Endothelial hypoxic preconditioning in rat hypoxic isolated aortic segments.

Our aim was to analyse endothelial hypoxic preconditioning after hypoxia-reperfusion (HR). Endothelial functionality was analysed through the vasorelaxation responses to acetylcholine (Ach) and the level of serine1177 phosphorylated endothelial nitric oxide synthase (eNOS) (ser1177-eNOS) measured by Western blot in in vitro hypoxic preconditioned (P + HR) isolated rat aortic segments. Relaxation in response to Ach was reduced in phenylephrine-precontracted aortic segments after HR (control: IC50, 5 +/- 2.5 x 10(-8) mol l(-1); HR: IC50, 3 +/- 1.2 x 10(-7) mol l(-1); P < 0.05). Ach-dependent vasodilatation was improved by P + HR. The content of ser1177-eNOS in the HR segments was 1.5-fold lower than in P + HR. Confocal microscopy showed an increased content of both superoxide anion and peroxynitrite in the vascular wall of HR aortic segments, which it was reduced by P + HR. Geldanamycin (10 microg ml(-1)), an agent known to inhibit heat shock protein 90 (hsp90), reduced the level of ser1177-eNOS in P + HR aortic segments. However in the presence of geldanamycin, endothelial hypoxic preconditioning persisted. We conclude that short periods of hypoxia induced endothelial hypoxic preconditioning that was accompanied by enhanced levels of ser1177-eNOS in the vascular wall. The fact that endothelial hypoxic preconditioning persisted in the presence of geldanamycin suggests that other molecular mechanisms are involved in the endothelial adaptation to HR injury.

Significance of the morphological patterns of electrograms recorded during ventricular fibrillation: an experimental study.

Mapping techniques are used to study the significance of the morphological patterns of the electrograms (EGMs) obtained during VF in an experimental model. In 24 isolated rabbit heart preparations recordings were made of activation during VF using a multiple electrode (121 unipolar electrodes) positioned on the lateral wall of the left ventricle. Three types of activation maps were selected: (A) with functional block of an activation front; (B) with epicardial breakthrough; and (C) with a single broad wavefront without block lines. The EGMs were classified as negative (Q), positive-negative with a predominance of the negative (rS) or positive wave (Rs), and positive (R). In 60 type A maps the morphology in the zone limiting the block line corresponded to an R wave in 55 (92%) cases and to Rs in 5 (8%) cases. In 67 type B maps, the EGM in the earliest activation zone most often showed Q wave morphology (48 [72%] cases), followed by rS (18 [27%] cases), and Rs morphology (1 [1%] case); in no case was R wave morphology seen. Finally, in 78 type C maps the morphology corresponded to a Q wave in 15 (19%) cases, rS in 38 (49%), Rs in 24 (31%), and R in a 1 (1%) case. The differences between the three types of maps were significant (P < 0.0001). Q wave EGM sensitivity for indicating the existence of an epicardial breakthrough pattern was 72%, with a specificity of 89%, and positive and negative predictive values of 76% and 87%, respectively. R wave EGM sensitivity for indicating the existence of conduction block was 92%, with a specificity of 99%, and positive and negative predictive values of 98% and 97%, respectively. R wave morphology is highly sensitive and specific for indicating conduction block. EGM recordings with initial positivity predominance are infrequent in the earliest activation zones of epicardial breakthrough during VF. The recording of the EGM with Q wave morphology indicates centrifugal activation from the explored zone.

Effects of acute reduction of temperature on ventricular fibrillation activation patterns.

Because of its electrophysiological effects, hypothermia can influence the mechanisms that intervene in the sustaining of ventricular fibrillation. We hypothesized that a rapid and profound reduction of myocardial temperature impedes the maintenance of ventricular fibrillation, leading to termination of the arrhythmia. High-resolution epicardial mapping (series 1; n = 11) and transmural recordings of ventricular activation (series 2; n = 10) were used to analyze ventricular fibrillation modification during rapid myocardial cooling in Langendorff-perfused rabbit hearts. Myocardial cooling was produced by the injection of cold Tyrode into the left ventricle after induction of ventricular fibrillation. Temperature and ventricular fibrillation dominant frequency decay fit an exponential model to arrhythmia termination in all experiments, and both parameters were significantly correlated (r = 0.70, P < 0.0001). Termination of the arrhythmia occurred preferentially in the left ventricle and was associated with a reduction in conduction velocity (-60% in left ventricle and -54% in right ventricle; P < 0.0001) and with activation maps predominantly exhibiting a single wave front, with evidence of wave front extinction. We conclude that a rapid reduction of temperature to <20 degrees C terminates ventricular fibrillation after producing an important depression in myocardial conduction.