Intermittent atrioventricular block: procainamide administration as a provocative test

Electrophysiological Testing for the Investigation of Bradycardias

In this article we review the role of electrophysiological testing in patients presenting with bradycardia due to sinus node or atrioventricular node disease. In sinus bradycardia the role of electrophysiology studies is not established. In AV conduction disturbances, an electrophysiology study may be necessary both for the establishment of atrioventricular block as the main cause of symptoms, and for identification of the anatomic site of block that may dictate the potential need of permanent pacing.

Value of EP Study and Other Cardiac Investigations

With the advent of implantable loop recorders capable of prolonged electrocardiographic monitoring, and following studies demonstrating the benefit of implantable cardioverter-defibrillator therapy in subgroups of patients with structural heart disease and depressed left ventricular function, the role of invasive cardiac electrophysiologic (EP) studies in patients with unexplained syncope has been substantially reduced. Nonetheless, in select high-risk patients presenting with unexplained syncope, EP studies still play an important role in identifying a diagnosis in these patients and assessing long-term risk of mortality.

The effect of intravenous procainamide on the HV interval at electrophysiologic study

The His bundle electrogram recorded at electrophysiologic study clearly differentiates atrioventricular (AV) node disease from distal conduction system disease. The distal conduction system may be tested further by infusing procainamide (10-15 mg/kg) intravenously. High-grade distal AV block or prolongation of the HV interval <80 ms was defined as an abnormal response to this test. We retrospectively reviewed the medical records of 79 patients who underwent electrophysiologic study with intravenous procainamide. An abnormal response to procainamide was observed in only 3% of 37 patients with a normal baseline HV (</= ms), in 48% of 27 patients with mild HV prolongation (56 to 70 ms), and in all 15 patients with moderate HV prolongation (<70 ms) (P <0.0001 for the trend). Procainamide induced high-grade AV block in 4 of 28 patients (14%) studied for syncope and in 1 of 51 patients (2%) studied for ventricular tachycardia. Syncope as the indication for electrophysiologic study (P = 0.05) and left bundle branch block morphology (P = 0.03) were predictors of high-grade AV block; baseline HV and QTc intervals were significantly prolonged in patients who developed AV block with procainamide. We identified a strong linear correlation (R = 0.85) between post-drug and baseline HV intervals, with a regression slope of 1.17 +/- 0.09 and an intercept (+/- standard error) of 5.8 +/- 5.0 ms. This linear response to procainamide and published prospective studies support pacing syncope patients with baseline HV <70 ms. Therefore, procainamide infusion during the electrophysiologic study of patients with undifferentiated syncope should be reserved for those with mild HV prolongation from approximately 55 to 70 ms.

Pharmacological stress testing of the His-Purkinje system in patients with bifascicular block

This literature review, based mainly on the English-language literature, focuses on pharmacological stress testing of the His-Purkinje system as part of an invasive electrophysiological study. The main target group for this investigation is patients with bifascicular block and syncope in which intermittent high grade AV block is suspected. Several drugs have been used for this purpose, mainly Class I antiarrhythmic agents such as ajmaline, procainamide, disopyramide, and flecainide. Most studies, unfortunately, suffer from limited patient numbers, lack of adequate control groups, and/or adequate follow-up. The sensitivity of the disopyramide stress test has been shown to be 75%-100% for prediction of impending high grade AV block. The specificity was > 90%. Studies on procainamide have shown a sensitivity of 60% but the specificity has not been assessed. There are no studies allowing a strict comparison of the diagnostic value of pharmacological provocation with different drugs. Based on the similarities of the electrophysiological effects on the His-Purkinje system of the above Class I agents, it is reasonable to assume that all of them might be of diagnostic value in the present clinical context, provided atrial and ventricular stimulation after drug is included in the protocol.

