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Coronary revascularization in patients with ischemic left ventricular dysfunction: review article

20 August 2019

REVIEW ARTICLE

Coronary revascularization in patients with ischemic left ventricular dysfunction: review article

Оlga Yepanchintseva1, N.B. Ivanyuk1, Y.A. Borhalenko1, Оleg Zharinov2, Borys Тоdurov1

1Institute of Cardiology of the Ministry of Health of Ukraine, Kiyv, Ukraine;

2National Medical Academy of Postgraduate Education “P. L. Shupyk” of the Ministry of Health of Ukraine, Kiyv, Ukraine.

 

Corresponding author:

Oleg Zharinov

National Medical Academy of Postgraduate Education “P. L. Shupyk” of the Ministry of Health of Ukraine

9, Dorohozhytska str., Kiyv, Ukraine, zip code 04112

e-mail: oleg_zharinov@hotmail.com

Short title: Coronary revascularization in patients with ischemic left ventricular dysfunction

What is not known yet, about the topic

The benefits of coronary artery bypass graft (CABG) surgery in the treatment of left ventricular ischemic dysfunction are not always evident, compared to other treatment methods, in particular, optimized drug treatment and percutaneous stenting.

Research hypothesis

Certain categories of patients have an increased benefit after CABG, compared to other methods of treating left ventricular dysfunction of ischemic origin.

Article’s added novelty on this scientific topic

At precise indications, after careful stratification of risks, CABG becomes a method of choice for the treatment of left ventricular dysfunction of ischemic origin for some categories of patients. Very important for success is the patient's viable myocardial reserve.

ABSTRACT

Introduction. Ischemic cardiomyopathy (IC) is the main cause of left ventricular dysfunction (LVD) in contemporary society. The survival prognosis and evolution of heart failure (HF) in IC patients are more unfavorable compared to other types of non-ischemic cardiomyopathies. Thanks to the improvement of cardiac surgery technology and the development of evidence-based medicine, the importance of revascularization in patients with CI and reduced left ventricular ejection fraction (LVEF) has increased significantly.

Material and methods. This article summarizes the existing methods of cardiac revascularization, as well as the choice of the optimal options of revascularization in patients with IC and LVD. We reviewed the literature using the PubMed search engine and journals in English and Russian from 1975 to 2019. We used the keywords: “coronary revascularization” and “left ventricular dysfunction”. There were 1900 articles assessed. The articles were selected according to their relevance, resulting in a final bibliography of 38 sources.

Results. Evidence-based medicine has shown that it is possible and advisable to undertake coronary artery bypass graft surgery (CABG) as an effective way to increase LVEF and improve the HF progression and the prognosis of survival. CABG is indicated for patients with left coronary artery stenosis, three-vessel or two-vessel disease, including the anterior descending artery, taking into account the severity of the lesion on the SYNTAX scale. Stenting is inferior to surgical revascularization regarding the influence on primary objectives, but it improves the quality of life of the patients with IC and reduced LVEF.

Conclusions. Coronary atherosclerosis is the most common cause of LVEF decrease and HF onset. Surgical revascularization may improve the heart pump function, with the condition that there is a sufficient amount of viable myocardium, in patients with ischemic LVD. The assessment of myocardial viability may be of supplementary importance when making decisions regarding the utility of CABG in multi vascular coronary artery disease, which is associated with a severe decrease in LVEF.

Keywords: coronary artery disease, heart failure, reduced left ventricular ejection fraction, myocardial revascularization.

INTRODUCTION

Heart failure (HF), along with reduced left ventricular ejection fraction (LVEF), leads to a poor survival prognosis and is associated with frequent hospitalizations due to blood circulation decompensation. According to the Framingham study, the mean life expectancy of patients with LVEF less than 20% and with clinical signs of heart failure is 1.7 years in males and 3.2 years in females [1]. Coronary atherosclerosis is the main cause of left ventricular systolic dysfunction (LVSD), the prognosis of survival in patients with ischemic cardiomyopathy (IC) being more limited compared to other non-ischemic cardiomyopathies [2]. At the same time, unlike many other causes of LVD, there is a chance of recovering the myocardial contractile function after revascularization in patients with IC.

