of ventricular tachycardia while receiving a drug that did not prevent induction of ventricular tachycardia.

Computer diagnosis of supraventricular and ventricular arrhythmias. A new esophageal technique

Computerized arrhythmia monitors recognize only a few of the significant arrhythmias and generally fail to detect arrhythmias of supraventricular origin. This is because conventional surface leads, which are sufficient for QRS recognition, are highly inadequate for automated P-wave detection. A new two-lead system, which includes a swallowable capsule-electrode for esophageal monitoring of atrial activity, is used in an on-line arrhythmia monitor. Three interval measurements (AA, AR and RR) and a QRS shape measurement provide the foundation for a detailed interpretation of each beat. Building on the single-beat analysis, a contextual diagnostic algorithm then recognizes and reports on-line the following arrhythmias: couplets, bigeminy, trigeminy, ventricular tachycardia, supraventricular tachycardia, atrial flutter, atrial fibrillation, ventricular tachycardia with retrograde conduction to the atria, first-degree block, second-degree block, Wenckebach periodicity, advanced block, third-degree block and sinus bradycardia.

Failure of surgery in preexcitation. Correlation with pathologic findings

A 37-year-old man with mitral stenosis and recurrent drug-resistant paroxysmal atrial fibrillation, paroxysmal supraventricular tachycardia, and preexcitation, underwent two surgical attempts to ablate an anomalous pathway (AP). Electrophysiologic study demonstrated a left posterior AP with a short antegrade refractory period. Epicardial mapping at the time of mitral valve replacement (left lateral thoracotomy) suggested a posterior right AP. Mitral valve replacement and incision of the left atrial wall failed to cure preexcitation. Epicardial mapping at a second operation (median sternotomy) demonstrated a subepicardial left posterior AP. Right atrial and atrial septal incisions failed to cure preexcitation. Serial section of the atrioventricular rings and conduction system demonstrated an intact left posterior anomalous atrioventricular muscle bundle with surgical incision placed above the plane of the mitral anulus.

Significance of chronic bifascicular block without apparent organic heart disease

Eighty-six of 452 patients (19%) with chronic bifascicular block were found to have no clinically apparent associated organic heart disease (OHD) and were defined as having primary conduction disease (PCD). Comparison of patients with PCD and OHD revealed a significantly lower incidence of the following clinical variables in the PCD patients (p less than 0.001): exertional angina, dyspnea, congestive heart failure, cardiomegaly, functional class I (all by study design), left bundle branch block and premature ventricular contractions. Both mean AH and HV intervals were significantly shorter in patients with PCD (p less than 0.01). The incidence of HV prolongation was 21% in PCD and 41% in OHD patients (p less than 0.001). All patients were prospectively followed for 21-2998 days with a mean +/- SEM of 1209 +/- 66 days for PCD and 1172 +/- 36 days for OHD. Atrioventricular (AV) block developed in three patients from the PCD group and 26 from the OHD group (NS), with spontaneous block occurring in one (1%) PCD patient and 19 (5%) OHD patients (p less than 0.05). Annual mortality due to sudden death as well as total cardiovascular mortality (including sudden death) for the 5-year follow-up was significantly lower in patients with PCD. Patients with PCD have significantly lower incidence of electrophysiologic abnormalities and subsequent spontaneous AV block as well as cardiovascular and sudden death mortality. The diagnosis of PCD based on clinical criteria probably underestimates the presence of underlying OHD, as suggested by a small but definite risk of cardiovascular mortality.

Effects of atropine on induction and maintenance of atrioventricular nodal reentrant tachycardia

The electrophysiologic effects of atropine were studied in 14 patients with dual atrioventricular (AV) nodal pathways and recurrent paroxysmal supraventricular tachycardia (PSVT). During PSVT, all patients used a slow pathway (SP) for antegrade and fast pathway (FP) for retrograde conduction. Atropine enhanced both SP antegrade and FP retrograde conduction, shown by a decrease in paced cycle lengths (atrial and ventricular) producing AV and ventriculoatrial block. Five patients had induction of sustained PSVT before and after atropine. Seven patients failed to induce or sustain PSVT before atropine, because of retrograde FP refractoriness. All seven had induction of sustained PSVT after atropine due to facilitation of FP retrograde conduction. Two patients had only single atrial echoes before atropine, reflecting SP antegrade refractoriness. After atropine, sustained PSVT was inducible in one, and nonsustained in the other, PSVT cycle length could be compared in seven patients before and after atropine and decreased from 383 +/- 25 to 336 +/- 17 (p less than 0.05). Thus, in patients with dual AV nodal pathways, atropine facilitated SP antegrade and FP retrograde conduction, shortened cycle length of PSVT and potentiated ability to sustain PSVT.

