NEW YORK (Reuters Health) – Cardiac magnetic resonance (CMR) can help diagnose acute myocarditis, German researchers say – but they warn against using it once symptoms become chronic.
“There are still important shortcomings of CMR imaging in patients with suspected chronic myocarditis,” Dr. Philipp Lurz from University of Leipzig-Heart Center told Reuters Health in an email.
In a study reported this month in JACC: Cardiovascular Imaging, Dr. Lurz and colleagues compared the diagnostic performance of CMR against the “gold standard” endomyocardial biopsy in 132 patients: 70 with suspected acute myocarditis (up to 14 days) and 62 with symptoms lasting more than 14 days.
Endomyocardial biopsy showed myocarditis in 62.9%, including 75.7% of patients with acute symptoms and 48.4% of those with chronic symptoms.
Overall, the presence of edema on CMR imaging was 56% sensitive, 65% specific, and gave a diagnostic accuracy of 59% for myocarditis. The presence of hyperemia and capillary leakage yielded a higher sensitivity (74%), lower specificity (33%), and similar overall accuracy (60%) for the diagnosis. Late gadolinium enhancement (LGE) was 69% sensitive, 46% specific, and 61% accurate in the diagnosis.
The presence of any two of these three findings yielded the highest diagnostic accuracy (68%) and sensitivity (76%), but specificity remained low (54%).
For patients with acute symptoms, the presence of two of the three CMR findings was associated with 81% sensitivity, 71% specificity, a 90% positive predictive value, a 55% negative predictive value, and 79% diagnostic accuracy.
In contrast, for patients with chronic symptoms, CMR yielded markedly lower values for sensitivity (63%), specificity (40%), positive predictive value (53%), negative predictive value (50%), and diagnostic accuracy (52%).
Diagnostic performance of CMR was best for patients with infarct-like myocarditis and patients with viral-positive myocardial inflammation on endomyocardial biopsy.
“Cardiac magnetic resonance imaging can be helpful as part of the diagnostic workup in patients with suspected acute myocarditis,” Dr. Lurz concluded. “However, endomyocardial biopsy remains the gold-standard for the diagnosis of myocarditis, especially in patients with chronic symptoms.”
“Further studies need to clarify whether newer imaging protocols such as T1 and T2 mapping sequences can improve the diagnostic performance of CMR imaging in suspected myocarditis,” Dr. Lurz added.
In an editorial, Dr. Godtfred Holmvang and Dr. G. William Dec from Massachusetts General Hospital in Boston wrote, “Endomyocardial biopsy has been the diagnostic ‘gold standard’ but is now seldom used due to the invasive nature, high rate of sampling error, and variability in diagnostic criteria and interpretation.”
“This study provides strong support for using CMR for confirmation when a diagnosis of myocarditis is entertained in patients who present with acute (up to 14 days) onset of symptoms,” the editorial concludes. “It also indicates a need for improvement before CMR can be relied on to differentiate myocarditis from multiple other forms of heart disease when the presentation is more chronic.”
J Am Coll Cardiol Img 2012;5:513-524,525-527.