Reduced Left Atrial Conduction Velocity in Patients With Hypertrophic Cardiomyopathy and Normal Left Atrial Voltage Presenting for Paroxysmal Atrial Fibrillation Ablation

Introduction: Patients with hypertrophic cardiomyopathy (HCM) exhibit abnormal cardiac tissue arrangement characterized as myocardial disarray. The incidence of atrial fibrillation (AF) is increased 4-fold in patient with HCM and confers a 4-fold increased risk of death. Catheter ablation is less effective in HCM, with a 2-fold increased risk of AF recurrence. The mechanisms of AF perpetuation and recurrence in HCM are poorly understood. We sought to investigate the left atrial conduction characteristics in patients with HCM, paroxysmal AF and normal left atrial bipolar voltage. Methods: We analyzed 24 consecutive patients with HCM and 24 consecutive controls, all presenting for radiofrequency (RF) ablation of paroxysmal atrial fibrillation. Only patients with normal left atrial voltage (mean voltage >0.8 mV) were included in the study. Intracardiac electrograms were extracted from CARTO (Biosense Webster Inc.) mapping system and analyzed using custom Matlab/Python code interfacing with Core OpenEP software. Conduction velocity was calculated using local activation time gradients. Results: There was no difference in baseline demographic characteristics or atrial size measured by echocardiography between HCM and control patients. Patients with HCM had significantly reduced atrial conduction velocity and conduction velocity dispersion compared to controls (Fig A,C) [0.62±0.03 m/s vs 0.44±0.04 m/s, p=0.002], despite no differences in bipolar voltage (Fig B,D) or voltage dispersion. Patients with HCM had significantly less freedom from AF than controls after catheter ablation [OR for recurrence 3.3 (1.02-10.90), p<0.05 vs control]. Conclusion: Atrial conduction velocity and dispersion is significantly reduced in patients with HCM and paroxysmal AF, possibly contributing to arrhythmia perpetuation and persistence after catheter ablation. This finding may be useful in characterizing left atrial properties beyond bipolar voltage.