Comparison of collateral vascular responses in the donor and recipient coronary artery during transient coronary occlusion assessed by intracoronary blood flow velocity analysis in patients

Applicability and Interpretation of Coronary Physiology in the Setting of a Chronic Total Occlusion

Concurrent coronary artery disease in a vessel remote from a chronic total occlusion (CTO) is common and presents a management dilemma. While the use of adjunctive coronary physiology to guide revascularization is now commonplace in the catheterization laboratory, the presence of a CTO provides a unique and specific situation whereby the physiological assessment is more complex and relies on theoretical assumptions. Broadly, the physiological assessment of a CTO relies on assessing the function and regression of collaterals, the assessment of the microcirculation, the impact of collateral steal as well as assessing the severity of a lesion in the donor vessel (the vessel supplying the majority of collaterals to the CTO). Recent studies have shown that physiological assessment of the donor vessel in the setting of a CTO may overestimate the severity of stenosis, and that after revascularization of a CTO, the index of ischemia may increase, potentially altering the need for revascularization. In this review article, we present the current literature on physiological assessment of patients with a CTO, management recommendations and identify areas for ongoing research.

Angiogenic gene therapy for refractory angina

INTRODUCTION

Stimulation of coronary collateral vessel growth by therapeutic angiogenesis (TA) offers an alternative treatment option for patients with refractory angina. Several TA modalities, including delivery to the heart of angiogenic growth factors (proteins or genes) and cells have been tested in clinical trials in the past two decades, but so far none of them resulted in significant therapeutic efficacy in large scale studies. This review attempts to identify the main obstacles hindering clinical success and recommends measures to overcome them in the future.

AREAS COVERED

After stating the medical need and rational for TA, and listing and briefly discussing past and current TA clinical trials, three main areas of obstacles are described: conceptual questions, technical limitations and clinical design uncertainties. Based on scientific and technical advances and lessons learned in past clinical trials, potential solutions to overcome some of these obstacles are proposed.

EXPERT OPINION

Several success criteria are identified, which apply to any TA approach of choice. It is emphasized, that each of these criteria needs to be met in future clinical trials to have a chance of therapeutic success.

Mechanistic, technical, and clinical perspectives in therapeutic stimulation of coronary collateral development by angiogenic growth factors

Stimulation of collateral vessel development in the heart by angiogenic growth factor therapy has been tested in animals and humans for almost two decades. Discordance between the outcome of preclinical studies and clinical trials pointed to the difficulties of translation from animal models to patients. Lessons learned in this process identified specific mechanistic, technical, and clinical hurdles, which need to be overcome. This review summarizes current understanding of the mechanisms leading to the establishment of a functional coronary collateral network and the biological processes growth factor therapies should stimulate even under conditions of impaired natural adaptive vascular response. Vector delivery methods are recommended to maximize angiogenic gene therapy efficiency and reduce side effects. Optimization of clinical trial design should include the choice of clinical end points which provide mechanistic proof-of-concept and also reflect clinical benefits (e.g., surrogates to assess increased collateral flow reserve, such as myocardial perfusion imaging). Guidelines are proposed to select patients who may respond to the therapy with high(er) probability. Both short and longer term strategies are outlined which may help to make therapeutic angiogenesis (TA) work in the future.

Influence of oxidative stress on the development of collateral circulation in total coronary occlusions

OBJECTIVES

The purpose of this study was to investigate whether the levels of total antioxidant capacity (TAC), total peroxide and oxidative stress index (OSI) are associated with the development of collaterals in total coronary occlusions.

DESIGN AND METHODS

Our study group contained 176 consecutive men patients with single-vessel TCO, 94 of whom had poorly developed coronary collateral, while 82 had well-developed coronary collateral. TAC and total peroxide concentration were measured of plasma. The ratio of TAC to total peroxide was accepted as an indicator of oxidative stress.

RESULTS

The values of total peroxide and OSI in the Group I were significantly lower than that in Group II (p<0.001, for both). TAC levels were significantly higher in patients with poorly developed collaterals than in well-developed collateral group (p<0.001). OSI values were also significantly different among the Rentrop class-0, -1, -2 and -3 (ANOVA p<0.001). We found significant correlations between collaterals score and TAC, total peroxide and OSI levels (p<0.001 for all). In multiple linear regression analysis, total peroxide and OSI were independent predictors of collaterals score (p=0.006 and p<0.001 respectively).

