Collateral-flow measurements in humans by myocardial contrast echocardiography: validation of coronary pressure-derived collateral-flow assessment

Algorithm for real-time analysis of intracoronary electrocardiogram

Introduction

Since its first implementation in 1985, intracoronary (ic) electrocardiogram (ECG) has shown ample evidence for its diagnostic value given the higher sensitivity for myocardial ischemia detection in comparison to surface ECG. However, a lack of online systems to quantitatively analyze icECG in real-time prevents its routine use. The present study aimed to develop and validate an autonomous icECG analyzing algorithm.

Materials and methods

This is a retrospective observational study in 100 patients with chronic coronary syndrome. From each patient, a non-ischemic as well as ischemic icECG at the end of a 1-min proximal coronary balloon occlusion was available. An ECG expert as well as the newly developed algorithm for autonomous icECG analysis measured the icECG ST-segment shift in mV for each icECG tracing.

Results

Intraclass correlation coefficient (ICC) demonstrated low variability between the two methods (ICC = 0.968). Using the time point of icECG recording as allocation reference for absent or present myocardial ischemia, ROC-analysis for ischemia detection by the manually determined icECG ST-segment shift showed an area under the curve (AUC) of 0.968 ± 0.021 (p < 0.0001). AUC for the algorithm analysis was 0.967 ± 0.023 (p < 0.0001; p = 0.925 for the difference between the ROC curve AUCs). Time to complete analysis was below 1,000 ms for the autonomous icECG analysis and above 5 min for manual analysis.

Conclusion

A newly developed autonomous icECG analysing algorithm detects myocardial ischemia with equal accuracy as manual ST-segment shift assessment. The algorithm provides the technical fundament for an analysing system to quantitatively obtain icECG in real-time.

Traditional Cardiovascular Risk Factors and Coronary Collateral Circulation: A Meta-Analysis

Objective: Patients with well-developed coronary collateral circulation (CC) usually have low mortality, improved cardiac function, and reduced infarct size. Currently, there is conflicting evidence on the association between traditional cardiovascular risk factors (diabetes, hypertension, and smoking habit) and CC.

Design: We performed a meta-analysis of case-control studies to better understand such associations.

Data Sources: We searched the MEDINE, EMBASE, and Science Citation Index databases to identify relevant studies.

Eligibility Criteria for Selecting Studies: Case control studies reporting data on risk factors (smoking habit, hypertension, and diabetes mellites) in comparing cases between poor CC and well-developed CC groups. Well-developed CC was the primary outcome of this meta-analysis

Data Extraction and Synthesis: Relevant data were extracted by two independent investigators. We derived pooled odds ratios (ORs) with random effects models. We performed quality assessments, publication bias, and sensitivity analysis to ensure the reliability of our results.

Results: In total, 18 studies that had 4,746 enrolled patients were analyzed. Our results showed that hypertension and smoking habit did not (OR = 0.94, 95% CI: 0.75–1.17, p = 0.564 and OR = 1.00, 95% CI: 0.84–1.18, p = 0.970, respectively), and diabetes did (OR = 0.50, 95% CI: 0.38–0.67, p = 0.00001) affect the development of CC.

Conclusion: Unlike hypertension and smoking habit, diabetes was associated with poor CC formation.

Trial Registration Number:https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=87821, identifier: CRD42018087821.

Detection of myocardial ischemia by intracoronary ECG using convolutional neural networks

INTRODUCTION

The electrocardiogram (ECG) is a valuable tool for the diagnosis of myocardial ischemia as it presents distinctive ischemic patterns. Deep learning methods such as convolutional neural networks (CNN) are employed to extract data-derived features and to recognize natural patterns. Hence, CNN enable an unbiased view on well-known clinical phenomenon, e.g., myocardial ischemia. This study tested a novel, hypothesis-generating approach using pre-trained CNN to determine the optimal ischemic parameter as obtained from the highly susceptible intracoronary ECG (icECG).

METHOD

This was a retrospective observational study in 228 patients with chronic coronary syndrome. Each patient had participated in clinical trials with icECG recording and ST-segment shift measurement at the beginning (i.e., non-ischemic) and the end (i.e., ischemic) of a one-minute proximal coronary artery balloon occlusion establishing the reference. Using these data (893 icECGs in total), two pre-trained, open-access CNN (GoogLeNet/ResNet101) were trained to recognize ischemia. The best performing CNN during training were compared with the icECG ST-segment shift for diagnostic accuracy in the detection of artificially induced myocardial ischemia.

RESULTS

Using coronary patency or occlusion as reference for absent or present myocardial ischemia, receiver-operating-characteristics (ROC)-analysis of manually obtained icECG ST-segment shift (mV) showed an area under the ROC-curve (AUC) of 0.903±0.043 (p<0.0001, sensitivity 80%, specificity 92% at a cut-off of 0.279mV). The best performing CNN showed an AUC of 0.924 (sensitivity 93%, specificity 92%). DeLong-Test of the ROC-curves showed no significant difference between the AUCs. The underlying morphology responsible for the network prediction differed between the trained networks but was focused on the ST-segment and the T-wave for myocardial ischemia detection.

CONCLUSIONS

When tested in an experimental setting with artificially induced coronary artery occlusion, quantitative icECG ST-segment shift and CNN using pathophysiologic prediction criteria detect myocardial ischemia with similarly high accuracy.

