Heart Block in Hypertrophic Cardiomyopathy

A 28-year old man, known case of HCM (IVS thickness 20mm, PW thickness 15mm) not on treatment, presented to our ER with syncope 3 episodes. He had third degree AV block in ECG. 

HCM is an autosomal dominant inherited genetic disease characterized by compensatory pathological LV hypertrophy due to sarcomere dysfunction. The incidence of arrhythmias in HCM is well documented. These arrhythmias include AF/Afl, SVT, Sinus node disease, ventricular arrhythmias. Ventricular arrhythmias like VPCs, couplets, and VT are very common (comprising 65% of arrhythmias in Holter monitoring). However, association of AV block in HCM is rarely documented in the literature.

First report of AV block associated with HCM is from Luisada in 1965. They reported AV block in a 10-year old boy who presented with headache during a clinic follow-up. In 1977, Spilkin and colleagues described the case of a 20-year old boy with HCM who subsequently developed AV block.

The cause of AV block in HCM is not clear. Histopathologic reports can describe possible causes. Maron et al—histopathologic examination of the AV nodal tissue was normal, however, continuity of the conduction system was interrupted in the bundle of His. Others reported interstitial fibrosis or myocardial necrosis in the conduction system.

Some believe that if AV block occurs and progresses rapidly to high grade block and then to severe syncope, as in our case, death will be inevitable. It is possible that the sudden appearance of high grade AV block is a more frequent cause of sudden death in adults with HCM than previously suspected. Neuromuscular disease, muscular dystrophy also has the similar presentation (HCM and AV block) but our patient has no symptoms and signs of neuropathy/myopathy. It should be noted that acute and subacute complete heart block are sequelae of alcohol septal ablation for HCM.

This patient was taken to the cath-lab and a temporary pacemaker inserted, now planning for permanent pacemaker insertion.

Ref

Luisada AA. Chic Med Sch Q. 1965;25:169-75
Spilkin S, et al. Circulation. 1977;55:418-22
Maron BJ, et al. Am Heart J 1981;101:857-60