Pathologic features of atrioventricular and intraventricular conduction disturbances in acute myocardial infarction

Anatomy, histology, and pathology of the cardiac conduction system--Part V

Although morphologic findings in many of the cardiac arrhythmias of acute and chronic disease have been elusive, the correlates of heart block (particularly atrioventricular block) are abundant. Pathologic features of sinoatrial, atrioventricular, and bundle-branch block are reviewed. Lev and Lenegre diseases (idiopathic bilateral bundle-branch fibrosis) are also reviewed.

Prinzmetal angina. Multifocal ischemia, recurrent AV block, and bradycardia with patent coronary arteries responsive to verapamil

Coronary vasospasm may result in recurrent angina pectoris and cause acute myocardial infarction. The extent to which the "sudden death syndrome" occurs is unknown. The case described herein is unique in that the clinical features, including hypotension, AV block, and ventricular arrhythmias, were similar to those seen in myocardial infarction with a poor prognosis, yet infarction was not documented. In subsequent, long-term follow-up evaluation, chest pain has been recurrent, but despite close observation, no further major cardiac complications have been documented. Long-term use of verapamil has contributed to better control of clinical symptomatology.

Bundle-branch block in the setting of acute anteroseptal myocardial infarction. Clinicopathological correlation

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Histopathology of the conduction system in patients with atrioventricular or intraventricular conduction disturbances

In 9 lethal cases where clinical signs gave rise to the suspicion of acute myocardial infarct (AMI) where well-characterized e.c.g.-changes, permanent or intermittent, were found by monitoring, a very careful autopsy of the heart was carried out, combined with a meticulous histological investigation of the conduction system. Acute changes of mild degree in the conduction system were found only in one case, possibly explaining the left bundle branch block found in this case. In the remaining cases, nothing but chronic changes were found and they did not exceed significantly the changes otherwise to be found in the agegroups concerned in a "control series" of violent deaths not preceded by symptoms of heart disease. According to an estimate there was good correlation between the conduction disturbances demonstrated and the localization of histopathological changes in seven of nine patients; in one of the latter correlation was relatively good; correlation was dubious only in one case. On this basis the authors conclude that present changes in the conduction system which are assumed mainly to be age-related, are the factors to determine the type of conduction disturbances from which the patient will suffer if acute heart ischaemia sets in, for instance due to an AMI, in fact, changes by which he will be predisposed to such disturbances.

Conduction system in a patient with Prinzmetal's angina and transient atrioventricular block

His bundle recordings obtained during and between attacks of Prinzmetal's variant angina and transient atrioventricular (A-V) block were followed by a comprehensive serial section study of the conduction system in a 33 year old woman. Recordings between attacks showed normal A-H and H-V intervals. During an attack there was block proximal to the His bundle recording site. Pathologic studies revealed severe narrowing of the right coronary artery. Arteriolosclerosis of the heart was diffuse. Insignificant changes were found in the approaches to the A-V node and the A-V node itself. Major changes found in the left bundle branch had no counterpart in the electrocardiogram; the discordance in these findings is discussed.

Intra-His bundle block complicating acute inferior myocardial infarction

The unexpected findings of atrioventricular block or delay in the His bundle and proximal branches are described in a 51-year-old man with acute inferior myocardial infarction with narrow QRS complexes. With the information from the His bundle electrogram, the site of atrioventricular block is precisely localized.

Complete heart block with normal QRS duration occurring distal to the his bundle in acute inferior myocardial infarction

A patient with acute inferior myocardial infarction developed on the second day complete heart block with normal QRS duration, and the block was found to be distal to the His bundle. To our knowledge, this is the first such documented case in the English literature. Failure of the preceding Wenckebach periods and of complete heart block to respond to intravenous atropine may be a clinical clue to the nature of this type of heart block. The implications and possible explanations are discussed in the light of recent knowledge concerning the nature of heart block in inferior wall myocardial infarction.

Premonitory sign of heart block in acute posterior myocardial infarction

The appearance of the ARS complex in leads V3R and V4R was analysed in a series of 94 patients with acute posterior myocardial infarction. The cases of posterior myocardial infarction with direct signs of injury (ST segment elevation with a rise of 0.5 mm or more of point F and/or QS pattern) in leads V3R and/or V4R were complicated three times as often by atrioventricular block as those in which such signs were absent (66% and 22%, respectively; P smaller than 0.001). When one of these signs was present in leads V3R and/or V4R, the disorder of conduction was "severe" (complete atrioventricular block or sinotrial block with pauses) in half the cases and "unstable" (bradycardia below 50 beats/min; ventricular pause with or without syncope; widening of QRS complex; ventricular hyperexcitability) in one-third, justifying the introduction of a stimulating catheter. Such disorders were found, respectively, only 1 in 7 (14%), and less than 1 in 10 (8%) when these signs were absent (P smaller than 0.001). The association of ST segment elevation and QS pattern was rarer (15 cases) than the isolated finding of either sign. It was found in the most severe disorders of atrioventricular conduction. The changes observed in leads V3R and/or V4R before the appearance of atrioventricular block enable one to predict which patients with posterior myocardial infarction are the most likely to develop atrioventricular block. These electrocardiographic features seem to indicate septal involvement.