In Cardiac Resynchronization Therapy: Should We Opt for AV Optimization?

Effect of atrioventricular conduction prolongation on optimization of paced atrioventricular delay for biventricular pacing after cardiac surgery

OBJECTIVES

Atrioventricular conduction prolongation (AVCP) in cardiac pacing is measurable and results primarily from delayed atrial conduction. Noninvasive methods for measuring atrial conduction are lacking. Accordingly, AVCP was used to estimate atrial conduction and investigate its role on the paced atrioventricular delay (pAVD) during biventricular pacing (BiVP) optimization.

DESIGN

Retrospective analysis of data collected as part of a randomized controlled study of temporary BiVP after cardiopulmonary bypass.

SETTING

Single-center study at university-affiliated tertiary care hospital.

PARTICIPANTS

Cardiac surgical patients at risk of left ventricular failure after cardiopulmonary bypass.

INTERVENTIONS

Temporary BiVP was optimized immediately after cardiopulmonary bypass. Vasoactive medication and fluid infusion rates were held constant during optimization.

MEASUREMENTS AND MAIN RESULTS

For each patient the AVCP and the pAVD producing the optimum (highest) cardiac output (OptCO) and mean arterial pressure (OptMAP) were determined. Patients were stratified into long- and short-AVCP groups. Overall AVCP (mean ± standard deviation) was 64 ± 28 ms. For the short-AVCP group (<64 ms, n = 3), AVCP, OptCO, and OptMAP were 40 ± 11, 120 ± 0, and 150 ± 30 ms, respectively, and for the long-AVCP group (>64 ms, n = 4), these same parameters were 89 ± 10, 218 ± 44, and 218 ± 29 ms. OptCO and OptMAP were significantly less in the short-AVCP group (p = 0.015 and p = 0.029, respectively).

CONCLUSIONS

AVCP varies widely after cardiopulmonary bypass, affecting optimum pAVD. Failure to correct for this can result in the selection of inappropriately short and potentially deleterious pAVDs, especially when nominal pAVD is used, causing BiVP to appear ineffective.

Recent advances in the application of computational mechanics to the diagnosis and treatment of cardiovascular disease

During the last 30 years, research into the pathogenesis and progression of cardiovascular disease has had to employ a multidisciplinary approach involving a wide range of subject areas, from molecular and cell biology to computational mechanics and experimental solid and fluid mechanics. In general, research was driven by the need to provide answers to questions of critical importance for disease management. Ongoing improvements in the spatial resolution of medical imaging equipment coupled to an exponential growth in the capacity, flexibility and speed of computational techniques have provided a valuable opportunity for numerical simulations and complex experimental techniques to make a contribution to improving the diagnosis and clinical management of many forms of cardiovascular disease. This paper contains a review of recent progress in the numerical simulation of cardiovascular mechanics, focusing on three particular areas: patient-specific modeling and the optimization of surgery in pediatric cardiology, evaluating the risk of rupture in aortic aneurysms, and noninvasive characterization of intraventricular flow in the management of heart failure.

Hemodynamic sensing using subcutaneous photoplethysmography

Pacemakers and implantable defibrillators presently operate without access to hemodynamic information. If available, such data would allow tailoring of delivered therapy according to perfusion status, optimization of device function, and enhancement of disease monitoring and management. A candidate method for hemodynamic sensing in these devices is photoplethysmography (PPG), which uses light to noninvasively detect changes in blood volume. The present study tested the hypotheses that PPG can function in a subcutaneous location, that the acute changes in blood volume it detects are directly proportional to changes in arterial pressure, and that optimum pacing intervals identified by it are concordant with those determined by arterial pressure. Aortic pressure and PPG were simultaneously recorded in 10 dogs under general anesthesia during changes in atrioventricular (AV) delay and bursts of rapid pacing to simulate tachyarrhythmias. Direct proportionality between transient changes in pressure and PPG waveforms was tested using regression analysis. Scatter plots had a linear appearance, with correlation coefficients of 0.95 (SD 0.03) and 0.72 (SD 0.24) for rapid-pacing and AV delay protocols, respectively. The data were well described by a directly proportional relationship. Optimum AV delays estimated from the induced changes in aortic pressure and PPG waveforms were concordant. This preliminary canine study demonstrates that PPG can function subcutaneously and that it may serve as a surrogate for acute changes in arterial pressure.