Safety of deferring angioplasty in patients with normal coronary flow velocity reserve

The impact of coronary microvascular dysfunction on the discordance between fractional flow reserve and resting full-cycle ratio in patients with chronic coronary syndromes

Background

Resting full-cycle ratio (RFR) is an alternative to fractional flow reserve (FFR) for the evaluation of borderline coronary artery lesions. Although FFR and RFR results are discordant in some cases, factors associated with the discordance remain unclear. The role of coronary microvascular dysfunction (CMD) is discussed as a potential mechanism to explain these discrepancies.

Aim

The study aimed to assess concordance between RFR and FFR in a real-life cohort from a high-volume center regarding the role of CMD.

Methods

Consecutive patients with borderline coronary lesions undergoing coronary functional testing for chronic coronary syndromes were included in the study. Measurements of RFR and FFR were performed alongside additional coronary flow reserve (CFR), resistance reserve ratio (RRR), and an index of microcirculatory resistance (IMR) measurements. CMD was defined according to the current guideline by either IMR ≥25 or CFR ≤2.0 in vessels with no significant stenosis.

Results

Measurements were performed in 157 coronary arteries, in 101 patients, with a median age of 66 y., 74% male, with prior history of arterial hypertension (96%), dyslipidaemia (91%), and diabetes (40%). The median value of vessel diameter stenosis was 45% according to QCA.

Overall, FFR and RFR values were significantly correlated (r = 0.66, p < 0.001), where positive FFR/negative RFR and negative FFR/positive RFR were observed in 6 (3.8%) and 38 (24.2%) of 157 vessels. The RFR/FFR discrepancy was present in 44 (28%) of measurements. CMD was confirmed in 28 (64%) of vessels with discrepant RFR/FFR and in 46 (41%) of vessels with concordant results (p = 0.01). In discordant RFR/FFR vessels, as compared to concordant ones, significantly lower values of CFR [median 1.95 (IQR: 1.37, 2.30) vs. 2.10 (IQR: 1.50, 3.00), p = 0.030] and RRR [median 2.50 (IQR: 1.60, 3.10) vs. 2.90 IQR (1.90, 3.90), p = 0.048] were observed.

Main predictors of RFR/FFR discrepancy in a univariate regression analysis were: higher age of patients [OR = 1.06 (1.01; 1.10), p = 0.010], presence of CMD [OR = 2.51 (1.23; 5.25), p = 0.012], lower CFR [OR = 1.64 (1.12; 2.56), p = 0.018], and lower RRR values [OR = 1.35 (95% CI: 1.03; 1.83), p = 0.038].

Conclusion

In discrepant RFR/FFR vessels, CMD is more prevalent than in concordant RFR/FFR measurements, which can be driven by lower CFR or RRR values. Further research is needed to confirm this observation.

Early effect of percutaneous coronary intervention of non-left anterior descending artery on coronary flow velocity reserve of left anterior descending artery assessed by transthoracic Doppler echocardiography

Background

Limited data are available regarding the influence of percutaneous coronary intervention (PCI) of non-totally occluded lesions (non-CTO) on the coronary flow of non-target vessels. We sought to investigate the short-term impact of the non-left anterior descending artery (non-LAD) PCI on the coronary flow physiology of LAD using transthoracic Doppler echocardiography (TDE).

Methods and results

We consecutively studied 50 patients who underwent successful PCI of non-LAD and non-CTO lesions and a coronary flow velocity assessment of LAD at rest and maximal hyperemia before and at 2 days after the procedure by TDE. Coronary flow velocity reserve (CFVR) was calculated as the ratio of hyperemic to resting diastolic peak velocity (hDPV/bDPV). We evaluated the changes in LAD coronary flow characteristics after PCI of non-LAD and explored the determinants of the change in LAD-CFVR. The median fractional flow reserve (FFR) of the culprit lesion and the LAD quantitative flow ratio (QFR) were 0.67 and 0.88, respectively. After non-LAD PCI, LAD-CFVR was decreased in 33 patients (66.0%). LAD-CFVR significantly decreased (pre-PCI: 2.41, post-PCI: 2.03, p = 0.001) due to a significant decrease in LAD-hDPV (P = 0.007). The prevalence of impaired LAD-CFVR (≤2.0) significantly increased (pre: 30%, post: 48%, P = 0.027). Multivariable linear regression analysis showed that pre-PCI LAD-CFVR was independent predictor of the change in LAD-CFVR after PCI.

Conclusions

LAD-CFVR significantly decreased after successful non-LAD PCI due to the postprocedural reduction of coronary flow assessed by LAD-hDPV.

