Effects of Cardiac Resynchronization Therapy on Diastolic Function: Evaluation by Radionuclide Angiography

While the beneficial effects of cardiac resynchronization therapy (CRT) on left ventricular (LV) systolic function have been demonstrated, no information is available regarding its effects on LV diastolic function during exercise. Using radionuclide angiography, we prospectively evaluated the effects of CRT on diastolic function at rest and during exercise in 15 patients consecutively referred for CRT. All patients underwent equilibrium Tc⁹⁹ radionuclide angiography with bicycle exercise performed (1) at baseline; (2) immediately after CRT implantation, in spontaneous rhythm and during CRT; and (3) after 3 months of biventricular stimulation. Diastolic function was assessed by measurements of peak filling rate (PFR). At baseline, activation of biventricular stimulation influenced PFR neither at rest (1.06 ± 0.34 vs 1.07 ± 0.50 mL/s during spontaneous rhythm, P = 0.9) nor during exercise (1.45 ± 0.62 vs 1.33 ± 0.48 mL/s, P = 0.3). At 3 months, improvements were observed in New York Heart Association functional class and systolic function. By contrast, no improvement in diastolic function was observed either at rest (PFR = 1.11 ± 0.45 vs 1.07 ± 0.50 mL/s in spontaneous rhythm at baseline, P = 0.6) or during exercise (1.23 ± 0.50 vs 1.33 ± 0.48 mL/s, P = 0.2). These observations indicate that the intermediate benefits conferred by CRT on LV systolic function at rest and during exercise were not accompanied by similar improvements in diastolic function .     

Multiple Vector Impedance Measurements During Biventricular Pacing: Feasibility and Possible Implications for Hemodynamic Monitoring

Background: Intracardiac impedance (ICZ) has been known to reflect contractile capacity of the heart, and a strong relationship has been documented between stroke volume and ICZ. In this pilot study, conducted in heart failure patients during implantation of a biventricular device, we investigated acute changes in multiple vector ICZ signals during different pacing modes, and whether ICZ can be used to monitor hemodynamic variations. Methods: Z1 and Z2 impedance signals were recorded in the right ventricle (RV), and between the left ventricle (LV) and RV, respectively, in 12 patients during four programming modes. ICZ signals were analyzed with respect to average and peak‐to‐peak (p2p) amplitude and systolic slope, and correlated with noninvasive hemodynamic and echocardiographic variables. Results: ICZ p2p amplitude decreased during LV stimulation both in Z1 and in Z2 configuration (P = 0.021 and P = 0.022 vs intrinsic conduction, respectively). No significant variations in average amplitude or systolic slope were observed. ICZ variables correlated directly with hemodynamic measures (r = 0.48, P < 0.05, between Z2 p2p amplitude and pulse pressure), LV ejection fraction (r = 0.32, P < 0.05, for Z1 average amplitude), RV ejection fraction (r = 0.75, P < 0.05, for Z1 p2p amplitude), and inversely with ventricular volumes. Conclusions: Variations in ICZ may be observed during different pacing modes and seem to correlate with hemodynamic and echocardiographic variables. Multiple vector ICZ measurement may be a feasible tool for hemodynamic assessment in patients treated with biventricular pacing.