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J Thorac Cardiovasc Surg 2003;126:2105-2106
© 2003 The American Association for Thoracic Surgery
Letter to the editor |
a Department of Pediatrics (Pediatric Cardiology), Leiden University Medical Center, Leiden, The Netherlands
b Department of Cardiology (Cardiac Physiology Laboratory), Leiden University Medical Center, Leiden, The Netherlands
c Department of CardioThoracic Surgery, Leiden University Medical Center, Leiden, The Netherlands
d Department of Pathology, The Netherlands Cancer Institute, Amsterdam, The Netherlands
e Department of Pediatrics (Pediatric Cardiology), Erasmus Medical Center—Sophia Children's Hospital, Rotterdam, The Netherlands
We thank Dr Sievers for his important comments. He is right in pointing out that pulmonary artery banding with the aim of training the subpulmonary ventricle is a delicate procedure that should be done with the utmost caution. The ability of the subpulmonary ventricle to adapt to the increased afterload imposed by the pulmonary artery constrictor depends on the age of the patient, baseline ventricular function, and the timing and level of afterload increase.1,2
Dr Sievers points out a study by his group in which it was shown that a slow progression of pressure loading (1.5 mm Hg/d) results in a lesser increase of right ventricular end-diastolic pressure and minimal changes in ejection fraction and end-systolic volume relative to a fast progression (3.6 mm Hg/d), thus suggesting better preservation of myocardial function.3 In addition, these results were supported by the finding that slow pressure loading resulted in a steeper slope of the relationship between maximal pressure and end-systolic volume, thus reflecting improved contractile performance. The reported functional impairment after fast pressure loading in the study of Lange and colleagues3 may be related to the simple fact that a load-dependent index of cardiac performance (ejection fraction) was used to quantify myocardial function after chronic right ventricular pressure overload.
In another article,4 we have published the hemodynamic results of our banding study. In that article we showed that stroke volume as well as ejection fraction were decreased, whereas compensatory ventricular dilatation (Frank-Starling mechanism) was not observed after chronic right ventricular pressure loading. In the study, right ventricular pressure overload at systemic (aortic) level was produced within a period of 2 weeks. However, according to the slope and intercept of the end-systolic pressure-volume relationship, right ventricular contractile performance was found to be significantly enhanced in these hearts. In addition, we have shown that abnormalities in diastolic function, associated with the (normal) hypertrophic response to pressure loading, may be held responsible for functional impairment of cardiac function after chronic right ventricular pressure loading.5
Part of the difference in results between our study and that of Lange and colleagues3 may be explained by the ages at which the pressure overload was applied. In the latter study, young piglets with an average body weight of 22.3 kg (range 17-32 kg) were subjected to slow progressive right ventricular pressure overload. Apart from differences in species, it is likely that these animals, according to their weight, were substantially older (probably several months 6) than the lambs used in our study (age 2-3 weeks, average body weight 6.4 ± 1.7 kg). This difference may have influenced the myocardial response to pressure loading. Finally, whereas the study by Lange and colleagues3 compared results of the banding in animals against their own prebanding values (each animal acted as its own control), we compared right ventricular function after 8 weeks of loading against an age-matched control group without banding.
We agree with Dr Sievers that adjustable constrictors should allow small and reproducible adjustments of the level of constriction. Precisely how small the adjustments can be made with our device cannot be inferred from our current results and needs further study.
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