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Aims: This study investigates whether subendocardial ischemia can be detected by measuring multilayer radial systolic strain from epicardial tissue Doppler imaging. Methods:In 10 anesthetized open-chest pigs an extracorporeal shunt from the proximal brachiocephalic to the left anterior descending coronary artery was constricted in steps. Color microsphere injections and short axis Tissue Velocity Imaging (TVI) recordings were performed with open shunt, with a non-significant stenosis, and with 2 steps of shunt flow reduction.Results: With open shunt and no transmural flow gradient, there was a gradient of peak ejection strain with high values subendocardially for both 4 and 2 layer measurements. For 2 layer measurement strain was 56.0 AE 10.5% subendocardially and 22.0 AE 5.2% subepicardially. A non-significant stenosis, not altering transmural flow distribution, reduced strain to 40.3 AE 5.4% in the endocardial half-layer. With reduced shunt flow resulting in subendocardial ischemia, peak ejection strain decreased further, primarily in inner wall layers, and postsystolic strain became evident. At severe stenosis (52.4 AE 1.8% shunt flow reduction) strain was reduced to 3.8 AE 3.6% in the subendocardium and 0.0 AE 2.6% in the subepicardium. Conclusion: Evaluation of myocardial function with multilayer radial systolic strain has a potential for detecting subendocardial ischemia.

In specific experimental protocols, the anaesthetic protocol described could allow the use of muscular paralysis in young domestic pigs, for instance when involving hypothermic cardiopulmonary bypass, cardioplegic arrest and reperfusion.

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Objective: Myocardial dysfunction after reperfusion can be a clinical problem in the early postoperative phase after on-pump cardiac surgery. The aim was, in an experimental setting, to investigate if administration of the b-adrenergic receptor blocker esmolol prior to cross-clamping for 80 min with cold oxygenated blood cardioplegia would improve myocardial protection and early postoperative function. Methods: Twenty-four anaesthetised pigs were randomly allocated into one of two equally sized groups and put on mild hypothermic cardiopulmonary bypass. Esmolol 1 mg kg À1 or saline was administered into the arterial line 4 min prior to aortic cross-clamp. Cardiac arrest during 80 min of cross-clamp was obtained with repeated antegrade cold oxygenated blood cardioplegia; the pigs were weaned from bypass following a standardised protocol. Left ventricular global and regional myocardial function and tissue blood flow were evaluated with conductance catheter, echocardiography and coloured microspheres at baseline and at 1, 2 and 3 h after declamping. Four animals did not fulfil the protocol and were excluded. Results: No significant differences between groups could be demonstrated for left ventricular global and local function and tissue blood flow at baseline. At 1 h after declamping the slope of preload recruitable stroke work (PRSW slope ) averaged 73.7 AE 12.7 mmHg (SD) in controls and 72.7 AE 11.1 mmHg in esmolol-treated animals. In controls PRSW slope decreased to 62.1 AE 11.0 and 58.4 AE 12.7 mmHg after 2 and 3 h, respectively ( p < 0.005 vs 1 h for both). In the esmolol-treated animals PRSW slope remained unchanged at 72.0 AE 11.4 and 73.7 AE 12.9 mmHg at 2 and 3 h after declamp and were significantly higher ( p < 0.025 and <0.001) than the corresponding values in the control group. The slope of the end systolic pressure volume relationship did not differ between groups at 1 and 2 h after declamp, but were 1.85 AE 0.86 and 2.51 AE 0.96 mmHg ml À1 in controls and in esmolol-treated animals, respectively, after 3 h ( p < 0.025). Conclusions: Esmolol administered prior to cold oxygenated cardioplegic arrest alleviates left ventricular dysfunction in the early hours after cardiopulmonary bypass. #

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