Quantitatively assessed coronary collateral circulation and restenosis following percutaneous revascularization

Coronary steal: how many thieves are out there?

The colorful term "coronary steal" arose in 1967 to parallel "subclavian steal" coined in an anonymous 1961 editorial. In both instances, the word "steal" described flow reversal in the setting of an interconnected but abnormal vascular network-in one case a left subclavian stenosis proximal to the origin of the vertebral artery and in the other case a coronary fistula. Over time, the term has morphed to include a larger set of pathophysiology without explicit flow reversal but rather with a decrease in stress flow due to other mechanisms. This review aims to shed light on this phenomenon from a clinical and a pathophysiological perspective, detailing the anatomical and physiological conditions that allow so-called steal to appear and offering treatment options for six distinct scenarios.

Association of Palmar Arch Collateral Function and Radial Artery Occlusion After Transradial Access

The prevalence and implications of radial artery occlusion (RAO) after transradial catheterization are an intensely discussed topic, resulting in numerous preventive strategies such as adjusted anticoagulation, residual-patency hemostasis, or distal puncture site. The present study aimed at assessing an association of palmar arch, in particular radial artery collateral function and RAO after transradial access (TRA) catheterization. Radial artery collateral function was determined using radial artery pressure signals in the nonobstructed vessel and during brief manual occlusion of the more proximal radial artery. Collateral flow index, the ratio of mean occlusive divided by mean nonocclusive arterial blood pressure, both subtracted by central venous pressure, was determined during manual RAO (radial artery collateral flow index [CFI_rad]). The presence or absence of RAO was determined by Doppler ultrasound at least 3 months after TRA. A total of 630 patients with TRA coronary angiography underwent palmar arch, that is, radial and radial plus ulnar artery collateral function assessment. CFI_rad was equal to 0.808 ± 0.144 (95% confidence interval 0.797 to 0.819). A total of 200 patients underwent Doppler ultrasound examination of their forearm arterial circulation 301 ± 140 days after TRA. Eight (4%) patients showed signs of RAO, 4 of whom (2%) had a complete RAO and 4 (2%) a stenosis above 30%. Patients with RAO showed a higher CFI_rad than those without RAO: 0.900 ± 0.074 versus 0.801 ± 0.154 (p = 0.006). In conclusion, complete RAO as determined by Doppler ultrasound later than 3 months after TRA is rare (2%). In the long run, RAO appears to be related to a very well-developed radial artery collateral function.

Impact of coronary collateral circulation on angiographic in-stent restenosis in patients with stable coronary artery disease and chronic total occlusion

OBJECTIVE

This study aimed to evaluate the relationship between coronary collateralization and in-stent restenosis (ISR) in stable coronary artery disease patients with chronic total occlusion (CTO) after percutaneous coronary intervention (PCI) with drug-eluting stent (DES) implantation.

METHODS

The degree of coronary collaterals supplying the distal aspect of a total occlusion from the contra-lateral vessel was graded according to Rentrop classification in 216 patients with stable angina undergoing successful DES based PCI for CTO. Univariable and multivariable logistic regression analyses were performed to assess the potential factors related to angiographic ISR during follow-up.

RESULTS

Despite similar number of diseased coronary arteries, good collateralization (Rentrop score 2 or 3) was more frequently associated with right coronary artery occlusion (60%), whereas poor collaterals (Rentrop score 0 or 1) occurred more often in left anterior descending artery occlusion (40%). Despite similar number of CTO intervened, stent length was longer in patients with good collateralization (59±27mm vs 47±23mm, p=0.001). At mean 18months, the rate of ISR did not significantly differ between patients with good collateralization and those with poor collateralization (12.7% vs 20.2%, p=0.148). At multivariable analysis, age (OR 1.058, 95%CI 1.015-1.104, p=0.008), history of diabetes mellitus (OR 2.382, 95%CI 1.109-5.116, p=0.026) and reference CTO vessel diameter (OR 0.219, 95% CI 0.051-0.951, p=0.043) were independent risk factors for ISR while Rentrop collateral grade (OR 0.795, 95% CI 0.365-1.732, p=0.414) was not associated with ISR.

CONCLUSIONS

The occurrence of ISR after successful DES based PCI for CTO may be not influenced by coronary collateralization.

