In addition, the majority of these patients, particularly those who remain symptomatic following CRT, undergo optimization of biventricular pacemaker. Unlike other reports that have looked at LV outflow velocity time integral (VTI) for improvement in cardiac output in response to various A to V and V to V changes, multiple parameters are evaluated, including mitral inflow filling time, premature mitral valve closure, mitral inflow atrial wave duration, pulmonary vein atrial reversal, and systolic/diastolic ratio, as well as pulmonary vein D wave deceleration time, mitral regurgitation severity, LV dP/dt when it can be evaluated by mitral regurgitation signal, and pulmonary artery pressure in response to changes in pacemaker settings, as well as inter-ventricular and intra-ventricular dyssynchrony by tissue velocity imaging during the interventricular changes. Strain imaging is used in some patients when tissue velocity imaging is not helpful.

In patients who are pacemaker-dependent, atrial pacing is performed at 90bpm to determine appropriately paced AV delay at higher heart rates. Finally, patients perform modest exercise in order to ensure appropriate increase in heart rate in those who are pacemaker-dependent and to determine chronotropic competence in those who are A sensing at baseline. This assists in determining upper rate limit and corresponding AV delay. Acute improvement in cardiac output has been found in patients in response to AV optimization and further improvement in response to interventricular optimization.²² In the process of collecting data, it appears that most patients maintain this improvement in their daily lives for several weeks following optimization.

Other Issues in Biventricular Pacemaker Programming

While it is possible to perform biventricular pacemaker optimization activity at the author’s center, this activity is demanding on resources. Personal interest, referring physician awareness of benefits of pacemaker optimization, and certain research protocols allow us to conduct this activity. However, pacemaker optimization is not routinely performed in many centers in the US, or it is performed only on a limited basis. Reasons for this include the need for advanced echo Doppler skills, the time needed to perform these procedures, a lack of protocols directing physicians on how to perform the procedure, and, most importantly, lack of reimbursement for the procedure. Even though pacemaker clinics are in place in various centers in the US, these are usually run by nurses who are limited to evaluating pacemaker thresholds, etc. These clinics could be an ideal platform for collaboration between electrophysiology and echo teams. Attention needs to be given not only to pacemaker thresholds, but also, importantly, to whether pacemaker programming is a leading maximum homodynamic benefit for a given patient.

There is also a need to develop methods that are less sophisticated but can still provide a reasonable guide to pacemaker programming with minimum expertise. A non-invasive device called SphygmoCor® system tonometer is currently being evaluated (Medical Inc., Lisle, Illinois) to see if it can track cardiac output in response to various A to V and V to V timings compared with echocardiography. Results indicate that there is concordance between echo Doppler ejection timing and SphygmoCor-derived radial artery systolic ejection in 80% of subjects.²³ Finally, many patients require repeat optimization because of cardiac remodeling. These results therefore suggest that clinics should evaluate and perform this optimization perhaps at about four- to six-monthly intervals on these subjects.