Background: The natural history of acute myocarditis is not well known. The aim of our study was to assess the spontaneous outcome of patients with this disease and its possible relation with progression to chronic dilated cardiomyopathy.
Methods: With this aim, we have carried out a prospective study of 99 patients consecutively diagnosed with acute myocarditis in our hospital from 1987 to April 1995, with a mean follow-up of 34 +/- 25 months. Acute myocarditis was diagnosed by clinical, echocardiographic and isotopic (detection of myocite damage) data, in absence of any other cardiac lesion.
Results: Mean age was 26 +/- 17 years; 70% of the patients were male. Initial symptoms were dyspnea in 58% of the patients, chest pain in 33% and arrhythmias in 9%. Severe heart failure was present in 62% of the patients, ventricular arrhythmias in 16% and supraventricular arrhythmias in 16%. Cardiothoracic index was 0.50 +/- 0.07. Left ventricular ejection fraction was 0.40 +/- 0.18, although in 44% of the patients it was lower than 0.30. Immunosuppressive therapy was not used in any case. Outcome was favorable in 70% of the patients, who had a normal ejection fraction, while 13% died or needed heart transplantation during follow-up and 17% progressed to stable chronic dilated cardiomyopathy. Final ejection fraction was 0.53 +/- 0.17, significantly higher than the initial, 0.40 +/- 0.18 (p < 0.05); this improvement in ejection fraction was mainly observed during the first month after diagnosis (0.49 +/- 0.18). The proportion of patients with an ejection fraction of less than 0.30 decreased from 44% to 21% at the end of follow-up.
Conclusions: Spontaneous outcome of acute myocarditis is good in the majority of patients, although an unfavourable evolution was observed in almost 30% of the patients (death, need of heart transplantation or chronic dilated cardiomyopathy). Improvement in ventricular function mainly occurs at short-term, during the first month of evolution in our study.