Clinical experience with a bradycardia indicating pacemaker

High-degree atrioventricular block during anti-arrhythmic drug treatment: use of a pacemaker with a bradycardia-detection algorithm to study the time course after drug withdrawal

AIM

This study examines the recurrence of high-degree atrioventricular block (AVB) during a follow-up period of 2 years in patients with restored AV node function after antiarrhythmic drug withdrawal at implantation of a pacemaker.

METHODS

Nine men and eight women (77 +/- 7 years) taking antiarrhythmic drugs (beta-receptor blockers in 15) and presenting with high-degree AVB were followed for 2 years after being taken off drugs upon receiving a permanent pacemaker with special bradycardia detection software.

RESULTS

At inclusion, surface ECG identified two subsets of patients: a QRS duration < 120 ms (n = 5) and those with a QRS duration > or =120 ms (n = 12). During the 2-year follow-up, progression to high-degree AVB occurred in these groups: 1/5 (20%) and 9/12 (75%) P < 0.05. Six patients had to be restarted on drugs, mostly beta-receptor blockers, due to atrial tachyarrhythmias: 3/5 and 3/12. In total, 16 patients (94%) either developed high-degree AVB needing pacing or atrial tachyarrhythmias requiring drug treatment.

CONCLUSION

Patients on beta-receptor blocking drugs and QRS width > or =120 ms developing high-degree AVB should be recommended a pacemaker without further investigation or observation.

Time Relation between a Syncopal Event and Documentation of Atrioventricular Block in Patients with Bifascicular Block: Clinical Implications

BACKGROUND

Transient high-degree atrioventricular (AV) block is a common cause of syncope in patients with bifascicular block (BFB) but the intermittent nature of AV block makes ECG documentation a challenge. A sensitive and safe tool to investigate BFB patients with syncope would be a bradycardia-detecting pacemaker, which provides a possibility of studying the time relation between the index syncopal episode and the development of high-degree AV block.

METHODS

Twenty-seven patients with BFB and syncope were studied prospectively. All patients received a single-chamber ventricular-based pacemaker with bradycardia-detecting ability. A bradycardia episode was defined as a heart rate of < 30 beats/min lasting > or = 6 s.

RESULTS

During a median follow-up of 60 months, a bradycardia event was detected in 14 patients (52%), of whom 13 also had documented high-degree AV block on ECG. The median time between the syncopal episode and the first pacemaker-detected bradycardia event was 5 months and after an additional median time of 6 months, high-degree AV block was documented on the ECG. In 10 of 13 patients (77%) high-degree AV block was documented within 24 months of the syncopal episode corresponding to an annual incidence of 19% during the first 2 years of follow-up in the study population.

CONCLUSION

In this group of BFB patients a syncopal episode was highly predictive of the development of high-degree AV block within 24 months, justifying pacemaker therapy without prior ECG verification.

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.

Head-up tilt test. A nonspecific method of evaluating patients with bifascicular block

BACKGROUND

Patients with bifascicular block have an increased risk of syncopal attacks, but the underlying mechanism often remains unclear despite an extensive diagnostic workup. The head-up tilt test has been established as an important diagnostic tool in the unmasking of vasovagal syncope in patients with unexplained syncope. Its role in the evaluation of patients with bifascicular block has not been studied.

METHODS AND RESULTS

A head-up tilt test, using a 60 degrees angle of tilt for 45 minutes without pharmacological provocation, was performed in 25 patients with bifascicular block and syncope that remained unexplained after an extensive invasive and noninvasive electrophysiological investigation. As a control group, 25 subjects with bifascicular block without syncope, matched for age, sex, left ventricular function, and underlying heart disease, were included. A positive head-up tilt test was found in 7 (28%) of the syncope patients and in 8 (32%) of the control subjects (P = NS). Six patients, of whom 3 had a positive tilt test, had recurrent syncopal attacks during 32 months of follow-up. None of the control subjects had syncope during follow-up.

CONCLUSIONS

This study gives rise to serious concern regarding the specificity of the head-up tilt test in patients with bifascicular block. A head-up tilt test should therefore be interpreted with caution, and its role as a diagnostic tool in this patient category remains to be established.