Pathophysiology of coronary collaterals

While the existence of structural adaptation of coronary anastomoses is undisputed, the potential of coronary collaterals to be capable of functional adaptation has been questioned. For many years, collateral vessels were thought to be rigid tubes allowing only limited blood flow governed by the pressure gradient across them. This concept was consistent with the notion that although collaterals could provide adequate blood flow to maintain resting levels, they would be unable to increase blood flow sufficiently in situations of increased myocardial oxygen demand.

However, more recent studies have demonstrated the capability of the collateral circulation to deliver sufficient blood flow even during exertion or pharmacologic stress. Moreover, it has been shown that increases in collateral flow could be attributed directly to collateral vasomotion.

This review summarizes the pathophysiology of the coronary collateral circulation, ie the functional adapation of coronary collaterals to acute alterations in the coronary circulation.

Coronary collaterals and risk for restenosis after percutaneous coronary interventions: a meta-analysis

BACKGROUND

The benefit of the coronary collateral circulation (natural bypass network) on survival is well established. However, data derived from smaller studies indicates that coronary collaterals may increase the risk for restenosis after percutaneous coronary interventions. The purpose of this systematic review and meta-analysis of observational studies was to explore the impact of the collateral circulation on the risk for restenosis.

METHODS

We searched the MEDLINE, EMBASE and ISI Web of Science databases (2001 to 15 July 2011). Random effects models were used to calculate summary risk ratios (RR) for restenosis. The primary endpoint was angiographic restenosis > 50%.

RESULTS

A total of 7 studies enrolling 1,425 subjects were integrated in this analysis. On average across studies, the presence of a good collateralization was predictive for restenosis (risk ratio (RR) 1.40 (95% CI 1.09 to 1.80); P = 0.009). This risk ratio was consistent in the subgroup analyses where collateralization was assessed with intracoronary pressure measurements (RR 1.37 (95% CI 1.03 to 1.83); P = 0.038) versus visual assessment (RR 1.41 (95% CI 1.00 to 1.99); P = 0.049). For the subgroup of patients with stable coronary artery disease (CAD), the RR for restenosis with 'good collaterals' was 1.64 (95% CI 1.14 to 2.35) compared to 'poor collaterals' (P = 0.008). For patients with acute myocardial infarction, however, the RR for restenosis with 'good collateralization' was only 1.23 (95% CI 0.89 to 1.69); P = 0.212.

CONCLUSIONS

The risk of restenosis after percutaneous coronary intervention (PCI) is increased in patients with good coronary collateralization. Assessment of the coronary collateral circulation before PCI may be useful for risk stratification and for the choice of antiproliferative measures (drug-eluting stent instead bare-metal stent, cilostazol).

The human coronary collateral circulation

BACKGROUND

Coronary collaterals are an alternative source of blood supply to myocardium jeopardized by ischaemia. Well-developed coronary collateral arteries in patients with coronary artery disease (CAD) mitigate myocardial infarcts and improve survival.

METHODS AND RESULTS

Collateral arteries preventing myocardial ischaemia during brief vascular occlusion are present in 1/3 of patients with CAD. Among individuals without relevant coronary stenoses, there are preformed collateral arteries preventing myocardial ischaemia in 20-25%. Collateral flow sufficient to prevent myocardial ischaemia during coronary occlusion amounts to double dagger25% of the normal flow through the open vessel. Myocardial infarct size, the most important prognostic determinant after such an event, is the product of coronary artery occlusion time, area at risk for infarction and the inverse of collateral supply. Coronary collateral flow can be assessed only during vascular occlusion of the collateral-receiving artery. The gold standard for coronary collateral assessment is the measurement of intracoronary occlusive pressure- or velocity-derived collateral flow index expressing collateral as a fraction of flow during vessel patency. Approximately one of five patients with CAD cannot be revascularized by percutaneous coronary intervention or coronary artery bypass grafting. Therapeutic promotion of collateral growth is a valuable treatment strategy in those patients.

CONCLUSIONS

Promotion of collateral growth should aim at inducing the development of large conductive collateral arteries (i.e. arteriogenesis) and not so much the sprouting of capillary like vessels (i.e. angiogenesis). Large conductive collateral arteries appear to be effectively promoted via the activation of monocytes/macrophages by means of granulocyte-colony stimulating factor or of augmenting coronary flow velocity.

