Diagnostic Methods Arrhythmiia

Differentiation of wide QRS complex tachycardias on surface electrocardiograms is difficult for physicians and computers due in part to their inability to identify atrial activity, specifically atrioventricular (AV) dissociation. We studied 20 examples ofAV associated rhythms and 17 examples ofAV dissociated ventricular tachycardia. We applied an algorithm consisting of subtraction of a mean beat from each individual beat in leads II and V, to generate remainder electrocardiograms. The remainder electrocardiograms were visually inspected for the presence of P wave candidates and then autocorrelated. AV dissociated P wave candidates were evident on visual inspection of remainder electrocardiograms in none of 20 AV associated and 15 of 17 AV dissociated rhythms. Atrial cycle length and the presence of AV dissociation were automatically detected by applying a peak selection algorithm to the autocorrelation function. AV association was detected in all 20 AV associated rhythms and AV dissociation was detected for 1 1 of 17 AV dissociated rhythms (sensitivity 65%, specificity 100%, positive and negative predictive accuracy 100%, 77%). The correlation coefficient of detected vs true atrial cycle length for the 11 correctly detected AV dissociated rhythms was r = .98. Visual inspection of the remainder electrocardiograms along with the original electrocardiogram may increase the ease with which human readers can identify the presence of AV dissociation and thus diagnose ventricular tachycardia. Computer diagnosis of wide QRS complex tachycardias should be significantly improved by use of this algorithm. Circulation 72, No. 5, 1028-1036, 1985. DETECTION of atrial activity is the most significant limiting factor of the accuracy of current algorithms for diagnosis of arrhythmias by computer. 1 The reason for this is that on the surface electrocardiogram, atrial activity is often represented by small amplitude waves that may be buried in QRS complexes or T waves. Of particular clinical significance is the detection of atrial activity, specifically atrioventricular (AV) dissociation, during a wide QRS complex tachycardia. While occasional instances of supraventricular tachycardias with AV dissociation have been reported, AV dissociation during a wide QRS complex tachycardia is considered virtually diagnostic for ventricular tachycardia.2 Wellens et al.3 found that approximately half From the Department of Electrical Engineering and Computer Science, Northwestern University, and the Division of Cardiology, Department of Medicine, Evanston Hospital, Evanston, IL, and Northwestern University Medical School, Chicago. Supported in part by a grant from Marquette Electronics, Inc. Address for correspondence: Steven Swiryn. M.D., Director, Cardiac Electrophysiology, Evanston Hospital, 2650 Ridge Ave., Evanston, IL 60201. Received March 18, 1985; revision accepted Aug. 8, 1985. 1028 of ventricular tachycardias are AV dissociated and fewer than one-third had a 1: 1 ventriculoatrial conduction ratio. The percentage of AV dissociated ventricular tachycardias increases somewhat when the ventricular rate exceeds 200 beats/min. Historically, arrhythmia algorithms have determined atrial activity by searching the isoelectric region between the end of the T wave and the beginning of the following QRS complex for P wave candidates.>l9 P waves have been found by a variety of approaches, such as slope measurement,'6 difference functions,17' 18 and matched filters.'9 Some algorithms for interpretation of arrhythmias assume any detected P wave candidate a valid P wave, while in others additional criteria must be fulfilled (e.g., those relating to expected P wave width, slope, and PR interval) to validate a P wave candidate. All of these methods of P wave detection depend on detectable P waves occurring between the end of the T wave and the beginning of the following QRS complex. Such methods are unlikely to be reliable at rapid ventricular rates since little CIRCULATION by gest on M ay 1, 2017 http://ciajournals.org/ D ow nladed from DIAGNOSTIC METHODS-ARRHYTHMIA or no isoelectric region is present between the end of the T wave and the beginning of the following QRS