Materials and methods:
This was a prospective single center study in the Department of Cardiology at a tertiary care center in India. A total of 400 consecutive subjects recently recovered (within 30-45 days) from COVID-19 infection were screened. All these subjects were COVID-19 positive in the past using reverse transcription-polymerase chain reaction (RT-PCR) swab test. Patients were considered recovered by the discharge criteria (normal temperature lasting longer than 3 days, resolved respiratory symptoms and two consecutive negative RT-PCR test results separated by at least 24 hours) and were isolated for a minimum of 14 days. Of the 400 subjects, 140 underwent two-dimensional (2D) speckle tracking echocardiography (STE) for detection of sub-clinical left ventricular dysfunction. Impaired global longitudinal strain (GLS) was reported in 39/140 (27.8%) of them. All COVID-19 recovered subjects with abnormal GLS were further screened for suitability for CMR. Subjects with: (1) a history of coronary artery disease, myocarditis, moderate to severe valvular dysfunction, atrial fibrillation or prior cardiomyopathy; (2) contradictions to gadolinium contrast; (3) severe renal insufficiency (creatinine clearance rate < 30 mL/min/1.73 m2; (4) pregnancy ; (5) unable to breath-hold and cooperate during CMR examination, (6) MRI image quality was not sufficient for analysis and (7) unwillingness to participate or provide informed consent were excluded. Post exclusion, 30 subjects were finally enrolled who underwent CMR at baseline and a follow-up scan six months later in those with abnormal findings in the initial scan. Additionally, 20 age and sex-matched healthy controls were enrolled who underwent CMR. All the control subjects had a normal electrocardiogram (ECG), echocardiography and had no antecedent history or serological evidence of prior COVID-19 infection. Baseline clinical and biochemical parameters including hemogram, liver and kidney function tests as well as inflammatory markers such as C-reactive protein (CRP), serum ferritin, interleukin (IL)-6, lactate dehydrogenase (LDH) and D-dimer were obtained at the time of admission during COVID-19 infection for all subjects. A written informed consent was obtained from all the subjects prior to a CMR scan. The study protocol was approved by the institutional ethics committee.