Congenital abnormalities of the conduction system in two patients with tachyarrhythmias

Serial sections of the conduction system (CS) were performed in two patients with recurrent tachyarrhythmias. Case 1, a 34-year-old female who had dual atrioventricular (AV) nodal pathways with recurrent paroxysmal supraventricular tachycardia, committed suicide. Autopsy revealed an abnormally formed atrial septum with insertion of eustachian valve on the AV part of the pars membranacea. The intercuspid portion of the pars membranacea was muscular. The AV node was located adjacent to the membranous part of the ventricular septum rather than the central fibrous body. In addition, there was an accessory anterior AV node on the parietal wall of the right atrium. Case 2, a 13-year-old boy with history of recurrent ventricular tachycardia, died suddenly. CS revealed a right-sided, markedly septated bundle. The first part of right bundle branch was divided into three parts, which later joined together. Both cases showed fatty infiltration of the atrial septum, more than normal for the age of the patients. The relationship of the recurrent tachyarrhythmias to the congenital abnormalities in the CS in the two cases and the fatty infiltration is reviewed.

Incidence and site of atrioventricular block in patients with chronic bifascicular block

Four hundred fifty-two patients with chronic bifascicular block and initially intact atrioventricular (AV) conduction were detected, studied, and prospectively followed between January 1970 and March 1978. There were 360 males and 92 females, ages 18--93 years (mean +/- SD, 62 +/- 15 years). Follow-up ranged from 29-2804 days (mean 1066 +/- 97 days). AV block (2 degrees or 3 degrees) developed in 29 patients, nine with apparent cause and spontaneously in 20. Cumulative annual incidence of all heart block for 1--5 years was, respectively, 4%, 5.9%, 8.7%, 10.1% and 11.3%, and for spontaneous block was 2%, 3.1%, 5.2%, 6.7%, and 7.1%. Sites of spontaneous block were probably or definitely AV nodal in ten, His bundle in one, and trifascicular in nine. Cumulative incidence of AV block in surviving bifascicular block patients is 11% at 5 years, with 7% reflecting spontaneous block. The probable or definite site of AV block varies and is trifascicular in less than half of the patients. The small incidence of trifascicular block probably explains the difficulty in predicting this complication with electrophysiological studies.

Paroxysmal supraventricular tachycardia induction in patients with Wolff-Parkinson-White syndrome

In 54 patients with pre-excitation, 30 (56%) had inducible A-V re-entrant paroxysmal tachycardia. Of these 30, 20 had spontaneous paroxysmal tachycardia (four also had atrial fibrillation), four had spontaneous paroxysmal atrial fibrillation, five had a history of palpitation without arrhythmia, and one was asymptomatic. In 24 patients (44%), paroxysmal tachycardia was not inducible. Of these 24, none had documented paroxysmal tachycardia, four had atrial fibrillation, none had palpitation without arrhythmia, and 11 were asymptomatic. The incidence of documented paroxysmal tachycardia was higher in the patients with inducible tachycardia (P less than 0.001). Tachycardia induction was noted in 20 of 20 patients with spontaneous paroxysmal tachycardia, eight of 12 patients with paroxysmal atrial fibrillation, five of 14 patients with palpitation and no arrhythmia, and one of 12 asymptomatic patients. The frequency of ability to induce paroxysmal tachycardia was significantly higher in both the patients with documented spontaneous paroxysmal tachycardia and the patients with paroxysmal atrial fibrillation than in the asymptomatic group (P less than 0.01).

Significance of left axis deviation in patients with chronic left bundle branch block

Forty-nine patients with chronic left bundle branch block and a normal frontal axis were compared with 53 patients with left bundle branch block and left axis deviation. The following clinical variables were more frequent (P less than 0.05) in patients with left axis deviation: greater age, exertional angina, congestive heart failure, cardiomegaly, cardiac functional class II to IV, coronary artery disease and presence of organic heart disease. Absence of organic heart disease (primary conduction disease) was seen only in patients with a normal axis. Patients with left axis deviation had longer (P less than 0.05) mean P-R, A-H and H-V intervals and atrial and atrioventricular (A-V) nodal effective refractory periods. All patients were prospectifely followed up for 30 to 2,271 days with a mean +/- standard error of the mean follo-up period of 538 +/- 72 for the group with a normal axis and 604 +/- 72 days for the group with left axis deviation (difference not significant). A-V block developed in three patients (6 percent) with left axis deviation and in none of those with a normal axis. The cumulative 4 year mortality rate for the entire group approached 75 percent. The patients with left axis deviation had greater cardiovascular mortality (P less than 0.05). In conclusion, among patients with left bundle branch block, those with left axis deviation have a greater incidence of myocardial dysfunction, more advanced conduction desease and greater cardiovascular mortality than those with a normal axis.

Electrophysiologic observations in a patient with bradycardia-dependent atrioventricular block

In a patient with atrioventricular (A-V) block distal to the His bundle (H), 1:1 A-V conduction with right bundle branch block and H-V interval of 70 msec was established with atrial pacing at rates of 120 to 150/min, suggesting that the A-V block was bradycardia-dependent. Advanced second degree A-V block distal to the H deflection occurred with atrial pacing at 160/min after completion of A-V nodal Wenckebach periodicity proximal to the H deflection because of the long H-H encompassing the blocked P wave. Atrial extrastimulus testing coupled with sinus rhythm (with A-V block) demonstrated that critical H1-H2 intervals of less than 545 msec allowed conduction to the ventricles. The H2-V2 interval shortened progressively from 290 to 70 msec with shortening of these critical H1-H2 intervals. Atrial extrastimulus testing coupled with an atrial driven cycle lenght of 500 mesc (with intact A-V conduction) revealed block of the H2 deflection with an H1-H2 interval longer than 540 msec. In conclusion, at critical diastolic intervals, impulses were blocked, creating a state of decreased responsiveness. If a cycle length of subsequent impulses was shorter than the critical diastolic blocking interval, membrane responsiveness gradually improved and conduction resumed. If a cycle length of subsequent impulses was longer than the critical blocking diastolic interval, A-V block was sustained. Blocked impulses continually penetrated to the site of block and reset the state of membrane responsiveness.

