This talk will focus on the use of cardiovascular magnetic resonance imaging to characterise myocardial injury. CMR is a unique imaging modality in that it is totally non-invasive, radiation free and is able to assess multiple parameters of the heart (such as function, viability, perfusion, oedema etc) all in one examination with high degree of accuracy and reproducibility. This talk will focus mainly on late gadolinium enhancement CMR (LGE-CMR), which assesses viability/fibrosis/necrosis and T2W imaging which assess myocardial oedema, which is an often an early feature of myocardial injury.
The development of the LGE-CMR technique has revolutionised the role of cardiovascular magnetic resonance in clinical and research practice. Specific patterns of fibrosis and scarring have been identified in many of the ischemic and non-ischemic cardiomyopathy states. Ischemic cardiomyopathy is characterized by sub-endocardial-based areas of late enhancement that correlate to irreversible myocardial necrosis on histopathology , a pattern consistent with the ‘‘wave front phenomenon’’ as described by Reimer and colleagues. Patients who have non-ischemic dilated cardiomyopathy may also have LGE-CMR evidence of scarring in up to 30% of cases; however, this is typically in a non-coronary distribution and frequently appears as a mid-wall striae.
Notwithstanding its role in diagnosis, potentially the most significant application of the LGE-CMR in cardiomyopathy patients is its emerging role in determining prognosis. Recent work suggests that the presence of delayed enhancement in dilated cardiomyopathy (DCM) patients might be associated with adverse clinical outcome over and above traditional risk factors. Furthermore, in ischemic heart disease (IHD), infarct size determined by LGE-CMR is a better predictor of inducible ventricular tachycardia on electrophysiological studies than LV ejection fraction.
T2-weighted CMR enables assessment of ischemic area at risk after Acute myocardial infarction (AMI). The area at risk is visualised as an hyper-intense portion of myocardium relative to normal myocardium. This zone represents myocardial oedema which starts to form during coronary occlusion. T2 weighted imaging also detects micro-vascular obstruction which is a marker for severe ischemic injury following AMI.