Q-Waves Associated With Postinfarct Chronic Total Occlusion Arteries Predict Non-Viable Myocardium Even in the Presence of Collaterals

Abstract: Background and Aim. The presence of grade 3 collaterals is known to be associated with viability in the presence of a chronic total occlusion (CTO). However, it is not clear whether this holds true even in patients who had ST-segment elevation myocardial infarction (STEMI). The aim of our study was to look at the viability of myocardium in patients with CTOs in both infarct-related and non-infarct related occluded vessels with grade 3 collaterals. Methods. We prospectively collected consecutive patients with CTOs who had good grade 3 collaterals and studied the viability of the myocardium in the segment perfused by these occluded arteries. Viability was assessed with a positron emission tomography (PET) scan with fluoro-deoxyglucose uptake. Results. A total of 75 patients (60 men and 15 women; age, 61 ± 9 years) were included in the study; of these, 25 patients had a previous MI with Q-waves on the electrocardiogram. All 25 patients (100%) with a previous MI had non-viable myocardium, while those without a history of previous MI had viable myocardium on the PET scan. The overall left ventricular function or regional wall-motion abnormality did not have an influence on the viability. Conclusion. In the presence of previous STEMI, if the infarct-related artery is a CTO,  the myocardium supplied by that vessel is most likely non-viable even in the presence of grade 3 collaterals. 

J INVASIVE CARDIOL 2020;32(8):E213-E215. Epub 2020 July 22.

Key words: chronic total occlusion, collaterals, coronary angiography, myocardial viability

A chronic total occlusions (CTO) is defined as a totally occluded coronary artery with no passage of contrast during coronary angiography (Thrombolysis in Myocardial Infarction grade 0 flow) that has been present for at least 3 months.¹ CTOs account for around one-third of patients undergoing coronary angiography, although the actual incidence depends on the patient population studied.² The incidence of CTOs can be as high as 60% in patients who have undergone previous coronary artery bypass grafting and as low as 10% in unselected populations.¹ There is considerable debate regarding the benefits of trying to open these chronically occluded vessels by percutaneous coronary intervention (PCI), given the higher than usual complication rates with variable success rates and prognostic benefit.³ 

Perhaps the most important factor to determine whether or not a patient should undergo CTO-PCI is viability, as it is clear that an occluded vessel that supplies non-viable myocardium should not be subject to PCI. There are many tests that determine viability, with positron emission tomography (PET) scan and cardiac magnetic resonance imaging (MRI) considered the gold standard. However, access to these tests is often limited at many institutions and involves further exposure to radiation or is unacceptable to the patient. 

One indirect method that might predict viability is the presence of collateral circulation to the distal bed of the occluded artery.⁴ It is safe to assume that if there is absolutely no perfusion, ie, no collaterals supplying the distal vessel, the myocardial bed of that vessel is very unlikely to be viable. The presence of collateral circulation to the distal part of the occluded vessel, however, only represents perfusion but does not imply viability. 

The aim of our study was to assess the value of the presence of collaterals in predicting viability and to determine the factors that affect it. 

Methods

This was a retrospective study where all consecutive adult patients >18 years old who were found to have a CTO on coronary angiography over a 2-year period (2016-2018) were evaluated for inclusion in the study. 

CTO patients were enrolled if they were found to have grade 3 collaterals and only 1 CTO vessel. Collaterals were graded by the degree of filling of the involved vessel beyond the CTO according to the Rentrop⁵ classification: grade 0 = no visible filling; grade 1 = sidebranch filling, but with no dye reaching the epicardial segment; grade 2 = partial epicardial filling; and grade 3 = complete filling of the epicardial segment. We excluded patients with grade 0-2 collaterals. Patients with >1 CTO vessel were not included, as it could affect the viability reporting. We also excluded CTO patients with previous coronary artery bypass grafting. 

All patients had an electrocardiogram (ECG) before coronary angiography, and underwent echocardiography, myocardial perfusion imaging, and PET scan for viability as part of the work-up for consideration of PCI to the CTO vessel. We then compared the results of the viability tests with the clinical features to determine if there were any features that predicted viability in the CTO territory.