Frequently, the reduced LVEF is due to the multi vascular coronary disease associated with diabetes mellitus, which are strong arguments for surgical myocardial revascularization. On the other hand, LVD is associated with a certain increase of the risk of a “major” cardiac surgery, being considered as a contraindication. The first attempts at surgical treatment of patients with IC and LVD were made almost half a century ago [3]. Initially, in patients with LVD, CABG was accompanied by increased mortality (from 1.4 to 18.6%) and many postoperative complications [4]. However, due to the rapid development of cardiac surgical techniques and the formation of an adequate evidence base, the role of revascularization in patients with ischemic LVD has gradually increased [5, 6, 7]. Still, according to a recent review of clinical practice, the incidence of coronary ventriculography (CVG) in patients with a newly diagnosed HF is insufficient [8]. In addition, there is a number of open questions about patient selection and the monitoring of the revascularization effectiveness, especially the possibility of LVD correction after surgery. This article summarizes the current understanding of the possibilities and the choice of the optimal revascularization method in patients with ischemic LVD and signs of HF.

Ischemic cardiomyopathy and myocardial viability

In 1970, G.Burch suggested the term “ischemic cardiomyopathy”, meaning the development of coronary ischemic disease with multivessel involvement, ventricular enlargement, and clinical symptoms of congestive heart failure [9]. The cause of myocardial dysfunction in these patients is the decrease in blood flow in subendocardial areas. The progressive decrease in the availability of macroergic compounds and acidosis leads to increased myocardial rigidity, and the heart overloading causes the expansion of its chambers. An important feature of IC is the potential reversibility of the LVD at the regional and global levels.

The term “viable myocardium” characterizes an ischemic area of the myocardium with a reduced functional capacity, which may have a limited amount of scar tissue, with the possibility of the functional recovery after the revascularization. In the context of the LVD evolution, the myocardial viability is assured by the significant decrease of energy consumption, also called hibernation. Hibernation should be distinguished from the concept of "inhibited myocardium" – a post-ischemic LVD condition that persists after reperfusion, despite the coronary blood flow recovery [10].

The determination of the area of viable myocardium using the stress echocardiography, infusion scintigraphy, or contrast magnetic resonance imaging may be useful for candidates for revascularization or cardiac transplantation, who have undergone an extended myocardial infarction with left ventricular aneurysm, and patients with IC and LVEF less than 35%, in the absence of a large scar.

It is important to mention that in many patients presenting these clinical and instrumental signs, dyspnea is often equivalent to angina pectoris, making it difficult to determine the treatment priorities. Although there is strong evidence of better survival rates among patients with viable myocardium, no direct proof of the role of viability assessment when choosing between medication and surgical revascularization has been detected [11].

CAGB versus medical therapy

The results of several studies have shown the possibility of improving the long-term survival rate in patients with IC and LVD after surgical revascularization, compared to medical therapy [12, 13]. In 1994, Yusuf et al. have performed a cumulative analysis of the data from the seven largest studies at that time, comparing the effects of CABG and drug therapy on the survival rate in 10 years (n=2650). More than 50% of patients were diagnosed with three-vessel coronary disease. In the CABG group, a positive effect on the survival rate and symptoms was registered, compared to the medical therapy: the mortality in 10 years being 26.4% and 30.5%, respectively (p=0.03). The absolute benefit of surgical revascularization was maximal in patients with LVD, whose mortality was almost two times lower [14].

It is worth mentioning that in the first revascularization studies, patients in the control group could not receive most of modern medicine. Back then, the statins and blockers of the renin-angiotensin system were not available yet; other agents with proven beneficial prognostic effects, such as antiplatelet agents, beta-blockers and mineralocorticoid receptor antagonists, were not routinely used. Of course, this particularity limits the possibility of extrapolating data to the current patient population with HF and LVD. However, according to evidence-based medicine, new, convincing data have recently emerged in the favor of CABG in LVD patients who received optimal drug therapy [15, 13].

In the STICH study, 1212 patients with IC and LVEF ≤35% (mean 27%) were randomized to CABG and optimal drug therapy. In 5 years, the incidence of deaths of any cause was not different in the compared groups. Meanwhile, the analysis of a number of secondary efficacy criteria (death of any cause or hospitalization for HF, death of any cause or hospitalization for cardiovascular reasons, death of any cause or need for revascularization) found the best results in the CABG group [13]. The 10-year STITCHES follow-up showed an absolute increase in the patients’ life expectancy after CABG by 1.44 years (7.73 versus 6.29 years, respectively). The obtained results are a convincing reason for the CABG implementation in patients with IC and LVD [16].

