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

The Significance of Thallium-201-Chloride SPECT Myocardial Perfusion Imaging in the Management of Patients With Stable Chronic Coronary Artery Disease

Background:

Patients with stable coronary artery disease (CAD) can be evaluated for myocardial viability by examining reverse redistribution of Thallium-201 (²⁰¹TI) through cardiac scintigraphy. There is limited knowledge about association of a reverse redistribution with favorable cardiac outcomes. In this study, we hypothesized that higher left ventricular ejection fraction (LVEF), lower myocardial necrosis, fewer ischemic events, and less angina will be associated with reverse redistribution of ²⁰¹TI imaging.

Methods:

Adult patients with stable CAD included in this study underwent exercise-redistribution Thallium single-photon emission computed tomography (SPECT) and were followed for one year. LVEF and regional wall motion abnormalities were evaluated with echocardiography, exercise duration by bicycle testing, and myocardial ischemia and viability by Thallium SPECT.

Results:

We studied 159 patients (87 men, 72 women, median age 60 years, range: 38-84) with well-developed collaterals. Those with reverse redistribution on SPECT (n = 61, 38.3%) had significantly better exercise tolerance (⩾85%; P < .001). Subjects with reverse redistribution had better LVEF (P < .001), wall motion parameters (P < .001), a lower degree of myocardial necrosis (P < .05), less angina during follow-up (P = .02), and fewer ischemic events whether treated with OMT or PCI (P < .001).

Conclusions:

Reverse redistribution of ²⁰¹Tl on scintigraphic images is a predictor of myocardial viability. Evidence from our study suggests that optimally treated chronic CAD patients with reverse redistribution may have lower likelihood of future adverse cardiovascular events and better prognosis.

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.

The collateral circulation of the heart in coronary total arterial occlusions in man: systematic review of assessment and pathophysiology

BACKGROUND

Anatomical and functional assessment of the collateral circulation of the heart in total arterial occlusions is challenging, and this is particularly true of the microcirculation. The pathophysiology of the collateral circulation has historically been and remains of considerable research focus but with diverging and sometimes conflicting results. Our purpose was to conduct a systematic review on the assessment and pathophysiology of the collateral circulation of the heart in total coronary arterial occlusions.

METHODS

We extracted data from Pubmed, Ovid, EMBASE, and Cochrane database from 1966 to December 2012. Two investigators independently reviewed the identified articles for eligibility and extracted the data.

RESULTS

Seventy-seven studies met inclusion criterion. An invasive assessment of the collateral circulation with pressure and/or Doppler wires is the gold standard in the assessment of collateral physiology and anatomy, although this can only be undertaken after successful passage of the sensor in the true lumen of the occluded vessel. A collateral circulation can provide resting metabolic requirements for the heart but invariably cannot meet demands on stress irrespective of the degree of collateralization as assessed by coronary angiography. In the case of myocardium subtending a totally occluded epicardial artery coronary collateral grading systems or physiological assessment of collateral flow is only moderately sensitive and poorly specific at predicting viability. Regression of collaterals seems more profound in totally occluded arteries versus nonoccluded lesions postrevascularization.

CONCLUSIONS

Key controversies in the assessment and pathophysiology of the collateral circulation of the heart in total coronary arterial occlusions are systematically evaluated.

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.

The collateral circulation of the heart

The coronary arteries have been regarded as end arteries for decades. However, there are functionally relevant anastomotic vessels, known as collateral arteries, which interconnect epicardial coronary arteries. These vessels provide an alternative source of blood supply to the myocardium in cases of occlusive coronary artery disease. The relevance of these collateral arteries is a matter of ongoing debate, but increasing evidence indicates a relevant protective role in patients with coronary artery disease. The collateral circulation can be assessed by different methods; the gold standard involves intracoronary pressure measurements. While the first clinical trials to therapeutically induce growth of collateral arteries have been unavailing, recent pilot studies using external counterpulsation or growth factors such as granulocyte colony stimulating factor (G-CSF) have shown promising results.

Assessment of leptomeningeal collaterals using dynamic CT angiography in patients with acute ischemic stroke

Whole-brain dynamic time-resolved computed tomography angiography (CTA) is a technique developed on the new 320-detector row CT scanner capable of generating time-resolved cerebral angiograms from skull base to vertex. Unlike a conventional cerebral angiogram, this technique visualizes pial arterial filling in all vascular territories, thereby providing additional hemodynamic information. Ours was a retrospective study of consecutive patients with ischemic stroke and M1 middle cerebral artery +/- intracranial internal carotid artery occlusions presenting to our center from June 2010 and undergoing dynamic time-resolved CTA and perfusion CT within 6 hours of symptom onset. Leptomeningeal collateral status was assessed by determining relative prominence of pial arteries in the ischemic region, rate and extent of retrograde flow, and various topographical patterns of pial arterial filling. Twenty-five patients were included in the study. We demonstrate the existence of the following novel properties of leptomeningeal collaterals in humans: (a) posterior (posterior cerebral artery (PCA)-MCA) dominant collateralization, (b) intra-territorial 'within MCA region' leptomeningeal collaterals, and (c) significant variability in size, extent, and retrograde filling time in pial arteries. We also describe a simple and reliable collateral grading template that, for the first time on dynamic CTA, incorporates back-filling time as well as size and extent of collateral filling.

