Medical and physiological considerations in the use of artificial cardiac pacing. I

Natural history of chronic second-degree atrioventricular nodal block

This report details our experience with documented chronic second-degree atrioventricular (AV) nodal block (proximal to His [H]) in 56 patients. Forty-six men (82%) and 10 women (18%), ages 18-87 years, were studied. Nineteen of the patients (34%) had no organic heart disease (including seven trained athletes) and 37 (66%) had organic heart disease. ECGs in all patients demonstrated episodes of type I second-degree block; five patients also had periods of 2:1 block. Prospective follow-up patients with no organic heart disease (157-2280 days, mean 1395 +/- 636 days) revealed one patient with clear indication for permanent pacing because of bradyarrhythmic symptoms (permanently placed on day 220 of follow-up). Two patients died nonsuddenly. In patients with organic heart disease (prospective follow-up of 60-2950 days, mean 1347 +/- 825 days), pacemakers were implanted in 10 patients, primarily for treatment of congestive heart failure in eight and syncope in two. Sixteen patients died -- three suddenly, seven with congestive heart failure, two of an acute myocardial infarction and four of causes unrelated to cardiac disease. In summary, chronic second-degree AV nodal block has a relatively benign course in patients without organic heart disease. In patients with organic heart disease, prognosis is poor and related to the severity of underlying heart disease.

Dissociation of the atrioventricular node in acute inferior wall myocardial infarction. 1. Transverse dissociation (alternate Wenckebach periods)

Two cases of alternate Wenckebach periods developing during the acute phase of inferior wall myocardial infarction are presented. In both cases, syncope occurred and severe bradyarrhythmia was recorded on the day of admission. Electrophysiologic study performed in one patient and a narrow QRS complex in the other patient during the alternate Wenckebach periods confirmed the atrioventricular node as the level of block. Transverse dissociation of the atrioventricular node with two (or more) levels of block is the most acceptable explanation for this phenomenon. We suggest that alternate Wenckebach periods occurring during the acute phase of inferior wall myocardial infarction is a severe bradyarrhythmia, and prophylactic temporary pacing is recommended.

Postoperative complete heart block in 64 children treated with and without cardiac pacing

Between 1957 and 1973, a total of 64 children had complete heart block during intracardiac surgery were treated by one of three methods: (1) No pacemaker: Six of the 13 patients in this group had reversion to sinus rhythm. Seven patients continued to have complete heart block, and five of these died of Stokes-Adams episodes. Two patients continue to have complete heart block without pacemaker insertion. (2) Temporary pacemaker: Seventeen of 25 patients had reversion to sinus rhythm and the temporary pacemaker was removed; the other 8 continued to have complete heart block. Five of the eight died--three of Stokes-Adams episodes and two at the time of cardiac reoperation. Three remain asymptomatic without placement of a permanent pacemaker. Six died of postoperative complications unrelated to heart block or pacemaker implantation. None of the other 20 experienced Stokes-Adams attacks. There was one late death in this group. Although there are problems in using permanent pacemakers and electrode systems, in these patients with operatively induced complete heart block their use was associated with a low mortality rate.

Treatment of the bradycardia-tachycardia syndrome with permanent demand pacing

The bradycardia-tachycardia syndrome (paroxysmal supraventricular tachycardia alternating with sinus bradycardia and episodes of sinus node arrest) has previously presented a complicated therapeutic dilemma when excitatory and suppressive drugs have been utilized. A patient with this syndrome successfully treated with a permanent ventricular transvenous demand pacemaker is presented. Various aspects of this syndrome as well as facets of diagnosis and treatment have been reviewed and discussed. Significant underlying cardiac disease was ruled out in this patient by the usual diagnostic methods including left heart catheterization and coronary angiography. An interesting possibility of the relationship of vagal stimulation secondary to hiatus hernia as an etiologic factor in this syndrome has been discussed. The opinion is expressed that the currently preferred method of treatment is the insertion of a permanent transvenous pacemaker alone or in conjunction with antiarrhythmic drugs, preferably digitalis and propranolol.

The effects of chronic ventricular pacing on the human conduction system

Six cardiac patients had His bundle electrograms obtained prior to ventricular pacing. Hours to days after constant pacing, repeat His bundle electrograms were obtained. The H-Q interval increased after pacing in 5 of the 6 patients. The average H-Q interval of 55.8 msec increased to the post pacing value of 67.5 msec (p smaller 0.02). Thus ventricular pacing can produce a conduction delay in the His Purkinje system.