Disopyramide stress test: a sensitive and specific tool for predicting impending high degree atrioventricular block in patients with bifascicular block

OBJECTIVE

To study the value of intravenous disopyramide as part of an invasive electrophysiological study in predicting impending high degree atrioventricular block in patients with bifascicular block.

DESIGN

An invasive electrophysiological study was performed in the basal state and after the infusion of disopyramide (2 mg/kg body weight). The progression to high degree atrioventricular block was assessed by bradycardia-detecting pacemakers or repeated 12-lead electrocardiogram recordings, or both.

PATIENTS

73 patients with bifascicular block were included, of whom 25 had a history of unexplained syncope. The remaining 48 patients had no arrhythmia related symptoms and were included as controls. All patients had an ejection fraction of > 35%.

RESULTS

After a mean follow up of 23 months, seven patients in the syncope group and three in the non-syncope group had a documented high degree atrioventricular block or pacemaker-detected bradycardia of < or = 30 beats/min for > or = 6 s. The sensitivity of the disopyramide test was 71% and the specificity 98%. The corresponding figures for an abnormal electrophysiological study in the basal state were 14% and 91%, respectively.

CONCLUSIONS

The sensitivity of an invasive electrophysiological study in patients with bifascicular block and syncope can be markedly increased by the use of intravenous disopyramide. A positive test is a highly specific finding and warrants pacemaker implantation.

Atrioventricular block progression in patients with bifascicular block assessed by repeated electrocardiography and a bradycardia-detecting pacemaker

Syncope may be due to intermittent high-degree atrioventricular (AV) block, but a cause-relation is sometimes difficult to prove. Diagnostic methods with high predictive value proven by instruments for safe and sensitive follow-up are needed. A bradycardia-detecting pacemaker was used in patients with bifascicular block, who had been the subjects of pharmacologic stress testing of the His-Purkinje system. Thirty-seven patients were included, of whom 26 had experienced at least 1 syncopal episode of suspected bradycardia origin, and 11 had previously documented transient high-degree AV block. The electrophysiologic study included injection of disopyramide 2 mg/kg (up to 150 mg) over 5 minutes. A positive test result was defined as spontaneous or pacing-induced His-Purkinje high-degree AV block after drug or a drug-induced HV prolongation of > or = 50%. Patients were followed an average 63 months with repeated electrocardiography and a diagnostic pacemaker (n = 23). Altogether, 24 patients had a significant bradycardia diagnosed by either or both methods. The sensitivity and positive predictive values were: HV interval > or = 70 ms at baseline, 47% and 88%; a positive disopyramide test result, 75% and 80%; and HV interval > or = 70 ms or a positive disopyramide test result, 93% and 74%, respectively. Thus, the diagnostic pacemaker is a safe and sensitive tool for evaluating the information obtained at electrophysiologic study, and pharmacologic stress testing with disopyramide has an informative value in patients with bifascicular block and syncope when results at baseline are inconclusive.

Follow-up of asystolic episodes in patients with cardioinhibitory, neurally mediated syncope and VVI pacemaker

The occurrence rate of spontaneous asystolic episodes during long-term follow-up in patients with abnormal asystolic responses induced by means of vasovagal maneuvers was evaluated. The heart rate of 23 patients (mean age 64 +/- 12 years; 6 women and 17 men) affected by neurally mediated syncope (mean 4.3 +/- 4.9 episodes) was continuously monitored by a specially designed implanted pacemaker able to detect and store in its memory all asystolic episodes lasting 3 to 6 or > 6 seconds. Asystolic, neurally mediated syncope was diagnosed when a reflex asystole of > 3 seconds was induced during carotid sinus massage (n = 22), eyeball compression test (n = 3) or head-up tilt test (n = 2). During a total of 357 months (mean 15 +/- 7) of monitoring, asystolic episodes occurred in 17 patients (74%): 1,765 episodes of 3- to 6-second (median 3) duration occurred in 14 patients, and 47 episodes of > 6-second (median 2) duration occurred in 11. The actuarial estimates of occurrence of asystolic episodes of > 3 and > 6 seconds were 82 and 53%, respectively, after 2 years of follow-up. Only 12 episodes of 3 to 6 seconds (0.7%), and 20 episodes of > 6 seconds (43%) resulted in presyncopal or syncopal symptoms. Thus, an asystolic response to vasovagal maneuvers predicts the occurrence of spontaneous asystolic episodes during follow-up. With few exceptions, spontaneous episodes are asymptomatic and their incidence is low.