Influence of coronary collateral flow on coronary diagnostic parameters: an in vitro study

Functional severity of coronary stenosis is often assessed using diagnostic parameters. These parameters are evaluated from the combined pressure and/or flow measurements taken at the site of the stenosis. However, when there are functional collaterals operating downstream to the stenosis, the coronary flow-rate increases, and the pressure in the stenosed artery is altered. This effect of downstream collaterals on different diagnostic parameters is studied using a physiological representative in vitro coronary flow-loop. The three diagnostic parameters tested are fractional flow reserve (FFR), lesion flow coefficient (LFC), and pressure drop coefficient (CDP). The latter two were discussed in recent publications by our group (Banerjee et al., 2007, 2008, 2009). They are evaluated for three different severities of stenosis and tested for possible misinterpretation in the presence of variable collateral flows. Pressure and flow are measured with and without downstream collaterals. The diagnostic parameters are then calculated from these readings. In the case of intermediate stenosis (80% area blockage), FFR and LFC increased from 0.74 to 0.77 and 0.58 to 0.62, respectively, for no collateral to fully developed collateral flow. Also, CDP decreased from 47 to 42 for no collateral to fully developed collateral flow. These changes in diagnostic parameters might lead to erroneous postponement of coronary intervention. Thus, variability in diagnostic parameters for the same stenosis might lead to misinterpretation of stenosis severity in the presence of operating downstream collaterals.

Impact of collateral flow on myocardial reperfusion and infarct size in patients undergoing primary angioplasty for acute myocardial infarction

BACKGROUND

The prognostic impact of baseline collateral flow of the infarct-related artery (IRA) in patients undergoing primary percutaneous coronary intervention (PCI) remains controversial. We sought to examine the impact of baseline collateral flow to the IRA on reperfusion success, infarct size, and clinical outcomes in patients undergoing primary PCI for acute myocardial infarction (AMI).

METHODS AND RESULTS

Acute procedural, 30-day, and 6-month clinical outcomes were assessed after primary PCI among patients enrolled in the EMERALD trial (n = 501 with AMI within 6 hours of onset). Patients with collateral flow to the IRA (Rentrop grade 2 or 3) more commonly had prior stable angina, less commonly had failed thrombolysis and left anterior descending artery occlusion, and presented with less ST-segment elevation. Myocardial reperfusion assessed by ST-segment recovery and myocardial blush was similar in patients with and without baseline collateral flow to the IRA. Infarct size (assessed by technetium Tc 99m sestamibi) was similar among patients with and without baseline collateral flow in anterior infarction (mean 28.5% vs 31.2%, respectively; P = .59) and nonanterior infarction (12.5% vs 12.1%, respectively; P = .81). There were no differences in the rates of major adverse cardiac events at 30 days or 6 months according to baseline IRA collateral flow.

CONCLUSIONS

Among patients undergoing primary PCI for AMI within 6 hours of symptom onset, we found no significant relationship between baseline collateral flow and either reperfusion success, infarct size, or subsequent clinical outcomes.

Clinical effectiveness of bare-metal stenting compared with balloon angioplasty in total coronary occlusions: insights from a systematic overview of randomized trials in light of the drug-eluting stent era

BACKGROUND

We sought to compare, using meta-analytic techniques, bare-metal stent versus balloon angioplasty in the percutaneous treatment of total coronary occlusions by means of a quantitative systematic review and to indicate new avenues for future treatments.

METHODS

MEDLINE and CENTRAL were searched. Inclusion criteria were random allocation, prospective comparison, and intention to treat. Random-effect odds ratios (ORs) with 95% confidence intervals (CIs) for death, myocardial infarction (MI), repeated revascularization, major adverse cardiac events (MACE), and angiographic restenosis and reocclusion were computed.

RESULTS

Nine trials (1409 patients) were included. Death rate was not different in the 2 groups, 0.4% after stenting versus 0.7% after balloon angioplasty (OR 0.72, 95% CI 0.21-2.50). MI rate was significantly increased after stenting (6.7% vs 3.4%, OR 2.06, 95% CI 1.22-3.46), mainly because of a higher rate of periprocedural non-Q-wave MI. By contrast, the risk of repeated revascularization was significantly reduced by stenting (17% vs 32%, OR 0.41, 95% CI 0.31-0.53). This yielded to an overall reduction in the rate of MACE after stenting (23.2% vs 35.4%, OR 0.49, 95% CI 0.36-0.68). Angiographic restenosis and reocclusion were also decreased by stent (41.1% vs 60.9%, OR 0.36, 95% CI 0.23-0.57; 6.8% vs 16%, OR 0.36, 95% CI 0.22-0.59, respectively).