The STICH study revealed the obvious dependence of patient survival on the viable myocardium volume. Preserved viability has generally shown a better survival rate after both CABG and conservative treatment, but did not represent a specific indicator of the potential benefits of surgical revascularization [11]. Obviously, the inconsistency of the obtained data is due to the relatively small number of cardiovascular events in the compared groups and the lack of a unified methodology for determining the viability of the myocardium. Overall, the viability assessment in a modern clinic can be considered as an additional criterion for predicting CABG outcomes in patients with initially reduced LV pump function [17].

CABG versus coronary artery stenting

According to evidence-based medicine, the results of surgical revascularization and coronary artery stenting in IC and LVD patients were compared in a small number of randomized and observational retrospective clinical trials. In a meta-analysis of 19 studies, involving 4766 patients with LVEF less than 40%, who underwent percutaneous interventions, hospital and annual mortality rates in patients with stents did not differ from those included in CABG studies [18]. Another study did not find any significant difference in the survival of patients with IC and LVD (LVEF less than 35% for 446 patients), after CABG and stenting, during a 36-months period of follow-up (72% vs. 69%, respectively) [19]. In the HEART study, stenting or CABG was performed in patients with ischemic LVD and viable myocardium. After 4 years, in the compared groups, there was no difference in mortality of any cause, as well as in the patients’ life quality. At the same time, a study of 138 patients was not strong enough to assess the differences between groups regarding their effect on “solid” outcomes [20]. The advantages of CABG, compared to coronary artery stenting in LVD patients, are identified in long-term observational studies with a large number of patients [21, 22]. At the same time, stenting represents a way of improving the quality of life of patients with adequate anatomical indications.

The benefit of CABG is most noticeable in patients with more prominent and more complex lesions of coronary stenoses. According to the analysis of the subgroup of patients with “stem” lesions in the SYNTAX study, the advantage of CABG results, compared to stenting, was evident in patients with moderate or severe coronary lesions, determined with the SYNTAX scale [23]. In the FREEDOM study, the positive effect of CABG on the survival rate was demonstrated in diabetic patients, who frequently present diffuse coronary artery disease [24]. Therefore, the presence of diabetes in patients with lesions of two or more coronary arteries (including reduced IC and LVEF) is a strong argument in favor of CABG, rather than stenting [25].

Revascularization according to the consensus recommendations

Firstly, European recommendations for the diagnosis and treatment of IC include indications for CVG in patients with HF [26]. Particularly, CVG is recommended for patients with angina pectoris, in whom myocardial revascularization is possible. Other indications for CVG are symptomatic ventricular arrhythmias or cardiac arrest history with successful resuscitation. CVG should also be considered in patients with HF and with moderate or high pre-tested IC risk and evidence of ischemia in non-invasive stress tests.

In patients with stable IC, the decision to perform revascularization is based on angiographic and clinical criteria, the purpose of revascularization being the improvement of the survival prognosis and/or quality of life [6]. Both objectives are, of course, relevant for patients with LVD of ischemic etiology. It is important to take into account the absence of a lower threshold for LVEF when assessing the possibility of revascularization. Moreover, the improvement of disease progression and prognosis after CABG is most pronounced in patients with ischemic LVD.

Choosing the optimal revascularization method, it is necessary to take into account not only the severity of subepicardial coronary artery atherosclerosis, but also the distal channel state, as well as the collateral blood flow. Ischemic LVD is frequently accompanied by a multivessel lesion, and LVEF decreases with the concomitant increase of the total lesion area of coronary vessels [27]. According to European recommendations [6], CABG is indicated for patients with left coronary artery stenosis, three-vessel or two-vessel disease, including the anterior descending artery, taking into account the severity of the lesion on the SYNTAX scale. Based on the results of the STICH study (not including patients with stem lesions and III-IV angina functional classes), CABG is recommended for patients with CI and LVEF ≤35%, lesions of the left anterior descending artery or multi-vessel disease, in order to reduce mortality and hospitalizations for cardiovascular causes [26]. LVD is a strong additional indication in favor of the bypass surgery in the presence of appropriate changes in coronary artery anatomy and clinical symptoms, because it is the category of patients with reduced LVEF where the most convincing evidence of the beneficial effect of revascularization on the survival is obtained [5, 14, 28, 29].