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.

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.

The role of collateral circulation in preserving myocardial function

The coronary collateral circulation is an alternative source of blood supply to the myocardium jeopardized by the failure of the original stenotic or occluded vessel to provide adequate blood flow to this region. One hundred coronary angiograms and left ventriculograms of patients with coronary artery disease from the Cardiology Department of University Clinics Centre in Sarajevo were reviewed. The role of collateral circulation in preserving myocardial function was assessed by comparing regional left ventricular contractility in 34 instances of total arterial occlusion and adequate colateral circulation with that in 34 instances of total arterial occlusion and inadequate collateral circulation. Among the group with adequate collaterals, regional left ventricular contraction was normal in 41%, hypokinetic in 53% and akinetic or dyskinetic in only 5%. Among the group with inadequate collaterals, regional contraction was normal in 9%, hypokinetic in 20 % and akinetic or dyskinetic in 70%. These data indicate that collateral circulation plays an important role in preserving myocardial contractility in patients with coronary artery disease.

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

AIMS

Myocardial blood flow (MBF) is the gold standard to assess myocardial blood supply and, as recently shown, can be obtained by myocardial contrast echocardiography (MCE). The aims of this human study are (i) to test whether measurements of collateral-derived MBF by MCE are feasible during elective angioplasty and (ii) to validate the concept of pressure-derived collateral-flow assessment.

METHODS AND RESULTS

Thirty patients with stable coronary artery disease underwent MCE of the collateral-receiving territory during and after angioplasty of 37 stenoses. MCE perfusion analysis was successful in 32 cases. MBF during and after angioplasty varied between 0.060-0.876 mL min(-1) g(-1) (0.304+/-0.196 mL min(-1) g(-1)) and 0.676-1.773 mL min(-1) g(-1) (1.207+/-0.327 mL min(-1) g(-1)), respectively. Collateral-perfusion index (CPI) is defined as the rate of MBF during and after angioplasty varied between 0.05 and 0.67 (0.26+/-0.15). During angioplasty, simultaneous measurements of mean aortic pressure, coronary wedge pressure, and central venous pressure determined the pressure-derived collateral-flow index (CFI(p)), which varied between 0.04 and 0.61 (0.23+/-0.14). Linear-regression analysis demonstrated an excellent agreement between CFI(p) and CPI (y=0.88 x +0.01; r(2)=0.92; P<0.0001).

CONCLUSION

Collateral-derived MBF measurements by MCE during angioplasty are feasible and proved that the pressure-derived CFI exactly reflects collateral relative to normal myocardial perfusion in humans.

Collateral circulation in human heart

The aim of the investigations was to demonstrate different types of collaterals of coronary arteries using the method of coronary angiography and injection-corrosion method. The investigations were carried out on 30 human cadaveric hearts from the Department of Anatomy, and 30 angiograms of patients from the Cardiology Department of Clinics Centre in Sarajevo. Clinical investigations were retrospective and prospective on patients that were treated in hospital, and on patients that just arrived in hospital (based on findings of coronary angiography). The results show the existence of different types of collaterals: intercoronary and intracoronary. We established collaterals in a case with occlusion of the right coronary artery and left coronary artery in which better development of collaterals was established. Our patients were classified in two groups: 1) Patients with good collaterals and good left ventricular function; 2) Patients with good collaterals and impaired left ventricular function. On the anatomical material we found different types of collaterals as well. Our results show that coronary angiography is useful diagnostic method for the demonstration of coronary collaterals.

Coronary collaterals by transthoracic echocardiography in coronary artery disease

Demonstration of coronary collaterals has been mostly done by coronary angiographic techniques. Coronary collaterals have been demonstrated by transthoracic echocardiography for patients with anomalous origin of coronary arteries from pulmonary artery. Indirect assessment of collaterals to an infarct-related artery has been done using myocardial contrast echocardiography. We describe in this article 3 patients with coronary artery disease in whom coronary collaterals were demonstrated by transthoracic echocardiography before angiography. To our knowledge, coronary collateral demonstration by transthoracic echocardiography before angiography in patients with coronary artery disease has not been previously reported.

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.