Functional assessment of myocardial ischaemia by intracoronary ECG

Introduction

In patients with chronic coronary syndrome, percutaneous coronary intervention targets haemodynamically significant stenoses, that is, those thought to cause ischaemia. Intracoronary ECG (icECG) detects ischaemia directly where it occurs. Thus, the goal of this study was to test the accuracy of icECG during pharmacological inotropic stress to determine functional coronary lesion severity in comparison to the structural parameter of quantitative angiographic per cent diameter stenosis (%S), as well as to the haemodynamic indices of fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR).

Method

The primary study endpoint of this prospective trial was the maximal change in icECG ST-segment shift during pharmacological inotropic stress induced by dobutamine plus atropine obtained within 1 min after reaching maximal heart rate(=220 - age). IcECG was acquired by attaching an alligator clamp to the angioplasty guidewire positioned downstream of the stenosis. For the pressure-derived stenosis severity ratios, coronary perfusion pressure and simultaneous aortic pressure were continuously recorded.

Results

There was a direct linear relation between icECG ST-segment shift and %S: icECG=−0.8+0.03*%S (r²=0.164; p<0.0001). There were inverse linear correlations between FFR and %S: FFR=1.1–6.1*10–3*%S (r²=0.494; p<0.0001), and between iFR and %S: iFR=1.27–8.6*10–3*%S (r²=0.461; p<0.0001). Using a %S-threshold of ≥50% as the reference for structural stenosis relevance, receiver operating characteristics-analysis of absolute icECG ST-segment shift during hyperemia showed an area under the curve (AUC) of 0.678±0.054 (p=0.002; sensitivity=85%, specificity=50% at 0.34 mV). AUC for FFR was 0.854±0.037 (p<0.0001; sensitivity=64%, specificity=96% at 0.78), and for iFR it was 0.816±0.043 (p<0.0001;sensitivity=62%, specificity=96% at 0.83).

Conclusions

Hyperaemic icECG ST-segment shift detects structurally relevant coronary stenotic lesions with high sensitivity, while they are identified highly specific by FFR and iFR.

Accuracy of intracoronary ECG parameters for myocardial ischemia detection

INTRODUCTION

The electrocardiogram (ECG) is a valuable diagnostic tool for the diagnosis of myocardial ischemia during acute coronary syndrome. Aside from the commonly used ST-segment shift indicative of ischemia, several other ECG parameters are pathophysiologically reasonable. Thus, the goal of this study was to assess the accuracy of different ischemia parameters as obtained by the highly susceptible intracoronary ECG (icECG).

METHOD

This was a retrospective observational study in 100 patients with chronic coronary syndrome. From each patient, a non-ischemic as well as ischemic icECG at the end of a one-minute proximal coronary balloon occlusion was available, and analysed twice by three different physicians, as well as once together for consensual results. The evaluated parameters were icECG ST-segment shift (mV), ST-integral (mV*sec), T-wave-integral (mV*sec), T-peak (mV), T-peak-to-end time (TPE; msec) and QTc-time (msec).

RESULTS

All six icECG parameters showed significant differences between the non-ischemic and the ischemic recording. Using the icECG recording during coronary patency or occlusion as criterion for absent or present myocardial ischemia, ROC-analysis of icECG ST-segment shift showed an area under the curve (AUC) of 0.963 ± 0.029 (p < 0.0001). AUC for ST-integral was 0.899 ± 0.044 (p < 0.0001), for T-wave integral 0.791 ± 0.059 (p < 0.0001), for T-peak 0.811 ± 0.057 (p < 0.0001), for TPE 0.667 ± 0.068 (p < 0.0001), and for QTc-time 0.770 ± 0.061 (p < 0.0001). The best cut-off point for the detection of ischemia by icECG ST-segment shift was 0.365 mV (sensitivity 90%, specificity 95%).

CONCLUSION

When tested in a setting with artificially induced absolute myocardial ischemia, icECG ST-segment shift at a threshold of 0.365 mV most accurately distinguishes between absent and present ischemia.

The Human Coronary Collateral Circulation, Its Extracardiac Anastomoses and Their Therapeutic Promotion

Cardiovascular disease remains the leading global cause of death, and the number of patients with coronary artery disease (CAD) and exhausted therapeutic options (i.e., percutaneous coronary intervention (PCI), coronary artery bypass grafting (CABG) and medical treatment) is on the rise. Therefore, the evaluation of new therapeutic approaches to offer an alternative treatment strategy for these patients is necessary. A promising research field is the promotion of the coronary collateral circulation, an arterio-arterial network able to prevent or reduce myocardial ischemia in CAD. This review summarizes the basic principles of the human coronary collateral circulation, its extracardiac anastomoses as well as the different therapeutic approaches, especially that of stimulating the extracardiac collateral circulation via permanent occlusion of the internal mammary arteries.

Invasive Assessment of the Human Arterial Palmar Arch and Forearm Collateral Function During Transradial Access

Background:

The present study aimed to quantitatively measure the pressure-derived function of the palmar arch and forearm arterial collateral circulation during transradial access.

Methods and Results:

Palmar arch and forearm collateral function was determined using radial artery pressure signals in the nonobstructed vessel and during brief manual occlusions of the more proximal radial artery and of the radial plus ulnar arteries. Collateral flow index (CFI), the ratio of mean occlusive divided by mean nonocclusive arterial blood pressure, both subtracted by central venous pressure, was determined for CFI during radial artery occlusion (CFI rad ) and CFI during radial plus ulnar artery occlusion. Before invasive CFI measurements, arterial palmar arch and forearm function was tested noninvasively by the modified Allen test (MAT). Two hundred fifty patients undergoing transradial access coronary angiography were included in the study. CFI rad was equal to 0.802±0.150 (95% CI, 0.783–0.820). CFI during radial plus ulnar artery occlusion was equal to 0.424±0.188 (95% CI, 0.400–0.447). There was an inverse linear relation between CFI rad and MAT in seconds (s): MAT=64−63×CFI rad ( r 2 =0.229; P <0.0001). Two hundred eleven patients had a normal and 39 patients an abnormal (>15 seconds) MAT. The group with normal MAT had a CFI rad of 0.830±0.111, and patients with abnormal MAT had a CFI rad of 0.648±0.224 ( P <0.0001).

