Clinical Characteristics and Prognostic Factors of Myocarditis in New Zealand Patients

Myocarditis is an inflammation of the heart muscle and an important cause of dilated cardiomyopathy. Its presentation is heterogeneous, and there are limited studies describing the clinical characteristics of these patients, or which factors predict adverse clinical outcomes. We performed a single-centre retrospective study to explore the clinical characteristics of patients with myocarditis.

Patients >15 years of age admitted to our centre with an ICD-10 diagnosis of myocarditis on their electronic discharge record between 2007 and 2016 were included. Clinical, biochemical and imaging factors were collected. The primary endpoint was combined major adverse cardiac events (MACE) consisting of all-cause mortality, decompensated heart failure leading to hospital admission, documented ventricular arrhythmia, recurrent myocarditis and heart transplantation.

During this period, 178 patients were found to have a diagnosis of myocarditis (71% men, median age 39 years). Men were significantly younger than women (36 vs 53 years, U=4,543, p<0.001). ST-elevation on electrocardiogram was recorded in 59% of patients, and these patients were more likely to be male (85% vs 66%, p=0.012), younger (median age 32 vs 44 years, U=4,129, p=0.001) and to have chest pain (94% vs 65%, p<0.001). At a maximal follow-up of 8 years (mean 4.5 years), MACE occurred in 26 patients. MACE was associated with the presence of dyspnoea (26% vs 9%; hazard ratio [HR] 3.33, 95% confidence interval [CI] 1.53-7.28; p=0.003), pulmonary congestion on chest X-ray (54% vs 11%; HR 5.51; 95% CI 2.3-13.23; p<0.001), and left ventricular ejection fraction <50% on transthoracic echocardiography (24% vs 8%; HR 3.22; 95% CI 1.28-8.12; p=0.013).

Myocarditis was more common in young men in our study. Factors associated with adverse outcomes in acute coronary syndromes were not seen in our younger population. Left ventricular dysfunction appears to be more important in predicting adverse outcomes in myocarditis.