Left Axis Deviation in Brugada Syndrome: Vectorcardiographic Evaluation during Ajmaline Provocation Testing Reveals...

Area of Science:

• Cardiology
• Electrophysiology
• Medical Diagnostics

Background:

• Brugada syndrome (BrS) is a genetic disorder affecting the heart's electrical system, increasing sudden cardiac death risk.
• Sodium channel blockers can unmask a type-1 electrocardiogram (ECG) pattern in BrS patients, sometimes accompanied by leftward frontal QRS-axis deviation.
• The underlying mechanisms driving this axis deviation in BrS remain incompletely understood.

Purpose of the Study:

• To determine the prevalence of leftward frontal QRS-axis deviation during ajmaline provocation testing in BrS patients.
• To investigate the electrophysiological basis of this axis deviation using vectorcardiography.
• To explore the relationship between axis deviation, conduction abnormalities, and repolarization patterns in BrS.

Main Methods:

• Analysis of a large cohort (n=1430) undergoing ajmaline provocation testing.
• Selection of patients with evoked type-1 BrS-ECG (n=345) for detailed analysis.
• Reconstruction and analysis of vectorcardiograms to assess depolarization and repolarization parameters, comparing patients with and without significant leftward axis shift (>30°).

Main Results:

• Leftward axis deviation occurred in 18% of BrS patients during provocation.
• This deviation was not linked to delayed terminal conduction in the right ventricular outflow tract but to proximal conduction slowing (p < 0.001).
• Patients with left axis deviation exhibited discordant repolarization, indicated by a significantly larger spatial QRS-T angle (p < 0.001).

Conclusions:

• Left axis deviation in BrS patients during sodium channel blocker challenge signifies additional proximal conduction slowing beyond the typical terminal conduction delay.
• This proximal slowing is associated with discordant repolarization, suggesting altered electrical activation and recovery sequences.
• The clinical significance and impact on risk stratification of this left axis deviation and associated repolarization abnormalities require further investigation.