Intracardiac impedance monitors stroke volume in resynchronization therapy patients

Monitoring of haemodynamic parameters or surrogate parameters of the left ventricle is especially important for patients under cardiac resynchronization therapy (CRT). Intracardiac impedance reflects left ventricular (LV) volume changes well in animal models. Since it is unknown whether this also holds in humans with heart failure (HF), we examined the correlation of LV intracardiac impedance with haemodynamic parameters in CRT patients for different positions of the LV lead.

In 14 HF patients with non-ischaemic cardiomyopathy (four female, age 70 +/- 6 years, NYHA 2.9 +/- 0.3, EF 26 +/- 6%), one or two suitable implantation sites for the LV lead were selected. Following atrial, right ventricular, and LV catheter positioning, a micro-manometer catheter was placed in the ascending aorta. Surface ECG, impedance, and aortic pressure were recorded during graded overdrive bi-ventricular pacing in DDD mode. The correlation between impedance and stroke volume (SV) or pulse pressure (PP) changes was compared for different LV lead positions. In total, 20 overdrive pacing tests were performed at six different LV lead positions. Strong correlations were found between stroke impedance (SZ) and SV (R = 0.82 +/- 0.16) as well as between SZ and PP (R = 0.81 +/- 0.16) without significant influence of LV lead position.

In HF patients, a strong correlation between changes in intracardiac impedance and LV SV was found. Typical LV lead implant positions have been tested and all appear to be suitable for this method of LV volume monitoring.