Recognition of Mutiple Tachyarrhythmias by Rate-Independent Means Using a Small Microcomputer M.A. TOOLEY, D.W. DAVIES, A.W. NATHAN, and A.J. CAMM From the Departments of Medical Electronics and Cardiology, St, Bartholomew's Hospital, London, United Kingdom TOOLEY, T.M.A., ET AL.: Recognition of Mutiple Tachyarrhythmias by Rate-Independent Means Using a Small Microcomputer, New implantable devices are now available that can offer different therapies for different arrhythmias but they need a method 0/ discriminating between these rhythms, Heart rate analysis is predominantly used to discern between sinus rhythm (Sfl) and pathological tachycardias but this may be of limited value when the rates of the rhythms are similar. An enhanced form of Gradient Pattern Detection (GPD) has been developed using an 8-bit microcomputer that can distinguish between SR and up to three other arrhythmias in real time. This is a method based on electrogram morphology where each rhythm's specific electrogram is classified by a sequence 0/gradient 'zones'. The micropro- cessor of the computer is 0/ simiJar processing power to ones used in current pacemakers. Five patients with multiple arrhythmias were studied. Four had ventricular tachycardia (VT) and one had three con- duction patterns during supraventricular tachycardia fSVTj. Bipolar endocardial right ventricular elec- trograms were recorded during SR and tachycardia in all patients. The computer would first 'learn' about each different rhythm by a semi-automatic means. Once all the rhythms were learned the program would enter the GPD onalysis phase. The computer would output a series of real-time rhythm specific marker codes onto a chart recorder as it recognized each rhythm. Sixteen different arrhythmias (13 VT, 3 SVT) were examined for this study. AU rhythms (including SR) were distinguished from each other except in the case of one patient with six VTs where two VTs had identical shapes and therefore could not be detected apart. The method would be a useful addition to heart rate analysis for future generations of microprocessor assisted pacemakers. (PACE, Vol. 14, February, Part II 1991} tachycardia recognition, antitachycardia pacing Introduction Abnormal tachycardias are increasingly being treated by implantable, microprocessor based pulse generators.^""* These devices offer different stimulation responses to treat different arrhyth- mias occurring in the same patient. The usual method for distinguishing between cardiac rhythms is to examine the repetition rate of the ongoing signal or characteristics of the rate.^ Rate analysis can be 'fooled' if sinus tachycardia and Address for reprints: M.A. Tooley. Departments of Medical Electronics and Cardiology, St. Bartholomew's Hospital, Lon- don, United Kingdom the abnormal rhythm have similar rates or when multiple arrhythmias occurring in the same pa- tient have similar rates. The result is that inap- propriate stimuli or shocks are delivered during sinus tachycardia or that stimuli are withheld dur- ing pathological tachycardias, A better method of discriminating hetween different rhythms would be to use a method that is not dependent on the repetition of the cardiac signal. Many methods have been proposed which profess to be better than rate analysis.'*"'^ It is doubtful whether these methods could be performed in real time using the 8-bit microprocessors of implantahle devices. We present a method that could be implanted in an 8-bit processor based device and which can dis- tinguish between four electrogram categories in PACE, Vol. 14 February 1991, Part II 337