| Summary: | Introduction: Implantable defibrillators (ICD's) are currently unable to assess the haemodynamic stability of arrhythmias and can occasionally deliver intracardiac shocks when patients are conscious. We investigated the use of trans-ventricular impedance (across the left ventricle {LV}) as a haemodynamic sensor during arrhythmias in man. Methodology: Trans-ventricular LV impedance and systemic blood pressure (BP) were continuously monitored during clinical VT stimulation studies. LV impedance was measured by injecting a biphasic rectangular current pulse of 600|uA amplitude at a sampling rate of 128 Hz between the distal poles of a standard quadripolar pacing/recording electrode positioned at the right ventricular (RV) apex, and the proximal poles of a decapolar catheter positioned within the coronary sinus (CS). Current was injected using an external pacemaker (INOS, Biotronik) connected to the poles of the RV & CS catheters. Haemodynamically unstable arrhythmias were defined as those needing urgent DC cardioversion for loss of consciousness. Results: 28 patients were studied. Unstable VT: 5 (18%), Stable VT: 5 (18%), SVT: 2 (7%). During haemodynamically unstable VT, the stroke impedance (SZ) - the difference between the end systolic and end diastolic impedance values - dropped to 22% of its original sinus rhythm value (standard deviation = 15 - 32%), which was associated with a simultaneous drop in mean arterial BP down to 13% of its original sinus rhythm value (standard deviation = 3 - 36%), p <0.001. During haemodynamically stable VT, SZ dropped to 58% of its original sinus rhythm value (standard deviation = 33 - 88%), which was associated with a simultaneous drop in mean arterial BP down to 55% of its original sinus rhythm value (standard deviation = 24 - 77%), p = 0.008. Conclusion: Trans-ventricular impedance was able to assess the pumping efficacy of the heart during sinus rhythm, ventricular pacing and ventricular arrhythmias, and correlated well with changes in blood pressure, but was still unable to discriminate between haemodynamically stable and unstable arrhythmias. Further studies are needed to determine the long-term stability of trans-ventricular impedance measurement as a reliable haemodynamic sensor.
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