Ann Thorac Surg 1997;63:1711-1712
© 1997 The Society of Thoracic Surgeons
Invited Commentary
Invited Commentary
Anthony P. Furnary, MD
Starr-Wood Cardiac Group of Portland, PC 9155 SW Barnes Rd, Suite 240 Portland, OR 97225-6629
See also page 1706.
Refinements in the clinical application of dynamic cardiomyoplasty continue to be spurred by hemodynamic and histological observations in the animal laboratory. This study by Takagi and colleagues is an elegant attempt to bring objectivity to the art of this evolving surgical technique. Takagi and colleagues' intent was to clarify the optimal wrapping tightness of the latissimus dorsi by directly quantifying (and varying) the epicardial pressure produced by the muscle wrap and relating that variable to cardiac function. Left ventricular pressure, wall tension, stroke volume, and ejection fraction were the measured endpoints performed in an acutely failing (ß-blocked) heart. Takagi and colleagues conclude that a tight wrap (with an epicardial pressure of 13 mm Hg) significantly reduced wall tension but at the same time induced the detrimental effects of lowered ventricular pressure and stroke volume in the unstimulated mode. The loose wrap (8 mm Hg epicardial pressure) did not impair unassisted stroke volume or ventricular pressure as much as the tight wrap, but was also not able to augment those parameters or decrease wall tension as well in the assisted mode as the tight wrap. Logically, the moderately tight (10 to 12 mm Hg) wrap was able to achieve the best of both scenarios by minimally depressing unassisted ventricular function while achieving satisfactory reductions in wall tension, assisted stroke volume, and ventricular pressure.
Although the objective quantification of these data is laudable, the likelihood of improved outcomes from the clinical application of these results is doubtful. The intraoperative art of performing the latissimus muscle wrap focuses on two factors: achieving complete ventricular coverage and not impending any cardiac inflow or outflow. Takagi and colleagues have focused their attention on the impedance of left ventricular inflow (due to wrap tightness) from the left atrium and its effect on the immediate efficiency of dynamic cardiomyoplasty. The problem with this hypothesis is threefold: it ignores the more clinically common obstructions to inflow and outflow, it ignores the fact that dynamic cardiomyoplasty is never used to acutely assist a failing heart, and it does not take into account the beneficial conformational changes that occur during the conditioning period in a pedicled skeletal muscle flap.
Acute intraoperative and postoperative decompensation is much more likely to be caused by inexact placement of fixation sutures, which restrict flow through low-pressure systems-inferior vena cava, left pulmonary vein, or the right ventricular outflow tract-than left ventricular compression due to a tight wrap. In addition, quantifying the optimal degree of tightness by measuring submuscular epicardial pressure in the operating room would make wrap completion unnecessarily cumbersome. Pragmatically, as long as the wrap fits comfortably (the equivalent of <8 mm Hg epicardial pressure) around the ventricles at the time of the operation, conformational adaptation will occur during the 12-week conditioning period, which allows the muscle to adopt a new optimal resting tension. This occurs through sarcomere deletion in response to a relaxed (shorter) resting length. Gealow and colleagues (reference 20 in Takagi and colleagues' article) have shown that stretching the latissimus dorsi to its in-situ length during cardiomyoplasty is not required for future biomechanical performance to be optimal. Thus, the exact epicardial pressure produced by the wrap has little to do with the long-term success of the procedure. As surgical logic would have it, all the objective science in the world still cannot remove the art of intraoperative surgical judgment from this evolving procedure.
Related Article
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Effects of Wrapping Tightness on Acute Cardiac Function in Dynamic Cardiomyoplasty
- Hisato Takagi, Hajime Hirose, Eisaku Sasaki, Michiya Bando, Yasunobu Furuzawa, Shinji Murakawa, and Yoshio Mori
Ann. Thorac. Surg. 1997 63: 1706-1711.
[Abstract]
[Full Text]
