Clinical Significance of Collaterals in Chronic Total Occlusions

Collateral circulation develops during the gradual progression of coronary occlusions in order to replace the original artery and supply blood to areas jeopardized by ischemia. However, the relevance of collaterals has remained controversial for many years.

Several works have suggested a rapid regression of collaterals after rechanneling of chronic total coronary occlusions, which could render the patient susceptible to an infarction in case of subsequent coronary occlusion due to restenosis or thrombosis.

However, the rate of infarction is significantly lower than the incidence of reocclusion, which might indicate indirectly that collaterals do not disappear completely and remain recruitable over time.

The clinical implication of this argument is still important because, even in the current generation drug-eluting stent era, the rates of thrombosis for patients with long lesions are significantly higher than the rates for average patients.

Also read: “CTO in patients with acute myocardial infarction increases long term mortality”.

This study seeks to demonstrate how changes in the collateral function and its clinical significance before and after coronary angioplasty compare between patients with acute coronary syndrome and total or nearly total occlusions in the culprit artery. At the same time, it also seeks to compare these outcomes with those of patients who suffer from chronic total occlusion.

The pressure-derived collateral pressure index, myocardial fractional flow reserve (FFRmyo), and coronary fractional flow reserve (FFRcor) at maximum hyperemia induced by intravenous adenosine were evaluated at baseline, immediately after angioplasty, and at one year in 23 patients with acute occlusion and 74 patients with chronic total occlusion.

The FFRmyo and FFRcor were significantly lower, and the pressure index significantly higher, in collateral vessels with chronic total occlusion when compared to collateral vessels with acute occlusion, both at baseline and after angioplasty. This means that collateral circulation exists in patients with acute occlusion, but it is not enough to compensate the flow from the occluded vessel (as opposed to what happens in patients with chronic occlusion, who present a much higher collateral flow).

Also read: “Success in CTOs caused by restenosis lowers cardiac mortality”.

As expected, there were significant increases in FFRmyo and FFRcor after angioplasty. The novelty is that the pressure index in collaterals did not change. This seems to confirm that collaterals remain recruitable after angioplasty, something that was true for both patient groups.

Patients with chronic total occlusion and a high collateral pressure index after angioplasty presented better outcomes only when FFRmyo after angioplasty was low.

With high FFRmyo after angioplasty, the prognosis was not modified by the collateral pressure index. This implies that if the outcome of angioplasty in the occluded artery is good enough to achieve a high FFRmyo, collateral vessel flow does not affect the prognosis. The explanation seems to be simple: In that case, collateral vessels is no longer necessary to supply blood to that myocardial area.

Conclusion

Recruitable coronary collateral flow does not regress completely immediately after angioplasty, both in patients with acute occlusion and with chronic occlusion. Despite good collaterals in patients with chronic total occlusion, aggressive efforts to reduce the ischemic burden might improve their clinical outcome.

Editorial

Even well-developed collaterals may not be sufficient to substitute normal coronary flow. All patients with total occlusion in this study presented collaterals that were good enough so as to prevent myocardial ischemia. However, their myocardial fractional flow reserve (FFRmyo) was below 0.8 in all cases. This suggests that chronic total occlusions imply a substantial ischemic burden (despite the development of good collateral circulation), which would warrant an indication of rechanneling.

Original title: Coronary Collaterals Function and Clinical Outcome Between Patients with Acute and Chronic Total Occlusion.

Reference: Jang Hoon Lee et al. J Am Coll Cardiol Intv 2017;10:585-93.

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