Novel application of quantitative flow ratio for predicting microvascular dysfunction after ST-segment-elevation myocardial infarction

OBJECTIVES

This study evaluated quantitative flow ratio (QFR) to predict microvascular dysfunction (MVD) in patients with ST-segment elevation myocardial infarction (STEMI).

BACKGROUND

QFR is a novel approach for the rapid computation of fractional flow reserve based on three-dimensional quantitative coronary angiography. We hypothesized that QFR computation could be used to predict MVD after STEMI.

METHODS

Indexes such as contrast-flow QFR (cQFR), fixed-flow QFR (fQFR), and hyperemic flow velocity (HFV) were calculated in 130 STEMI patients with culprit lesion with ≥50% diameter stenosis and TIMI flow grade 2/3 in the spontaneously recanalized culprit artery on initial angiography. MVD was defined as microvascular obstruction determined by contrast-enhanced cardiac magnetic resonance at a median of 5 days after percutaneous coronary intervention.

RESULTS

Patients were divided into the MVD group (76/130, 58.5%) and non-MVD group (54/130, 41.5%). Patients with MVD had higher cQFR-fQFR value (0.080 ± 0.058 vs. 0.038 ± 0.039, p < .001) and lower modeled HFV (0.096 ± 0.044 vs. 0.144 ± 0.041 m/s, p < .001). Receiver operator characteristic curve analysis revealed that both the cQFR-fQFR value (area under the curve, AUC = 0.716, p < .001) and modeled HFV (AUC = 0.805, p < .001) had high specificity and positive predictive value to predict MVD. In multivariable logistic analysis, cQFR-fQFR was identified as an independent predictor of MVD (odds ratio = 9.800, p < .001).

CONCLUSIONS

This proof-of-concept study suggested that QFR computation may be a useful tool to predict MVD after STEMI (Trial Registration:NCT03780335).

Relationship between FFR, CFR and coronary microvascular resistance - Practical implications for FFR-guided percutaneous coronary intervention

Objective

The aim was threefold: 1) expound the independent physiological parameters that drive FFR, 2) elucidate contradictory conclusions between fractional flow reserve (FFR) and coronary flow reserve (CFR), and 3) highlight the need of both FFR and CFR in clinical decision making. Simple explicit theoretical models were supported by coronary data analyzed retrospectively.

Methodology

FFR was expressed as a function of pressure loss coefficient, aortic pressure and hyperemic coronary microvascular resistance. The FFR-CFR relationship was also demonstrated mathematically and was shown to be exclusively dependent upon the coronary microvascular resistances. The equations were validated in a first series of 199 lesions whose pressures and distal velocities were monitored. A second dataset of 75 lesions with pre- and post-PCI measures of FFR and CFR was also analyzed to investigate the clinical impact of our hemodynamic reasoning.

Results

Hyperemic coronary microvascular resistance and pressure loss coefficient had comparable impacts (45% and 49%) on FFR. There was a good concordance (y = 0.96 x − 0.02, r² = 0.97) between measured CFR and CFR predicted by FFR and coronary resistances. In patients with CFR < 2 and CFR/FFR ≥ 2, post-PCI CFR was significantly >2 (p < 0.001), whereas it was not (p = 0.94) in patients with CFR < 2 and CFR/FFR < 2.

Conclusion

The FFR behavior and FFR-CFR relationship are predictable from basic hemodynamics. Conflicting conclusions between FFR and CFR are explained from coronary vascular resistances. As confirmed by our results, FFR and CFR are complementary; they could jointly contribute to better PCI guidance through the CFR-to-FFR ratio in patients with coronary artery disease.

Prognostic Value of Transthoracic Doppler Echocardiography Coronary Flow Velocity Reserve in Patients with Nonculprit Stenosis of Intermediate Severity Early after Primary Percutaneous Coronary Intervention

BACKGROUND

Treatment of nonculprit coronary stenosis during primary percutaneous coronary intervention in patients with ST-segment elevation myocardial infarction may be beneficial, but the mode and timing of the intervention are still controversial. The aim of this study was to examine the significance and prognostic value of preserved coronary flow velocity reserve (CFVR) in patients with nonculprit intermediate stenosis early after primary percutaneous coronary intervention.

METHODS

Two hundred thirty patients with remaining intermediate (50%-70%) stenosis of non-infarct-related arteries, in whom CFVR was performed within 7 days after primary percutaneous coronary intervention, were prospectively enrolled. Twenty patients with reduced CFVR and positive results on stress echocardiography or impaired fractional flow reserve underwent revascularization and were not included in further analysis. The final study population of 210 patients (mean age, 58 ± 10 years; 162 men) was divided into two groups on the basis of CFVR: group 1, CFVR > 2 (n = 174), and group 2, CFVR ≤ 2 (n = 36). Cardiac death, nonfatal myocardial infarction, and revascularization of the evaluated vessel were considered adverse events.