Retrograde block during dual pathway atrioventricular nodal reentrant paroxysmal tachycardia

There are limited reported data regarding the occurrence of retrograde block during dual pathway atrioventricular (A-V) nodal reentrant paroxysmal tachycardia. This study describes two patients with this phenomenon. The first patient had 2:1 and type 1 retrograde ventriculoatrial block during the common variety of A-V nodal reentrance (slow pathway for anterograde and fast pathway for retrograde conduction). Fractionated atrial electrograms suggested that the site of block was within the atria. The second patient had type 1 retrograde block (between the A-V node and the low septal right atrium) during the unusual variety of A-V nodal reentrance (slow pathway for retrograde and fast pathway for anterograde conduction). The abolition of retrograde block by atropine suggested that the site of block was within A-V nodal tissue. Both cases demonstrate that intact retrograde conduction is not necessary for the continuation of A-V nodal reentrant paroxysymal tachycardia. Case 2 supports the hypothesis that the atria are not a requisite part of the A-V nodal reentrant pathway.

Clinical, electrocardiographic and electrophysiologic observations in patients with paroxysmal supraventricular tachycardia

Seventy-nine patients without ventricular preexcitation but with documented paroxysmal supraventricular tachycardia were analyzed. Electrophysiologic studies suggested atrioventricular (A-V) nodal reentrance in 50 patients, reentrance utilizing a concealed extranodal pathway in 9, sinus or atrial reentrance in 7 and ectopic automatic tachycardia in 3. A definite mechanism of tachycardia could not be defined in 10 patients (including 7 whose tachycardia was not inducible). The three largest groups with inducible tachycardias were compared in regard to age, presence of organic heart disease, rate of tachycardia, functional bundle branch block during tachycardia and relation of the P wave and QRS complex during tachycardia. A-V nodal reentrance was characterized by a narrow QRS complex and a P wave occurring simultaneously with the QRS complex during tachycardia. Reentrance utilizing a concealed extranodal pathway was characterized by young age, absence of organic heart disease, fast heart rate, presence of bundle branch block during tachycardia and a P wave following the QRS complex during tachycardia. Sinoatrial reentrance was characterized by frequent organic heart disease, a narrow QRS complex and a P wave in front of the QRS complex during tachycardia. In conclusion, a mechanism of paroxysmal supraventricular tachycardia could be defined in most patients. Observations of clinical and electrocardiographic features in these patients should allow prediction of the mechanism of the tachycardia.

Self-initiated conversion of paroxysmal atrial flutter utilizing a radio-frequency pacemaker

A patient is described with drug-resistant recurrent paroxysmal atrial flutter. Electrophysiologic studies demonstrated that flutter was inducible with rapid atrial stimulation (stimulation rates of 375 to 400/min) and convertible with rapid atrial stimulation (rates of 400 to 460/min). Because of the latter response, a radio-frequency atrial pacemaker was implanted, which allowed self-initiated conversion of flutter episodes with rapid stimulation.

Electrophysiologic effects of lidocaine on sinus node and atrium in patients with and without sinoatrial dysfunction

Electrophysiological studies were conducted in 13 patients with normal sinus node function and 14 with sinus node dysfunction before and after intravenous lidocaine. Mean +/- SEM sinus cycle length significantly shortened from 810 +/- 34.3 to 774 +/- 34.3 msec in patients with normal sinus node (P less than 0.001) and from 1061 +/- 67.6 to 1016 +/- 64.5 msec in patients with sinus node dysfunction (P less than 0.025) after lidocaine. Mean sinus recovery time was 1027 +/- 49.4 before and 1026 +/- 52.5 msec after lidocaine in patients with normal sinus node (NS) and 1269 +/- 97.7 before and 1170 +/- 73.8 msec after lidocaine in patients with sinus node dysfunction (P less than 0.05). Mean calculated sinoatrial conduction time was 87 +/- 9.5 before and 90 +/- 9.2 msec after lidocaine in patients with normal sinus node (NS) and 80 +/- 10.3 before and 96 +/- 10.2 msec after lidocaine in patients with sinus node dysfunction (P less than 0.001). Mean atrial effective and functional refractory periods were not significantly changed with lidocaine. Thus lidocaine shortened sinus cycle length in both groups, without affecting atrial refractoriness. Lidocaine appeared to depress perinodal tissue only in patients with sinus node dysfunction. The abbreviation of sinus recovery time in patients with sinus node dysfunction could reflect increased sinus automaticity and/or increased perinodal refractoriness, allowing entrance block to occur. This mechanism may explain why sinus arrest has been noted in some patients during lidocaine administration.

