Right Ventricular Pacing in Pulmonary Arterial Hypertension

In pulmonary arterial hypertension (PAH), progressive pulmonary vascular remodeling leads to supraphysiologic right ventricular (RV) afterload. Pharmacologic trials have shown that aggressive upfront treatment reversing pulmonary vascular remodeling successfully increases RV function and improves survival. To date, however, there are no proven treatments that target RV contractile function. Echocardiographic studies of RV dysfunction in the setting of pressure overload have demonstrated intra and interventricular dyssynchrony even in the absence of overt right bundle branch block (RBBB). Electrophysiologic studies of patients with chronic thromboembolic disease (CTEPH) at the time of pulmonary endarterectomy have shown prolongation of action potential and slowed conduction in the right ventricle which has correlated with echocardiographic measures of dyssynchrony. Cardiac MRI measures of RV strain in patients with PAH demonstrated simultaneous initiation of RV and left ventricular (LV) contraction, but delayed peak RV strain suggesting that interventricular dyssynchrony is a mechanical rather than electrical phenomenon. Prior studies of RV dysfunction in an animal model, computer model, congenital heart disease, and CTEPH have suggested acute hemodynamic benefits of RV pacing. However, RV pacing has not been studied in patients with PAH. Furthermore, it remains unclear if pacing particular regions of the RV can achieve a hemodynamic benefit and what cost this hemodynamic improvement may incur with regards to myocardial energetics and wall stress. Therefore, the investigators propose to examine RV electrical activation in PAH, map the area of latest activation, and then evaluate the hemodynamic and energetic effects of RV pacing in these patients.