Ann Thorac Surg 2007;83:1758-1759
© 2007 The Society of Thoracic Surgeons
Original Articles: Cardiovascular
Invited commentary
Craig Selzman, MD
Division of Cardiothoracic Surgery, University of North Carolina, CB #7065, 3040 Burnett-Womack Building, Chapel Hill, NC 27599-7065
(Email: selzman{at}med.unc.edu).
Many patients presenting for cardiac surgery have significant left ventricular hypertrophy, commonly from long-standing hypertension or valvular heart disease. Several groups in the last 5 years have reported that left ventricular hypertrophy predicts excessive rates of morbidity and mortality in patients having cardiac surgery. Left ventricular hypertrophy is troublesome in that myocardial perfusion, particularly to the subendocardium, is not predictably homogenous. This issue becomes even more pertinent with coexisting coronary artery disease. The optimal strategy for protecting hypertrophied hearts, including types of cardioplegia and routes of delivery, remains an active debate both experimentally and clinically.
Wang and colleagues [1] continue their work analyzing myocardial energetics associated with different protection strategies. They have previously demonstrated that simultaneous antegrade and retrograde cardioplegia improved myocardial perfusion relative to antegrade alone cardioplegia in nonhypertrophied pig hearts. They now apply their sophisticated methods of measuring myocardial oxygenation and metabolism (near infrared spectroscopy and P31-magnetic resonance spectroscopy) to the clinical paradigm of beating heart valve surgery. In particular, they compare the effects of normothermic, normokalemic antegrade perfusion versus normothermic, normokalemic simultaneous antegrade and retrograde perfusion on energy utilization in hypertrophied hearts. They hypothesize that because antegrade perfusion in hearts with extensive hypertrophy or coronary artery disease is insufficient and because retrograde perfusion is heterogeneous and spares the right ventricle, normothermic, normokalemic simultaneous antegrade and retrograde perfusion would be the ideal method of perfusion. To the contrary, they demonstrate that compared with antegrade perfusion, simultaneous perfusion actually resulted in decreased myocardial perfusion and a worse energetic profile.
Although the goals of this study are laudable, the conclusions are difficult to place in perspective because of several limitations particularly related to experimental design. Importantly, there is no control group of nonhypertrophied hearts. As such it remains unclear if their findings are related to the hypertrophied hearts or their delivery strategy, especially as this is a novel platform for this group (ie, beating heart). In that light, their design should have included a continuous retrograde perfusion group (as this has been successfully described in the clinical setting with beating heart valve surgery). The clinical situation they propose is protection for the heart during beating heart surgery. Unfortunately the first thing they do with the isolated pig heart preparation is perform cold cardioplegic arrest which is exactly what is trying to be avoided. Therefore in vivo confirmation of their observations would be welcomed. Several smaller, but important issues include the model of decreasing left anterior descending coronary artery flow (and therefore pressure) as a surrogate for coronary artery disease and the use of a crystalloid versus blood perfusate.
The current study optimistically raises our awareness about the potential advantages of beating heart valve surgery. The reduction of putative adverse effects associated with global myocardial ischemia and reperfusion in these hypertrophied hearts is quite attractive. Yet, this must be weighed against the possibility of poorly protecting a heart that is consuming more oxygen (ie, the beating heart) than those that are consuming less oxygen (ie, the arrested heart). Thus, prior to full acceptance of the beating heart revival, myocardial protection strategies will need more rigorous experimental and clinical testing.
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References
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- Wang J, Liu H, Salerno TA, et al. Does normothermic normokalemic simultaneous antegrade/retrograde perfusion improve myocardial oxygenation and energy metabolism for hypertrophied hearts? Ann Thorac Surg 2007;83:1751-1759.[Abstract/Free Full Text]
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Does Normothermic Normokalemic Simultaneous Antegrade/Retrograde Perfusion Improve Myocardial Oxygenation and Energy Metabolism for Hypertrophied Hearts?
- Jian Wang, Hongyu Liu, Tomas A. Salerno, Bo Xiang, Gang Li, Marco Gruwel, Michael Jackson, Darren Manley, Boguslaw Tomanek, Roxanne Deslauriers, and Ganghong Tian
Ann. Thorac. Surg. 2007 83: 1751-1758.
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