13th International Congress
THE "NEW FRONTIERS"
OF ARRHYTHMIAS 1998

January 24-31, 1998
Marilleva, Trento, Italy

S-115

Improved supraventricular and ventricular tachycardia discrimination using electrogram morphology in an implantable cardioverter defibrillator

Mae-Mae Shieh, Lisa Clem, Lisa Malden, April Pixley, Eric Fain.
St. Jude Medical, Sunnyvale, Usa

Introduction

Implantable cardioverter defibrillators have been shown to be highly effective in the treatment of ventricular arrhythmias^1-5. However, accompanying this extremely high sensitivity (i.e., appropriate ventricular tachycardia diagnosis) is the inappropriate treatment of supraventricular rhythms (i.e., atrial fibrillation, sinus tachycardia, etc.) which the device misinterprets as ventricular tachycardia due to accompanying high ventricular rate. The incidence of inappropriate therapies due to supraventricular tachycardia has been reported in up to 25% of patients^6-8. This undesirable consequence not only has negative effects on patient comfort and psychological well-being, but has the potential to be proarrhythmic by inducing ventricular tachycardia or ventricular fibrillation.

Other criteria, in addition to ventricular rate, have been introduced to device detection algorithms to help reduce the incidence of inappropriate therapies due to supraventricular tachycardia and thereby increase specificity. One of these discriminators is interval stability, which measures the variability of ventricular interval cycle lengths. A common characteristic of atrial fibrillation is irregular ventricular intervals while ventricular tachycardia typically exhibits very stable ventricular intervals. Another discriminator algorithm is sudden onset, which measures the abruptness in the onset of the fast ventricular rate. This algorithm is intended to differentiate between the gradual onset of rate in sinus tachycardia and the abrupt onset of ventricular tachycardia.

Another criterion which has been shown to be an effective discriminator between ventricular tachycardia and supraventricular tachycardia is endocardial ventricular morphology^9-16. These morphology algorithms reported in the literature are typically computationally intense since they compare a test QRS complex to a reference (i.e., template) complex on a point-by-point basis. These algorithms require unacceptably high current for use in an implantable cardioverter defibrillator. The challenge for implantable defi-brillator manufacturers is to design a robust and accurate morphology algorithm which can operate in real-time and within the current drain limitations of the implantable defibrillator. Therefore, we evaluated the performance of the morphology algorithm implemented in the Ventritex Contour MD / Angstrom MD implantable defibrillators.