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Second-degree atrioventricular block in the His-Purkinje system following acute myocardial infarction. Clinical
Insights
Second-degree atrioventricular block in acute myocardial infarction patients evolves within the His-Purkinje system. This study observed changes in conduction delay, progressing from Mobitz type 2 to Wenckebach patterns.
Area of Science:
- Cardiology
- Electrophysiology
- Medical Research
Background:
- Atrioventricular (AV) block is a critical complication of acute myocardial infarction (AMI).
- Understanding the His-Purkinje system's role in AV block evolution is crucial for patient management.
Observation:
- Continuous electrocardiographic monitoring and serial His bundle recordings were used in four AMI patients.
- Three patients with anterior wall infarction developed right bundle-branch block and left anterior hemiblock before second-degree AV block.
- The fourth patient with prior conduction disease developed AV block after a lateroposterior infarction.
Findings:
- In all cases, the second-degree atrioventricular block was localized to the His-Purkinje system.
- Initially, three patients showed Mobitz type 2 block with minimal conduction delay, progressing to Wenckebach conduction with significant delay.
- One patient displayed the reverse progression, and three regained 1:1 AV conduction, though one experienced repetitive His-Purkinje block upon rapid atrial pacing.
Implications:
- The His-Purkinje system is a primary site for AV block development and evolution in AMI.
- Serial His bundle recordings can elucidate the dynamic changes in conduction during AMI.
- These findings enhance our understanding of the electrophysiological mechanisms underlying AV block in myocardial infarction.
Abstract:
The evolution of second-degree atrioventricular block in the His-Purkinje system was studied in four patients with acute myocardial infarction, utilizing continuous electrocardiographic monitoring and serial His bundle recordings. Three patients had anterior wall infarction; all developed acute right bundle-branch block and two also showed a left anterior hemiblock one to four hours prior to onset of second-degree atrioventricular block. The fourth patient had an old anteroseptal infarction and chronic right bundle-branch block and left anterior hemiblock; he developed second-degree atrioventricular block following an acute lateroposterior infarction. His bundle electrograms were obtained during the insertion of a temporary ventricular pacemaker within the first 24 hours of onset of chest pain. A second His bundle electrogram was obtained during removal of the temporary paceemaker 7 to 14 days after the first recording. In all cases the block was localized in the His-Purkinje system. In three patients the first His bundle recording showed second-degree atrioventricular block with minimal increment of delay in conduction (3 to 10 msec) prior to the blocked beat (equivalent of Mobitz type 2 block). The second His bundle electrogram showed the development of significant increment of delay in conduction (35 to 210 msec) prior to block (equivalent of Wenckebach conduction). The fourth patient illustrated the reverse order of the observations seen in the other three. Three patients showed resumption of 1:1 atrioventricular conduction; however, when one patient was challenged with rapid atrial pacing, he developed repetitive block in the His-Purkinje system.