Impedance cardiography as a noninvasive technique for atrioventricular interval optimization in cardiac resynchronization therapy

Introduction: Impedance cardiography (IC) and Doppler echocardiography (DE) are two noninvasive methods to evaluate hemodynamics in patients with dual-chamber pacemakers. The aim of the present study was to compare both techniques in respect to their ability of AV-interval optimization in cardiac resynchronization therapy (CRT) based on cardiac output (CO) measurements. Methods and Results: Twenty-four patients (64 +/- 8 years) with congestive heart failure (EF < 35%; NYHA III-IV) and LBBB (> 150 ms) were evaluated at baseline and 1 month after implantation of a CRT-D. The optimal AV interval was defined by IC and subsequently by transaortic flow DE as the interval corresponding to the highest CO measured at different AV intervals, varying from 60 to 200 ms (with 20 ms increments). For standardization and comparison of both techniques, a fixed atriobiventricular pacing rate of 90 beats/min was used. Absolute values of COmax were higher by IC (5.8 +/- 0.9 l/min) as compared to DE (4.6 +/- 0.9 l/min, p < 0.01). The optimal AV interval as determined by IC varied interindividually from 80-180 ms (mean: 121 +/- 18 ms). In DE, the range was also 80-180 ms with the mean optimal AV interval of 128 +/- 23 ms. Thus, there was a strong correlation for AV-interval optimization in CRT between both methods (r = 0.74; p < 0.001). Conclusion: In CRT, AV-interval optimization based on CO values determined by IC correlates closely to those measured by transaortic flow DE. Impedance cardiography as an easy and cost-effective technique for AV-interval optimization is a promising alternative for routine management of heart failure patients on a beat-to-beat analysis during CRT follow-up.