CONCLUSION

This study clearly demonstrates that the level of OSI is independently and positively associated with the presence of collateral circulation in total coronary occlusion patients.

Coronary collaterals during single-vessel coronary angioplasty: effects of nitroglycerin

BACKGROUND

Although the protective role of collaterals in coronary artery disease (CAD) is well known, the influence of drugs on collateral function remains controversial.

HYPOTHESIS

We aimed to investigate prospectively the prevalence of spontaneously visible and recruitable coronary collaterals in consecutive patients with single-vessel CAD and the effect of systemic administration of nitroglycerin on these types of collaterals during percutaneous transluminal coronary angioplasty (PTCA).

METHODS

Ipsi- and contralateral coronary artery contrast injections were performed before and during PTCA. Simultaneously with balloon occlusion, we measured coronary artery occlusion pressure via the balloon catheter. All measurements were repeated after administration of 0.5 mg of nitroglycerin intravenously.

RESULTS

Of 101 consecutive patients, 24% had spontaneously visible and 30% had recruitable collaterals. Contralateral collaterals were five times more frequent than ipsilateral collaterals. Presence of collaterals was highly associated with the degree of coronary stenosis. Coronary occlusion pressure was higher in patients with than in those without collaterals. Collaterals prevented pain and ischemia during PTCA, and in this respect spontaneously visible collaterals were more effective than recruitable collaterals. There was no effect of systemic administration of nitroglycerin on appearance or occlusion pressure of coronary collaterals.

CONCLUSION

Coronary collaterals were found in more than half of patients with single-vessel CAD, as the prevalence of recruitable collaterals was slightly higher than that of spontaneously visible collaterals. Nitroglycerin did neither recruit nor augment coronary collaterals.

Blood flow velocity in donor coronary artery depends on the degree and pattern of collateral vessel development: A study using thrombolysis in myocardial infarction frame count method

To understand the influence of collateral vessels on the coronary flow, TIMI frame count (TFC) method was applied as a measure of mean coronary blood flow velocity in artery giving collateral blood supply to the other artery in angiograms of 76 patients with single occluded coronary artery: RCA giving collaterals to occluded LAD or LAD giving collaterals to occluded RCA. As a control group, TFC was applied in angiograms of 30 patients with mild or no coronary artery disease. TFC was lower (faster blood flow) in LAD giving collaterals to occluded RCA (43 patients) than in LAD in control group (21.8 +/- 10.5 vs. 33.9 +/- 20.8 frames; P < 0.01). Higher degree of collateral vessels (Rentrop classification) and mixed- and distal-type collaterals (through the interventricular septum and heart apex) was associated with lower TFC. There was no difference in TFC in the RCA giving collaterals to an occluded LAD (33 patients) compared to the TFC in RCA in control group (16.6 +/- 9.0 vs. 18.5 +/- 6.0; P = NS), even in angiograms with higher degree of collateral vessel development. TFC was lower (faster blood flow) only in subgroups with mixed (proximal and distal types together in the same patient) and distal (through the interventricular septum and the apex of the heart) collateral types. A delayed contrast appearance in occluded LAD compared to occluded RCA has been found (35.1 +/- 16.1 vs. 20.2 +/- 7.3 frames; P < 0.001) with earlier contrast appearance in occluded LAD when proximal collateral vessels (through the conal and acute marginal branches of RCA) were presented. The coronary flow in donor arteries depends not only on the degree but also on the pattern of collateral vessels. The simple TFC method may facilitate the study of collateral filling pattern and offer insight into the influence of collaterals on the ventricular function.

Angiographic assessment of collateral connections in comparison with invasively determined collateral function in chronic coronary occlusions

BACKGROUND

The evaluation of new therapeutic modalities to induce collateral growth in coronary artery disease require improved methods of angiographic characterization of collaterals, which should be validated by quantitative assessment of collateral function.

