Extreme interatrial conduction delay and regularization of atrial arrhythmias in a subgroup of patients with hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) patients may develop interatrial activation delay, indicated by a complete separation of the right and left atrial activation on the ECG. This study aimed to determine the prevalence of interatrial activation delay and the relation to atrial tachycardia (AT) cycle length (CL) in HCM patients. 159 HCM patients were included (mean age 52 ± 14 y). In group I (n = 15, 9%) patients had atrial arrhythmias and progressive ATCL. In group II (n = 22, 14%) patients had a stable ATCL. In group III (n = 122, 77%) HCM patients without AT were included. P wave morphology and change in P wave duration (ΔP and Pmax) and changes in ATCL (ΔATCL) were analyzed. Mean follow-up was 8.7 ± 4.7 years. In group I 33% (n = 5) had separated P waves. In group II no P wave separation was identified (OR 1.50 [1.05–2.15], p = 0.007). In group I patients were older compared to group III (62.6 ± 15.1 vs. 50.2 ± 14.0 y, p = 0.002) and had longer follow-up (13.4 ± 2.2 vs. 7.8 ± 4.6 y, p < 0.001). In group III Pmax and ΔP were significantly lower (105.1 ± 22.0 ms and 8.9 ± 13.2 ms, both p < 0.0001). Group I patients had an increased LA size compared to group II (61.1 ± 11.6 vs. 53.7 ± 7.5 mm, p = 0.028) and higher E/A and E/E prime ratios (p = 0.007; p = 0.037, respectively). In group I 93.3% of the identified mutations were typical Dutch founder mutations of the MYBPC3 gene. In HCM patients a unique combination of separated P waves and regularization of ATs is associated with larger atria, higher LA pressures and myosin binding protein mutations.