A counterpoint paper: Comments on the electrocardiographic part of the 2018 Fourth Universal Definition of Myocardial Infarction.

The Fourth Universal Definition of Myocardial Infarction (FUDMI) [published simultaneously in 2018 in numerous journals including Circulation, Journal of the American College of Cardiology and European Heart Journal] focuses mainly on the distinction between non-ischemic myocardial injury and myocardial infarction (MI), along with the role of cardiovascular magnetic resonance, in order to define the etiology of myocardial injury. As a consequence, there is less emphasis on updating the parts of the definition concerning the electrocardiographic (ECG) changes related to MI. Evidence of myocardial ischemia is a prerequisite for the diagnosis of MI and the ECG is the main available tool for i) detecting acute ischemia, ii) triage and iii) risk stratification upon presentation. This review focuses on multiple aspects of ECG interpretation that we firmly believe should be considered for incorporation in any future update to the Universal Definition of MI. Our counterpoint view is that: a) the use of the ECG following coronary artery bypass surgery should be better explored and defined; b) the emphasis in the FUDMI on convex versus concave ST-elevation, which is questionable, should be balanced by the fact that many patients with true ST-elevation MI (STEMI) present with a concave form of ST elevation; c) reciprocal ST-depression in STEMI caused by right coronary artery or left circumflex artery occlusion, should be set against the fact that not all anterior STEMIs present with reciprocal ST-depression which can also be seen in cardiomyopathy and left ventricular hypertrophy; d) the "posterior" leads V7-V9 should be placed on a horizontal line from V4, rather than follow the 5th intercostal space; e) ST-depression in V1-V3 is not a manifestation of ischemia of the basal inferior segment, placed horizontally; f) Interpreting ST-T changes in patients with conduction abnormalities and pacemakers should be further defined.

Chimerism and microchimerism of the human heart: evidence for cardiac regeneration.

For decades, it has been widely accepted that the heart is a terminally differentiated organ that is unable to regenerate. Studies of recipients of hearts donated by other humans have shed light on the regenerative potential of the human heart. Investigators have been able to trace the Y chromosome by fluorescence in situ hybridization or polymerase chain reaction, or both, in sex-mismatched heart recipients. Cardiac chimerism has been reported, with concentrations of chimeric cells ranging from 0.04% to 10.0%. Cardiac chimerism after bone marrow or progenitor cell transplantation has also been reported to a low extent (approximately 0.20%), suggesting that a fraction of the extracardiac cells that colonize the myocardium are of bone marrow origin. Cardiac chimerism after pregnancy with male offspring (fetal cell microchimerism) has also been demonstrated. Cells of fetal origin have been shown to be capable of differentiating into myocardial cells. Collectively, we show that chimerism studies provide a proof of concept of a process that it is likely to be part of normal cardiac homeostasis in humans but apparently insufficient for cardiac repair in diseased hearts.