[Anisotropic impulse conduction characteristics in chronic myocardial infarct. The importance for initiation and perpetuation of ventricular tachycardia].
The underlying mechanism of most ventricular tachycardias in the setting of chronic myocardial infarction is reentrant excitation. At that time, the active membrane properties like upstroke velocity and amplitude of action potentials of muscle fibers surviving in the border zone of the infarction have returned nearly completely to normal. Anisotropic conduction characteristics, however, importantly contribute to the electrophysiologic properties of the epicardial and/or endocardial border zones in chronic myocardial infarction. In normal myocardial tissue with tight coupling between muscle fibers, conduction velocity is slower for impulses propagating transverse to fiber orientation compared to longitudinal to fiber orientation due to a higher effective axial resistivity ("uniform" anisotropy). With infarct healing, connective tissue invading into the epicardial border zone separates surviving muscle fiber bundles and thereby decreases cell-to-cell coupling ("non-uniform" anisotropy). In this setting, excitation waves propagate transverse to fiber orientation in an irregular sequence and conduction velocity in this direction is significantly reduced without occurrence of acute ischemia. Block of conduction waves propagating longitudinally to fiber orientation may lead to activation of the area distal to the block with long delay by very slow transverse wavefronts. This long delay allows fibers proximal to the line of block to regenerate excitability, and reentrant excitation may be initiated. The common pathway of figure-eight tachycardias preferentially orientates longitudinally to fiber orientation. Very slow conduction transverse to fiber orientation at the pivoting points of reentrant circuits may lead to the occurrence of excitable gaps.
Kottkamp
H
H
Medizinische Klinik und Poliklinik, Innere Medizin C (Kardiologie/Angiologie, Westfälische Wilhelms-Universität Münster.
Hindricks
G
G
Haverkamp
W
W
Shenasa
M
M
Borggrefe
M
M
Breithardt
G
G
D000818:Animals; D002304:Cardiac Pacing, Artificial; D004562:Electrocardiography / Q000295:instrumentation*; D006329:Heart Conduction System / Q000503:physiopathology*; D006352:Heart Ventricles / Q000503:physiopathology; D006801:Humans; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D017180:Tachycardia, Ventricular / Q000503:physiopathology*
Anisotrope Erregungsleitungscharakteristika in chronisch infarziertem Myokard. Die Bedeutung für Initiierung und Aufrechterhaltung von Kammertachykardien.