Measurement Precision in the Optimization of Cardiac Resynchronization Therapy

Abstract

Background Cardiac resynchronization therapy improves morbidity and mortality in appropriately selected patients. Whether atrioventricular (AV) and interventricular (VV) pacing interval optimization confers further clinical improvement remains unclear. A variety of techniques are used to estimate optimum AV/VV intervals; however, the precision of their estimates and the ramifications of an imprecise estimate have not been characterized previously. Methods and Results An objective methodology for quantifying the precision of estimated optimum AV/VV intervals was developed, allowing physiologic effects to be distinguished from measurement variability. Optimization using multiple conventional techniques was conducted in individual sessions with 20 patients. Measures of stroke volume and dyssynchrony were obtained using impedance cardiography and echocardiographic methods, specifically, aortic velocity-time integral, mitral velocity-time integral, A-wave truncation, and septal-posterior wall motion delay. Echocardiographic methods yielded statistically insignificant data in the majority of patients (62%–82%). In contrast, impedance cardiography yielded statistically significant results in 84% and 75% of patients for AV and VV interval optimization, respectively. Individual cases demonstrated that accepting a plausible but statistically insignificant estimated optimum AV or VV interval can result in worse cardiac function than default values. Conclusions Consideration of statistical significance is critical for validating clinical optimization data in individual patients and for comparing competing optimization techniques. Accepting an estimated optimum without knowledge of its precision can result in worse cardiac function than default settings and a misinterpretation of observed changes over time. In this study, only impedance cardiography yielded statistically significant AV and VV interval optimization data in the majority of patients.

A clinical feasibility study of atrial and ventricular electromechanical wave imaging

“…The availability of this information has the potential to guide optimization of CRT and device programming. Optimization of device programming is frequently not pursued by practitioners, in large part due to lack of effective tools and methodologies (19). EWI could be uniquely positioned to provide critical information for these purposes, given that it is noninvasive, non-ionizing, low-cost, and can be readily implemented in most ultrasound scanners already available at the point of care.…”

Rate-adaptive AV delay and exercise performance following cardiac resynchronization therapy

“…Mokrani et al demonstrated a difference in the optimal AV delay at rest and on exercise depending on whether LVOT VTI or maximum LVFT was employed. (10) Using the iterative method, the exact mechanism that the operator is attempting to manipulate, (timing of ventricular filling) is viewed directly, rather than employing a surrogate outcome measure such as LVOT VTI, which is subject to significant variation due to small changes in the angle between the incident ultrasound beam and the outflow tract with respiration, an effect particularly exaggerated during exercise (23,24). As the maximum improvement in cardiac output with AV delay optimization is in the region of 15-20% (1), any technique with a reported reproducibility of 4-10% during optimal resting conditions should be interpreted with caution during exercise, and may underlie the reported mixed results using these methods (5,6,10).…”

Ballistocardiography — A method worth revisiting

“…This optimization has relied so far mostly on the experience of the cardiologist, and echocardiography measurements. It has been shown recently though that even echocardiographic data, thought to be the non-invasive ‘gold-standard’, does not lead to reliable tuning [26]. …”