Does a Moderately Dilated Ascending Aorta Continue to Dilate After AVR for Severe AS?

Abstract & Commentary

By Andrew J. Boyle, MBBS, PhD, Assistant Professor of Medicine, Interventional Cardiology, University of California, San Francisco

Source: Gaudino M, et al. Aortic expansion rate in patients with dilated post-stenotic ascending aorta submitted only to aortic valve replacement. J Am Coll Cardiol 2011;58:581-584.

In patients with severe valvular aortic stenosis (AS), ascending aortic dilatation is common, and is thought to be due to the alterations in flow caused by the stenotic valve. Surgical aortic valve replacement (AVR) is the treatment of choice for severe AS. When there is severe ascending aortic dilatation, concomitant replacement of the aortic root can be performed. In cases of mild aortic dilatation, only AVR is performed. However, in cases of moderate aortic dilatation, it is controversial whether isolated AVR or combined AVR plus replacement of the ascending aorta should be performed. Gaudino and colleagues studied the natural history of moderate ascending aortic dilatation to determine the rate of expansion of the aorta once the valve had been replaced. Over a 10-year period, 93 patients with isolated severe valvular AS in a tricuspid aortic valve and a moderately dilated ascending aorta (50–59 mm diameter) underwent AVR at their institution without repair of the ascending aorta. These patients were followed for 14.7 ± 4.8 years. Exclusion criteria were aortic diameter ≥ 60 mm, the presence of a bicuspid aortic valve, connective tissue disease, or significant coronary artery disease requiring concomitant coronary artery bypass graft (CABG). Paired CT scans of the aorta before surgery and at long-term follow-up were available in 64 patients.

The mean age was 67 years and 69% were male. Importantly, hypertension was present in only 44%. Mechanical valves were used in 71%. Surgical mortality was 1% (one patient). Over the 14-year follow-up, there was no change in aortic diameter following AVR (56 ± 2 mm before vs 57 ± 11 mm after; P = NS). The mean expansion rate of the aorta was 0.3 ± 0.2 mm per year and no statistical association was found between any clinical variable and aortic dilatation. Long-term mortality was 17% and in no cases was the death attributable to aortic pathology. The authors conclude that in the absence of connective tissue diseases, AVR alone is sufficient to prevent further expansion of the aorta in patients with moderate post-stenotic dilation of the ascending aorta, and that aortic replacement can probably be reserved for patients with a long life expectancy.

Commentary

This is a very interesting study that may inform cardiac surgeons on whether they need to perform aortic root replacement at the time of AVR. It is important to emphasize that this does not apply to patients with aortic regurgitation, connective tissue disease such as Marfan's syndrome, or biscuspid aortic valve. The current recommendations are to replace the aortic root in these patients, and this study excluded these patients, so the results should not be extrapolated to these groups. It is likely that the pathology leading to aortic dilatation cases of aortic pathology is very different than that in isolated AS, where it is believed that the altered flow patterns across the stenotic valve lead to the aortic dilatation. This study is congruent with this theory, because once the valvular pathology is removed by AVR, the dilatation ceases. Furthermore, the very slow rate of aortic expansion in this study following AVR (0.3 mm per year) compares very favorably with prior reports in aortic aneurysms or unoperated AS, where the rates of expansion have been shown to be much faster.

Hypertension is an important contributor to arterial pathology in general, but more specifically to aortic atherosclerosis and dilatation. Hypertension was only documented in 44% of patients in this study. We are not told how well the blood pressure was controlled, and this may be an important contributing factor to aortic dilatation. The importance of blood pressure control in these patients cannot be overemphasized. This study suggests that isolated AVR may be a reasonable option in patients with moderate post-stenotic aortic dilatation. Cardiac surgeons may be pleased to hear that the more complex and invasive surgical option of ascending aortic replacement may not be required for all of these patients.