CONCLUSIONS

In total coronary occlusions, stenting yields an important benefit over balloon angioplasty in reduction of MACE, repeated revascularizations, and angiographic restenosis and reocclusion. However, these events remain frequent. Moreover, the finding of an increased rate of periprocedural minor myocardial damage after stenting casts caution. New strategies aimed to reduce the need of repeated revascularizations and periprocedural MIs should be further investigated.

Does a well developed collateral circulation predispose to restenosis after percutaneous coronary intervention? An intravascular ultrasound study

OBJECTIVE

To evaluate whether a well developed collateral circulation predisposes to restenosis after percutaneous coronary intervention (PCI).

DESIGN

Prospective observational study.

PATIENTS AND SETTING

58 patients undergoing elective single vessel PCI in a tertiary referral interventional cardiac unit in the UK.

METHODS

Collateral flow index (CFI) was calculated as (Pw-Pv)/(Pa-Pv), where Pa, Pw, and Pv are aortic, coronary wedge, and right atrial pressures during maximum hyperaemia. Collateral supply was considered poor (CFI < 0.25) or good (CFI > or = 0.25).

MAIN OUTCOME MEASURES

In-stent restenosis six months after PCI, classified as neointimal volume > or = 25% stent volume on intravascular ultrasound (IVUS), or minimum lumen area < or = 50% stent area on IVUS, or minimum lumen diameter < or = 50% reference vessel diameter on quantitative coronary angiography.

RESULTS

Patients with good collaterals had more severe coronary stenoses at baseline (90 (11)% v 75 (16)%, p < 0.001). Restenosis rates were similar in poor and good collateral groups (35% v 43%, p = 0.76 for diameter restenosis, 27% v 45%, p = 0.34 for area restenosis, and 23% v 24%, p = 0.84 for volumetric restenosis). CFI was not correlated with diameter, area, or volumetric restenosis (r2 < 0.1 for each). By multivariate analysis, stent diameter, stent length, > 10% residual stenosis, and smoking history were predictive of restenosis.

CONCLUSION

A well developed collateral circulation does not predict an increased risk of restenosis after PCI.

Impact of coronary collaterals on outcome following percutaneous coronary intervention (from the National Heart, Lung, and Blood Institute Dynamic Registry)

Coronary collateral circulation is beneficial in patients with coronary artery disease, but controversy still exists regarding the association between angiographic collaterals and outcome after percutaneous coronary intervention (PCI). We compared the baseline characteristics and cumulative 1-year event rates of consecutive patients undergoing PCI by target vessel collateral status-no angiographic evidence of collateral circulation (NC; n = 5051), treated artery supplied collaterals (SC; n = 239), and treated artery received collaterals (RC; n = 893)-using the National Heart, Lung, and Blood Institute Dynamic Registry. Patients in the SC group were older and had more previous coronary bypass surgery, myocardial infarction, co-morbid illness, and heart failure than the NC and RC groups and had less often undergone revascularization for acute myocardial infarction (p <0.01 for all). The total angiographic PCI success was comparable for the SC and NC groups but higher than for the RC group (94.1% vs 94.4% vs 83.9%, respectively; p <0.001). Overall stent use was 77.5% and was highest in the SC group (82.4%, p <0.001). At 1 year, significant differences in outcome were observed by collateral status. Compared with the NC group, patients with PCI of a SC artery had higher adjusted mortality (relative risk [RR] 1.95, 95% confidence interval [CI] 1.27 to 3.01, p = 0.002) and death/myocardial infarction (RR 1.75, 95% CI 1.26 to 2.45, p <0.001) rates. Patients with PCI of a RC vessel, conversely, had lower adjusted death/myocardial infarction (RR 0.72, 95% CI 0.54 to 0.96, p = 0.02) and repeat revascularization (RR 0.73, 95% CI 0.59 to 0.91, p = 0.005) rates. In conclusion, our results suggest that PCI on collateralized vessels is warranted, but that patients with PCI in arteries that supply collaterals are a high-risk group that may benefit from closer follow-up and complete revascularization.

