Time-dependent response of both ventricles after septal ablation: implications for biventricular support after left ventricular assist device placement

OBJECTIVES: An ovine model of septal ablation was studied to elucidate the mechanisms involved in right ventricular failure when commencing left ventricular mechanical assistance. The disruption of ventricular interdependence after acute and chronic septal injury was examined.

METHODS: Twelve sheep underwent percutaneous transluminal septal myocardial ablation using 0.6 mL ethanol. Twelve other sheep underwent a sham procedure. Left ventricular and right ventricular pressure and volume (conductance) response 15 minutes and 4 weeks postinjury were measured. Ultrasonic crystals measured chamber dimensions and wall movement. Areas at risk and infarct zones were quantified.

RESULTS: Compared with sham, ablation chronically reduced systolic interventricular septal thickening (18.4% +/- 5.8% vs 7.3% +/- 3.1%; P < .001) and acutely increased right ventricular ejection fraction (37.6% +/- 8.5% vs 69.9% +/- 7.2%; P < .001), preload recruitable stroke work (42.0 +/- 4.4 erg x 10(3) vs 48.7 +/- 2.0 erg x 10(3), P < .001), end-systolic elastance (1.03 +/- 0.19 mm Hg mL(-1) vs 1.31 +/- 0.18 mm Hg mL(-1); P < .001), and Tau (24.9 +/- 3.8 ms vs 29.6 +/- 8.2 ms; P < .001). In contrast, for left ventricular ejection fraction (55.5% +/- 5.9% vs 38.9% +/- 7.7%; P < .001), preload recruitable stroke work (85.9 +/- 10.6 mm Hg vs 66.5 +/- 9.6 mm Hg; P < .001) and elastance (2.13 +/- 0.51 mm Hg mL(-1) vs 1.81 +/- 0.44 mm Hg mL(-1); P < .001) were reduced, but Tau increased (22.0 +/- 3.5 ms vs 28.9 +/- 5.8 ms; P < .001) and remained elevated at 4 weeks compared with sham. The area at risk was the same between groups, and injury was limited to the septum (17.2% +/- 2.7% vs 2.9% +/- 5.8%; P < .001).

CONCLUSIONS: Acute and chronic hemodynamic responses are distinctly different after septal injury; the acute response demonstrates a paradoxical motion. Resolution of this motion at 4 weeks is suggestive of reduced septal compliance and buttressing. Ventricular interactions after placement of a left ventricular assist device will vary depending on the injury duration.