Fractional flow reserve (FFR) is increasingly used to evaluate the functional significance of epicardial coronary disease. When compared with non-invasive techniques this index has superior sensitivity and specificity, is largely independent of prevailing haemodynamic conditions and has an unequivocal normal value. Furthermore, it can be used at the time of invasive coronary assessment. FFR measurements are invaluable for evaluation of intermediate coronary lesions but clinical decisions must be based on accurate measurements and an understanding of the limitations of the data supporting its use. This article identifies procedural and clinical issues pertaining to measurement of FFR and identifies potential pitfalls and situations where interpretation can be difficult; for example, the presence of serial stenoses and left main stem disease, its use in specific conditions such as diffuse epicardial disease, microvascular abnormalities, left ventricular dysfunction and acute coronary syndromes. (+info)
Cardiac magnetic resonance perfusion imaging for the functional assessment of coronary artery disease: a comparison with coronary angiography and fractional flow reserve.
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AIMS: Cardiac magnetic resonance perfusion imaging (CMRI) is a promising technique for non-invasive measurement of myocardial perfusion reserve. Fractional flow reserve (FFR) is an established invasive method for functional assessment of coronary artery disease (CAD). To prospectively assess the diagnostic value of CMRI for the detection of haemodynamically significant coronary lesions, compared with coronary angiography (CA) and FFR. METHODS AND RESULTS: Forty-three patients with suspected or known CAD underwent CA, CMRI, and FFR measurement. First pass magnetic resonance perfusion examination was performed during hyperaemia (140 microg/kg/min adenosine over 6 min) and at rest. One hundred and twenty-nine perfusion territories were assessed by semi-quantitative evaluation of signal intensity-time curves using the myocardial perfusion reserve index (MPRI) [upslope(stress(corrected))/upslope(rest(corrected))]. Perfusion territories were categorized as normal (coronary stenosis < or = 50%), intermediate (stenosis > 50% and FFR > 0.75), or severe (stenosis > 50% and FFR < or = 0.75 or total occlusion). MPRI values (+/-SD) were significantly different between the three categories [normal, 2.2 +/- 0.5 vs. intermediate, 1.8 +/- 0.5 (P = 0.005) and intermediate vs. severe, 1.2 +/- 0.3 (P < 0.001)]. An MPRI cut-off value of 1.5 (derived from receiver operating characteristics analysis) distinguished haemodynamically relevant (severe) from non-relevant (normal and intermediate) stenoses with a sensitivity of 88% (CI 74-100%) and a specificity of 90% (CI 84-96%). CONCLUSION: In contrast to earlier studies that compared CMRI with morphological examination (CA) alone, the present study compared CMRI with CA plus a standard invasive functional assessment (FFR) and demonstrated that CMRI is able to distinguish haemodynamically relevant from non-relevant coronary lesions with a high sensitivity and specificity and may therefore contribute to clinical decision-making. (+info)
Evaluation of the haemodynamic characteristics of drug-eluting stents at implantation and at follow-up.
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AIMS: The aim of this study was to investigate the physiologic parameters: fractional flow reserve (FFR), hyperaemic trans-stent gradient (HTG), and wall shear stress (WSS) at implantation and at 6-month follow-up in the drug-eluting sirolimus stent and in its bare metal counterpart implanted in pairs within the same patient. METHODS AND RESULTS: Twenty patients, accepted for percutaneous coronary intervention of at least two coronary arteries with comparable vessel and stenosis characteristics, received at random one sirolimus-eluting stent and one bare metal stent (BMS). Coronary pressure, FFR, HTG, and WSS were measured just after stent implantation and at 6-month follow-up. At 6-month follow-up, FFR was significantly higher in the sirolimus group compared with the bare metal group (0.91+/-0.05 vs. 0.83+/-0.10, P=0.027) and HTG was significantly lower (1.2+/-1.2 vs. 7.5+/-8.1 mmHg, P<0.001). In-stent WSS at 6 months remained normal in the sirolimus group but was elevated in the bare metal group (1.6+/-0.7 vs 3.9+/-3.1 Pa, respectively, P=0.003). CONCLUSION: The physiologic characteristics of the drug-eluting sirolimus stents were superior to those of the equivalent BMS. Six months after implantation, FFR was significantly higher, HTG was significantly lower in arteries treated by a sirolimus stent, and normal WSS was maintained within the drug-eluting stent. (+info)
The diastolic flow velocity-pressure gradient relation and dpv50 to assess the hemodynamic significance of coronary stenoses.
