Quantitative assessment of myocardial infarction: On the relationship between anatomy and electrophysiology using MRI and ECG

Both presence and extent of myocardial infarction are important prognostic factors for mortality and quality of life in patients with ischemic heart disease. Thus, it is of great clinical importance to be able to diagnose and characterize myocardial infarction. One way to diagnose myocardial infarction is by using the 12-lead electrocardiogram(ECG). For estimation of infarct size and location from infarctrelated ECG changes, the so called Selvester QRS scoring system can be used. This system is based on a forwardmodeling of the myocardial activation sequence. To further develop QRS scoring and for better understanding the pathophysiologic basis for infarct-related ECG changes, it is fundamental to understand how anatomic infarct characteristics relate to changes in the 12-lead ECG. The current reference standard for non-invasive visualization of myocardial infarction is delayed contrast-enhanced magnetic resonance imaging (DE-MRI). Hence, DEMRI can be used to define the anatomic correlate to infarct-related QRS changes. Paper I demonstrated that there was a good correlation between QRS score and infarct size by DE-MRI in patients with reperfused first-time infarction. Furthermore, the data showed that QRS score was related to infarct transmurality, whereas presence of Q waves was not indicative of transmural infarction. Indeed, Paper II revealed that the endocardial extent of infarction was a stronger determinant for presence of pathological Q waves than was infarct transmurality in patients with reperfused first-time infarction. In Paper III, the sequential changes of the infarction, left ventricular function and QRS score were studied in patients with reperfused first-time infarction. It was shown that almost two thirds of the total decrease in infarct size seen after one year occurred during the first week after infarction. Furthermore, regional wall thickening was shown to decrease progressively with increased infarct transmurality. Also, the timing and magnitude of decrease in infarct size assessed by DE-MRI was shown to correlate to the decrease in QRS score. Finally, Paper IV demonstrated that in patients with chronic anterior infarction, frequently suffering from severe remodeling and left ventricular aneurysm, QRS score was only moderately correlated to infarct size assessed by DE-MRI. In summary, DE-MRI has been used to describe the anatomical correlate to infarct-related QRS changes in acute, evolving, and healed myocardial infarction.