The American recommendations on CABG also indicate that the presence and severity of LVD is one of the clinical factors that influence the choice of the optimal revascularization method. According to the authors, the existing database has some limitations, especially in patients with severe LVD, but the data on CABG efficacy are more relatable than the available information on cardiac stenting. Clinical parameters, such as the anatomy of coronary arteries, the presence of diabetes mellitus or chronic renal disease, as well as the patient’s opinion, are important in choosing the management strategy of patients with IC and LVD, the final decision being taken by consensus of both the interventionist and the cardiac surgeon [5].

In cases of significant decrease in LVEF, the final decision on the utility of CABG may be based on the evaluation of myocardial viability. In particular, the lack of convincing evidence of recurrent ischemia in association with a small area of viable myocardium is considered an argument against surgical treatment. Overall, patient selection criteria for revascularization, depending on the state of myocardial viability, have not yet been clearly defined because of the lack of evidence and the lack of a coherent research methodology. It should also be mentioned that patients with terminal HF may be candidates for heart transplantation.

Revascularization effectiveness criteria

Unlike in the randomized trials, where the effect of revascularization is assessed by “solid” results, in clinical practice, the main criteria for the effectiveness of the intervention are the changes in the heart pump function and the quality of life, primarily determined by clinical symptoms. The increase in LVEF positively influences the evolution and prognosis of the disease [30]. The majority of studies have shown a positive effect of the revascularization on the global heart pump function and local contractility in the functional shunt area of patients with LVEF less than 40-30% [31, 32, 33]. Higher LVEF increase was recorded after myocardial revascularization in patients with poorer initial indices of the left ventricular ejection fraction [34]. In the same time, in patients with initially preserved LVEF, a slight decrease in LVEF was observed in the postoperative period [35]. In the initial study of the authors (n=111), LVEF median 6-12 months after CABG increased from 35% (IQR 30-39%) to 42% (IQR 35-45%) on average – by 18.9% (IQR 5.3-32.4%) [36]. Moreover, in most cases, the increase in LVEF was noticed not immediately, but at the end of the first month after the surgery has been performed. With the extension of the postoperative monitoring period, the LVEF improvement achieved in the first follow-up year does not increase, the LVEF indicator usually reaching “plateau” [37]. Obviously, it is still necessary to study the predictors of positive or negative dynamics of LVEF in patients with coronary artery disease after CABG.

Another sensitive indicator of the revascularization outcome is the reduction of clinical symptoms and the improvement of the quality of life associated with the patients’ health. This aspect of the patients with IC and LVD can be determined not only by LVEF and HF functional class according to NYHA classification, but also by age, gender, and comorbidities. The appropriate selection of patients for surgical revascularization allows us to expect an improvement in post-interventional life quality indicators in the great majority of patients, and this improvement is more evident than that based on medication solely [38]. Coronary artery stenting has a greater positive influence on the quality of life shortly after the intervention, while the CAGB has rather a long-term benefit, which is apparent 6-12 months after surgery.

CONCLUSIONS

Coronary atherosclerosis is, at this moment, the most common cause of LVEF decrease and HF onset. Surgical revascularization may improve the heart pump function, with the condition that there is a sufficient amount of viable myocardium, in patients with ischemic LVD. According to evidence-based medicine, the efficacy of CABG surgery in patients with multi vascular lesions of the coronary bed and LVD has been shown by LVEF correction, progression, and prognosis improvement, compared to medical treatment. Percutaneous intervention is inferior to surgical revascularization in terms of its effect on “solid” outcomes but can provide an improvement in the quality of life of patients with ischemic LVD. The assessment of myocardial viability may give additional information on the utility of CABG in the presence of multi vascular coronary heart disease, which is associated with a severe LVEF decrease.

Declaration of conflicting interests

Nothing to declare.

Authors` contribution

All authors contributed to the elaboration of the manuscript. All authors have read and approved the final version of the manuscript.

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