Effect ofAltered Activation Sequence on Epicardial QRSTAreaandRefractory Period inDogs

Background. Weinvestigated theeffects ofactivation sequenceoncardiac surface QRSTareas andrefractory periods inexperiments on dogs. Meth.ods andResults. Right andleft ventricular pacingswereperformed, andthepacing site was altered every6 minutes. After 4 minutes ofa given pacing, 54unipolar electrograms distributed overtheentire cardiac surface were recorded. Next, refractory periods atelectrode sites nearpacing electrodes were measured. Paired right ventricular/left ventricular (RV/LV) pacing data wereobtained six orseventimes ineachsample. Although theQRSTisoarea maps during thetwoactivation orders werequalitatively similar, itwas recognized consistently from theright ventricle-left ventricle difference map thatleads aroundtheRVfree wallhadpositive values andthat leads aroundtheLVfree wallandapexhadnegative values. Compared withthe same leads atRV andLVpacing, QRSTareaswere larger whenpacing sites were nearthe leads. Thelocal QRSTareasofindividual leads atwhich we measured local refractory period wereconsistently larger during drive fromproximal pacing sites thanduring drive fromdistant pacing sites. Refractory periods were consistently longer during proximal pacing thanduring distal pacing, andthere was a positive correlation between change inlocal QRSTareaand change inrefractory period (r=0.64) during altered activation sequence,whereas there was an inverse correlation between change inQRSTareaandchange inrefractory period (r=-0.91) during localized myocardial warming. Conclusions. Bothlocal QRST areasandlocal refractory periods were dependent on the activation sequence,andthere was a positive correlation between QRSTareasandrefractory periods during various activation sequences (Circulation 1991;84:1346-1353) R) ecently, thebodysurface distribution of OQRSTareahasbeenreported tobea useful parameter inevaluating cardiac states athigh risk ofventricular arrhythmiasl-4 andin diagnosing myocardial infarction inthepresence of intraventricular conduction disturbances.5-7 Thebasis forthese findings isthat QRSTareareflects local recovery properties andislargely independent of ventricular activation sequence. QRSTareashavebeenpostulated todepend on differences inthedurations ofintrinsic ventricular