Ventricular Fibrillation inHypertrophic Cardiomyopathy IsAssociated With Increased Fractionation ofPaced Right Ventricular Electrograms

Background. Intraventricular conduction inhypertrophic cardiomyopathy (HCM)hasbeencharacterized totestthehypothesis thatmyofibrillar disarray will causedispersion ofactivation throughout the ventricular myocardium. Methods andResults. Of37patients withHCM,fourhadspontaneous ventricular fibrillation (VF), five hadnonsustained ventricular tachycardia (VT), 13hadno risk factors, and15hada family history of suddendeath. Thesepatients andfourcontrols werestudied bypacing onesite intheright ventricle and recording electrograms fromthree other right ventricular sites. Theseelectrograms were high-pass filtered toemphasize smalldeflections duetoactivation ofsmallbundles ofmyocytes close totheelectrode. Intraventricular conduction curveswereobtained withS1S2 coupling intervals decreasing in1-msec steps from479msec toventricular effective refractory period (VERP). These curveswererepeated bypacing eachRVsite inturnandwerecharacterized bytwoparameters: thepoint atwhichlatency increased by 0.75 msec/20 msecreduction oftheS1S2 coupling interval andan increaseinelectrogram duration between an S1S2of350msec andVERP.Patients withVF,VT,andfamily history ofsudden deathhada mean increase inelectrogram duration of12.8(2.9-32.3) msec versus4.6(-4.2to14.0) msec inlow-risk patients andcontrols. Electrogram latency increased atan S1S2 of363msec intheVF group(342-386), 269msec inthecontrols (266-279), and326msecinthenon-VF group(260-399). Discriminant analysis separated VF patients fromtheremainder (p<0.0001) andVF,VT,andfamily history ofsudden death patients fromthelow-risk andcontrol groups(p<10-6). Conclusions. Patients withHCM who are atnrskofsuddendeathhaveincreased dispersion and inhomogeneity ofintraventricular conduction, andthismay create theconditions forreentry and arrhythmogenesis. (Circulation 1992;86:467-474)