Conclusions:

Direct invasive hemodynamic assessment of the palmar arch and forearm arterial function reveals collateral supply to the briefly occluded in comparison to the patent radial artery of 0.802. During external occlusion of both radial and ulnar artery, CFI amounts to an unexpectedly high value of 0.424.

The effect of pegylated granulocyte colony-stimulating factor on collateral function and myocardial ischaemia in chronic coronary artery disease: A randomized controlled trial

OBJECTIVE

To test the effect of long-term pegfilgrastim on collateral function and myocardial ischaemia in patients with chronic stable coronary artery disease (CAD).

METHODS

This was a prospective clinical trial with randomized 2:1 allocation to pegfilgrastim or placebo for 6 months. The primary study endpoint was collateral flow index (CFI) as obtained during a 1-minute ostial coronary artery balloon occlusion. CFI is the ratio of mean coronary occlusive divided by mean aortic pressure both subtracted by central venous pressure (mm Hg/mm Hg). Secondary endpoints were signs of myocardial ischaemia determined during the same coronary occlusion, that is quantitative intracoronary (i.c.) ECG ST-segment shift (mV) and the occurrence of angina pectoris. Endpoints were obtained at baseline before and at follow-up after three subcutaneous study drug injections.

RESULTS

Collateral flow index in the pegfilgrastim group changed from 0.096 ± 0.076 at baseline to 0.126 ± 0.070 at follow-up (P = 0.0039), while in the placebo group CFI changed from 0.157 ± 0.146 to 0.122 ± 0.043, respectively (P = 0.29); the CFI increment at follow-up was +0.030 ± 0.075 in the pegfilgrastim group and -0.034 ± 0.148 in the placebo group (P = 0.0172). In the pegfilgrastim group, i.c. ECG ST-segment shift changed from +1.23 ± 1.01 mV at baseline to +0.93 ± 0.97 mV at follow-up (P = 0.0049), and in the placebo group, it changed from +0.98 ± 1.02 mV to +1.43 ± 1.09 mV, respectively (P = 0.05). At follow-up, the fraction of patients free from angina pectoris during coronary occlusion had increased in the pegfilgrastim but not in the placebo group.

CONCLUSION

Pegfilgrastim given over the course of 6 months improves collateral function in chronic stable CAD, which is reflected by reduced myocardial ischaemia during a controlled coronary occlusion.

Effect of Permanent Right Internal Mammary Artery Closure on Coronary Collateral Function and Myocardial Ischemia

BACKGROUND

The objective of this study is to test the effect of permanent right internal mammary artery device closure on coronary collateral function and myocardial ischemia.

METHODS AND RESULTS

This was a prospective, open-label clinical trial in 50 patients with coronary artery disease. The primary study end point was coronary collateral flow index as obtained during a 1-minute proximal right coronary artery (RCA) and left coronary artery balloon occlusion at baseline before and at follow-up examination 6 weeks after distal right internal mammary artery device closure. Collateral flow index is the ratio between simultaneously recorded mean coronary occlusive pressure divided by mean aortic pressure, both subtracted by central venous pressure. Secondary study end points were fractional flow reserve during vessel patency, the quantitative intracoronary ECG ST-segment elevation, and angina pectoris during the same 1-minute coronary occlusion. Collateral flow index in the untreated RCA and left coronary artery changed from 0.071±0.082 at baseline to 0.132±0.117 (P<0.0001) at follow-up examination and from 0.106±0.092 to 0.081±0.079 (P=0.29), respectively. RCA fractional flow reserve increased significantly (P=0.0029) from baseline to follow-up examination, despite deferral of coronary intervention in all patients. There was a decrease in intracoronary ECG ST-elevation during RCA occlusion from baseline to follow-up examination (P=0.0015); it did not change in the left coronary artery. Angina pectoris during RCA occlusion tended to occur in fewer patients at follow-up versus baseline examination (P=0.06).

CONCLUSIONS

Permanent right internal mammary artery device closure seems to augment extracardiac ipsilateral coronary supply to the effect of reducing ischemia in the dependent myocardial region.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT02475408.

Physical exercise and quantitative lower limb collateral function

Objective

This study tested the hypothesis that global physical activity and physical performance parameters are directly related to invasively obtained left superficial femoral artery (SFA) collateral flow index (CFI).

Background

So far, the association between different measures of physical exercise activity and quantitative lower limb collateral function has not been investigated.

Methods

The primary study end point was pressure-derived CFI as obtained during a 3 min left SFA balloon occlusion. CFI is the ratio of simultaneously recorded mean SFA distal occlusive pressure divided by mean aortic pressure, both subtracted by central venous pressure. As independent variables, the items of the Global Physical Activity Questionnaire (GPAQ) and physical exercise performance (maximal workload in watts) as achieved during a bicycle or treadmill exercise test were determined. The secondary study end point was transcutaneous left calf partial oxygen pressure (PO₂ in mm Hg) divided by transcutaneous PO₂ at a non-ischaemic reference site as obtained simultaneously to CFI measurement.