Sites of conduction disease in aortic stenosis: significance of valve gradient and calcification

Electrophysiologic studies were done in 32 patients with aortic stenosis. In 24 patients with intact A-V conduction, A-H intervals ranged from 55 to 145 msec and were prolonged in two. Two had split His bundle potentials. The H-V intervals ranged from 25 to 94 msec and were prolonged in 12. The mean H-V interval was 63 +/- 2.6 msec in 12 patients with calcific aortic stenosis compared with 50 +/- 4.9 msec in 12 without calcification (P less than 0.05). The mean H-V in 10 patients with aortic gradients greater than 40 mm Hg was 62 +/- 5.6 msec compared with 47 +/- 3.1 msec in nine with gradients less than 40 (P less than 0.05). In patients with aortic stenosis and A-V block, the site of the block was distal to the His bundle in three and within the His bundle in five. All eight had calcified valves. Aortic stenosis was commonly associated with latent and manifest conduction disease in the His bundle and the trifascicular conduction system. Conduction disease was more extensive with calcified valves and greater valve obstruction.

The determinants of atrioventricular nodal re-entrance with premature atrial stimulation in patients with dual A-V nodal pathways

In patients with dual atrioventricular (A-V) nodal pathways, atrial extrastimulus testing induces either no echoes, single atrial echoes (Ae), or repetitive re-entrance (repetitive atrial and ventricular beating). We examined the fast and slow pathways properties in 38 patients with dual pathways in order to delineate the determinants of re-entrance. Seventeen patients had no Ae. Of these, six had no V-A conduction and 11, intact V-A conduction. The mean paced ventricular cycle length producing retrograde V-A block (VABCL) in this group (a measure of retrograde fast pathway refractoriness) was 552 +/- 32 msec (mean +/- SEM; 10 pts). In contrast, all 21 patients with Ae had intact V-A conduction with mean VABCL of 382 +/- 21 msec (14 pts) (P less than 0.05). Repetitive re-entrance occurred only when Ae conducted to the ventricles. Seven patients had only single Ae. The mean paced atrial cycle length producing Wenckebach periodicity (CLAWP) in this group (a measure of antegrade slow pathway refractoriness) was 490 +/- 31 msec (5 pts). Fourteen patients had repetitive re-entrance. The mean CLAWP in this group was 399 +/- 18 msec (8 pts) (P less than 0.05). In conclusion, our results suggest that in patients with dual pathway, the occurrence of single or repetitive re-entry is dependent upon measurable slow and fast pathway properties.

Sudden death in patients with chronic bifascicular block

Prospective follow-up studies of 277 patients with chronic bifascicular block showed that 30 patients developed sudden cardiac death (SCD). Cumulative one-, two-, and three-year SCD mortality was computed. The patients that developed SCD were compared with the remaining patients (209 alive and 38 dead). The groups were similar in regard to age, sex, AH, and HV intervals. The following were more frequent in the SCD group (P less than .05): angina, previous myocardial infarction, heart failure, cardiomegaly, left bundle-branch block, premature ventricular beats, and ventricular tachycardia. Ventricular fibrillation was the cause of death in four cases of SCD where terminal ECG documentation was available. We concluded that SCD is a major cause of mortality in patients with chronic bifascicular block. The association of SCD with coronary disease and ventricular dysrhythmia suggested ventricular fibrillation as a frequent mechanism.

An unusual variety of atrioventricular nodal re-entry due to retrograde dual atrioventricular nodal pathways

Three patients with paroxysmal supraventricular tachycardia (PSVT) had discontinuous ventriculo-artrial conduction curves (V1-V2, A1-A2), suggesting dual A-V nodal pathways. Ventricular echoes occurred simultaneously with sudden increase of V-A interval. These echoes were characterized by retrograde P waves occurring in front of QRS, suggesting utilization of a slow pathway for retrograde conduction and a fast pathway for antegrade conduction. In case one, atropine improved retrograde slow pathway and antegrade fast pathway conduction and made A-V nodal re-entry sustained, resulting in PSVT (with retrograde P in front of the QRS). In cases 2 and 3, atropine markedly shortened retrograde fast pathway refractory period and slightly improved antegrade slow pathway conduction. The discontinuous V1-V2, A1-A2 curves and echoes were no longer demonstrable. However, with improvement of retrograde fast pathway and antegrade slow pathway conduction, A-V nodal re-entrant echoes and PSVT were observed, utilizing the slow pathway for antegrade conduction and the fast pathway for retrograde conduction (P simultaneous with QRS).

