INTRODUCTION

The results of aortic valve replacement are uncertain among patients with severe aortic stenosis, reduced LV ejection fraction (LVEF), and low transvalvular mean gradient. Although these patients represent a small substrate, roughly about 5% of patients with aortic stenosis, they also form the most controversial subset. Higher perioperative risk and reduced late outcome compared with controls have been reported in patients with reduced LVEF [1].

Left ventricular dysfunction may be secondary to long standing severe aortic stenosis along with myocardial fibrosis, extensive coronary artery disease, or prior myocardial infarction.

In such circumstances, the LV dysfunction is not likely to improve after aortic valve replacement. Some advocate that aortic valve replacement should not be considered in this subgroup of patients.

Clinical data in this group is limited about the outcome of patients with aortic stenosis, decreased ejection Fraction, and low transvalvular mean gradient who undergo aortic valve replacement. Therefore, we tested the hypothesis that aortic valve replacement in patients with aortic stenosis, LVEF < 35%, and transvalvular mean gradient ,30 mm Hg can be performed at an acceptable operative risk with improvement in ejection Fraction. [2]

For patients with small size annulus, mechanical valve prosthesis with better effective orifice area compared to bioprosthetic valve of same size can help to avoid severe Patient prosthesis mismatch. Aortic root enlargement is an alternative option.

MATERIALS & METHODS

Between December 2015 and August 2018, 32 patients with left ventricular ejection fraction (EF) ≤ 35% and severe aortic stenosis with transvalvular mean gradient < 30 mm Hg underwent aortic valve replacement at Prince of Wales hospital, Sydney.

The mean preoperative characteristics included ejection fraction< 35; aortic valve mean gradient 24± 4 mm Hg; aortic valve area- 0.7±0.2sq.cm. Simultaneous coronary artery bypass graft surgery was performed in 12 patients.

Inclusion criteria were: LVEF < 35 %, and aortic valve area (AVA) of < 1 cm2 (additionally confirmed at surgery). Patients were excluded if had concomitant valvular operations other than aortic valve replacement, previous aortic valve replacement .

Preoperative clinical, echocardiographic, hemodynamic, coronary and operative data were reviewed in 32 consecutive patients who fulfilled entry criteria.

Table 1

PRE OPERATIVE CLINICAL DATA

Mean age of the patients was 75 years and included 18 females out of 32 patients.28 patients presented with dyspnea while 16 patients complained of angina .Syncopal attack was present in 8 patients while one patient was in cardiogenic shock. 26 out of 32 patients were in NYHA class III or IV.

Table 2

ECHOCARDIOGRAPHIC DATA

All patients had LV ejection fraction < 35%. Left ventricle was grossly dilated with mean of 59±12 mm (EDD). Mean transvalvular gradient was 23±4 mm Hg. Aortic valve area was less than 1 sq.cm in all patients.

Table 3

OPERATIVE DATA

Table 4

VALVE SIZES USED

26 patients underwent elective surgical procedure. Coronary artery bypass grafting was done in 12 patients. 8 patients received aortic valve size less than 23 mm.18 patients had mechanical valve prosthesis and 14 patients had bioprosthetic valve implantation. Mean cross- clamp time was 71±27 min.

Table 5

CHOICE OF VALVE ( Tissue vs Metallic )

OBSERVATION

Perioperative (30-day) mortality was 3.1 % (1 of 32 patients). The mean aortic prosthesis size was 23±1.8 mm. Postoperative functional improvement occurred in most patients. 75% (n=24) were severely symptomatic (NYHA class III or IV) before and only 18.6% (n=6) were severely symptomatic after operation- First follow-up being six weeks post-surgery.

At 6 months follow-up, interventricular septal wall thickness regressed from 14±2 to 12±1 mm and posterior wall thickness from 13±3 to 11±2mm. Postoperative EF was assessed in survivors; 80.6% (n=26) showed a positive change. The mean change was an increase of 10±12 EF units. Positive change in EF was related to smaller preoperative aortic valve area.

In patients with small size annulus choice of mechanical valve prosthesis (18/32) with larger effective orifice area compared to same size bioprosthetic valve prevented severe patient prosthesis mismatch (PPM) . Aortic Root enlargement was not done in any of the patients.

DISCUSSION

In severe aortic stenosis, LV systolic function declines secondary to afterload mismatch, and the mean pressure gradient generated by the left ventricle may be low despite the presence of severe aortic stenosis.  LV dysfunction secondary to afterload mismatch, as seen in severe aortic stenosis, aortic valve replacement results in improvement in EF symptoms and survival.[3]

The lack of data on the outcome of aortic valve replacement in patients with aortic stenosis and LV dysfunction with low mean gradient led us to review 32 such patients in an attempt to determine perioperative mortality, overall survival, and predictors of outcome.

Small valve prostheses have higher transvalvular gradients than larger prostheses.  The failure to decrease afterload effectively with smaller aortic prostheses in these patients with low preoperative mean transvalvular gradient may influence surgical outcome.

The problem of valve-prosthesis–patient mismatch is also potentially important regarding this series of patients. This may account, in part, for the increased mortality noted among patients with the smallest prostheses.[4] Small-size mechanical valves generally have larger EOAs than small-size bioprosthetic valves. In some instances, patients with a small annulus may therefore benefit from a mechanical valve. However, a root enlargement to allow implantation of a larger bio-prosthesis may also be an option to avoid Patient Prosthesis Mismatch [5]

An improvement in postoperative LVEF of 10 EF units was noted in our study. Proper case selection, differentiating True severe Aortic stenosis from Pseudo Severe Aortic stenosis can help in proper patient selection. Dobutamine stress test, CT Aortic valve calcium scoring are important preoperative test to select cases with True Severe Aortic stenosis. Patients in this substrate who are operative risk should be offered Trans Aortic Valve Implantation.

CONCLUSION

Patients with low-gradient aortic stenosis represent a small but controversial subset. The early and intermediate follow-up results are acceptable compared with those of age- and sex-matched controls.

Marked improvement in symptoms and LVEF occurred in 96.5 % of the survivors. We submit that patients with severe aortic stenosis, reduced LV function, and low mean gradient, contrary to previous recommendations and despite increased operative mortality, should not be denied aortic valve replacement, given the substantial potential clinical benefit.

Patient with small size annulus can avoid severe patient prosthesis mismatch with mechanical prosthesis with larger effective orifice area compared to bioprosthetic valve of same size. Root enlargement is an alternative choice but comes at a price of increased cross clamp time.