Results

Of the 110 study patients undergoing diagnostic coronary angiography, 79 belonged to the group without and 31 with engagement in regular intensive leisure time physical activity according to GPAQ. Left SFA CFI tended to be lower in the group without than with intensive leisure time physical activity: 0.514 ±0.141 vs 0.560 ±0.184 (p =0.0566). Transcutaneous PO₂ index was associated with simultaneous left SFA CFI: CFI =018 +0.57 PO₂ index; p<0.0001. Maximal physical workload was directly associated with left SFA CFI: CFI =0.40 +0.0009 maximal workload; p =0.0044.

Conclusions

Quantitative left SFA collateral function is directly reflected by maximal physical workload as achieved during an exercise test.

Trial registration number

NCTO02063347.

Intraindividual Variability and Association of Human Collateral Supply to Different Arterial Regions

The intraindividual variability and association of human collateral functional supply to different arterial regions is unknown. The primary study end point was collateral flow index (CFI) as obtained in the coronary artery (CA), renal artery (RA), left superficial femoral artery (SFA), and left subclavian artery (SCA) of the same individual. CFI is the ratio between simultaneously recorded mean arterial occlusive pressure divided by mean aortic pressure both subtracted by mean central venous pressure. In 100 patients admitted for diagnostic coronary angiography, CFI was assessed in 3 arterial regions (CA, RA, and SFA), 13 patients underwent CFI measurements in all 4 territories. By quantitative coronary angiography, 82 patients had a stenosis <50% in diameter in the CA who underwent CFI measurement. CFI in the CA, RA, left SFA, and left SCA region amounted to 0.110 ± 0.093, 0.119 ± 0.082, 0.512 ± 0.147, and 0.563 ± 0.155, respectively (p <0.0001). There was a direct and linear correlation between CA and SFA CFI: CFI_SFA = 0.47 + 0.47CFI_CA (r(2) = 0.05; p = 0.0259). In patients with CFI values in all 4 arterial regions, an inverse linear relation between left SFA and left SCA CFI was observed: CFI_SCA = 0.91-0.67CFI_SFA (r(2) = 0.36; p = 0.0305). In conclusion, intraindividual, preexistent collateral function is widely varying between different arterial supply areas. On average, collateral flow ranges from approximately 12% in comparison to flow during arterial patency in the coronary and renal circulation to over 50% in the left SFA and left SCA, that is, circle of Willi's territory. CA and SFA CFIs are directly related to each other.

Collateral Circulation in Chronic Total Occlusions – an interventional perspective

Human coronary collaterals are inter-coronary communications that are believed to be present from birth. In the presence of chronic total occlusions, recruitment of flow via these collateral anastomoses to the arterial segment distal to occlusion provide an alternative source of blood flow to the myocardial segment at risk. This mitigates the ischemic injury. Clinical outcome of coronary occlusion ie. severity of myocardial infarction/ischemia, impairment of cardiac function and possibly survival depends not only on the acuity of the occlusion, extent of jeopardized myocardium, duration of ischemia but also to the adequacy of collateral circulation. Adequacy of collateral circulation can be assessed by various methods. These coronary collateral channels have been used successfully as a retrograde access route for percutaneous recanalization of chronic total occlusions. Factors that promote angiogenesis and further collateral remodeling ie. arteriogenesis have been identified. Promotion of collateral growth as a therapeutic target in patients with no suitable revascularization option is an exciting proposal.

Innate collateral segments are predominantly present in the subendocardium without preferential connectivity within the left ventricular wall

Functional collateral vessels often stem from outward remodelling of pre-existing connections between perfusion territories. Knowledge of the distribution and morphology of innate collateral connections may help in identifying myocardial areas with protection against risk for ischaemia. The coronary network of six healthy canine hearts was investigated with an imaging cryomicrotome. Innate collateral connections ranged from 286 to 1015 μm in diameter. Left ventricular collateral density (number per gram of tissue) was about five in the subendocardium vs. 2.5 in the mid-myocardium (P < 0.01) and 1.3 in the epicardium (P < 0.01). Subendocardial collateral connections were oriented parallel to the long axis of the heart. For the major coronary arteries, five times more intracoronary than intercoronary connections were found, while their median diameter and interquartile range were not significantly different, at 96.1 (16.9) vs. 94.7 (18.9) μm. Collateral vessels connecting crowns from sister branches from a stem are denoted intercrown connections and those within crowns intracrown connections. The number of intercrown connections was related to the mean tissue weight of the crowns (y = 0.73x - 0.33, r2 = 0.85, P < 0.0001). This relation was likewise found to describe intercoronary connections. The median collateral diameter and length were independent of the tissue volumes bridged. We conclude that connectivity and morphology of the innate collateral network are distributed with no preference for intra- or intercrown connections, independent of stem diameter, including epicardial arteries. This renders all sites of the myocardium equally protected in case of coronary artery disease. The orientation of subendocardial collateral vessels indicates the longitudinal direction of subendocardial collateral flow.

Direct quantitative assessment of the peripheral artery collateral circulation in patients undergoing angiography

BACKGROUND

Despite the fact that numerous studies have pursued the strategy of improving collateral function in patients with peripheral artery disease, there is currently no method available to quantify collateral arterial function of the lower limb.