The diagnostic sensitivity of electrophysiologic testing in patients with syncope caused by transient bradycardia

Although electrophysiologic testing accurately delineates abnormalities in patients with fixed cardiac-conduction defects, its sensitivity in identifying transient rhythm disturbances is unknown. We prospectively studied 21 patients who had electrocardiographically documented intermittent atrioventricular block (n = 13) or sinus pauses (n = 8) causing syncope, but whose cardiac rhythm had reverted to normal by the time of referral. There were 14 men and 7 women, with a mean age (+/- SD) of 63 +/- 13 years. Fourteen patients had organic heart disease, and 8 were taking cardioactive medications. Electrophysiologic testing was performed before the implantation of a permanent pacemaker. Only three of the eight patients with documented sinus pauses had abnormalities during their tests that suggested the correct diagnosis (sensitivity, 37.5 percent), including a prolonged sinus-node recovery time in one and carotid-sinus hypersensitivity in two. Three of the eight patients had abnormalities detected that were unrelated to syncope, including atrial flutter, dual atrioventricular nodal pathways, and sustained monomorphic ventricular tachycardia. Of the 13 patients with documented atrioventricular block, only 2 had abnormalities suggesting the correct diagnosis (sensitivity, 15.4 percent). Additional observations unrelated to syncope among these 13 patients included abnormal sinus-node function, atrial flutter, and atrial fibrillation causing hypotension. These preliminary observations suggest that a negative electrophysiologic test in a patient with a normal cardiac rhythm who has experienced syncope does not exclude a transient bradyarrhythmia as a cause of the syncope. Furthermore, electrophysiologic testing may sometimes reveal unrelated rhythm disturbances that may mistakenly be designated as the cause of the syncope.

Clinical implications of electrophysiology study findings in patients with chronic bifascicular block and syncope

Electrophysiology study was performed in 93 patients with bifascicular block and unexplained syncope. Clinical evidence of organic heart disease was present in 33 (35%). Electrophysiological abnormalities were detected in 45 patients (48%). Of these, 36 had distal conduction disease, including 28 with an HV interval greater than 55 ms (mean 76.4 ms), and eight who developed infraHisian block following either intravenous procainamide (four) or atrial pacing (four). Sick sinus syndrome was evident in six patients and a further two had carotid sinus hypersensitivity. Sustained monomorphic ventricular tachycardia (VT) was induced in only three patients, two of whom also had prolonged HV interval. Among the 93 patients, 45 had therapy which was guided by positive findings at electrophysiology study (Group 1). Of these, 42 received permanent pacemakers, two were treated with combined permanent pacing and antiarrhythmic drug therapy, and one was treated with antiarrhythmic drug alone. In addition, eight patients without electrophysiologic abnormalities were treated empirically by pacing (Group 2). Finally, 40 patients without electrophysiologic abnormalities received no specific therapy (group 3). At a mean follow-up of 39 months (range two-125 months), recurrence of syncope had occurred in 4% of Group 1 patients, and 25% of Group 3 patients (p less than 0.05). No patient in Group 2 had had recurrence. Total mortality was 40%, including 47% of patients in Group 1, 25% of Group 2, and 35% of Group 3. Death was sudden in seven patients. We concluded that among patients with bifascicular block and syncope, therapy directed by findings at electrophysiology study was associated with symptomatic improvement, but mortality was not significantly influenced.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of metal detector gates on implanted permanent pacemakers

The effect of metal detector security gates, such as are used in airports, was tested in 103 nonselected pacemaker patients. Various types of single and dual chamber units were examined, using telemetry during the test. Pulse rate and duration were measured immediately before and after the procedure. No ill effect was seen on any of the units tested, pacemaker inhibition was not observed, and programmability was not affected. Metal detector security gates have no effect on implanted permanent pacemakers.

