Intramyocardial block in patients with atrioventricular block

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).