Assessing left atrial systolic contribution via pressure-volume loops in murine HFpEF

Left atrial (LA) myopathy plays a critical role in the pathophysiology of heart failure with preserved ejection fraction (HFpEF). This study aimed to evaluate LA function in a murine model of hypertension-induced HFpEF, with and without obesity, by analyzing left ventricular (LV) pressure signals to quantify the contribution of LA systole to total LV volume. HFpEF was induced in C57BL/6J mice using the SAUNA model, which involves uninephrectomy, chronic aldosterone infusion, and high-salt drinking water for four weeks. To model obesity-associated HFpEF, a high-fat diet (HFD) was added to the SAUNA protocol. Invasive hemodynamic measurements were obtained, and a novel method was developed to assess atrial systole using the second-order derivative of the LV pressure signal during diastolic filling. SAUNA HFpEF mice exhibited preserved LVEF, moderate hypertension, pulmonary congestion, and diastolic dysfunction as evidenced by a prolonged time constant of relaxation (Tau). In sham control mice, atrial systole accounted for 23.0 ± 2.4% of LV volume, whereas this contribution was significantly reduced to 13.9 ± 2.3% in SAUNA HFpEF mice (P < 0.01). In obese sham controls, atrial systole contributed 53.1 ± 2.2%, which was markedly decreased to 36.8 ± 3.6% in obese-SAUNA HFpEF mice (P < 0.003). This novel method enables precise quantification of LA systolic contribution to LV filling in mice and highlights the pathophysiological effects of hypertension and obesity on LA function in HFpEF.