Aim: We sought to determine whether myocarditis can be a major cause of acute electrical instability or clinical deterioration in HCM patients.
Methods and results: A total of 119 HCM patients (69 M/50F, mean age 41 +/- 8), 42 with acute clinical deterioration and 77 clinically stable, underwent cardiac catheterization with left ventricular endomyocardial biopsy and gene analysis of major sarcomeric proteins. Endomyocardial tissue was processed for histology, immunohistochemistry, and polymerase chain reaction for the most common cardiotropic viruses. Controls were surgical samples from 50 patients with mitral stenosis. All 119 patients showed histological findings suggestive of HCM. In addition, CD45RO+ lymphocytes (> or =14/mm(2)) with focal necrosis of the adjacent severely hypertrophied and often disorganized myocytes, consistent with an overlapping active myocarditis, were observed in 28 of 42 unstable and none of 77 stable HCM patients. A viral genome was detected in 14 of 28 patients with myocarditis and in none of HCM patients without and in none of controls. No correlation between sarcomeric protein gene mutations and HCM clinical profile was observed.
Conclusion: Myocarditis, often viral, represents a common cause of acute clinical deterioration in HCM. Its recognition can potentially affect disease prognosis and treatment.