METHODS AND RESULTS

Pressure-derived collateral flow index (CFIp, calculated as (occlusive pressure-central venous pressure)/(aortic pressure-central venous pressure); pressure values in mm Hg) of the left superficial femoral artery was obtained in patients undergoing elective coronary angiography using a combined pressure/Doppler wire (n=30). Distal occlusive pressure and toe oxygen saturation (Sao2) were measured for 5 minutes under resting conditions, followed by an exercise protocol (repetitive plantar-flexion movements in supine position; n=28). In all patients, balloon occlusion of the superficial femoral artery over 5 minutes was painless under resting conditions. CFIp increased during the first 3 minutes from 0.451±0.168 to 0.551±0.172 (P=0.0003), whereas Sao2 decreased from 98±2% to 93±7% (P=0.004). Maximal changes of Sao2 were inversely related to maximal CFIp (r(2)=0.33, P=0.003). During exercise, CFIp declined within 1 minute from 0.560±0.178 to 0.393±0.168 (P<0.0001) and reached its minimum after 2 minutes of exercise (0.347±0.176), whereas Sao2 declined to a minimum of 86±6% (P=0.002). Twenty-five patients (89%) experienced pain or cramps/tired muscles, whereas 3 (11%) remained symptom-free for an occlusion time of 10 minutes. CFIp values were positively related to the pain-free time span (r(2)=0.50, P=0.002).

CONCLUSIONS

Quantitatively assessed collateral arterial function at rest determined in the nonstenotic superficial femoral artery is sufficient to prevent ischemic symptoms during a total occlusion of 5 minutes. During exercise, there is a decline in CFIp that indicates a supply-demand mismatch via collaterals or, alternatively, a steal phenomenon. CLINICAL TRIAL REGISTRATION-URL: http://www.clinicaltrials.gov. UNIQUE IDENTIFIER: NCT01742455.

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.

Minimal effect of collateral flow on coronary microvascular resistance in the presence of intermediate and noncritical coronary stenoses

Depending on stenosis severity, collateral flow can be a confounding factor in the determination of coronary hyperemic microvascular resistance (HMR). Under certain assumptions, the calculation of HMR can be corrected for collateral flow by incorporating the wedge pressure (P(w)) in the calculation. However, although P(w) > 25 mmHg is indicative of collateral flow, P(w) does in part also reflect myocardial wall stress neglected in the assumptions. Therefore, the aim of this study was to establish whether adjusting HMR by P(w) is pertinent for a diagnostically relevant range of stenosis severities as expressed by fractional flow reserve (FFR). Accordingly, intracoronary pressure and Doppler flow velocity were measured a total of 95 times in 29 patients distal to a coronary stenosis before and after stepwise percutaneous coronary intervention. HMR was calculated without (HMR) and with P(w)-based adjustment for collateral flow (HMR(C)). FFR ranged from 0.3 to 1. HMR varied between 1 and 5 and HMR(C) between 0.5 and 4.2 mmHg·cm(-1)·s. HMR was about 37% higher than HMR(C) for stenoses with FFR < 0.6, but for FFR > 0.8, the relative difference was reduced to 4.4 ± 3.4%. In the diagnostically relevant range of FFR between 0.6 and 0.8, this difference was 16.5 ± 10.4%. In conclusion, P(w)-based adjustment likely overestimates the effect of potential collateral flow and is not needed for the assessment of coronary HMR in the presence of a flow-limiting stenosis characterized by FFR between 0.6 and 0.8 or for nonsignificant lesions.

A more sensitive pressure-based index to estimate collateral blood supply in case of coronary three-vessel disease

With progressive occlusion of a coronary main artery, some anastomotic vessels are recruited in order to supply blood to the ischemic region. This collateral circulation is an important factor in the preservation of the myocardium until reperfusion of the area at risk. An accurate estimation of collateral flow is crucial in surgical bypass planning as it alters the blood flow distribution in the coronary network and can influence the outcome of a given treatment for a given patient. The evaluation of collateral flow is frequently achieved using an index based on pressure measurements. It is named Collateral Flow Index (CFI) and defined as: (P(w)-P(v))/(P(ao)-P(v)), where P(w) is the pressure distal to the thrombosis, P(ao) the aortic pressure and P(v) the central venous pressure. We propose here another index, that is more sensitive to the P(w) value and could thus describe the role of collateral flow with more precision. We illustrate this idea using some clinical pressure measurements in patients with severe coronary disease (stenoses on the left branches and total occlusion of the right coronary artery).

Theoretical study of the flow rate toward the right heart territory in case of total occlusion of the right coronary artery

In this work, patients with severe coronary disease and chronic occlusion of the right coronary artery (RCA) are studied. In this clinical situation, the collateral circulation is an important factor in the preservation of the myocardium until reperfusion of the area at risk. An accurate estimation of collateral flow is crucial in surgical bypass planning as it can influence the outcome of a given treatment for a given patient. The evaluation of collateral flow is frequently achieved using an index (CFI, Collateral Flow Index) based on pressure measurements. Using a model of the coronary circulation based on hydraulic/electric analogy, we demonstrate, through theoretical simulations, that a wide range of fractional collateral flow values can be obtained for any given distal pressure difference depending on the values of the capillary and collateral resistances.

