Clinical aspects of high-grade heart-block

Isolated congenital complete atrioventricular block in adult life. A prospective study

BACKGROUND

The prognosis of congenital complete atrioventricular block (CCHB) is usually considered favorable in adults. This belief is based on studies comprising a limited number of patients and with rather short observation times. In the present study, the natural history of the disease was investigated by a prospective follow-up through decades of adult life of patients with a large group having well-defined CCHB without structural heart disease.

METHODS AND RESULTS

The diagnostic criteria of CCHB proposed by Yater were applied. Patients registered as having CCHB in 1964, supplemented by younger patients all without symptoms during their first 15 years of life, were selected. The study was limited to patients with isolated, complete, permanent block. An interview was conducted with all patients and clinical follow-up data obtained. There were finally 102 patients, 61 women and 41 men. In November 1994, the time of observation, after the age of 15 years in survivors, was between 7 and 30 years. The mean age at follow-up or at death was 38 years, median age 37 years, and range 16 to 66 years. Stokes-Adams (SA) attacks occurred in 27 patients, in 8 with a fatal outcome. The first attack was fatal in 6 of these 8 patients. Nineteen survived and a pacemaker (PM) was implanted thereafter. Another 8 patients received a PM because of repeated fainting spells, and 27 others have had a PM implanted for other reasons such as fatigue, effort dyspnea, dizziness, ectopies during exercise tests, mitral regurgitation, and a low ventricular rate (VR). VR decreased with age, with a mean rate at 15 years of 46 beats per minute (bpm), at 16 to 20 years of 43 bpm, at 21 to 30 years of 41 bpm, at 31 to 40 years of 40 bpm, and after 40 years of age of 39 bpm. SA attacks occurred in all 7 patients with prolonged QTc time. Low VR at rest or at work, presence of bundle-branch block pattern, low working capacity, and ectopies at rest and/or during effort were not statistically significant risk factors. SA attacks occurred in 6 patients without any of these signs. Mitral regurgitation developed in 16 patients and 4 died. A PM reduced the risk of death. A change to a lower degree of block occurred in 6 patients.

CONCLUSIONS

Prophylactic PM treatment is recommended even for symptom-free adults with CCHB because of the high incidence of unpredictable SA attacks with considerable mortality from first attacks, a gradually decreasing VR, significant morbidity, and a high incidence of "acquired" mitral insufficiency.

Orthostatic and exercise-induced advanced nodal atrioventricular block

A 69-year-old woman was referred for asthenia and dizziness when walking in the last two months. No clinical abnormalities were found, and sinus rhythm was present when lying down. On orthostatism and walking, advanced AV block developed. Atropine and isoproterenol ameliorated the AV conduction abnormality, suggesting a nodal block. The patient remained asymptomatic after pacemaker implantation.

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.

Exercise-induced distal atrioventricular block

Three patients with 1:1 atrioventricular (AV) conduction at rest developed fixed 2:1 or 3:1 AV block during treadmill exercise testing. Electrophysiologic study documented block distal to the AV node in all three patients, and suggested that the exercise-induced block occurred because of increased atrial rate and abnormal refractoriness of the His-Purkinje conduction system. The findings in these three patients suggest that high grade AV block appearing during exercise reflects conduction disease of the His-Purkinje system rather than of the AV node, even in the absence of bundle branch block. Patients with this diagnosis should be considered for permanent cardiac pacing.

Second-degree atrioventricular block

1) While it is possible only one type of second-degree AV block exists electrophysiologically, the available data do not justify such a conclusion and it would seem more appropriate to remain a "splitter," and advocate separation and definition of multiple mechanisms, than to be a "lumper," and embrace a unitary concept. 2) The clinical classification of type I and type II AV block, based on present scalar electrocardiographic criteria, for the most part accurately differentiates clinically important categories of patients. Such a classification is descriptive, but serves a useful function and should be preserved, taking into account the caveats mentioned above. The site of block generally determines the clinical course for the patient. For most examples of AV block, the type I and type II classification in present use is based on the site of block. Because block in the His-Purkinje system is preceded by small or nonmeasurable increments, it is called type II AV block; but the very fact that it is preceded by small increments is because it occurs in the His-Purkinje system. Similar logic can be applied to type I AV block in the AV node. Exceptions do occur. If the site of AV block cannot be distinguished with certainity from the scalar ECG, an electrophysiologic study will generally reveal the answer.

Remission and recovery from chronic, established, complete heart block

The return of A-V conduction is described in a patient after two decades of high-grade or complete congenital heart block. Similar cases have been reported by others, with remission or even recovery commencing up to the fourth decade or later. A similar phenomenon is also described in four patients with acquired heart block of four to ten years' duration; in them, remission was usuallly brief but persisted for seven years in one patient. No full report of this seems to have been published previously. Possible explanations are discussed, but no conclusion is reached. Apart from its interest, the phenomenon is of importance with respect to the selection of demand-type electronic pacemakers in the management of patients with heart block.

Significance of exercise-induced second degree atrioventricular block

A case of second degree, type II, atrioventricular block precipitated by exercise is presented. It is suggested that exercise and other vagolytic manoeuvres may be used as a means of differentiating type I from type II atrioventricular block: the conduction disturbance of type I improves with exercise, whereas that of type II deteriorates with exercise.

