title: There is no transmural heterogeneity in an index of action potential duration in the canine left ventricle.
abstract: BACKGROUND
  Transmural heterogeneity in ventricular repolarization demonstrated in vitro has been difficult to confirm in vivo. Whether this discrepancy reflects a physiological phenomenon or a methodological problem remains a vivid matter of debate despite a plethora of experimental work. Therefore, we have measured the relevant electrophysiological parameters first in vivo and repeated these in the same heart and at identical sites in vitro. Methodological issues were tackled by using both unipolar and bipolar recordings. Physiological issues were explored by measuring both local and functional electrophysiological parameters.
  
  
  METHODS
  In 10 healthy dogs, 2 high-resolution needle electrodes were inserted into the left ventricle. Effective refractory periods (ERP) as well as activation recovery intervals (ARI) were determined at each electrode along both needles at basic cycle lengths (BCL) of 850 and 300 ms, respectively. After excision of the heart, ERP and ARI measurements were repeated in the arterially perfused wedge preparations.
  
  
  RESULTS
  First, we observed that ERPs and ARIs were significantly shorter in vivo than in vitro. Mean ERPs and ARIs of all muscle layers were relatively uniform throughout the ventricular wall in vivo. The transition from the in vivo to the in vitro preparation was associated with a significant albeit small increase of mean ARIs in the subendocardium, whereas interlayer differences in mean ERPs did not reach statistical significance as in vivo.
  
  
  CONCLUSIONS
  In the intact canine left ventricular wall, a more or less homogeneous distribution in transmural ERP and ARI is present.
authors: University of Heidelberg, Department of Cardiology, Heidelberg, Germany. Frederik_Voss@med.uni-heidelberg.de
authors: Frederik
authors: F
authors: Voss
authors: Tobias
authors: T
authors: Opthof
authors: Jens
authors: J
authors: Marker
authors: Alexander
authors: A
authors: Bauer
authors: Hugo A
authors: HA
authors: Katus
authors: Ruediger
authors: R
authors: Becker
mesh_terms: D000200:Action Potentials; D000818:Animals; D004285:Dogs; D004567:Electrodes, Implanted; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D006352:Heart Ventricles; D008297:Male; D013997:Time Factors; D016276:Ventricular Function / Q000502:physiology*