The significance of second degree atrioventricular block and bundle branch block. Observations regarding site and type of block

His bundle (H) electrograms were recorded in 15 patients with second degree atrioventricular (A-V) block and bundle branch block and these patients were prospectively followed. Site of block was proximal to H in four (BPH), distal to H in nine (BDH), and undetermined in two (studied during 1:1 conduction). Surface electrocardiographic features were retrospectively examined to determine the value of these recordings in predicting the site of block. Patients with type I block, with or without type II or 2:1 block, had BPH. Patients with type II block, 2:1 block, or type II combined with 2:1 block had BDH. Heart failure was more common in those with BPH (three of four patients as compared to three of nine patients with BDH). Syncope developed more commonly in patients with BDH (six of nine patients) as compared to those with BPH (one of four patients). Permanent pacing was indicated in three of four patients with BPH, nine of nine patients with BDH, and one of two patients with block at undetermined site because of syncope or heart failure. Five of nine patients with BDH required pacemakers within ten days of initial admission.

Most patients with second degree A-V block and bundle branch block will need permanent pacing. In patients with 2° BDH, pacemakers are indicated whether or not symptoms are present because of high risk of syncope and potential risk of sudden death. In asymptomatic patients with 2° BPH, careful observation is indicated.

Digitalis in the sick sinus syndrome. The effects of digitalis on sinoatrial automaticity and atrioventricular conduction

The effect of digitalis in patients with sinoatrial node dysfunction was studied. Atrial pacing studies were performed while His bundle electrograms were recorded in fourteen patients with sinus bradyeardia, syncope, or related symptoms. Measurements were repeated after 0.01 mg/kg ouabain, followed in some by 1 mg atropine. Ouabain produced a significant shortening of sinoatrial recovery time, but no significant change in heart rate. Atropine normalized sinoatrial recovery times in most patients. This study demonstrates that digitalis causes an increase in automaticity in the sick sinus syndrome as reflected by a shortened sinoatrial recovery time. The efficacy of contemplated therapeutic agents in sick sinus syndrome can be evaluated by rapid atrial pacing. When clinically indicated, digitalis may be used for congestive heart failure or tachyarrhythmias in the sick sinus syndrome in the absence of significant A-V conduction disease.

Histopathology of heart block complicating acute myocardial infarction. Correlation with the His bundle electrogram

Histopathological studies of the conduction system were related to His bundle electrogram recordings in seven patients with acute myocardial infarction and atrioventricular (A-V) conduction disturbances. The three patients with inferior infarctions had normal width QRS complexes and delay or block of the impulses above the His bundle. Recent ischemic changes were present in the A-V node in two cases and in the distal conduction system in all three cases. In the four patients with antero-septal infarction and right bundle branch block (RBBB), either the H-V interval was prolonged or block was present below the H spike. The A-H interval was normal in each of these cases, and the A-V node was not affected by the recent infarction. The right bundle branch was involved in all four of these cases and two patients also had involvement of the left bundle branch. In general there was a good correlation between the sites of heart block as defined by the His bundle electrogram and the histopathological analysis of the cardiac conduction system.

Artificial pacemakers: indications and management

The development of artificial pacemakers for the electrical control of the cardiac rhythm has greatly enhanced the physician's ability to treat cardiac dysrhythmias. Pacemakers have been useful in treating Stokes-Adams syndrome and symptomatic bradyeardias; they have helped control the occurrence of tachyarrhythmias and have played an important role in the management of arrhythmias accompanying myocardial infarctions. With their more frequent use, pacemakers have contributed to our knowledge of underlying conduction and natural pacemaker disorders. As new indications for artificial pacemaking have been elucidated, more complex pulse generators have been developed, and newer technics found for their insertion. In spite of recent development the pulse generators in general use have a limited useful lifetime.

This paper reviews the indications for pacemaker insertion that are commonly employed. In addition, an approach to the problem of pulse generator replacement is presented.

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.