Atrial pacing at multiple sites in the Wolff-Parkinson-White syndrome

Atrial pacing at multiple sites was used in an attempt to predict the site of pre-excitation in 5 patients with Wolff-Parkinson-White syndrome with 5 different anomalous pathway locations (right anterior, right posterior, septal, left posterior, and left lateral). At least 3 atrial pacing sites were tested in each patient. Pacing sites tested included high right atrium, low lateral right atrium, low septal right atrium, proximal coronary sinus, and distal coronary sinus. Atrial stimulation sites with shortest and longest stimulus-delta intervals could be identified in each patient, the shortest stimulus-delta interval in each case ranging from 60 to 80 ms. The difference between the shortest and longest stimulus-delta interval in each case ranged from 60 to 110 ms. It was suggested that the site with the shortest stimulus-delta interval corresponded to a site close to the atrial insertion of the anomalous pathway. This hypothesis was confirmed in all cases (3 with epicardial mapping and 2 with retrograde atrial activation data). In conclusion, atrial pacing at multiple sites is helpful in predicting the site of anterogradely conducting anomalous pathways, and appears particularly useful for differentiation of right posterior, left posterior, and septal pre-excitation.

The antiarrhythmic efficacy of intravenous therapy with disopyramide phosphate

Disopyramide phosphate was administered intravenously to 57 patients with 60 episodes of arrhythmia (21 supraventricular and 39 ventricular) as a 2 mg/kg bolus. Conversion to sinus rhythm was achieved in three (38 percent) of eight patients with atrial flutter, two (20 percent) of ten patients with atrial fibrillation, one (33 percent) of three patients with paroxysmal atrial tachycardia, and two (50 percent) of four patients with sustained ventricular tachycardia. In nine (75 percent) of 12 patients with nonsustained ventricular tachycardia, suppression of the arrhythmia was accomplished following the intravenous bolus of disopyramide. In 18 (78 percent) of 23 patients with frequent ventricular premature contractions, greater than 50 percent suppression of the ventricular premature contractions was achieved. These effects were satisfactorily maintained in six (86 percent) of seven patients with nonsustained ventricular tachycardia and in 14 (88 percent) of 16 patients with frequent ventricular premature contractions in whom therapy with disopyramide phosphate was continued as a 20 mg/hour intravenous drip infusion for up to 24 hours. Side effects were observed in only eight patients (14 percent) and were primarily anticholinergic in nature. Transient hypotension, not necessitating treatment with pressor agents, was observed in three patients (5 percent), in two of whom discontinuance of therapy with disopyramide was deemed necessary. Intravenous therapy with disopyramide in the dosage regimen employed appears to be moderately effective against supraventricular arrhythmia and particularly effective against ventricular arrhythmia with minimal toxicity. It appears to be a suitable alternative to intravenous therapy with lidocaine and has the additional advantage of availability for oral administration.

Participation of fast and slow A-V nodal pathways in tachycardias complicating the Wolff-Parkinson-White syndrome. Report of a case

Electrophysiological studies in one patient with type B pre-excitation and dual A-V nodal pathway revealed several types of paroxysmal narrow QRS tachycardia (PSVT). One type of PSVT reflected antegrade fast A-V nodal pathway and retrograde anomalous pathway conduction. This PSVT was characterized by early retorgrade activation of right atrial appendage, P following QRS and cycle length of 290 to 350 msec. A second PSVT reflected antegrade slow A-V nodal pathway and retrograde anomalous pathway conduction. This PSVT was characterized by early retrograde activation of right atrial appendage, P following QRS, and cycle length of 440 msec. A third PSVT reflected A-V nodal re-entrance with antegrade slow pathway and retrograde fast pathway conduction. This PSVT was characterized by normal retrograde atrial activation sequences, P simultaneous with QRS, and cycle length of 320 msec. All PSVT inductions could be explained in terms of antegrade and retrograde properties of fast and slow A-V nodal and anomalous pathways.

Recent insights into paroxysmal supraventricular tachycardia--an integrated approach to diagnosis and therapy

Paroxysmal supraventricular tachycardia may result from re-entrance in the AV node, the normal A-V pathway with an accessory AV connection, in the sino-atrial node, in the atria, or else reflect ectopic impulse formation in a spontaneously automatic supraventricular focus. Electrocardiographic criteria which are helpful in differentiating these mechanisms involve an analysis of cycle length, changes in cycle length with intermittent bundle branch block, P wave morphology and the relationship of P wave to QRS complex, P-R interval, the presence of A-V block during tachycardia and the influence of autonomic tone on the tachycardia. Electrophysiologic studies further elucidate mechanism by demonstrating the mode of induction and termination of the tachycardia, the characteristics of antegrade and retrograde A-V conduction curves and refractory periods, atrial activation sequence of echo beats and the influence of premature beats introduced during tachycardia. These features are summarised in Table 1. Therapy can be accurately planned according to the results of experimental administration of antiarrhythmic agents and of pacing sequences upon induction and termination of tachycardia in the catheterisation laboratory.