Quantification of coronary microvascular resistance using angiographic images for volumetric blood flow measurement: in vivo validation

Structural coronary microcirculation abnormalities are important prognostic determinants in clinical settings. However, an assessment of microvascular resistance (MR) requires a velocity wire. A first-pass distribution analysis technique to measure volumetric blood flow has been previously validated. The aim of this study was the in vivo validation of the MR measurement technique using first-pass distribution analysis. Twelve anesthetized swine were instrumented with a transit-time ultrasound flow probe on the proximal segment of the left anterior descending coronary artery (LAD). Microspheres were injected into the LAD to create a model of microvascular dysfunction. Adenosine (400 μg·kg(-1)·min(-1)) was used to produce maximum hyperemia. A region of interest in the LAD arterial bed was drawn to generate time-density curves using angiographic images. Volumetric blood flow measurements (Q(a)) were made using a time-density curve and the assumption that blood was momentarily replaced with contrast agent during the injection. Blood flow from the flow probe (Q(p)), coronary pressure (P(a)), and right atrium pressure (P(v)) were continuously recorded. Flow probe-based normalized MR (NMR(p)) and angiography-based normalized MR (NMR(a)) were calculated using Q(p) and Q(a), respectively. In 258 measurements, Q(a) showed a strong correlation with the gold standard Q(p) (Q(a) = 0.90 Q(p) + 6.6 ml/min, r(2) = 0.91, P < 0.0001). NMR(a) correlated linearly with NMR(p) (NMR(a) = 0.90 NMR(p) + 0.02 mmHg·ml(-1)·min(-1), r(2) = 0.91, P < 0.0001). Additionally, the Bland-Altman analysis showed a close agreement between NMR(a) and NMR(p). In conclusion, a technique based on angiographic image data for quantifying NMR was validated using a swine model. This study provides a method to measure NMR without using a velocity wire, which can potentially be used to evaluate microvascular conditions during coronary arteriography.

Safety of diagnostic balloon occlusion in normal coronary arteries

Diagnostic coronary balloon occlusion (CBO) is mandatory for collateral function assessment, during angioscopy and optical coherence imaging, and when using certain coronary protection devices against emboli. Thus far, the safety of diagnostic CBO regarding procedural and long-term complications in normal coronary arteries has not been studied. In 316 patients, diagnostic CBO was performed for collateral function measurement in 426 angiographically normal vessels. The angioplasty balloon was inflated for 60 to 120 seconds using inflation pressures of 1 to 3 atm, followed by control angiography during and after CBO. Patients were divided into groups with entirely normal (n = 133) and partially normal (n = 183) vessels. Primary end points were procedural and long-term complications. De novo stenosis development was assessed by quantitative coronary angiography in 35% of the patients. Secondary end points were cardiac events at 5 years of follow-up. Procedural complications occurred in 1 patient (0.2%). In 150 repeat angiographic procedures in 92 patients (follow-up duration 10 +/- 15 months), quantitative coronary angiography revealed no difference in percentage diameter narrowing between baseline and follow-up (4.1% vs 3.9%, p = 0.69). During follow-up periods of 14 and 72 months, respectively, a new stenotic lesion was detected in 1 patient in each group (1.3%). Major cardiac events and percutaneous coronary intervention for stable angina were less frequent in the group with entirely normal than with partially normal vessels (0.8% vs 5.5%, p = 0.02, and 0.8% vs 18%, p <0.0001). In conclusion, low-inflation pressure diagnostic CBO in angiographically normal coronary arteries bears a minimal risk for procedural and long-term complications and can therefore be regarded as a safe procedure.

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.

Coronary pressure measurement based decision making for percutaneous coronary intervention

The fractional flow reserve (FFR) is a simple, reliable, and reproducible physiologic index of lesion severity. In patients with intermediate stenosis, FFR≥0.75 can be used to safely defer percutaneous coronary intervention (PCI), and patients with FFR≥0.75 have a very low cardiac event rate. Coronary pressure measurement can determine which lesion should be treated with PCI in patients with tandem lesions, and PCI on the basis of FFR has been demonstrated to result in an acceptably low repeat PCI rate. FFR can identify patients with equivocal left main coronary artery disease who benefit from coronary bypass surgery. Coronary pressure measurement distinguishes patients with an abrupt pressure drop pattern from those with a gradual pressure drop pattern, and the former group of patients benefit from PCI. Coronary pressure measurement is clinically useful in evaluating sufficient recruitable coronary collateral blood flow for prevention of ischemia, which affects future cardiac events. FFR is useful for the prediction of restenosis after PCI. As an end-point of PCI, FFR ≥0.95 and ≥0.90 would be appropriate for coronary stenting and coronary angioplasty, respectively. In summary, if you encounter a coronary stenosis in doubt you should measure pressure rather than dilate it.

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.

Interferon-β Signaling Is Enhanced in Patients With Insufficient Coronary Collateral Artery Development and Inhibits Arteriogenesis in Mice

Stimulation of collateral artery growth in patients has been hitherto unsuccessful, despite promising experimental approaches. Circulating monocytes are involved in the growth of collateral arteries, a process also referred to as arteriogenesis. Patients show a large heterogeneity in their natural arteriogenic response on arterial obstruction. We hypothesized that circulating cell transcriptomes would provide mechanistic insights and new therapeutic strategies to stimulate arteriogenesis. Collateral flow index was measured in 45 patients with single-vessel coronary artery disease, separating collateral responders (collateral flow index, >0.21) and nonresponders (collateral flow index, ≤0.21). Isolated monocytes were stimulated with lipopolysaccharide or taken into macrophage culture for 20 hours to mimic their phenotype during arteriogenesis. Genome-wide mRNA expression analysis revealed 244 differentially expressed genes (adjusted P , <0.05) in stimulated monocytes. Interferon (IFN)-β and several IFN-related genes showed increased mRNA levels in 3 of 4 cellular phenotypes from nonresponders. Macrophage gene expression correlated with stimulated monocytes, whereas resting monocytes and progenitor cells did not display differential gene regulation. In vitro, IFN-β dose-dependently inhibited smooth muscle cell proliferation. In a murine hindlimb model, perfusion measured 7 days after femoral artery ligation showed attenuated arteriogenesis in IFN-β–treated mice compared with controls (treatment versus control: 31.5±1.2% versus 41.9±1.9% perfusion restoration, P <0.01). In conclusion, patients with differing arteriogenic response as measured with collateral flow index display differential transcriptomes of stimulated monocytes. Nonresponders show increased expression of IFN-β and its downstream targets, and IFN-β attenuates proliferation of smooth muscle cells in vitro and hampers arteriogenesis in mice. Inhibition of IFN-β signaling may serve as a novel approach for the stimulation of collateral artery growth.