Comparison between patients with and without reliable ventricular escape rhythm in the presence of long standing complete atrioventricular block

The underlying heart rhythm was evaluated in 74 patients with complete atrioventricular block and had a permanent pacemaker implantation. The pacing was inhibited for 10 seconds or until the patient developed symptoms of presyncope or syncope. Fifty-six patients (74%) had a reliable escape with a mean cycle length of 2010 +/- 596 msec and a mean escape interval of 2335 +/- 971 msec. In 93% of these patients the escape interval was < 4 seconds. The patients without reliable escape (24%), developed symptoms only after a mean of 7153 +/- 1875 msec. The duration of the conduction disorder was longer in the patients without escape and the intraventricular conduction was slower. More patients without escape were treated and antiarrhythmic agents. Forty-eight patients were followed for 1 year and underwent at least two different studies and 13% had different results at different tests. In conclusion, patients without reliable escape have a longer history of conduction disorder, a slower intraventricular conduction, and are frequently treated with antiarrhythmic agents. Even patients with reliable escape occasionally may show a greater pacemaker dependence; therefore, they should also be considered as pacemaker dependent.

The future of single chamber pacing

Although dual chamber pacemakers have held much interest in pacing over the past several years, single chamber pacing remains the modality of choice, worldwide, in the greatest proportion of patients. Atrial or ventricular demand pacing is safe and effective in the majority of patients. In addition, sensors may be used to increase ventricular pacing rate in order to improve cardiac performance.

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.

Pacemaker dependence in patients with bifascicular block during acute anterior myocardial infarction

Eleven patients with bifascicular block complicating anteroseptal acute myocardial infarction were studied to determine the effect of prophylactic permanent pacing; eight of them also had transient high grade atrioventricular block during the acute phase of the infarction. One month after the infarction an electrophysiological study was performed and a bradycardia indicating pacemaker implanted. All the patients were followed for two years. Six had bradycardia detected, two of whom did not have high grade atrioventricular block during the index infarction. Seven patients died, four of them suddenly. There was no correlation between the electrophysiological findings and subsequent development of bradycardia. Thus pacemaker dependence seems to be common in patients with bifascicular block complicating acute myocardial infarction. Mortality is, however, also high in patients treated with pacemakers. Prospective studies to determine the predictive factors in those patients with an anterior acute myocardial infarction and who benefit from a combination of permanent pacemaker treatment and antiarrhythmic treatment are needed.

Pacemaker dependence in transient high-grade atrioventricular block

In a prospective study 16 patients who had been given a pacemaker because of symptomatic high-grade atrioventricular block and whose conduction had been recovered were checked for their dependence on the pacemaker. During a follow-up time ranging from 32 to 158 months (median 62 months) six patients proved to be dependent on the device owing to the development of recurrent stable high-grade atrioventricular block. The subsequent return of atrioventricular block was evidently not associated with etiology, age, sex, ECG-pattern or length of follow-up period. Five additional patients equipped with a bradycardia-indicating pacemaker all proved to be pacemaker-dependent after a follow-up time ranging from 1-20 months (median 7 months), even though atrioventricular conduction had recovered and its presence had been confirmed at regular outpatient checks. It is thus evident that the conventional clinical methods are of limited value for examining the course of conduction defect and assessing the prognosis for patients whose spontaneous cardiac activity has returned after periods of symptomatic high-grade atrioventricular block. When a bradycardia-indicating pacemaker was furnished, pacemaker dependence was demonstrated in most of the patients whose atrioventricular conduction had recovered. This confirms that pacing introduced because of symptomatic high-grade atrioventricular block should not be discontinued even if a conducted heart rhythm has been established and maintained for long periods.