Arrhythmias documented by 24 hour continuous electrocardiographic monitoring in 50 male medical students without apparent heart disease

Results are reported of portable 24 hour dynamic electrocardiographic monitoring in 50 male medical students without cardiovascular disease, as defined by normal clinical and noninvasive cardiovascular examination. During waking periods, maximal sinus rates ranged from 107 to 180 beats/min (mean +/- 5). Twenty-five subjects (50 percent) had episodes of marked sinus arrhythmia as defined by spontaneous changes in adjacent cycle lengths of 100 percent or more. Fourteen subjects (28 percent) had sinus pauses of more than 1.75 seconds, usually during sinus arrhythmia. Transient nocturnal type I second degree atrioventricular (A-V) block was noted in three subjects (6 percent). Of 28 patients (56 percent) having atrial premature beats, only 1 (2 percent) had more than 100 such beats (141) in 24 hours. Of 25 patients (50 percent) having premature ventricular contractions, only 1 (2 percent) had more than 50 such contractions (86) in 24 hours. In conclusion, frequent atrial and ventricular premature beats are unusual in a young adult male population. In contrast, bradyarrhythmias (including marked sinus arrhythmia with sinus pauses, sinus bradycardia and nocturnal A-V block) are common. These findings are useful in evaluating the clinical significance of arrhythmias detected with portable monitoring.

Effects of cycle length on atrial vulnerability

The effect of cycle length on atrial vulnerability was studied in 14 patients manifesting reproducible repetitive atrial firing during atrial extra-stimulus (A2) testing. Repetitive atrial firing was defined as the occurrence of two or more premature atrial responses with return cycle (A2-A3) of 250 msec or less and subsequent mean cycle length of 300 msec or less, following A2. The zone of repetitive atrial firing could be defined in terms of its longest and shortest A1-A2 coupling intervals. Each patient was tested at a long cycle length (CL1) (mean 884 msec) and a short cycle length (CL2) (mean 557 msec). CL1 was sinus rhythm and CL2, an atrial paced rhythm. Repetitive atrial firing occurred in two patients at CL1 and in all patients at CL2. Of the former two patients (group 2), the zone of repetitive atrial firing was markedly widened in one at CL2 due to a shortening of atrial functional refractory period (FRP) at CL2. In the other, zone of repetitive atrial firing could not be totally defined due to induction of sustained atrial flutter preventing definition of atrial FRP. The occurrence of repetitive atrial firing at only CL2 in 12 patients (group 1) reflected: 1) a shortening of atrial FRP from 294 +/- 11 msec at CL1 to 242 +/- 10 msec at CL2 (mean +/- SEM; P less than 0.01), allowing delivery of A2 at shorter coupling intervals (9); 2) the new occurrence of repetitive atrial firing at A1-A2 coupling intervals achievable at both cycle lengths (1); or 3) both effects (2). In conclusion, decrease of cycle length potentiated atrial vulnerability. This demonstration implies that atrial pacing could potentiate occurrence of paroxysmal atrial fibrillation or flutter.

Familial atrial tachyarrhythmia with short PR interval

A family had an unusual and perhaps unique familial dysrhythmia. The proband had a short PR interval with normal QRS and chronic recurrent paroxysmal atrial tachycardia (Lown-Ganong-Levine syndrome). The arrhythmia produced left ventricular dysfunction. Both paroxysmal atrial tachycardia (PAT) and left ventricular dysfunction were reversed with administration of digoxin and propranolol hydrochloride. Three family members had paroxysmal or chronic atrial fibrillation, first diagnosed at a relatively young age (23 years, 38 years, and early 40s, respectively). Five additional family members had short PR intervals with normal QRS, and eight other family members had borderline short PR intervals. The mode of inheritance appeared to be autosomal dominant with varying expressivity. We have described a familial syndrome characterized by PAT or atrial fibrillation in its advanced form with short PR interval as a possible identifying trait. The future course of members with isolated short PR is unknown.

Clinical significance of prolonged sinoatrial conduction time

Prolonged (greater than 152 msec) calculated sinoatrial conduction times (SACT) were found in 24 of 470 patients studied by the atrial extrastimulus technique, ranging from 155 to 220 msec (180+/-4.4; mean+/-SEM). There were 18 males and six females with ages of 29 to 85 (mean 65+/-2.6). Electrocardiographic monitoring revealed significant sinus or atrial dysrhythmias in 19 (79%) patients. Of these 19, 15 had persistent sinus bradycardia and/or sinoatrial block, three had sinus bradyarrhythmia with paroxysmal atrial tachycardia, and one had isolated atrial tachycardia. Additional electrophysiological evidence of sinus node or atrial dysfunction was present in 11 patients. Four patients needed permanent pacing during follow-up (mean follow-up period of 427+/-39 days) because of symptomatic bradyarrhythmia. Three patients died, none suddenly. In conclusion, prolonged calculated SACT was associated with a high incidence of electrocardiographic and electrophysiologic abnormalities of sinus node and/or atrium. Despite this, bradyarrhythmic morbidity was relatively low, suggesting that prolonged sinoatrial conduction time in the absence of symptoms is not an indication for prophylactic pacing.

