Transmural repolarization gradients in vivo: the flukes and falls of the endocardium
Authors: M Vos
Journal: Cardiovascular Research (2001)

within the myocardial wall.Understanding these limitathis issue.tions is crucial to determine the role of the M-cell in the repolarization gradients within the whole heart situation.In the early 90's the Antzelevitch group described the The complex ventricular architecture, the repolarization M-cell [1], in which the M originally refers to midmyocar-parameter, the inter-electrode resolution, the location and dium but has also been used for Masonic or Moe, as an regularity of the focus and the anesthesia are all of acknowledgement to the people behind the initiative to methodological importance.perform research in Utica, NY.Since its introduction thereThe heterogeneity in the transmural APD is therefore has been accumulating in-vitro evidence that this cardiac difficult to visualize in situ, especially considering there is cell type electrophysiologically and pharmacologically already a gradient existing between endo-and epicardium.differs from (sub-)epi-and (sub-)endocardial cells of the A hypothetical contribution of the M-cell should give a left ventricular free wall.biphasic pattern: an increase from (sub)endocardium to the In vitro studies revealed that the intrinsic differences in M-layer(s), and a decrease from M to (sub)epicardium with morphology and duration of the action potential (APD) of an epicardial APD shorter than the APD of the (sub)enthe different cell layers are emphasized under less physio-docardium (black bars; Fig. 1).Thus, the lack of consislogical circumstances, such as bradycardia, sudden rate tency in describing such a biphasic gradient in vivo could changes or acquired long QT, which can be induced by be based on lack of definitions, discrepancies in metheither drugs or pathological conditions.These M-cells odology and absence of repolarization enhancing could be an important arrhythmogenic factor, responsible (patho)physiological circumstances.for both initiation and perpetuation of ventricular arrhyth-In this issue of Cardiovascular Research, Taggart and mias.coworkers [3] are the first to investigate the repolarization The question whether dispersion of repolarization exists gradient in a selected group of patients by using a plunge also in the in-vivo situation is keeping many researchers electrode with 5 recording sites showing electrograms and busy.Anyukhovosky et al. [2] have provided us with a ARIs.We would like to compliment them with this theoretical explanation about the discrepancy in findings tremendous effort to obtain signals from 21 subjects.They between groups on the basis of intercellular coupling.took basic research a step further by lifting the in-vivo Because the intact heart cell-to-cell communication is search for the M-cell to the clinic.considered optimal, absence or a very small transmural Their technique, however, has limitations possibly dispersion of repolarization will be seen.The greatest prohibiting the visualization of the detailed transmural differences in APD will therefore be visualized in isolated gradient of repolarization.To prove the contribution of the myocytes obtained from the different layers.M-cell, the different layers to this gradient should be However, there are important technical limitations, exactly recorded.According to textbook literature, a mean which will influence the visualization of repolarization left ventricular free wall thickness in humans is 10.962 mm [4].Until now, no data are available about the size of the endocardial, midmyocardial and epicardial layers.