MIXED VENOUS OXYGEN-SATURATION FOR DIFFERENTIATING STABLE FROM UNSTABLE TACHYCARDIAS

Current antitachycardia systems are incapable of adequately distinguishing stable from unstable tachycardias. Previously, integration of a pressure sensor or an impedance sensor, together with electrogram analysis, has been investigated as an improved method of identifying unstable arrhythmias. A mixed venous oxygen saturation sensor was investigated for differentiating stable from unstable paced and induced tachycardias in 10 patients. During rapid pacing at 600, 500, 400, 350, 300, and 250 msec cycle lengths, mixed venous oxygen saturation decreased as cycle length decreased. For any given cycle length, rapid ventricular pacing tended to result in greater mixed venous oxygen desaturation compared with atrial pacing. Mixed venous oxygen saturation decreased similarly during induced ventricular tachycardias at cycle lengths > 230 msec. However, ventricular tachycardias at cycle lengths less-than-or-equal-to 230 msec and ventricular fibrillation had no effect on mixed venous oxygen saturation until after termination. Subsequently, a mixed venous oxygen saturation-tiered therapy algorithm (cycle length less-than-or-equal-to 230 msec = unstable; cycle length > 230 msec and MVO2 greater-than-or-equal-to 6% over 30 seconds = unstable) was developed and was tested retrospectively in 113 paced and induced tachyarrhythmias in these 10 patients for detecting unstable tachycardias (defined as a decrease from baseline systolic arterial pressure of greater-than-or-equal-to 50 mm Hg at 15 seconds). The mixed venous oxygen algorithm had 93% sensitivity and 96% specificity compared with rate-only (rate greater-than-or-equal-to 170 beats/min) detection with 93% sensitivity and 71% specificity. Therefore a tiered therapy antitachycardia device could integrate zoned rate detection with mixed venous oxygen saturation to improve detection specificity of current antitachycardia systems.