Programmed stimulation after anterior myocardial infarction complicated by bundle branch block--late ventricular tachyarrhythmias and outcome

One hundred and thirty consecutive patients with anterior myocardial infarction complicated by bundle branch block were retrospectively analyzed. Sixty died within 1 week of infarction. Of the remaining 70 patients, 36 had electrophysiology study with programmed stimulation 8-90 (mean 20) days after infarction. Of these, nine patients (35%) who clinically had not manifested either ventricular tachycardia or ventricular fibrillation more than 72 hours after infarction, had inducible ventricular tachycardia which was sustained more than 30 seconds in eight patients. By contrast, assessment of atrioventricular conduction added little to clinical management, long-term follow-up, extending up to 127 months, was available both in those patients whose therapy was directed by electrophysiology study, and was assessed among the other 34 patients who survived at least 7 days after myocardial infarction, but who did not undergo electrophysiology study. While the overall mortality was 55%, the majority of deaths (22/35) occurred within 4 months of infarction and many long-term survivors enjoy a gratifying quality of life. Although programmed stimulation in survivors of anterior myocardial infarction complicated by bundle branch block may identify a high risk subgroup, a prospective randomized trial is required to define the utility of more aggressive stimulation protocols following NASPE recommendations, to identify subgroups of patients in whom newer therapeutic interventions, including antiarrhythmic agents, electrical devices and surgery may be indicated.

Role of invasive electrophysiologic testing in patients with symptomatic bundle branch block

Electrophysiologic testing was performed in 112 symptomatic patients with bundle branch block. Abnormalities included HV interval 70 ms or longer (35 patients), infra-Hisian block with atrial pacing (6 patients) and sinus node dysfunction (23 patients). Inducible ventricular tachycardia occurred in 47 patients (42%). Therapy was based on the electrophysiologic test result: group I--16 patients with no therapy (normal study results); group II--34 patients with permanent pacing alone; group III--39 patients with antiarrhythmic therapy alone; and group IV--21 patients with both antiarrhythmic therapy and permanent pacing. Cumulative 4-year survival rates were 83% in group I, 84% in group II, 63% in group III and 84% in group IV (mean follow-up 2.5 years). Recurrent syncope occurred in 19% of group I, 6% of group II, 33% of group III and 19% of group IV. In symptomatic patients with bundle branch block and normal electrophysiologic test results, prognosis is good without treatment. In patients undergoing permanent pacing based on electrophysiologic testing, survival is good and rate of symptom recurrence is low. Electrophysiologic testing identifies patients with inducible ventricular tachycardia for whom antiarrhythmic therapy is indicated but who nevertheless have a poor prognosis.

Clinical intracardiac electrophysiologic testing: technique, diagnostic indications, and therapeutic uses

Clinical cardiac electrophysiologic testing has evolved rapidly since 1968, when the technique was first described. In an electrophysiologic study, electrode catheters are positioned within the heart to record electrical activity from the atrium, atrioventricular conduction tissue, and ventricle. Programmed stimulation is then performed, which involves pacing of the atrium or ventricle and introducing critically timed premature stimuli during sinus rhythm or paced rhythm. The use of programmed stimulation in conjunction with intracardiac recordings in electrophysiologic studies has facilitated the diagnosis of mechanisms of arrhythmias and the assessment of therapy. Electrophysiologic testing is useful in selected patients with sinus node dysfunction, conduction system disorders, supraventricular tachycardia, ventricular tachycardia, or ventricular fibrillation and in survivors of out-of-hospital cardiac arrest and patients with symptomatic but unsubstantiated rhythm disturbances. Therapeutic approaches that can be assessed by electrophysiologic testing include serial drug testing to determine the effectiveness of antiarrhythmic agents, antitachycardia pacing, the implantable defibrillator, transcatheter ablation, and electrophysiologically guided surgical procedures. In this review, we discuss the methods of electrophysiologic testing, its clinical applications in diagnosing the various cardiac rhythm disturbances, and its use in assessing various therapeutic modalities.