METHODS AND RESULTS

In 100 patients with total chronic occlusion of a major coronary artery (duration >2 weeks) collaterals were assessed angiographically by the Rentrop grading, by their anatomic location, and by a new grading of collateral connections (CC grade 0: no continuous connection, CC1: threadlike continuous connection, CC2: side branch-like connection). The interobserver variability was 10%. Collateral function was assessed by Doppler flow (average peak velocity) and pressure recordings distal to the occlusion before recanalization. A collateral resistance index (RColl) was calculated. Recruitable collateral flow was measured during a final balloon inflation >30 minutes after the baseline measurement. The comparison of the anatomic location, the Rentrop, and the collateral connection grade showed only for the latter an independent and significant relation with RColl. CC2 collaterals preserved regional left ventricular function better than did CC1 collaterals and provided a higher collateral flow reserve during adenosine infusion. CC0 collaterals were predominantly observed in recent occlusions of 2 to 4 weeks' duration, with the highest RColl. During balloon reocclusion, recruitable collateral function was best preserved with CC2 and least with CC0.

CONCLUSIONS

The angiographic grading of collateral connections in total chronic occlusions could differentiate collaterals according to their functional capacity to preserve regional left ventricular function and was closely associated with invasively determined parameters of collateral hemodynamics.

Direct assessment of coronary steal and associated changes of collateral hemodynamics in chronic total coronary occlusions

BACKGROUND

Coronary steal can occur in collateral-dependent myocardium during pharmacologically induced vasodilation. This study assessed coronary steal invasively in chronic total coronary occlusions (TCOs).

METHODS AND RESULTS

In 35 consecutive patients with a percutaneous transluminal coronary angioplasty of a TCO (duration >4 weeks), coronary flow velocity (APV) by a Doppler wire and distal pressure (P(D)) by a pressure wire were assessed in the collateral-dependent vascular bed before dilatation. Indexes of peripheral resistance (R(P)) and for the collateral pathway, including the donor artery segment (R(CP)), were calculated. Changes of these parameters were assessed during intravenous adenosine (140 microg x kg(-1) x min(-1)). Adenosine caused a decrease of APV, ie, coronary steal, in 13 patients (37%; group S), an increase in 11 patients (group R), and no change in 11 patients (group N). Angiographic analysis of collateral pathways showed no difference between the groups, except that in group S all collateral connections were continuously visible but no large collaterals (>0.5 mm) were found. In group N, collaterals were least developed. The increase of APV in group R was associated with a decrease of R(P), whereas R(CP) remained unchanged. In contrast, group S showed no change in R(P) but a significant increase of R(CP), indicating an increased resistance of the donor segment.

CONCLUSIONS

Coronary steal is observed in about one third of TCOs and is associated with specific hemodynamic changes of R(P) and R(CP). Steal occurred only with well-developed angiographically visible collaterals but not with very large collaterals.

Collateral function in chronic total coronary occlusions is related to regional myocardial function and duration of occlusion

BACKGROUND

Collateral circulation can maintain myocardial function and viability in chronic total coronary occlusion (TCO). The present study evaluates the relation of myocardial function and duration of occlusion to collateral function.

METHODS AND RESULTS

A total of 50 patients underwent a successful recanalization of a TCO (>4 weeks' duration). Collateral function was assessed by intracoronary Doppler and pressure recordings before the first balloon inflation and after PTCA had been completed. Collateral function was assessed by Doppler- (CFI(D)) and pressure-derived collateral flow indices (CFI(P)), as well as indices of collateral (R(Coll)) and peripheral resistance (R(P)). Patients with normokinesia had lower R(Coll) (4.9+/-2.5 versus 11.8+/-8.2 mm Hg. cm(-1). s(-1); P=0.033) and lower R(P) (3.8+/-1.9 versus 6.1+/-4.1 mm Hg. cm(-1). s(-1); P=0.031) than those with akinesia. Patients with akinesia and a TCO duration of </=3 months had the highest R(Coll) and R(P), whereas those with akinesia and a longer TCO duration had similar collateral function as patients with normokinesia. After PTCA, CFI(D) and CFI(P) decreased from 0.37+/-0.20 to 0.21+/-0.17 (P<0.001) and from 0.44+/-0.12 to 0.36+/-0.11 (P<0.001), respectively, with an increase in R(Coll) of 139+/-128% (P<0.001) and R(P) by 65+/-99% (P=0.003). This attenuation of collateral function was less pronounced with epicardial collaterals than with intramyocardial collaterals.

