**2.2 Experimental study to determine the suitable size and shape of cardiac support net**

In order to eliminate the arbitrary adjustment of the cardiac support net, we need to determine the most appropriate size before the operation. For this purpose, we investigated the systolic and diastolic functions of the right and left ventricles with different sizes of the cardiac support net in a porcine model of chronic heart failure (HF). The HF model was established by rapid atrial pacing (200 bpm for 3 weeks) using a commercial intravenous pacing leadwire and an experimental pacing system (Taishoikakikai Co, Osaka, Japan).

After 3 weeks of rapid pacing, LVDd increased from 34.2 ± 7.0 to 51.0 ± 4.5 mm, and LVDs increased from 24.0 ± 7.1 mm to 46.3 ± 5.2 mm5., respectively. LVEF decreased from 60.6 ± 12.5 to 20.8 ± 8.5% (**Table 1**). We then examined the effects on right and left ventricular pressure-volume relations. The Sigma5 system (CardioDynamics, Zoetermeer, The Netherlands) was used. End-systolic and enddiastolic pressure-volume relations were measured by rapid volume loading with 500 ml of lactated Ringer's solution. The solution was equilibrated with blood before infusion.

We found that the slope of Emax (= end-systolic pressure-volume ratio), which is the most reliable systolic function independent of preload and afterload conditions, became steeper in both right and left ventricles when smaller nets were applied


**Table 1.**

*Change in UCG parameters before and after rapid pacing.*

(**Figures 2** and **3a**: Improvement in Contractility). However, the end-diastolic pressure-volume relation (EDPVR) also shifted to the left and upward, indicating a worsening of diastolic function (**Figures 2** and **3b**) [10]. The deterioration of the right ventricular diastolic function was more pronounced than that of the left ventricle, especially at 85% of the original heart size (**Figure 3b**). There was a point at which RVEDV stopped increasing in response to rapid volume loading, and from that point only RVEDP increased (**Figure 2b**). This phenomenon was speculated to be due to compression of the right ventricle by the left ventricle and the cardiac support net, which prevented right ventricular dilation. The cardiac support net lowers Ptm, thereby improving left ventricular contractility. However, the positive effect of the cardiac support net on systolic function is offset by the decrease in stroke volume due to the worsening of right ventricular diastolic function [8].
