Abstract 8927: Double-hump Syndrome: The Presence Of Extreme Interatrial Conduction Delay is Associated With Regularization and Progressive Slowing of Atrial Arrhythmias in a Subgroup of Patients With Hypertrophic Cardiomyopathy

Abstract

Background: In patients with hypertrophic cardiomyopathy (HCM) extreme interatrial activation delay (IAD), indicated by complete separation of the right and left atrial activation on the surface ECG (double hump P wave), was associated with regularization and increase of the cycle length (CL) of recurrent atrial tachycardias (ATs).We aimed to determine the prevalence and the predisposing clinical factors for this clinical entity. Methods: We used data from our HCM registry (n=174 pts, mean age: 53±14 yrs). Data of patients with separated P wave, regularization and slowing of ATs (group I, 5 pts, 2.9%) were compared with 122 control patients with HCM without ATs (group II.). The following parameters were analyzed: P wave morphology and change in P wave duration (ΔP and Pmax), changes in AT CL (ΔATCL), echocardiography parameters including interatrial septal thickness (IAS-T), E/A ratio, E/E prime ratio and fractional shortening (FS) and results of genetic testing. Results: Overall, 9 pts (5.1%) had double hump P waves. This was associated with AT CL prolongation in 5 pts, who were older (66±11 yr vs. 50±14 yr, p=0.016) and had longer follow-up (13,8±1,8 years vs. 7,8± 4,7 years, p=0.005). The ΔATCL was 121±134 ms (range [40-360]) in group I. Echocardiography confirmed double mitral and tricuspid inflow A waves in all group I. pts. Pmax and ΔP were significantly larger in group I (166±33 ms vs. 105±22 ms, p<0.001; 52±26 ms vs. 9±13 ms, p<0.001, respectively). Group I. had an increased LA size as compared to group II. (58±12 mm vs. 45±8 mm, p=0.001) and higher E/A and E/E prime ratios (1,99±1,2 vs. 1,23±0,5, p=0.005 and 20,9±13 vs. 13,1±6,0, p=0.011, respectively). There were no differences in IAS-T and in FS (superior IAS: 4,4±0,1 mm vs. 5,2±1,7 mm, p=NS; inferior IAS: 5,8±0.1 mm vs. 5,7±2,2 mm, p=NS; 38,4±5 % vs. 40,4±9 %, p=NS, respectively). All identified mutations were typical Dutch founder mutations of the MYBPC3 gene. Conclusions: A subgroup of HCM patients have an unique combination of symptoms of separated P wave, regularization and slowing of ATs. Interatrial conduction delay is not related to IAS-T, however, it is associated with larger atria and higher LA pressures. The presence of double hump syndrome is associated with MYBPC3 myosin binding protein mutations.