Determinants of target vessel failure in chronic total coronary occlusions after stent implantation. The influence of collateral function and coronary hemodynamics

OBJECTIVES

The goal of this study was to assess the influence of collateral function, coronary hemodynamics, and the angiographic result on the risk of target vessel failure (TVF) after recanalization of a chronic total coronary occlusion (CTO).

BACKGROUND

Collaterals may have an adverse effect on TVF.

METHODS

In 111 consecutive patients, a CTO (duration >2 weeks) was successfully recanalized with stent implantation. Collateral function was assessed by intracoronary Doppler flow velocity and pressure recordings distal to the occlusion. Baseline collateral function was determined before the first balloon inflation, and recruitable collateral function after stenting during a balloon reocclusion. Finally, the coronary flow velocity reserve (CFVR) and the fractional flow reserve (FFR) were measured.

RESULTS

Angiographic follow-up after 5 +/- 4 months in 106 patients showed a reocclusion in 17% and a restenosis in 36%. The major determinants of TVF were the stent length (p < 0.01) and number of implanted stents (p < 0.01). No difference was observed in baseline or recruitable collateral function between patients with and without TVF; 52% of patients had a CFVR >or= 2.0, and only 18% a CFVR >or=2.5 after percutaneous transluminal coronary angioplasty, but neither cutoff-value predicted TVF. A low FFR discriminated patients with reocclusion (0.81 +/- 07 vs. 0.86 +/- 08, p < 0.05) but not with restenosis (0.87 +/- 0.06).

CONCLUSIONS

This study showed that there is no relation between a well-developed collateral supply and the risk of TVF in recanalized CTOs. This was rather determined by the stented segment length. There was also no adverse effect of the frequently observed impaired CFVR on TVF, whereas a low FFR was associated with a higher risk of reocclusion.

Physiologically assessed coronary collateral flow and adverse cardiac ischemic events: a follow-up study in 403 patients with coronary artery disease

OBJECTIVES

We sought to evaluate whether coronary collateral flow is clinically relevant for future cardiac ischemic events.

BACKGROUND

The link between good collateral supply related to less myocardial damage and fewer cardiac events has not been established prospectively beyond doubt.

METHODS

In 403 patients with stable angina pectoris undergoing percutaneous transluminal coronary angioplasty (PTCA) and quantitative collateral assessment, the occurrence of major adverse cardiac events ([MACE] cardiac death, myocardial infarction, unstable angina pectoris) and stable angina pectoris was monitored during follow-up. Collateral flow index (CFI) was determined using intracoronary pressure or Doppler guidewires. Mean aortic ([P(ao)] mm Hg) and distal coronary artery occlusive pressure ([P(occl)] mm Hg) during balloon angioplasty (PTCA), or distal coronary flow velocity time integral during ([V(occl)] cm) and after ([V(ø-occl)] cm) PTCA were measured continuously. Pressure-derived CFI was calculated as follows: (P(occl) - 5)/(P(ao) - 5). Doppler-derived CFI: V(occl)/V(ø-occl). Patients were subdivided into a group with well (CFI > or = 0.25) and poorly developed collaterals (CFI < 0.25).

RESULTS

Average follow-up was 94 +/- 56 (15 to 202) weeks. There were 134 patients with CFI >or =0.25 (61 +/- 11 years) and 269 with CFI <0.25 (61 +/- 10 years). The overall cardiac ischemic event rate (MACE and stable angina pectoris) during follow-up was 23% in patients with CFI > or =0.25 and 20% in patients with CFI <0.25 (p = NS). However, only 2.2% of patients with good collateral flow suffered a major cardiac ischemic event, compared with 9.0% among patients with poorly developed collaterals (p = 0.01). The incidence of stable angina pectoris was significantly higher in patients with well developed collaterals than in those with poorly developed collaterals (21% vs. 12%; p = 0.01).

CONCLUSIONS

In this relatively large population with chronic stable coronary artery disease undergoing quantitative collateral measurement, the beneficial impact of well developed collateral vessels on the occurrence of future major cardiac ischemic events is clearly demonstrated.

