Ann Thorac Surg 1995;60:1274
© 1995 The Society of Thoracic Surgeons
Invited Commentary
Invited Commentary
Thomas P. Graham, Jr, MD
Division of Pediatric Cardiology, Vanderbilt University School of Medicine, Room D-2220 MCN, Nashville, TN 37232-2572
See also page 1267.
There have been a number of previous observations that acute volume reduction occurs after both the Fontan operation and the hemi-Fontan operation for patients with functional single-ventricle anatomy. Rychik and associates have demonstrated that volume decrease and wall thickness increase are considerably greater early after the Fontan operation than after the hemi-Fontan operation. In addition, patients with ventricular septal defect and large left-to-right shunt have geometric changes of an intermediate degree between Fontan and hemi-Fontan patients. As Rychik and associates point out, there are a number of factors potentially influencing the varying degrees of early left ventricular geometric change after operation in these patients. These factors include (1) intrinsic properties of the myocardium and (2) the filling pressures and forces contributing to the volume that is presented to the left ventricle after the operation. As documented in the references to this article, it has been suggested by animal studies that the myocardium is less compliant in the neonatal or immature heart because of a relatively high content of total collagen and type I collagen. In the present study, in which the Fontan patients were older than the hemi-Fontan patients, a less compliant heart due to younger age would have resulted in smaller hearts in the hemi-Fontan patients—an effect directly opposite to the data presented. Thus, one would have to look elsewhere to explain the lower volume and increased wall thickness in the older Fontan patients.
Because increased ventricular wall mass has been shown to be a factor contributing to poor outcome and decreased distensibility, this factor is probably one of the most important causes contributing to the smaller volumes postoperatively in the Fontan patients. In addition, as Rychik and associates point out, after the Fontan operation the complete cardiac output must flow passively through the pulmonary vascular bed without the impelling force of a ventricular pump. In the hemi-Fontan operation, inferior vena caval blood flows directly into the atrium and ventricle and continues to have an impact on ventricular filling that is not present in the post-Fontan patients. These two factors, the increased ventricular mass and the different postoperative hemodynamics, which contribute to a decrease in transpulmonary flow, undoubtedly play the major roles in causing the smaller ventricle in the post-Fontan patients.
There is one other factor that can contribute to postoperative myocardial changes in diastolic function. Inadequate myocardial protection during intraoperative ischemia can occur during the Fontan repair because of the severe hypertrophy and frequently the extended times of ischemic arrest needed to perform complex Fontan repairs. In general, ischemic times are shorter in the hemi-Fontan operation, and the risk of myocardial damage due to hypoxia should be less.
These studies point to the need for further data quantifying mass, volume, and diastolic function and determining the effects of these variables on outcome for both the hemi-Fontan and Fontan operations. A better understanding of these factors should lead to improved patient selection for each operation and hopefully better short- and long-term outcomes for patients whose anatomy precludes biventricular repair.
Related Article
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Acute Changes in Left Ventricular Geometry After Volume Reduction Operation
- Jack Rychik, Marshall L. Jacobs, and William I. Norwood, Jr
Ann. Thorac. Surg. 1995 60: 1267-1273.
[Abstract]
[Full Text]
