Continuous Right Ventricular Volume Assessment by Catheter Measurement of Impedance for Antitachycardia System Control

Current implantable defibrillators are unable to differentiate between hemodynamically stable and unstable arrhythmias. This may result in unnecessary high energy shocks during arrhythmias that are better managed with other interventions. This study assessed the efficacy of the impedance catheter in sensing relative volumetric changes in the right ventricle as a measure of the hemodynamic status during an arrhythmia. During electrophysiological testing, 37 arrhythmias were induced in 12 patients aged 28-74 years. Rhythms recorded were: (A) hemodynamically stable tachyarrhythmias (supraventricular tachycardia and sustained monomorphic ventricular tachycardia)--21 episodes; and (B) hemodynamically unstable ventricular arrhythmias causing syncope (hypotensive ventricular tachycardia and ventricular fibrillation)--16 episodes. During unstable arrhythmias, stroke impedance (32 +/- 17%), arterial systolic pressure (40 +/- 11%), and right ventricular pulse pressure (15 +/- 20%), expressed as percentages of corresponding sinus rhythm values, were significantly lower than in stable arrhythmias (84 +/- 26%, 72 +/- 8%, and 111 +/- 37%, respectively); P less than 0.001. There was a good correlation between stroke impedance and mean arterial pressure during arrhythmia (r = 0.84). Impedance sensing is a practical method for distinguishing between hemodynamically stable and unstable arrhythmias. Implementation of hemodynamic sensing into the algorithm of future antitachycardia systems may improve the management of arrhythmias by adding options for selective pace termination or cardioversion.