Influence of coronary collateral flow on restenosis following primary angioplasty for acute myocardial infarction

We investigated the influence of collateral flow on restenosis in 156 consecutive acute myocardial infarction (AMI) patients treated with primary angioplasty within 12 hr of symptom onset. Collateral flow was quantitatively assessed using the pressure-derived fractional collateral flow (PDCF) index. Follow-up angiography was performed at 6 months. The patients were classified into two groups according to the PDCF index: group I (PDCF index > 24%; n = 55) with good collaterals and group II (PDCF index < or = 24%; n = 101) with poor collaterals. Baseline characteristics were similar between the two groups, with the exception of peak levels of creatine kinase, angiographic collaterals, and TIMI flow 3 after intervention. The binary restenosis rate was 31.8% in group I and 32.9% in group II (P = NS). Use of the stents was the only independent predictor of binary restenosis. In conclusions, well-developed collaterals measured by PDCF may not predict restenosis following primary angioplasty for AMI.

Washout collaterometry: a new method of assessing collaterals using angiographic contrast clearance during coronary occlusion

OBJECTIVE

To investigate the hypothesis that the time to washout of radiographic contrast medium trapped distal to an occluded collateral receiving vessel is inversely related to collateral flow, and that this provides an accurate method for characterising coronary collaterals.

METHODS

An intracoronary pressure derived collateral flow index was determined in 54 patients undergoing percutaneous transluminal coronary balloon angioplasty (PTCA). The study group was subdivided according to whether the collateral vessels were sufficient (n = 17) or insufficient (n = 37) to prevent ECG signs of myocardial ischaemia during PTCA. Washout collaterometry-an angiographic washout method-was carried out simultaneously; after injection of radiographic contrast medium into the collateral receiving vessel followed immediately by vascular occlusion, the number of heart beats was counted until approximately half the length of the epicardial vessel was cleared of contrast.

RESULTS

The collateral flow index was higher (0.28 (0.09) v 0.12 (0.07); p < 0.0001) and the contrast washout time shorter (8.0 (2.9) v 17.5 (6.7) heart beats; p < 0.0001) in patients with sufficient versus insufficient collaterals. There was an inverse correlation between contrast washout time and collateral flow index (r = 0.72, p < 0.0001). Washout of contrast distal to the occluded vessel within 11 heart beats correctly determined sufficient and insufficient collaterals with 88% sensitivity and 81% specificity.

CONCLUSIONS

Washout collaterometry is a new radiographic contrast washout method based on the inverse relation between collateral flow and the time to clearance of radiographic dye injected into the ipsilateral vessel during PTCA. It appears to be an accurate method of characterising coronary collateral vessels.

Influence on collateral flow of recanalising chronic total coronary occlusions: a case-control study

OBJECTIVE

To assess the effect of recanalisation on collateral flow in a case-control study in patients with and without chronic total coronary occlusions.

DESIGN

In 54 patients undergoing percutaneous transluminal coronary angioplasty (PTCA) (mean (SD) age 61 (6) years), coronary collateral flow was measured by intracoronary pressure or Doppler guide wires at the end of repeated balloon occlusions. Coronary collateral flow index (collateral flow relative to normal antegrade flow) during the first two balloon inflations in 27 patients with a chronic total occlusion (occlusion group) was compared with that of 27 patients matched for age, sex, and collateral flow index at the first occlusion and with a coronary artery diameter stenosis </= 80% (stenosis group).

RESULTS

Following revascularisation, collateral flow index decreased in 17 of the patients in the occlusion group (63%) and in eight of the patients in the stenosis group (30%) (p = 0.03 between groups). The overall change of collateral flow index between the first and the second balloon occlusion was -0.04 (0.01) in the occlusion group (p = 0.07 for paired comparison; from 0.29 (0.17) to 0.25 (0.14)), and +0.02 (0.06) in the stenosis group (p = 0.06 for paired comparison; from 0.27 (0.13) to 0.30 (0.15)). The trend to collateral enhancement in the stenosis group differed significantly from the occlusion group (p = 0.01).

CONCLUSIONS

While repeated coronary balloon occlusions induce collateral recruitment in the majority of patients with moderate stenoses, recanalisation of chronic total coronary occlusions is more often associated with collateral flow reduction. A later decrease in collateral flow by involution of collateral channels cannot be excluded by this study but has not been reported so far.