Photon counting cardiac CT for differential diagnosis of myocardial injury

Background The diagnostic approach to symptomatic acute myocardial injury without overt signs of myocardial infarction remains poorly standardized. Cardiac computed tomography (CT) is usually used to exclude vascular causes (pulmonary embolism, aortic dissection and coronary disease), while cardiac magnetic resonance (CMR) is the reference for myocardial tissue characterization. Photon-counting CT (PCCT) represents a major technological advancement of CT; however, its improvement of soft-tissue characterization remains poorly explored in this setting. Purpose To evaluate if PCCT can aid in the differential diagnosis of myocardial injury combining vascular and myocardial tissue evaluation. Methods From November 2023 a prospective cohort of patients was enrolled. Inclusion criteria were: symptomatic laboratory evidence of acute myocardial injury, and either a low-to-intermediate pre-test probability of coronary artery disease (CAD) - with PCCT used as first-line imaging - or documented angiographically unobstructed coronary arteries. Main exclusion criteria were: ST-segment elevation myocardial infarction, severe renal impairment (eGFR ≤30 mL/min/1.73 m²), iodine contrast allergy. Results 24 consecutive patients were enrolled. PCCT was feasible and provided a diagnosis in 100% of patients confirmed by CMR: 14 (58%) myocarditis, 1 (4%) “hot-phase” of arrhythmogenic cardiomyopathy (ACM) due to delayed enhancement and fatty infiltration of the right ventricle (subsequent genetic testing revealed a DSG2 class IV mutation), 1 (4%) Takotsubo syndrome, 8 (33%) ischemic aetiologies. In 10 patients (42%) there was an agreement between clinical suspicion and PCCT diagnosis, all suspected of myocarditis. In the remaining 14 patients (58%), PCCT led to diagnostic reclassification: ischemic lesions were found in two patients suspected of aortic dissection affected by Marfan and Takayasu syndrome respectively. A myocarditis and an ACM were diagnosed in two patients with suspect ischemic aetiology due to the angiographic finding of anomalous origin of coronary arteries. A myocarditis was found in a suspected pulmonary embolism due to previously undocumented right ventricular dilatation in Ebstein anomaly. Two myocarditis were diagnosed in patients with a suspected ischemic aetiology. Five suspected myocarditis had a limited ischemic lesion with microvascular obstruction (in one case a paradoxical embolism was suspected due to the detection of an interatrial defect). One patient with suspected Takotsubo syndrome showed a complex CAD with ischemic lesion in the distal anterior and apical segments. One patient suspected of recurrent myocarditis was reclassified as Takotsubo syndrome. Conclusions PCCT enables early and accurate differentiation between ischemic and non-ischemic causes of myocardial injury, impacting diagnostic classification and guiding subsequent management.Central illustrationbaseline characteristics