CONCLUSIONS

Collateral function was better in patients with TCO and normal regional function than in those with impaired regional function. In the latter group, collateral function improvement was time dependent. After recanalization, the recruitable collateral function was attenuated because of an increase of R(Coll) and R(P).

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.

Simultaneous intracoronary velocity- and pressure-derived assessment of adenosine-induced collateral hemodynamics in patients with one- to two-vessel coronary artery disease

OBJECTIVES

The purpose of this investigation in patients with poorly and well developed coronary collaterals was to assess the influence of collateral and collateral adjacent vascular resistances and, in part, a stenotic lesion of the collateral supplying vessel on the hemodynamic collateral responses to adenosine.

BACKGROUND

In humans, little is known about the functional behavior of the coronary collateral circulation.

METHODS

In 50 patients with one- and two-vessel coronary artery disease (CAD) undergoing percutaneous transluminal coronary angioplasty (PTCA), collateral flow index (CFI, no unit) changes and vascular resistance index (R, cm/mm Hg) changes of the collateral (R(coll)) and the distal collateral receiving (R4) vessel in response to adenosine (140 microg/min/kg IV) were measured by intracoronary (i.c.) Doppler and pressure guidewires. The variables were determined at baseline and during adenosine in patients with poor (angiographic collateral degree before PTCA <2 of 0 to 3) and good coronary collaterals.

RESULTS

Pressure-derived CFI (CFI(p)) decreased under adenosine in patients with poor collaterals, and it increased in the group with good collaterals. There were inverse correlations between the adenosine-induced change in CFI(p) and the change in R(coll) (r = 0.61, p = 0.0001). In the group with good, but not with poor collaterals, there was also a significant correlation between CFI(p) increase and the decrease in R4, between the severity of the contralateral stenosis and CFI(p) augmentation and among the left versus right coronary artery as ipsilateral vessel and CFI(p) change.

CONCLUSIONS

Overall, patients with well, versus poorly developed coronary collaterals do better regarding the capacity to increase collateral flow in response to adenosine. In patients with good, but not poor, collaterals, an adenosine-induced collateral flow increase depends on the ipsilateral distal vascular resistance decrease, but is also directly influenced by the severity of a contralateral stenosis and probably by the size of the collateralized vascular bed.

Quantification of collateral flow in humans: a comparison of angiographic, electrocardiographic and hemodynamic variables

OBJECTIVES

Evaluation of collateral vascular circulation according to hemodynamic variables and its relation to myocardial ischemia.

BACKGROUND

There is limited information regarding the hemodynamic quantification of recruitable collateral vessels.

METHODS

Angiography of the donor coronary artery was performed before and during balloon coronary occlusion in 63 patients with one vessel disease. Patients were divided into groups of those with an absence of collateral vessels (group 1, n = 10), those with recruitable collateral vessels (group 2, n = 23) and those with spontaneously visible collateral vessels (group 3, n = 30). During balloon inflation the coronary wedge/aortic pressure ratio (Pw/Pao) was determined as were collateral blood flow velocity variables, using a 0.014" Doppler guide wire. Myocardial ischemia was defined as > or =0.1 mV ST-shift on a 12 lead electrocardiogram at 1 min coronary occlusion.

RESULTS

Myocardial ischemia was present in all patients of group 1, in 14 patients of group 2 and in 3 patients of group 3. Recruitable collateral flow without ischemia showed similar hemodynamic values as in group 3 while these values were similar to group 1 in regard to the presence of recruitable collateral vessels showing ischemia. Logistic regression analysis revealed both Pw/Pao and Vi(col) as independent predictors for the function of collateral vessels.

CONCLUSIONS

Hemodynamic variables of collateral vascular circulation are better markers of the functional significance of collateral vessels than is coronary angiography. The total collateral blood flow velocity integral and coronary wedge/aortic pressure ratio are good and independent predictors of the function of collateral vessels producing complementary information.