Effect of intravenous and oral acebutolol in patients with bundle branch block

We studied the effect of intravenous (1 mg/kg) and oral (400 mg) acebutolol on atrioventricular conduction in 22 patients with idiopathic bundle branch block and 1 to 1 atrioventricular conduction. Seven patients had previously symptomatic complete heart block (Group 1) and 15 were asymptomatic with bundle branch block only (Group 2). Following intravenous acebutolol heart rate decreased 82 +/- 16 to 63 +/- 16/min (P less than 0.01), A-H interval lengthened 98 +/- 22 to 121 +/- 30 msec (P less than 0.005) and H-V time was prolonged 60 +/- 13 to 70 +/- 17 msec (P less than 0.02) in those with previous heart block. The corresponding changes in the patients with no previous block were 74 +/- 14 to 61 +/- 8/min (P less than 0.01), 90 +/- 17 to 109 +/- 22 msec (P less than 0.05) and 48 +/- 15 to 56 +/- 14 msec (P less than 0.01). There was no difference between the basal or induced changes between these two groups. After intravenous acebutolol infusion 2 of 6 patients with previous spontaneous heart block and none of those without previous heart block developed atrioventricular block distal to His. The induced block was temporary (less than 10 min) and corresponded to the time of peak plasma acebutolol levels. Temporary atrioventricular block followed oral acebutolol administration in 4/7 patients with previous spontaneous heart block and 0/14 in those without block. In patients with bundle branch block intravenous acebutolol prolonged H-V conduction times in 19/20 patients and intravenous and oral acebutolol induced A-V block in 4/7 patients with previous spontaneous block.(ABSTRACT TRUNCATED AT 250 WORDS)

Rate-dependent effects of procainamide on His-Purkinje conduction in man

Microelectrode studies in isolated cardiac tissues have shown that the depressant effect of several antiarrhythmic drugs on the maximal upstroke velocity of the cardiac action potential is rate-dependent. To determine whether this effect of antiarrhythmic drugs is seen in humans, 14 patients undergoing atrial pacing at several rates were prospectively studied before and after the infusion of procainamide (15 mg/kg). The HV interval (His-Purkinje conduction rate) and the QRS duration (intraventricular conduction rate) were measured. Before procainamide infusion, atrial pacing did not significantly prolong the maximal HV interval (from 54 +/- 15 to 58 +/- 13 ms). After procainamide infusion (mean serum level 10.0 +/- 3 micrograms/ml) atrial pacing at an average of 5 pacing rates significantly prolonged the HV interval (from 67 +/- 18 to 80 +/- 20 ms, p less than 0.001). The extent of HV prolongation with atrial pacing after procainamide infusion was independent of the HV interval at rest before procainamide. The duration of the QRS complex also tended to prolong with atrial pacing after procainamide infusion, but this prolongation was not statistically significant. Thus, procainamide produces a rate-dependent depressant effect on His-Purkinje and intraventricular conduction, confirming observations made in isolated tissue preparations.

Disopyramide induced second and third degree atrioventricular block in patients with bifascicular block. An acute stress test to predict atrioventricular block progression

Syncopal attacks in patients with bifascicular block may be due to both ventricular tachyarrhythmias and intermittent atrioventricular block in addition to non-cardiac causes and lead to antiarrhythmic treatment with drugs or pacemaker or both. The acute electrophysiological effect of intravenous disopyramide 2 mg/kg body weight given over five minutes on the His-Purkinje system was assessed in 27 patients with chronic bifascicular block undergoing evaluation for permanent pacemaker treatment. The predictive value of this pharmacological stress test as regards the development of atrioventricular block during follow up was analysed. The HV interval increased (mean 43%) and the QRS duration was prolonged (mean 24%). Intrahisian or infrahisian second or third degree atrioventricular block occurred in 14 patients after disopyramide administration, requiring temporary pacing in four of them. Before the electrophysiological study 15 of the 27 patients had had at least two syncopal attacks of suspected cardiac origin but no evidence of second or third degree atrioventricular block. Second or third degree atrioventricular block was subsequently recorded in five of these 15 patients during a mean of two years follow up. The sensitivity, specificity, and predictive value of second or third degree atrioventricular block produced by disopyramide administration including subsequent atrial pacing--a positive disopyramide test--as regards later development of atrioventricular block were 80%, 90%, and 80% respectively. Intravenous administration of disopyramide to patients with bifascicular block and syncopal attacks of suspected cardiac origin may provoke atrioventricular block and asystole requiring immediate temporary pacing. Furthermore, a positive disopyramide test seems to have a significant value in predicting the later development of atrioventricular block.

