Introduction: Inappropriate ICD shocks are due to incorrect detection and discrimination based on IEGM and heart rate. Hemodynamic monitoring may be a useful function in ICDs. Dynamic cardiogenic impedance (CI) is the continuous (beat to beat) monitoring of cardiac function with the potential to provide hemodynamic monitoring. We hypothesized that impedance has additional benefits over heart rate in that CI carries more hemodynamical information than heart rate. To study this further, the correlation between varying hemodynamics and CI was examined in situations when heart rate change was eliminated. Methods: We analyzed CI data from 11 impedance configurations recorded in 8 anesthetized pigs receiving injections of Nitroprusside and Verapamil in sequence. Heart rate was maintained constant through either atrial pacing or DDD BiV pacing. Aortic and right ventricular blood pressure (AP and RVP) as well as arterial carotid and arterial femoral blood flow (ACF and AFF) was continuously recorded. Correlation was studied using cross-validated multivariate regression models with 10 features from single impedance configurations. Models were made across all subjects. Coefficients of determination (R2) were calculated. Significance was calculated using random permutation tests. Results:Drug injections successfully created a temporary drop by 30-50% in blood pressures and AFF in all 8 animals during which heart rate was successfully maintained at a constant level in each animal (110-130 BPM). The total number of heart beats analyzed was 12,913. Impedance based multivariate regression models successfully showed significant correlation between CI and blood pressures or flows; R2 = 0.91, p < 0.003 for mean AFF with RVtip-RVcoil bipolar CI; R2 = 0.85, p < 0.003 for max slope of AP with LV-RA bipolar CI; R2 = 0.94, p < 0.003 for min RVP with LV-RA bipolar CI. Conclusions:This prospective pre-clinical study has shown that there is a significant and strong correlation between dynamic cardiogenic impedance and hemodynamics during constant heart rate. It may ultimately provide true hemodynamic monitoring in ICDs.
Boston, MA: HRS , 2012.