Outcomes of Mixed Cardiac Inflammatory Syndrome Compared to Acute Pericarditis or Myocarditis

Background: Acute idiopathic pericarditis is frequently accompanied by myocardial involvement (mixed cardiac inflammatory syndrome, MICS). It remains unclear if MICS is a complication of acute pericarditis, which can lead to cardiac tamponade, or represents concomitant acute pericarditis and myocarditis, which may be complicated by cardiogenic shock, ventricular tachycardia, and atrioventricular block. The aim of the study was to compare the baseline characteristics and outcomes of patients with acute idiopathic pericarditis, MICS, and acute idiopathic myocarditis.

Methods: The cohort included 317 consecutive patients (77% male; median age 41 years, range 18-89 years) admitted to a single tertiary medical center in 2006-2017 with acute idiopathic pericarditis (n=169), MICS (n=79), or acute idiopathic myocarditis (n=69). The medical files were retrospectively reviewed for clinical, and laboratory data, in-hospital complications (major cardiac events of cardiac tamponade, cardiogenic shock, and ventricular tachycardia, and large pericardial effusion), life-saving interventions, and outcome.

Results: The MICS group was characterized by intermediate values between the pericarditis and myocarditis group of mean age, level of C-reactive protein, and frequency of pericardial effusion. The frequency of major cardiac events in the MICS group was lower than in the pericarditis group (3.9% vs 17.4%, p=0.038) and similar to the myocarditis group. Fifteen patients (4.7%) needed life-saving interventions, with no difference in rates among the groups. There were no in-hospital deaths. During follow-up (median 45 months, range 12-140 months), 2 patients died, both with myocarditis (p=0.0468 compared to the other groups). Recurrence was recorded in 63 patients (19.9%). The rate of recurrence in patients with MICS was lower than in patients with pericarditis and higher than in patients with myocarditis (p=0.002). A seasonal pattern was observed only for pericarditis (p <0.0001).

Conclusions: The lesser frequency of major cardiac events in the MICS group relative to the pericarditis group together with the similar use of life-saving measures in all three groups suggests that the benign outcome of the patients with MICS was at least partly attributable to good management. MICS shares certain characteristics with acute idiopathic pericarditis and other characteristics with acute myocarditis, and rates/levels of still other factors fall between the two.

Key Words: acute idiopathic pericarditis, myopericarditis, perimyocarditis, myocarditis, mixed inflammatory cardiac syndrome