Electrophysiologic evaluation of syncope in patients with bifascicular block

Thirteen patients with syncope and bifascicular block were evaluated by electrophysiologic study (EPS) including programmed stimulation. The mean age was 62 years. Six patients had coronary artery disease, three had cardiomyopathy, and four showed no evidence of organic heart disease. Holter monitoring and neurologic evaluation were nondiagnostic in all patients prior to EPS. EPS demonstrated inducible ventricular tachycardia (VT) in four patients, an HV interval greater than or equal to 70 msec in four, intra- and infra-His block with atrial pacing in one, and was nondiagnostic in four patients. Four of six patients with an HV interval greater than or equal to 70 msec or pacing-induced infranodal block were treated with permanent pacemakers, four of four patients with VT received antiarrhythmic therapy, and three of four patients with nondiagnostic studies received no therapy (one patient received a permanent pacemaker). During a mean follow-up period of 19 months (range 3 to 60 months) all but three patients have been free of syncope. One patient with VT did not take prescribed antiarrhythmic therapy, another patient with VT died suddenly; the remaining patient had a normal study and basilar migraines were subsequently diagnosed. We conclude that: (1) ventricular tachycardia may be a significant cause of syncope in patients with bifascicular block and was induced by programmed stimulation in approximately one third of patients studied; (2) EPS including programmed stimulation is helpful in delineating both the etiology of syncope and appropriate treatment in patients with bifascicular block. A negative study may also be of prognostic value.

Electrophysiologic studies in patients with bundle branch block

A total of 401 patients with chronic bundle branch block underwent electrophysiologic studies and were followed for a mean of approximately 30 months. Patients with an infranodal conduction time (H-Q) greater than or equal to 70 ms had a significantly higher incidence of progression to spontaneous second-degree or third-degree atrioventricular (AV) block (12%) compared with those with H-Q less than 70 ms (3.5%). The incidence of AV block was 25% for those with H-Q greater than or equal to 100 ms. Although the incidences of all deaths and cardiac deaths were higher for the H-Q greater than or equal to 70 ms group, there was no statistically significant difference in the incidence of sudden deaths in the two groups. A subgroup of 77 patients underwent prophylactic pacemaker insertion based on the presence of transient neurologic symptoms and/or a prolonged H-Q interval. We found no significant difference in the incidence of relief of symptoms or incidence of cardiac or sudden deaths between paced and unpaced groups. A subgroup of 25 patients with syncope underwent ventricular stimulation studies and ventricular tachycardia was induced in 14. We conclude that a markedly prolonged H-Q interval (greater than or equal to 100 ms) may be of value in detection of spontaneous AV block. Prophylactic pacing is of no value in either relief of symptoms or prolongation of life. Complete electrophysiologic studies, including ventricular stimulation studies, are indicated for patients with bundle branch block and syncope.

Atrial pacing in ventricular tachycardia and supraventricular tachycardia with aberrant intraventricular conduction: diagnostic and therapeutic implications

The diagnostic and potential therapeutic value of rapid right atrial pacing in ventricular tachycardia and supraventricular tachycardia with aberrant intraventricular conduction, was examined. The effect of right atrial pacing at incremental rates beginning 10 bpm above the rate of the tachycardia was studied in five patients with ventricular tachycardia, and in four patients with supraventricular tachycardia with rate-related bundle branch block aberration, the mechanism of tachycardia having been demonstrated at electrophysiology study. Atrial pacing resulted in persistent (four) or occasional (one) normalisation of the QRS complexes to that seen in sinus rhythm in those five patients with ventricular tachycardia. The intraventricular conduction pattern persisted with atrial pacing in those patients with supraventricular tachycardia and aberrant intraventricular conduction. This confirms that atrial pacing is a useful and simple diagnostic test in wide QRS tachycardia, which does not require sophisticated electrophysiological facilities. In three of the patients with ventricular tachycardia, atrial pacing terminated the arrhythmia, suggesting potential therapeutic use of rapid atrial pacing in such patients.