The use of unipolar intracardiac impedance for discrimination of haemodynamically stable and unstable arrhythmias in man

Aims To determine the feasibility of discriminating haemodynamically stable from unstable arrhythmias using right ventricular (RV) unipolar intracardiac impedance (Z). Methods and results A quadrapolar temporary pacing electrode was positioned at the RV apex and unipolar impedance was measured between the tip electrode and a surface patch electrode. Changes in peak-to-peak Z amplitude were measured simultaneously with surface ECG and blood pressure during induced arrhythmias. Haemodynamic instability was defined as a systolic pressure of < 90 mmHg. There were 25 episodes of ventricular fibrillation (VF) induced in 15 patients, 18 episodes of ventricular tachycardia in 16 patients, and 33 episodes of supraventricular tachycardia (SVT) in 16 patients. Compared with the baseline rhythm, mean Z amplitude reduced from 51.3 +/- 7.7 to 11.2 +/- 7.4 Ohm (P < 0.001) during VF, from 52.2 +/- 6.3 to 21.7 +/- 10.1 Ohm (P < 0.01) during haemodynamically unstable VT, from 55.0 +/- 6.9 to 39.9 +/- 11 Ohm (ns) during stable VT, and from 56.4 +/- 8.4 to 36.9 +/- 9.3 Ohm during SVT (P < 0.001). Conclusion Right ventricular unipolar impedance is an adequate sensor for determining mechanical ventricular contraction and acts as a surrogate marker for a fall in arterial blood pressure during VF. However, for ventricular and supraventricular tachycardias, variations between patients did not allow adequate discrimination between stable and unstable arrhythmias.