The pathophysiology of tachycardia-dependent paroxysmal atrioventricular block after acute myocardial ischemia. Experimental and clinical observations

The pathophysiology of paroxysmal A-V block (PAVB) was studied in 20 anesthetized dogs after ligation of the anterior septal artery. Simultaneous recording of leads II and aV R , as well as intracardiac recordings from the His bundle (Hb) and both bundle branches, were monitored. In 18 of 20 experiments, PAVB was localized in the Hb. In all experiments, PAVB occurred subsequent to Mobitz type II A-V block. In eight experiments, PAVB occurred spontaneously during sinus rhythm and was preceded by a period of Wenckebach periodicity superimposed upon a 2:1 A-V block. Vagal-induced slowing of the sinus rate resulted in immediate resumption of 1:1 A-V conduction. In 18 experiments, PAVB was induced by atrial pacing at a critical heart rate in each case (180-300 beats/min). Evidence is presented that A-V conduction was consistently blocked below a critical H-H interval. Slowing the pacing rate, termination of pacinig or increasing the pacing rate until physiological A-V nodal block occurred, all could result in a longer H-H interval and immediate resumption of A-V conduction. When the critical heart rate for PAVB was maintained, a slow idioventricular escape rhythm occurred.

Five patients who developed PAVB after acute myocardial ischemia are also reported providing the clinical counterpart for the experimental observations. In all five cases, PAVB occurred on acceleration of the sinoatrial rate (105-140 beats/min) which was spontaneous in two and induced by drugs given for varied therapeutic indications in three (isoprenaline in two and atropine sulfate in one). In all five, PAVB was associated with Mobitz type II and/or 2:1 A-V block. These experimental and clinical observations suggest that PAVB after acute myocardial ischemia appears to be due to a tachycardia-dependent repetitive concealed conduction in the ischemic His-Purkinje system, probably mainly in the Hb. The clinical observations point out potential consequences of a rapid atrial rate in patients with acute myrocarcial ischemia and type II A-V block.

Depression of escape pacemakers associated with rapid supraventricular rate in patients with atrioventricular block

Intermittent failure of escape pacemakers to maintain an effective rate when the supraventricular rate was rapid was observed in three patients with complete, or high degree atrioventricular block. In two of these patients asystole or slowing of escape pacemaker rate to less than 20 per minute was reproduced by atrial pacing at rates from 125 to 150 per minute. We localized the site of the block and the site of escape pacemaker proximal to the bifurcation of the His bundle in all patients. We assume that a critical increase in atrial rate facilitates penetration of the nonconducted supraventricular impulses into the area of block causing discharge of the escape pacemaker. We suggest that such concealed discharge of escape pacemakers should be considered as a cause of slow and variable rate of escape pacemakers in patients with block proximal to the bifurcation of the His bundle.

Cardiac arrhythmias. 5. Disturbances in cardiac conduction and their management

A simple classification of atrioventricular block, criteria for diagnosis, and suggested therapy are discussed. The differences between Mobitz I and II second-degree A-V block are reviewed.

Good management of patients who have bundle-branch or other forms of intraventricular block depends on informed judgment which includes consideration of (1) the effect of intraventricular conduction disturbances on the pumping action of the heart, and (2) the likelihood that a specific intraventricular conduction disturbance will be complicated by complete heart block.

Evidence suggests that common forms of intraventricular disturbance, unlike ventricular fibrillation, do not alter significantly the pumping action of the heart. The role of intraventricular conduction disturbances in the genesis of ventricular fibrillation is assessed.

We concluded that only when right bundle-branch block is combined with block of the anterior or posterior fascicle of the left bundle branch is complete heart block sufficiently imminent to warrant special concern. If bilateral block is associated with symptoms of episodic severe bradycardia, pacemaker therapy is indicated.

Significance of high degree atrioventricular block in acute posterior myocardial infarction. The importance of clinical setting and mechanism of block

This report evaluates the morbidity and mortality, during hospitalization and follow-up, of a subgroup of patients with posterior or diaphragmatic myocardial infarction (PDMI) who developed high degree A-V block via a type I mechanism and in the absence of power failure (pulmonary edema or cardiogenic shock). This subgroup was not at any higher risk of hospital morbidity, hospital mortality, or 1-year mortality than three other groups: (a) patients with PDMI but neither high degree A-V block nor initial power failure; (b) patients with other infarct sites who developed high degree A-V block in the absence of power failure; and (c) patients with other infarct sites but neither high degree A-V block nor initial power failure. The significance of subgrouping patients with high degree A-V block by the quantity of clinical heart failure is exemplified by a review of the literature and the present study.

Aetiology of chronic heart block. A clinico-pathological correlation in 65 cases

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Observations on heart block during continuous electrocardiographic monitoring in myocardial infarction

Complete heart block (CHB) was observed in 24 of 350 patients with myocardial infarction who were studied under conditions of continuous electrocardiographic monitoring. CHB occurred predominantly in posterior and anteroseptal infarctions. In posterior infarction CHB was observed in patients who also developed first degree (1°) and types I and II second degree (2°-I and 2°-II) atrioventricular (A-V) block but not bundle-branch block (BBB). In anteroseptal infarction CHB was found in patients with BBB, occasionally in patients with 2°-II A-V block, but not in patients with 1° and 2°-I A-V block. Right BBB with a Q wave in lead V 1 was the usual form of BBB observed in patients with CHB and anteroseptal infarction. One mechanism for sudden death in anteroseptal infarction is the abrupt development of CHB following the onset of BBB. Evidence is presented attributing CHB to a lesion in the A-V node in posterior infarction and to bilateral BBB in anteroseptal infarction.

Electrocardiographic findings in patients with complete atrioventricular block

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Natural history and clinical significance of arrhythmias after acute cardiac infarction

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Artificial pacing by electrode catheter for heart block or asystole complicating acute myocardial infarction

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