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Intramyocardial block in patients with atrioventricular block

Guoliang Li1,2, Ardan M Saguner3, Deniz Akdis3

  • 1Unité de Rythmologie, Institut de Cardiologie, Hôpital de la Salpetrière, Paris, France.

Journal of Investigative Medicine : the Official Publication of the American Federation for Clinical Research
|March 9, 2018
PubMed

Insights

Patients with atrioventricular (AV) block exhibit intramyocardial block, indicating impaired ventricular activation within the heart muscle. This finding may explain why Torsades de pointes (TdP) episodes often self-terminate.

Area of Science:

  • Cardiology
  • Electrophysiology
  • Myocardial Conduction

Background:

  • Atrioventricular (AV) block is well-researched, but intramyocardial conduction in these patients remains largely uninvestigated.
  • Understanding intra-cardiac electrical propagation is crucial for managing arrhythmias like Torsades de pointes (TdP).

Purpose of the Study:

  • To investigate and demonstrate the presence of intramyocardial block in patients diagnosed with AV block.
  • To correlate intramyocardial conduction abnormalities with the occurrence of TdP and ventricular activation patterns.

Main Methods:

  • Prospective study of five consecutive patients with spontaneous high-grade AV block and TdP.
  • Utilized a standard United States Catheter Instruments (USCI) endocardial temporary catheter positioned at the right ventricle (RV) apex.
  • Analyzed the morphology of endocardial electrograms (EGMs) during basic rhythm and TdP episodes.

Main Results:

  • EGMs revealed sharp, high-amplitude deflections alongside low-amplitude far-field potentials within the QRS complex in all patients.
  • These patterns indicate zones of electrically depressed or silent myocardium exceeding the catheter's interelectrode distance (12 mm).
  • Intramyocardial block was confirmed, demonstrating conduction issues within the myocardium alongside AV conduction system problems.

Conclusions:

  • This study provides the first evidence of intramyocardial block in patients with spontaneous AV block.
  • The presence of diffuse non-conducting myocardium is a potential factor explaining the spontaneous termination of most TdP episodes.
  • Findings suggest a link between intramyocardial conduction defects and the self-limiting nature of TdP, potentially preventing degeneration into ventricular fibrillation (VF).

Keywords:
cardiology

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