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To evaluate the hemodynamic impact of coronary stenoses, the fractional (FFR) or coronary flow velocity reserve (CFVR) usually is measured. The combined measurement of instantaneous flow velocity and pressure gradient (v-dp relation) is rarely used in humans. We derived from the v-dp relation a new index, dp(v50) (pressure gradient at flow velocity of 50 cm/s), and compared the diagnostic performance of dp(v50), CFVR, and FFR. Before coronary angiography was performed, patients underwent noninvasive stress testing. In all coronary vessels with an intermediate or severe stenosis, the flow velocity, aortic, and distal coronary pressure were measured simultaneously with a Doppler and pressure guidewire after induction of hyperemia. After regression analysis of all middiastolic flow velocity and pressure gradient data, the dp(v50) was calculated. With the use of the results of noninvasive stress testing, the dp(v50) cutoff value was established at 22.4 mmHg. In 77 patients, 124 coronary vessels with a mean 39% (SD 19) diameter stenosis were analyzed. In 43 stenoses, ischemia was detected. We found a sensitivity, specificity, and accuracy of 56%, 86%, and 76% for CFVR; 77%, 99%, and 91% for FFR; and 95%, 95%, and 95% for dp(v50). To establish that dp(v50) is not dependent on maximal hyperemia, dp(v50) was recalculated after omission of the highest quartile of flow velocity data, showing a difference of 3%. We found that dp(v50) provided the highest sensitivity and accuracy compared with FFR and CFVR in the assessment of coronary stenoses. In contrast to CFVR and FFR, assessment of dp(v50) is not dependent on maximal hyperemia. (+info)
Effect of coronary stenosis on adjacent bed flow reserve: assessment of microvascular mechanisms using myocardial contrast echocardiography.
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BACKGROUND: During coronary stenosis, flow reserve in the adjacent nonstenotic bed decreases, but the microvascular mechanisms are unknown. Because myocardial contrast echocardiography (MCE) assesses microvascular physiology, we used it to relate flow reserve to intramyocardial blood volume in the adjacent bed. METHODS AND RESULTS: A noncritical left anterior descending (LAD) stenosis was created in 10 dogs. MCE was performed and myocardial blood flow was measured with neutron-activated microspheres and flow probes. Data were collected at baseline, hyperemia, and hyperemia and stenosis. Hyperemia was induced with an A2A receptor agonist. MCE acoustic intensity in the LAD and left circumflex (LCx) regions were fit to the following: y=A(1-e(-beta t)), where A, beta, and A x beta reflect intramyocardial blood volume, red cell velocity, and flow, respectively. During hyperemia alone, LCx probe and microsphere flows and MCE-derived red cell velocity increased from baseline (30+/-14 versus 125+/-62 mL/min, P<0.0005; 1.5+/-0.5 versus 6.6+/-2.0 mL x min(-1) x g(-1), P<0.0005; and 0.53+/-0.14 versus 0.96+/-0.45 second(-1), P=0.030, respectively); intramyocardial blood volume was unchanged. LAD stenosis during hyperemia decreased LCx probe flow (125+/-62 versus 110+/-57 mL/min; P<0.05), microsphere flow (6.6+/-2.0 versus 4.2+/-2.1 mL x min(-1) x g(-1); P<0.0005), and MCE-derived flow (0.57+/-0.29 versus 0.45+/-0.33 second(-1); P=0.032). LCx bed intramyocardial blood volume concurrently increased (0.61+/-0.14 versus 0.70+/-0.15; P<0.01). CONCLUSIONS: Coronary stenosis impairs flow reserve in the adjacent nonstenotic bed, in which intramyocardial blood volume increases. MCE suggests compensatory recruitment of microvascular anastomotic collateral networks that augment stenotic bed flow reserve, but at the expense of the adjacent bed. Adjacent bed collateral microcirculation thus participates in the regulation of collateral flow and appears functionally significant during coronary stenosis. (+info)
Impaired myocardial perfusion reserve in experimental hypercholesterolemia is independent of myocardial neovascularization.