Coronary collateral flow in response to endurance exercise training

BACKGROUND

In humans, it is not known whether physical endurance exercise training promotes coronary collateral growth. The following hypotheses were tested: the expected collateral flow reduction after percutaneous coronary intervention of a stenotic lesion is prevented by endurance exercise training; collateral flow supplied to an angiographically normal coronary artery improves in response to exercise training; there is a direct relationship between the change of fitness after training and the coronary collateral flow change.

METHODS AND RESULTS

Forty patients (age 61+/-8 years) underwent a 3-month endurance exercise training program with baseline and follow-up assessments of coronary collateral flow. Patients were divided into an exercise training group (n=24) and a sedentary group (n=16) according to the fact whether they adhered or not to the prescribed exercise program, and whether or not they showed increased endurance (VO2max in ml/min per kg) and performance (W/kg) during follow-up versus baseline bicycle spiroergometry. Collateral flow index (no unit) was obtained using pressure sensor guidewires positioned in the coronary artery undergoing percutaneous coronary intervention and in a normal vessel. In the vessel initially undergoing percutaneous coronary intervention, there was an increase in collateral flow index among exercising but not sedentary patients from 0.155+/-0.081 to 0.204+/-0.056 (P=0.03) and from 0.189+/-0.084 to 0.212+/-0.077 (NS), respectively. In the normal vessel, collateral flow index changes were from 0.176+/-0.075 to 0.227+/-0.070 in the exercise group (P=0.0002), and from 0.219+/-0.103 to 0.238+/-0.086 in the sedentary group (NS). A direct correlation existed between the change in collateral flow index from baseline to follow-up and the respective alteration of VO2max (P=0.007) and Watt (P=0.03).

CONCLUSION

A 3-month endurance exercise training program augments coronary collateral supply to normal vessels, and even to previously stenotic arteries having undergone percutaneous coronary intervention before initiating the program. There appears to be a dose-response relation between coronary collateral flow augmentation and exercise capacity gained.

Beneficial effect of recruitable collaterals: a 10-year follow-up study in patients with stable coronary artery disease undergoing quantitative collateral measurements

BACKGROUND

The prognostic relevance of the collateral circulation is still controversial. The goal of this study was to assess the impact on survival of quantitatively obtained, recruitable coronary collateral flow in patients with stable coronary artery disease during 10 years of follow-up.

METHODS AND RESULTS

Eight-hundred forty-five individuals (age, 62+/-11 years), 106 patients without coronary artery disease and 739 patients with chronic stable coronary artery disease, underwent a total of 1053 quantitative, coronary pressure-derived collateral measurements between March 1996 and April 2006. All patients were prospectively included in a collateral flow index (CFI) database containing information on recruitable collateral flow parameters obtained during a 1-minute coronary balloon occlusion. CFI was calculated as follows: CFI = (P(occl) - CVP)/(P(ao) - CVP) where P(occl) is mean coronary occlusive pressure, P(ao) is mean aortic pressure, and CVP is central venous pressure. Patients were divided into groups with poorly developed (CFI < 0.25) or well-grown collateral vessels (CFI > or = 0.25). Follow-up information on the occurrence of all-cause mortality and major adverse cardiac events after study inclusion was collected. Cumulative 10-year survival rates in relation to all-cause deaths and cardiac deaths were 71% and 88%, respectively, in patients with low CFI and 89% and 97% in the group with high CFI (P=0.0395, P=0.0109). Through the use of Cox proportional hazards analysis, the following variables independently predicted elevated cardiac mortality: age, low CFI (as a continuous variable), and current smoking.

CONCLUSIONS

A well-functioning coronary collateral circulation saves lives in patients with chronic stable coronary artery disease. Depending on the exact amount of collateral flow recruitable during a brief coronary occlusion, long-term cardiac mortality is reduced to one fourth compared with the situation without collateral supply.

The effect of electrical neurostimulation on collateral perfusion during acute coronary occlusion

Background

Electrical neurostimulation can be used to treat patients with refractory angina, it reduces angina and ischemia. Previous data have suggested that electrical neurostimulation may alleviate myocardial ischaemia through increased collateral perfusion. We investigated the effect of electrical neurostimulation on functional collateral perfusion, assessed by distal coronary pressure measurement during acute coronary occlusion. We sought to study the effect of electrical neurostimulation on collateral perfusion.

Methods

Sixty patients with stable angina and significant coronary artery disease planned for elective percutaneous coronary intervention were split in two groups. In all patients two balloon inflations of 60 seconds were performed, the first for balloon dilatation of the lesion (first episode), the second for stent delivery (second episode). The Pw/Pa ratio (wedge pressure/aortic pressure) was measured during both ischaemic episodes. Group 1 received 5 minutes of active neurostimulation before plus 1 minute during the first episode, group 2 received 5 minutes of active neurostimulation before plus 1 minute during the second episode.