Electrophysiologic effects of atropine on sinus node and atrium in patients with sinus nodal dysfunction

Electrophysiologic studies were conducted in 21 patients with sinus nodal dysfunction before and after intravenous administration of 1 to 2 mg of atropine. The mean sinus cycle length (+/- standard error of the mean) was 1,171 +/- 35 msec before and 806 +/- 29 msec after administration of atropine (P less than 0.001). Mean sinus nodal recovery time determined at a aced rate of 130/min and maximal recovery time were, respectively, 1,426 +/- 75 and 1,690 +/- 100 msec before and 1,169 +/- 90 and 1,311 +/- 111 msec after atropine (P less than 0.001 and less than 0.001). Mean calculated sinoatrial conduction time, measured in 16 patients, was 113 +/- 8 msec before and 105 +/- 9.7 msec after atropine (difference not significant). Mean atrial effective refractory period, measured at an equivalent driven cycle length, was 262 +/- 11.1 msec before and 256 +/- 10.3 msec after atropine (not significant). Mean atrial functional refractory period was 302 +/- 12.5 msec before and 295 +/- 11.3 msec after atropine (not significant). The shortening of sinus cycle length and sinus recovery time with atropine was similar to that noted in patients without sinus nodal dysfunction. In contrast, atropine had insignificant effects on sinoatrial conduction and atrial refractoriness in this group whereas it shortens both in normal subjects. This finding may reflect altered perinodal and atrial electrophysiologic properties in patients with sinus node disease.

Quantification of human atrioventricular nodal concealed conduction utilizing S1S2S3 stimulation

We studied antegrade concealed conduction of atrial extrastimuli (A2) that blocked in the atrioventricular (AV) node in eight subjects, using a third extrastimulus (A3), coupled at decreasing coupling intervals to A2. Three A1-A2 intervals were tested in each subject: late (just shorter than AV nodal effective refractory period), intermediate, and early (just longer than atrial functional refractory period). The curves relating the following variables were constructed for each A2: A1-A3, H1-H3 and A2-A3, A3-H3. The former was compared to the control A1-A2, H1-H2 curve. Concealment of A2 was demonstrated in all eight subjects at the three tested values of A1-A2. The A2-A3, A3-H3 curve allowed analysis of AV nodal conduction time (A3-H3) and AV nodal recovery time (defined as the shortest A2-A3 at which the impulse conducted to the His bundle) at identical values of A2-A3. In all subjects the timing of blocked A2 had minimal effect on both AV nodal conduction time and recovery time. In five of the eight subjects a late A2 sporadically conducted to the His bundle. Conduction of A2 to the His bundle resulted in marked lengthening of both AV nodal conduction and recovery times. Concealed conduction of A2 was always demonstrated, but the degree of concealment was relatively fixed, whether A2 was an early, intermediate, or late blocked premature beat. Slow conduction of A2 had a much greater effect than concealment of A2 on subsequent impulse conduction.

Pathologic correlations in three cases of bilateral bundle branch disease with unusual electrophysiologic manifestations in two cases

Examination of the conduction system in three patients with bifascicular block who had electrophysiologic studies forms the basis for this report. Patients 1 and 2 had left bundle branch block and Patient 3 right bundle branch block and left axis deviation. The H-V interval was prolonged in each case (70, 65 and 60 msec, respectively). Serial section examination of the conduction system revealed sclerodegenerative involvement of both bundle branches in all cases. In Case 1, atrial extrastimulus testing converted left to right bundle branch block; in Case 2, it delineated a sinus echo zone with repetitive sinus nodal reentrance. In the latter case serial section revealed extensive amyloid infiltration of the approaches to the sinoatrial (S-A) node and the atrial preferential pathways. In Case 3, with right bundle branch block and left axis deviation, serial section revealed greater involvement of the anterior part of the main left bundle branch than of the posterior portion as well as involvement of the second part of the right bundle branch. The study revealed excellent correlation between electrophysiologic and pathologic findings in three cases of intraventricular conduction disease and demonstrated an anatomic basis for the electrophysiologic findings resembling alternating bilateral bundle branch block. Sinus nodal reentrance may be related to disease in the approaches to the S-A node thereby causing delay in perinodal tissue allowing sinus reentrance. Finally in Case 3, the anatomic substrate for left axis deviation may lie in a greater involvement of the anterior portion than of the posterior portion of the main left bundle rather than in the corresponding portions of the periphery.

Electrophysiologic effects of atropine on human sinus node and atrium

Electrophysiologic studies were conducted in 17 patients without apparent sinus node disease before and after intravenous administration of 1 to 2 mg of atropine. Mean values in milliseconds (+/- standard error of the mean) before and after administration of atropine were as follows: sinus cycle length 846 +/- 26.4 versus 647 +/- 20.0 (P less than 0.001); sinus nodal recovery time 1,029 +/- 37 versus 774 +/- 36 (P less than 0.001); mean calculated sinoatrial (S-A) conduction time 103 +/- 5.7 versus 58 +/- 3.9 (P less than 0.001); mean P-A interval 34 +/- 1.5 msec versus 31 +/- 1.5 (P less than 0.05); mean atrial effective and functional refractory periods during sinus rhythm 285 +/- 11.3 versus 238 +/- 7.9 and 331 +/0 11.6 versus 280 +/- 8.6, respectively (P less than 0.001 for both); mean atrial effective and functional refractory periods measured at equivalent driven cycle length 239 +/- 7.7 versus 213 +/- 7.4 and 277 +/- 11.4 versus 245 +/- 9.5, respectively (P less than 0.001 for both). In conclusion, atropine shortened sinus cycle length, sinus nodal recovery time and calculated S-A conduction time. The shortening of atrial refractory periods with atropine implies that vagotonia prolongs atrial refractoriness in man.