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Our objective was to investigate the functional role of hypercholesterolemia-associated myocardial neovascularization in early atherosclerosis using the antiangiogenic thalidomide. Experimental atherosclerosis is characterized by myocardial neovascularization, associated with a decrease in myocardial perfusion response to challenge, coronary endothelial dysfunction, and high oxidative stress. However, the functional significance of these neovessels is not known. Three groups of pigs (n = 6 each) were studied after 12 wk of normal or hypercholesterolemic diet without (HC) or with thalidomide (HC + Thal). Myocardial perfusion and permeability were assessed at baseline and in response to cardiac challenge, using electron beam computed tomography, and coronary endothelial function was assessed using organ chambers. Myocardial samples were scanned ex vivo with a three-dimensional microscopic computed tomography scanner, and the spatial density of the myocardial microvessels was quantified. Growth factors and oxidative stress were measured in the myocardial tissue. As a results of these procedures, myocardial perfusion response to adenosine and dobutamine was blunted in both HC and HC + Thal pigs compared with normal pigs (P < 0.05, HC and HC + Thal vs. normal) as was the coronary endothelial function. Myocardial permeability response to adenosine was increased in both HC and HC + Thal pigs compared with normal pigs (P < 0.05, HC and HC + Thal vs. normal, and HC + Thal vs. HC). The microvascular density was increased in HC pigs compared with normal pigs but normalized in HC + Thal pigs (P < 0.001 HC vs. normal and HC + Thal). HC + Thal pigs showed decreased expression of Flk-1 and basic FGF but increased expression of VEGF compared with normal and HC pigs. Oxidative stress was increased in both HC and HC + Thal pigs compared with normal pigs. In conclusion, chronic administration of thalidomide attenuates myocardial neovascularization in experimental HC pigs without affecting myocardial perfusion response to stimulation. This suggests that the myocardial neovascularization may not contribute to the attenuated myocardial perfusion response in hypercholesterolemia. (+info)
Assessment of intermediate severity coronary lesions in the catheterization laboratory.
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The management of intermediate coronary lesions, defined by a diameter stenosis of 40% to 70%, continues to be a therapeutic dilemma for cardiologists. The 2-dimensional representation of the arterial lesion provided by angiography is limited in distinguishing intermediate lesions that require stenting from those that simply need appropriate medical therapy. In the era of drug-eluting stents, some might propose that stenting all intermediate coronary lesions is an appropriate solution. However, the possibility of procedural complications such as coronary dissection, no reflow phenomenon, in-stent restenosis, and stent thrombosis requires accurate stratification of patients with intermediate coronary lesions to appropriate therapy. Intravascular ultrasound (IVUS) and fractional flow reserve index (FFR) provide anatomic and functional information that can be used in the catheterization laboratory to designate patients to the most appropriate therapy. The purpose of this review is to discuss the critical information obtained from IVUS and FFR in guiding treatment of patients with intermediate coronary lesions. In addition, the importance of IVUS and FFR in the management of patients with serial stenosis, bifurcation lesions, left main disease, saphenous vein graft disease, and acute coronary syndrome will be discussed. (+info)
Preservation of coronary reserve by ivabradine-induced reduction in heart rate in infarcted rats is associated with decrease in perivascular collagen.
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We tested the hypothesis that chronically reducing the heart rate in infarcted middle-aged rats using ivabradine (IVA) would induce arteriolar growth and attenuate perivascular collagen and, thereby, improve maximal perfusion and coronary reserve in the surviving myocardium. Myocardial infarction (MI) was induced in 12-mo-old male Sprague-Dawley rats, which were then treated with either IVA (10.5 mg.kg(-1).day(-1); MI + IVA) or placebo (MI) via intraperitoneal osmotic pumps for 4 wk. Four weeks of IVA treatment limited the increase in left ventricular end-diastolic pressure and the decrease in ejection fraction but did not affect the size of the infarct, the magnitude of myocyte hypertrophy, or the degree of arteriolar and capillary growth. However, treatment reduced interstitial and periarteriolar collagen in the surviving myocardium of MI + IVA rats. The reduced periarteriolar collagen content was associated with improvement in maximal myocardial perfusion and coronary reserve. Although the rates of proliferation of periarteriolar fibroblasts were similar in the MI and MI + IVA groups, the expression levels of the AT(1) receptor and transforming growth factor (TGF)-beta(1) in the myocardium, as well as the plasma level of the ANG II peptide, were lower in treated rats 14 days after MI. Therefore, our data reveal that improved maximal myocardial perfusion and coronary reserve in MI + IVA rats are most likely the result of reduced periarteriolar collagen rather than enhanced arteriolar growth. (+info)