Atrioventricular conduction defects in patients presenting with syncope and normal PR interval

Images

Mobitz type II block without bundle-branch block

His bundle (H) electrograms were recorded in three patients with Mobitz type II block and narrow QRS. Block was secondary to digitalis intoxication in one patient. In the second patient, who had first-degree A-V block, type II block occurred with atrial pacing at a slightly increased heart rate. In the third patient, who had corrected transposition of the great vessels, type II block occurred spontaneously. In two additional patients, block simulating type II block was noted. In one, block of single P waves occurred with carotid massage. In the other, Wenckebach periods with small increments in P-R (and P-H) intervals resembled episodes of type II block. In all five patients, block was proximal to H, suggesting the A-V node as the site of block. The conduction defects in these patients were not progressive; none of the patients needed a pacemaker.

Although these mechanisms were identified in patients with narrow QRS complexes, they could occur with bundle-branch block suggesting an erroneous diagnosis of bilateral bundle-branch disease. It is concluded that His bundle recording is helpful in delineating these benign forms of block. The site of block may be a more important determinant of prognosis than the type of block.

Right bundle-branch block associated with left superior or inferior intraventricular block associated with acute myocardial infarction

Over an 11-year period, 28 instances of acute myocardial infarction and bilateral bundle-branch block were encountered. Twenty-two of these patients had right bundle-branch block and left axis deviation, and six had right bundle-branch block and block of the inferior radiation of the left bundle. The overall incidence of complete heart block in these 28 cases was 21%. In-hospital mortality for the whole group was 36%, whereas it was 33% for those patients who developed complete heart block. From these results it is concluded that for the patient with bilateral bundle-branch block and acute myocardial infarction the prophylactic insertion of a temporary transvenous pacemaker is not only warranted, but is probably indicated.

Site of heart block in acute myocardial infarction

Bundle of His electrograms were recorded in eight patients with acute myocardial infarction and heart block. Three patients with diaphragmatic myocardial infarction (DMI) and one with subendocardial infarction were characterized by slowing or block above the bundle of His and A-V junctional escape rhythms during periods of advanced or complete block. An additional patient with DMI had block in the His bundle itself. Intraventricular conduction in the above patients was characterized by normal H-Q intervals (35 to 60 msec) and absence of widened QRS. In contrast, three patients with anterior infarction (AMI) manifested complete block below the bundle of His and idioventricular escape. P-H intervals were normal (80 to 140 msec) and A-V conduction was considered unaffected. Our electrophysiologic observations coupled with previous clinical, anatomic, and pathologic findings suggest that the heart block in DMI is usually due to an ischemic lesion of the A-V node, while heart block in AMI is due to necrosis involving both bundle branches.

Wenckebach and Mobitz type II A-V block due to block within the His bundle and bundle branches

Fourteen patients with conduction defects were analyzed by using bundle of His (BH) recordings. The BH electrograms were validated by BH and right atrial pacing (AP). In 12 patients with Mobitz type II A-V block, failure in impulse transmission for the dropped beats was localized distal to the recording site of the BH. Three of these 12 patients showed normal QRS complexes. In two of these three, the QRS complexes remained unchanged during intermittent periods of complete heart block (CHB), and thus represent His bundle rhythm with subsidiary pacemaker arising above the bifurcation of the BH. The A-H time in this group of 12 patients ranged from 60 to 160 msec and the H-V time ranged from 40 to 90 msec. At any atrial rate (NSR or AP) conduction time through the A-V node (A-H), and His-Purkinje system (H-V) remained constant. With increasing atrial (A) rates during AP, the number of impulses blocked distal to the BH increased. At high AP rates Wenckebach phenomenon between A and BH occurred concomitantly with block distal to the BH.

Of the two additional patients studied, the one with Wenckebach type 2° A-V block during NSR and a narrow QRS complex had the delay localized between two recorded and validated BH potentials ("split" BH). The other patient, with 1:1 A-V conduction during NSR and left bundle-branch block, developed Wenckebach cycles during AP at 110 beats/min. The progressive delay in the P-R interval was localized in the His-Purkinje system (HPS) probably in the right bundle.

Our data support the clinical observations that Mobitz II A-V blocks are associated with bilateral bundle-branch block as well as with BH lesions. The ECG is of limited value in the localization of the delays occurring at two sites simultaneously: namely, in the A-V node and the HPS. Furthermore, demonstration of the Wenckebach cycles within the HPS (BH or either bundle branch), which cannot be determined from the surface ECG, has important clinical implications.