Ventricular Reconstruction Hypothesis
In patients with HFrEF there are often changes in left ventricular structure and function, which include remodelling of the left ventricle from its normal elliptical shape to a more spherical shape, resulting in a less efficient ventricle and a worse prognosis. SVR has been shown in observational studies to reverse-remodel the left ventricle and restore some of its original functional capacity.24,25 The procedure involves removing akinetic or dyskinetic segments of the anterior wall and reshaping the left ventricle to restore its original elliptical form. These techniques were developed from operations for left ventricle aneurysms by Vincent Dor26 and others.
It was uncertain from these observational studies whether SVR combined with coronary artery bypass surgery would result in improved outcomes for patients with ischaemic cardiomyopathy compared with coronary bypass surgery alone, especially when combined with medical treatment. This led to the design of the SVR arm of the STICH trial, the only randomised trial to question the role of SVR in patients with HFrEF. Patients were eligible if they had significant coronary stenosis amenable to surgical revascularisation, severe systolic dysfunction with an LVEF <35 % and dominant left ventricular anterior akinesia or dyskinesia amenable to SVR. A total of 1,000 patients were randomised to the arm comparing isolated coronary bypass surgery versus coronary bypass and SVR against the background of medical treatment. Primary outcome was a composite of all-cause mortality and hospital re-admission.
Patients who underwent SVR had significantly lower LV volumes on short-term follow-up with a reduction of end-systolic volume of 19 % versus 6 % in those receiving coronary surgery alone. But this reduction in left ventricle volume was small compared with the previous observational studies in which volume reductions of 33 %27 and 72 %25 were achieved. There was no significant difference between the two treatments for the primary outcome at 4-year follow-up. There were also no differences between the two groups in terms of secondary outcomes, including repeat admission to hospital, symptoms or quality of life.28 SVR added to coronary bypass surgery does not appear to improve quality of life compared with coronary bypass surgery alone, but does increase healthcare costs.29
There has been a great deal of discussion aimed at reconciling the difference between the observational data supporting SVR and the findings from the STICH trial. A secondary analysis examined the influence of baseline left ventricular volumes and LVEF on outcomes. Contrary to the widely held view by surgeons enthusiastic about SVR that patients with larger, already remodelled left ventricles would benefit from coronary bypass surgery plus SVR instead of isolated coronary surgery, patients with smaller baseline left ventricular end-systolic and end-diastolic diameters were more likely to benefit, suggesting a role for SVR before extensive remodelling has occurred.30,31 Furthermore, the extent of myocardial viability in the dysfunctional anterior wall does not appear to be an important determinant of survival in patients undergoing SVR.32
It is difficult to imagine another trial of this nature, which was an enormous international effort, being carried out. The vital questions for surgeons willing to take on these patients are: how much asynergy exists; is there sufficient compensatory muscle to restore function; what is the ventricular volume? It could be that a smaller randomised trial with a more homogeneous patient group, minimal or no angina and agreed physiological end-points could be conducted.
The Role for Mitral Valve Repair
Mitral regurgitation as a result of left ventricular dysfunction and remodelling is a common feature in patients with coronary artery disease and HFrEF, especially after an inferior or infero- lateral myocardial infarct. Ischaemic mitral regurgitation is primarily, but not exclusively, a ventricular disease arising from mitral annular dilatation and restricted closure of the mitral valve leaflets due to tethering associated with left ventricular wall dysfunction.33
Ischaemic mitral regurgitation is a powerful marker of poor prognosis in patients with coronary artery disease and left ventricular dysfunction.34,35 The results of surgery for ischaemic mitral regurgitation are unproven and unpredictable in improving patient outcomes and have not been tested against medical treatment in a prospective randomised trial. Unfortunately, surgical mitral valve repair is often not durable in ischaemic mitral regurgitation due to progression of the underlying left ventricular dysfunction.36 Data from the (Randomised Ischemic Mitral Regurgitation (RIME) trial, a prospective randomised comparison of coronary bypass surgery alone versus surgery combined with mitral annuloplasty for moderate ischaemic mitral regurgitation, showed a significant improvement in the primary outcome, myocardial oxygenation consumption at 1 year (22 % increase from baseline for coronary bypass gratfing plus mitral annuloplasty versus 5 % for coronary bypass gratfing alone; p<0.001).37 There was also greater symptomatic improvement and significant reverse remodelling. This confirmed and extended the findings of a previous randomised trial of moderate ischaemia.38 Data from the National Heart, Lung, and Blood Institute Cardiothoracic Surgery Network randomised trial for severe ischaemic mitral regurgitation reported greater durability with mitral valve replacement compared with repair among experienced surgeons.39 Unfortunately, myocardial viability was not examined in this study and the trial was not powered to assess clinical outcomes.
Transcutaneous mitral valve repair is of special interest in high-risk surgical patients. Promising results have been reported in such patients who remain symptomatic despite modern medical treatment and cardiac resynchronisation therapy.40 There is a randomised trial of transcatheter valve repair versus medical management currently underway that may clarify whether targeting the mitral valve in addition to medical treatment improves the outcome of patients with ischaemic mitral regurgitation.41