In the name of God Presentation by: Dr. Isa Khaheshi Cardiovascular Research Center, Modarres hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran

Circulation Journal,May 2016 Controversies in Cardiovascular Medicine

Should chronic total occlusions (CTOs) of coronary arteries be revascularized by coronary artery bypass graft (CABG)surgery? Yet CTOs are common and are more commonly revascularized by CABG than by percutaneous coronary intervention (PCI).

CTOs are common findings on coronary arteriogram. Although there has been extensive literature on the subject of PCI for CTOs, there is less literature on CABG for CTOs.

CTOs were defined as 100% coronary occlusion present for at least 3 months.

Christofferson et al studied 8004 consecutive patients undergoing diagnostic catheterization at a single institution between 1990 and 2000. Among patients with significant coronary artery disease and a CTO, 11% were treated with PCI, 40% with CABG, and 49% with medical therapy. In comparison, among patients with significant coronary artery disease but no CTO,36% were treated with PCI, 28% with CABG, and 35% medically (P<0.0001). In a multivariable analysis, the presence of a CTO was associated with reduced odds of undergoing PCI

Multivessel disease, not a CTO, was found on multivariable analysis to be associated with the increased choice of CABG. However, multivessel disease and CTO are collinear, and it difficult to know which is the main driver in decision making.

Canadian Multicenter Chronic Total Occlusions Registry Almost half of the patients with CTOs were treated medically, and 25% underwent CABG PCI was performed in 30%, with 70% success rate.

Although more patients with CTOs have historically been treated with CABG than PCI, technical advancements in PCI of CTOs may be expected to drive more patients with CTOs to being treated with PCI.

The Need for Viability in the Subtended Zone a prerequisite for revascularizing CTOs is that the myocardium in the subtended zone be viable. Data show improved survival after revascularization in patients with left ventricular dysfunction and viable myocardium but not in the absence of viability. However, randomized trial data have not been shown to support the importance of viability testing.

Assessing viability is difficult and uncertain Assessing viability is difficult and uncertain. If left ventricular function is absolutely normal, then viability is essentially certain. However, quite often, the wall motion will not be normal , in which case the wall motion abnormalities will most likely include the CTO subtended zone.

Sometimes a transthoracic echocardiogram will show the zone to be akinetic and thin, consistent with a myocardial infarction in this zone. The wall there will most likely be scar tissue. In such a case, return of function with revascularization seems unlikely.

However, there are patients in whom wall motion is not normal but in whom the myocardium has not thinned out. In such cases, there may be subendocardial scar with normal tissue above it extending to the epicardium. The subendocardial scar, which cannot contract, may pose a mechanical limitation on the amount of return of function that can be expected

There is literature on assessing viability with thallium-201, technetium-99m sestamibi, positron emission tomography, dobutamine stress echocardiography, and myocardial resonance imaging(MRI).

MRI with late gadolinium enhancement is generally recognized as the gold standard for assessing the presence of scar in the myocardium. MRI correlates well with positron emission tomography for areas of scar, finding scar somewhat more frequently and with higher spatial resolution.

However, the routine use of MRI to guide revascularization is limited by expense and availability. It is not part of routine clinical decision making to assess viability with either positron emission tomography or MRI before revascularization.

Although there is difficulty in establishing viability and potential return of function when revascularization of CTOs is being considered, assessment of viability should be considered before surgical revascularization.

What are the indications for revascularizing CTOs The possible reasons are to relieve angina, to prolong life, and perhaps to relieve or prevent heart failure. Relief of angina seems relatively straightforward. If the zone subtended by the CTO is viable but ischemic at rest or with exercise, it could cause angina.

This might well be relieved with revascularization, consistent with the literature that revascularization relieves angina. Angina relief after PCI for CTOs has been studied, but the literature on angina relief after CABG for CTOs is limited.

The decision to revascularize with CABG instead of PCI is currently being made despite considerable uncertainty. There are limited clinical data comparing CABG with PCI for CTOs. The decision will be driven by the patient’s overall condition and the angiographic findings, particularly the suitability of the occlusion for PCI and the suitability of the downstream vessel for surgery.

CTOs and Complete Revascularization CABG for CTOs will often be part of a strategy of offering complete revascularization. Although patients who have CABG with complete revascularization have better outcomes than patients without revascularization, a few limitations should be noted.

First, there is no universally accepted definition of complete revascularization. Thus, complete revascularization may not require bypassing smaller vessels or vessels where the subtended zone is not viable. No randomized trial has compared patients with complete and incomplete CABG. Indeed, there are only observational comparisons.

Literature on CABG for CTOs

Can CABG for CTOs Be Justified? The literature reveals that CTOs are more often treated with CABG than with PCI. However, the literature on surgical outcome of CTOs is quite limited. CABG is a treatment for angina, and although limited, the published data suggest that CABG for CTOs reduces angina. we do not know whether the CTO was the primary driver or a contributing factor.

Thus, it would seem that the patients with multivessel disease in whom CTOs are bypassed as part of CABG seeking complete revascularization would be the most appropriate.

When the CTO is the primary driver in multivessel disease,CABG is not as well justified. Despite excellent outcomes for minimally invasive surgery, isolated CABG for an isolated CTO of the LAD cannot be justified on the basis of preventing future events compared with either medical therapy or PCI.

Appropriate Use Criteria for CTO Revascularization in Patients Without Previous CABG These recommendations cover only isolated single-vessel CTOs and make no recommendation between PCI and CABG.

As with other non–acute coronary syndrome patients, those with more severe symptoms on antianginal therapy and with greater evidence of ischemia on noninvasive testing are considered more appropriate for revascularization.

At present, in the absence of adequate clinical trial data, anginal symptoms, evidence of ischemia in viable myocardium in the subtended zone, angiographic appropriateness, and an overall strategy for complete revascularization must be used to consider which patients should be treated with CABG for CTOs.

Patients not suitable for PCI on angiographic grounds, those with both CTO and non-CTO lesions in multiple vessels, patients with intolerable angina, and those with evidence of viability in the zone subtended by the CTO would be most suitable for surgical revascularization.

Angina would be best evaluated with a validated tool such as the Seattle Angina Questionnaire. The suitability of patients with a mix of these 3 characteristics is shown in Table 3, scaled from 1 to 4 stars corresponding to lowest to highest suitability for CABG. This simple set of recommendations can be considered only preliminary pending better outcomes data.

The ability to revascularize CTOs with PCI has improved dramatically in recent years. The use of CTO-PCI is spreading quickly worldwide across CABG anatomic categories such as LMS disease, LAD disease, and MVD disease

In the absence of randomized trials, careful observational comparative-effectiveness studies are needed. What should not be acceptable is to indefinitely continue performing CABG for CTOs routinely in the absence of data suggesting that such procedures lead to better outcomes, economic and clinical, compared with other therapeutic options.

On the basis of the available evidence, we strongly suggest that all patients with CTO be carefully discussed at multidisciplinary heart team meetings that include a balanced professional representation of surgeons and interventional cardiologists, Bearing in mind that at this stage for CTO patients with LMS disease, LAD disease, and MVD, CTO-PCI may have a role only for a certain sick populations deemed not to be suitable for CABG.

Thanks a lot for your attention