Electrophysiological studies in patients with chronic recurrent ventricular tachycardia

Seventeen consecutive patients with chronic recurrent ventricular tachycardia (VT) were studied in an attempt to delineate the reproducibility and mechanism of this arrhythmia. Six patients had nonsustained and 11 had sustained VT. The following electrophysiological techniques were utilized in an attempt to reproduce VT: 1) rapid atrial and ventricular pacing (17 pts); 2) atrial extrastimulus technique (17 pts); 3) ventricular extrastimulus technique (17 pts); 4) V1V2V3 stimulation technique (5 pts); 5) ventricular pacing from two or more sites (5 pts). Ventricular tachycardia was induced in six of 11 (54%) patients with sustained VT. However, in four there was only a single induction and only in the remaining two patients could VT be repetitively induced. In the latter two patients ventricular tachycardia was induced with both atrial and ventricular stimulation. Ventricular tachycardia could not be induced in any patient with nonsustained VT, although three had spontaneous episodes of ventricular tachycardia during study. In conclusion, in the present series of patients with chronic recurrent VT, this rhythm could not be reproducibly induced in the majority of patients in the cardiac catheterization laboratory utilizing catheter stimulation techniques.

Angina-like syndrome with diazoxide therapy for hypertensive crisis

In 14 patients with hypertensive crisis treated with diazoxide, close monitoring of blood pressure, heart rate, and symptoms was performed. Standard 12-lead electrocardiograms were recorded before and after diazoxide. All patients showed a significant fall in blood pressure after drug administration. Seven patients (50%) showed significant ST-T changes after diazoxide. Six patients (43%) developed substernal discomfort demonstrated by substernal pain of tightness. Five patients (35%) had both chest discomfort and ST-T changes. One of these patients with substernal pain and ST elevation had evidence of acute myocardial infarction with serial enzyme studies. In the patients with significant ST-T changes, the average fall in blood pressure was significantly greater than the average fall in blood pressure in the patients without significant ST-T changes. These findings suggest that both ST-T changes and substernal discomfort were due to myocardial ischemia secondary to a sudden severe drop in blood pressure.

Prospective observations in patients with chronic bundle branch block and marked H-V prolongation

Eighteen of 388 patients with chronic bundle branch block, studied electrophysiologically and followed prospectively, had H-V intervals of 80 msec or greater. Five patients were functional class I, five class II, seven class III, and one class IV. Follow-up ranged from 103 to 1919 days (mean 711 +/- 118). Three patients needed permanent pacing for the following indications: sino-atrial block, sinus bradycardia post-cardiac surgery, and 2 degrees block distal to the His bundle. Six patients died, three suddenly, and three nonsudden. The five initially asymptomatic patients are alive and without pacemakers (mean follow-up 732 +/- 139 days). Although marked H-V prolongation was associated with high morbidity and mortality in this small series, this was only in patients with symptomatic heart disease. Asymptomatic patients (five patients) had a benign clinical course. Prophylactic pacing would probably not modify clinical course in the former group, and is probably not indicated in the latter group. Longer follow-up will be needed for definitive prognostication.

Catheter mapping of retrograde atrial activation. Observations during ventricular pacing and AV nodal re-entrant paroxysmal tachycardia

A systematic study of retrograde atrial sequence at commonly used electrode catheter recording sites in 8 patients without, and in 4 patients with AV nodal re-entrant paroxysmal tachycardia was made. During right ventricular pacing, the retrograde atrial activation sequence was low septal right atrium--proximal coronary sinus--distal coronary sinus--high right atrium. During the episodes of paroxysmal tachycardia, a similar pattern was observed. This information should be helpful in the understanding of abnormal activation sequences in patients with paroxysmal supraventricular tachycardia in whom retrogradely conducting anomalous pathways are suspected.

Electrophysiological and clinical observations in patients with alternating bundle branch block

Electrophysiological studies (His bundle recordings and atrial stimulation) were performed in nine patients who manifested periods of both right and left bundle branch block (RBBB and LBBB). In seven of the patients, alternating bundle branch block appeared to reflect intermittent or chronic bundle branch block superimposed on incomplete (but electrocardiographically complete) block of the contralateral bundle branch. In three of these seven, shift from one bundle branch block pattern to the other was associated with reproducible change in H-V (mean change 30 msec), and could be induced by alteration of cardiac rate with carotid massage, coupled atrial stimulation, and rapid atrial pacing. In one of the seven, RBBB with a P-R of 0.20 seconds preceded chronic LBBB with a P-R of 0.24 seconds, implying that RBBB had been incomplete. In three of the seven, although a definite mechanism of alternation could not be demonstrated, transient contralateral bundle branch block occurred superimposed on chronic ipsilateral bundle branch block, implying that the ipsilateral block was incomplete. Two patients manifested periods of narrow QRS, LBBB, RBBB, and paroxysmal A-V block. Based upon pathological data (one case), this pattern appeared to reflect a lesion involving the distal His bundle and proximal bundle branches. In the total group of patients, clinical course was primarily determined by the severity of heart disease and not by occurrence of A-V block. The conduction defect in the majority of patients was surprisingly benign.