Results

In group 1 the Pw/Pa ratio decreased by 10 ± 22% from 0.20 ± 0.09 to 0.19 ± 0.09 (p = 0.004) when electrical neurostimulation was deactivated. In group 2 the Pw/Pa ratio increased by 9 ± 15% from 0.22 ± 0.09 to 0.24 ± 0.10 (p = 0.001) when electrical neurostimulation was activated.

Conclusion

Electrical neurostimulation induces a significant improvement in the Pw/Pa ratio during acute coronary occlusion.

Collateral density, remodeling, and VEGF-A expression differ widely between mouse strains

Substantial variability exists in collateral density and ischemia-induced collateral growth among species. To begin to probe the underlying mechanisms, which are unknown, we characterized two mouse strains with marked differences in both parameters. Immediately after femoral artery ligation, collateral and foot perfusion were lower in BALB/c than C57BL/6 (P < 0.05 here and below), suggesting fewer pre-existing collaterals. This was confirmed with angiography and immunohistochemistry (approximately 35% fewer collaterals in the BALB/c's thigh). Recovery of hindlimb perfusion was attenuated in BALB/c, in association with 54% less collateral remodeling, reduced angiogenesis, greater ischemia, and more impaired hindlimb use. Densities of CD45+ and CD4+ leukocytes around collaterals increased similarly, but TNF-alpha expression was 50% lower in BALB/c, which may contribute to reduced collateral remodeling. In normal tissues, compared with C57BL/6, BALB/c exhibit an altered arterial branching pattern and, like skeletal muscle above, have 30% fewer collaterals in intestine and, remarkably, almost none in pial circulation, resulting in greatly impaired perfusion after cerebral artery occlusion. Ischemic induction of VEGF-A was attenuated in BALB/c. Analysis of a C57BL/6 x BALB/c recombinant inbred strain dataset identified a quantitative trait locus for VEGF-A mRNA abundance at or near the Vegfa locus that associates with lower expression in BALB/c. This suggests a cis-acting polymorphism in the Vegfa gene in BALB/c could contribute to reduced VEGF-A expression and, in turn, the above deficiencies in this strain. These findings suggest these strains offer a model to investigate genetic determinants of collateral formation and growth in ischemia.

Incidence and angiographic predictors of collateral function in patients with stable coronary artery disease scheduled for percutaneous coronary intervention

OBJECTIVES

To investigate the incidence and angiographic predictors of functional collateral perfusion in patients with stable coronary artery disease, scheduled for elective PCI.

BACKGROUND

Functional collateral perfusion is defined as a Pw/Pa ratio>or=0.24. Since this can only be measured intracoronary, it is important to investigate baseline clinical and angiographic predictors for functional collateral perfusion.

METHODS

Collateral perfusion was measured during balloon inflation, with the use of a pressure-monitoring guide wire. Baseline clinical and angiographic characteristics were analyzed and collateral grading was done according to Rentrop's classification for coronary angiograms.

RESULTS

Functional collateral perfusion was found in 40 of the 89 patients (45%). Angiographic signs of collaterals (Rentrop>or=1) were present in 15 of the 89 patients. Of the 40 patients with the functional collateral perfusion 11 patients (28%) had Rentrop>or=1; of the 49 patients without functional collaterals there were 4 patients with Rentrop>or=1 (8%) (P=0.02). There were no significant differences in baseline clinical characteristics or in other angiographic characteristics.

CONCLUSIONS

In patients with stable coronary artery disease scheduled for elective PCI, 45% have functional collaterals. Rentrop's angiographic classification can be used to predict the presence or absence of functional collaterals, however with a rather modest positive and negative predictive value.

Coronary collateral function long after drug-eluting stent implantation

OBJECTIVES

This study was designed to compare coronary collateral function in patients after bare-metal stent (BMS) or drug-eluting stent (DES) implantation.

BACKGROUND

Drug-eluting stents have an inhibitory effect on the production of cytokines, chemotactic proteins, and growth factors, and may therefore negatively affect coronary collateral growth.

METHODS

A total of 120 patients with long-term stable coronary artery disease (CAD) after stent implantation were included. Both the BMS group and the DES group comprised 60 patients matched for in-stent stenosis severity of the vessel undergoing collateral flow index (CFI) measurement at follow-up and for the duration of follow-up. The primary end point of the investigation was invasively determined coronary collateral function 6 months after stent implantation. Collateral function was assessed by simultaneous aortic, coronary wedge, and central venous pressure measurements (yielding CFI) and by intracoronary electrocardiogram during balloon occlusion.

RESULTS

There were no differences between the groups regarding age, gender, body mass index, frequency of cardiovascular risk factors, use of cardiovascular drugs, severity of CAD, or site of coronary artery stenoses. Despite equal in-stent stenosis severity (46 +/- 34% and 45 +/- 36%) and equal follow-up duration (6.2 +/- 10 months and 6.5 +/- 5.4 months), CFI was diminished in the DES versus BMS group (0.154 +/- 0.097 vs. 0.224 +/- 0.142; p = 0.0049), and the rate of collaterals insufficient to prevent ischemia during occlusion (intracoronary electrocardiographic ST-segment elevation > or =0.1 mV) was higher with 50 of 60 patients in the DES group and 33 of 60 patients in the BMS group (p = 0.001).

CONCLUSIONS

Collateral function long after coronary stenting is impaired with DES (sirolimus and paclitaxel) when compared with BMS. Considering the protective nature of collateral vessels, this could lead to more serious cardiac events in the presence of an abrupt coronary occlusion.