Chronic high-rate pacing induces heart failure with preserved ejection fraction-like phenotype in Ossabaw swine

The lack of pre-clinical large animal models of heart failure with preserved ejection fraction (HFpEF) remains a growing, yet unmet obstacle to improving understanding of this complex condition. We examined whether chronic cardiometabolic stress in Ossabaw swine, which possess a genetic propensity for obesity and cardiovascular complications, produces an HFpEF-like phenotype. Swine were fed standard chow (lean; n = 13) or an excess calorie, high-fat, high-fructose diet (obese; n = 16) for ~ 18 weeks with lean (n = 5) and obese (n = 8) swine subjected to right ventricular pacing (180 beats/min for ~ 4 weeks) to induce heart failure (HF). Baseline blood pressure, heart rate, LV end-diastolic volume, and ejection fraction were similar between groups. High-rate pacing increased LV end-diastolic pressure from ~ 11 ± 1 mmHg in lean and obese swine to ~ 26 ± 2 mmHg in lean HF and obese HF swine. Regression analyses revealed an upward shift in LV diastolic pressure vs. diastolic volume in paced swine that was associated with an ~ twofold increase in myocardial fibrosis and an ~ 50% reduction in myocardial capillary density. Hemodynamic responses to graded hemorrhage revealed an ~ 40% decrease in the chronotropic response to reductions in blood pressure in lean HF and obese HF swine without appreciable changes in myocardial oxygen delivery or transmural perfusion. These findings support that high-rate ventricular pacing of lean and obese Ossabaw swine initiates underlying cardiac remodeling accompanied by elevated LV filling pressures with normal ejection fraction. This distinct pre-clinical tool provides a unique platform for further mechanistic and therapeutic studies of this highly complex syndrome.