RESULTS

Mean follow-up duration was 47 ± 16 months. Mean CFVR for the whole group was 2.36 ± 0.40. There were six adverse events (3.4%) related to the nonculprit coronary artery in group 1, including one cardiac death, one ST-segment elevation myocardial infarction, and four revascularizations. In group 2, there were 30 adverse events (83.3%, P < .001 vs group 1), including two cardiac deaths, two ST-segment elevation myocardial infarctions, and 26 revascularizations.

CONCLUSIONS

In patients with CFVR > 2 of the intermediate nonculprit coronary lesion, deferral of revascularization is safe and associated with excellent long-term clinical outcomes.

Invasive physiological indices to determine the functional significance of coronary stenosis

Physiological measurements are now commonly used to assess coronary lesions in the cardiac catheterisation laboratory, and this practice is evidence-based and supported by clinical guidelines. Fractional flow reserve is currently the gold standard method to determine whether coronary lesions are functionally significant, and is used to guide revascularization. There are however several other physiological measurements that have been proposed as alternatives to the fractional flow reserve. This review aims to comprehensively discuss physiological indices that can be used in the cardiac catheterisation laboratory to determine the functional significance of coronary lesions. We will focus on their advantages and disadvantages, and the current evidence supporting their use.

Positron Emission Tomography-Determined Hyperemic Flow, Myocardial Flow Reserve, and Flow Gradient-Quo Vadis?

Positron emission tomography/computed tomography (PET/CT) applied with positron-emitting flow tracers such as ¹³N-ammonia and ⁸²Rubidium enables the quantification of both myocardial perfusion and myocardial blood flow (MBF) in milliliters per gram per minute for coronary artery disease (CAD) detection and characterization. The detection of a regional myocardial perfusion defect during vasomotor stress commonly identifies the culprit lesion or most severe epicardial narrowing, whereas adding regional hyperemic MBFs, myocardial flow reserve (MFR), and/or longitudinal flow decrease may also signify less severe but flow-limiting stenosis in multivessel CAD. The addition of regional hyperemic flow parameters, therefore, may afford a comprehensive identification and characterization of flow-limiting effects of multivessel CAD. The non-specific origin of decreases in hyperemic MBFs and MFR, however, prompts an evaluation and interpretation of regional flow in the appropriate context with the presence of obstructive CAD. Conversely, initial results of the assessment of a longitudinal hyperemic flow gradient suggest this novel flow parameter to be specifically related to increases in CAD caused epicardial resistance. The concurrent assessment of myocardial perfusion and several hyperemic flow parameters with PET/CT may indeed open novel avenues of precision medicine to guide coronary revascularization procedures that may potentially lead to a further improvement in cardiovascular outcomes in CAD patients.

Myocardial blood flow: Putting it into clinical perspective

In recent years, positron emission tomography/computed tomography (PET/CT)-determined myocardial perfusion in conjunction with myocardial blood flow (MBF) quantification in mL·g(-1)·min(-1) has emerged from mere research application to initial clinical use in the detection and characterization of the coronary artery disease (CAD) process. The concurrent evaluation of MBF during vasomotor stress and at rest with the resulting myocardial flow reserve (MFR = MBF during stress/MBF at rest) expands the scope of conventional myocardial perfusion imaging not only to the detection of the most advanced and culprit CAD, as evidenced by the stress-related regional myocardial perfusion defect, but also to the less severe or intermediate stenosis in patients with multivessel CAD. Due to the non-specific nature of the hyperemic MBF and MFR, the interpretation of hyperemic flow increases with PET/CT necessitates an appropriate placement in the context with microvascular function, wall motion analysis, and eventually underlying coronary morphology in CAD patients. This review aims to provide a comprehensive overview of various diagnostic scenarios of PET/CT-determined myocardial perfusion and flow quantification in the detection and characterization of clinically manifest CAD.

Coronary physiology assessment in the catheterization laboratory

Physicians cannot rely solely on the angiographic appearance of epicardial coronary artery stenosis when evaluating patients with myocardial ischemia. Instead, sound knowledge of coronary vascular physiology and of the methods currently available for its characterization can improve the diagnostic and prognostic accuracy of invasive assessment of the coronary circulation, and help improve clinical decision-making. In this article we summarize the current methods available for a thorough assessment of coronary physiology.

Current concepts of integrated coronary physiology in the catheterization laboratory

Over the last 15 years, the use of invasive coronary physiology in the catheterization laboratory has demonstrated favorable outcomes for decision making in patients with intermediate single-vessel stenoses, complex bifurcation and ostial branch stenoses, multivessel coronary artery disease, and left main stenoses. A recent large multicenter study (FAME [FFR versus Angiography for Multivessel Evaluation]) found that a physiologically-guided approach was superior to the standard angiographically-guided approach for percutaneous revascularization in patients with multivessel coronary artery disease. This review addresses selected pertinent concepts and studies supporting the integration of coronary physiology in the catheterization laboratory for optimal patient outcomes.