The ECG was analyzed for presence of pathological Q-waves. The PET scan at our institution was performed as per standard protocols using fluoro-deoxyglucose (FDG) and a multidetector gamma camera. 

Statistical analysis. Analysis was performed using SPSS, version 22 (SPSS). All continuous variables were expressed as mean ± standard deviation. The mean differences between two groups for continuous variables were compared by the 2-tailed Student’s t-test. Categorical variables were compared by the Chi-square test. A P-value ≤.05 was considered statistically significant.

Results

A total of 75 patients fulfilled criteria for enrollment. There were 60 men and 15 women, with a mean age of 61 ± 9 years. Fifty patients (37 men [74%], mean age, 61.2 ± 9.1 years) were found to have viable myocardium, while 25 patients (23 men [92%]; mean age, 62.3 ± 8.4 years) had non-viable myocardium in the CTO-supplied territories. There was no difference in the age or sex distribution within the two groups. The cardiovascular risk factors, such as diabetes and hypertension, were also equal in the two groups. However, there were slightly more smokers in the non-viable myocardium group than in the viable myocardium group. 

The distribution of the occluded artery was the same in both groups. Most of the patients in both groups were symptomatic (88% in the non-viable group and 94% in the viable group). However, the main symptom in the viable group was chest pain (62% vs 16% in the non-viable group; P<.001) and the main symptom in the non-viable group was breathlessness (80% vs 52% in the viable group; P=.01). The left ventricular ejection fraction was also significantly lower in the non-viable group (35.2 ± 8.4% vs 41.6 ± 15.1% in the viable group; P<.01). 

The most significant difference, however, was the fact that all patients in the non-viable group had a history of previous MI and had Q-waves on the ECG, while those in the viable group did not have a history of previous MI and did not have Q-waves on the ECG. 

Discussion

Assessment of viability is perhaps the most important factor that determines whether or not a patient with a CTO will undergo PCI.⁶ Intervention for CTO is often time consuming, with a slightly higher complication rate and lower success rate compared with non-CTO PCI.⁷ Therefore, given this higher risk, CTO-PCI is only worth undertaking if the benefits are high and there is scope for improvement of either symptoms or prognosis, both of which depend on whether the myocardium supplied by the occluded vessel is viable. 

Our data suggest that even in the presence of grade 3 collaterals, which would give the maximum flow to the myocardial bed of the occluded vessel, if the patient has had a previous MI with presence of Q-waves on the ECG, the myocardium is non-viable. In this scenario, it is not worth wasting resources or time in performing viability studies. On the other hand, if the patient has grade 3 collaterals but no Q-waves on the ECG and no history of prior MI, it is safe to assume that the myocardium is most likely viable. This is in keeping with previous studies, which have shown viability in the presence of grade 3 collaterals in the absence of previous MI.⁴ However, our study is the first to evaluate this in patients with previous MI. 

It is also interesting to note that in our study, patients with non-viable myocardium had a lower left ventricular ejection fraction than those with viable myocardium. In addition, those with non-viable myocardium did not experience chest pain as often as those with viable myocardium, but mainly had breathlessness, which was likely due to the impaired left ventricular function. We could conclude that the absence of chest pain is also a likely indicator of non-viable myocardium. 

Study limitations. One of the main limitations of our study is the small sample size. Despite this, our results are strongly suggestive of the predictors of non-viability. This is a single-center, retrospective study. Prospective studies with a large sample size would be beneficial to conclusively state that prior MI with Q-waves on the ECG preclude viability even in the presence of grade 3 collaterals. 

Conclusion

In patients with a CTO and grade 3 collaterals supplying the distal vessel, the myocardium is most likely to be viable if the patient has not had a previous MI or does not have Q-waves on the ECG. Larger, prospective studies, however, are needed to conclusively state that these patients do not need further viability testing prior to revascularization.

From the Department of Medicine, Sultan Qaboos University Hospital, Muscat, Oman.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript accepted April 9, 2020.

Address for correspondence: Sunil K. Nadar, MD, Department of Medicine, Sultan Qaboos University Hospital, P.O. Box 38, Muscat 123, Oman. Email: sunilnadar@gmail.com

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