Arrival ofexcitation atright ventricular apical endocardium inWolff-Parkinson- White syndrome typeA,with andwithout right bundle-branch block'

Filtered bipolar right ventricular apical (RVA)andHisbundle electrograms, using electrodes only i mm apart, wererecorded intwopatients withintermittent WPW typeA withandwithout 'complete' right bundle-branch block. Inbeats withexclusive normal pathway conduction and'complete' right bundle-branch block, theHV andV-RVAintervals represented His-to-left ventricular endocardial andleft ventricular endocardial-RVA conduction times, respectively. TheH-RVAinterval was determined byaddition ofthese twointervals. In'fusion' beats resulting fromAV conduction through bothnormal andaccessorypathways, theduration oftheH-RVAinterval wassimilar tothat ofbeats withexclusive normal pathway conduction, suggesting thatthough theventricles werepre-excited through an accessorypathway theRVA was still activated viatheimpulse emerging fromtheright bundle-branch. Inbeats withexclusive, orpredominant, accessory pathway conduction anda WPW typeA morphology, theH-RVA'interval' was 'shorter-thannormal', suggesting thattheRVA was notactivated bytheimpulse traversing thenormal pathway butby the onepropagating fromthepre-excited site. Thecorresponding V-RVAintervals (giving a rough estimate ofconduction time frompre-excited site toRVA)werelonger (IioandI20msec,respectively) thanintwo other patients withWPW type B.Intracardiac recordings haveenhanced ourknowledge oftheventricular activation process inWPW type A,either pureorassociated with'complete' right bundle-branch block. Thediagnosis ofright bundle-branch blockin patients withWolff-Parkinson-White syndrome (WPW)hasbeenasubject ofconsiderable debate andspeculation (Pick andFisch, I958; Robertson etal., I963; Laham, I969; Schamroth, I97i). The