Differential effects of abrupt cycle length changes on the refractoriness of accessory pathway, His-Purkinje system, atrial and ventricular myocardium in Wolff-Parkinson-White syndrome

Dynamic effects of exercise and different escape rhythms on the supernormal period of an accessory pathway

Spontaneous conduction during the supernormal period (SNP) of accessory pathways (AP) is rare and observed only during atrio-ventricular block (AVB). The effect of exercise and different escape rhythms on the SNP is unknown. We evaluated these factors on the SNP of a para-Hisian AP after a failed ablation complicated by AVB. The SNP onset and duration were later and longer during paced versus junctional rhythm. Exercise caused linear shortening of the SNP that was directly related to junctional cycle length. The SNP is a dynamic window shifting in parallel with AP refractoriness and affected by exercise and type of escape rhythm.

Comparative accuracy of the vectorcardiogram and electrocardiogram in the localization of the accessory pathway in patients with Wolff-Parkinson-White syndrome: validation of a new vectorcardiographic algorithm by intraoperative epicardial mapping and electrophysiologic studies

The scalar electrocardiograms (ECGs) and vectorcardiograms (VCGs) of 41 patients with Wolff-Parkinson-White (WPW) syndrome were used to compare the accuracy of these techniques in the identification of the site of preexcitation. The location of the accessory pathway (AP) was determined by endocavitary electrophysiologic studies in all patients and the location was confirmed during intraoperative epicardial mapping in 28 of them. The ECGs were classified according to Gallagher's criteria and with Milstein's algorithm, whereas the VCGs were classified according to a new two-step algorithm. The presence of multiple accessory pathways and coexisting myocardial infarctions were major limitations in both the VCG and ECG classification procedures. In patients with a single accessory pathway, three AP localizations (right free ventricular wall, posterior, or left free ventricular wall) were identified with the first step of the VCG algorithm, with an overall sensitivity (96.5%), specificity (90.7%), and positive predictive values (80%) that were greater than those obtained with the ECG Milstein algorithm (77.1%, 91.5%, and 75%, respectively). The second step of the VCG algorithm made it possible to identify an AP location in one of the following sites: anterior right, lateral right, posterior right, posterior left, lateral left, or anterior left ventricle. The overall sensitivity, specificity, and positive predictive values were greater for the second step of the VCG algorithm than for the ECG criteria proposed by Gallagher (43.6% versus 39.3%, 92.1% versus 87.4%, and 51.5% versus 33.3%, respectively). It was concluded that the VCG seems to be more specific and sensitive than the ECG in the identification of the preexcitation site and should be given preference in the initial evaluation of the WPW syndrome.