Usefulness of coronary flow reserve measured by echocardiography to improve the identification of significant left anterior descending coronary artery stenosis assessed by multidetector computed tomography

Multidetector computed tomography (MDCT) detects coronary artery disease. However, an overestimation of coronary artery stenosis and artifacts can prevent accurate identification of significant coronary narrowing. The combination of MDCT with coronary flow reserve (CFR), the hyperemic/baseline peak flow velocity ratio, measured by transthoracic Doppler echocardiography might be helpful. We studied 144 consecutive patients with CFR and quantitative coronary angiography, obtained using both MDCT and invasive coronary angiography (reference method). It was hypothesized that the CFR might provide an incremental value to MDCT in detecting significant (> or =70%) left anterior descending (LAD) coronary artery stenosis. A CFR cutoff of <2 was used to discriminate significant stenosis. CFR was feasible in 141 (98%) of 144 patients, and MDCT was feasible in 131 (91%) of 144 patients (p <0.02). In a univariate model, the prediction of significant LAD stenosis was slightly, but significantly (p <0.0001), better with CFR (sensitivity 90%, specificity 96%, positive predictive value 84%, negative predictive value 97%, and diagnostic accuracy 94%, chi-square = 97.5) than with MDCT (sensitivity 80%, specificity 93%, positive predictive value 71%, negative predictive value 95%, diagnostic accuracy 90%, chi-square = 63.2). When the findings from transthoracic Doppler echocardiography and MDCT agreed, the diagnostic accuracy increased (96%; chi-square = 86.1, p <0.0001). In a multivariate prediction of significant LAD stenosis using a logistic neural network, CFR overshadowed MDCT, and the area under the receiver operating curve was 0.99. Of the 13 patients missed by MDCT, the diagnostic accuracy of transthoracic Doppler echocardiography to predict significant LAD stenosis was 100%. Thus, CFR could improve the diagnostic accuracy of MDCT to detect significant LAD stenosis.

Comparison of pressure measurement, dobutamine contrast stress echocardiography and SPECT for the evaluation of intermediate coronary stenoses. The COMPRESS trial

BACKGROUND

DSE and SPECT are two well-established methods to non-invasively investigate the functional significance of coronary artery stenoses in patients with coronary artery disease. The measurement of Fractional Flow Reserve has emerged a new invasive reference standard for lesion specific quantification of coronary artery stenoses. The objective of our prospective study was to compare sensitivity and specificity of Dobutamine Stress Echocardiography (DSE) and Single Photon Emission Computer tomography (SPECT) with the pressure derived Fractional Flow Reserve (FFR) for the identification of hemodynamic relevant coronary lesions in patients with predominately coronary multivessel disease and angiographically intermediate stenoses.

METHODS

Inclusion criteria were a coronary lesion of 50-75% diameter stenosis by visual assessment in patients with known or suspected CAD. SPECT, DSE and FFR testing was performed within one week of coronary angiography.

RESULTS

The study comprised 48 consecutive symptomatic patients. In 41 cases, a coronary multivessel disease was present. Mean FFR was 0.80 +/- 0.13 (0.41-1.0). Overall sensitivity of DSE and SPECT was 67% and 69% whereas specificity reached 77% and 87%. However, sensitivity was significantly reduced if the target lesion was located distally. DSE showed poor results if the lesions were located in the circumflex artery or if a history of prior myocardial infarctions was present.

CONCLUSION

DSE and SPECT are both useful methods for the non-invasive assessment of coronary artery disease. DSE showed reasonable combination of sensitivity and specificity even in patients with multivessel disease. Although use of noninvasive stress tests is only limited in patients with prior myocardial infarctions and invasive stress testing should be preferred in these patients.

The prognostic value of combined intracoronary pressure and blood flow velocity measurements after deferral of percutaneous coronary intervention

OBJECTIVES

We evaluated deferral of PCI of intermediate coronary lesions (IL) using fractional (FFR) and coronary flow reserve (CFR) hyperemic stenosis resistance index (HSR) in patients with a negative or nondiagnostic and noninvasive stress tests.

BACKGROUND

Outcome after deferral of PCI of IL with discordant results between FFR and CFR is unknown.

METHODS

PCI was deferred in 186 IL (mean diameter stenosis: 52%). Patients were divided according to the results of FFR and CFR in group A; FFR >or= 0.75 and CFR >or= 2.0 (n = 129), group B; FFR >or= 0.75 and CFR 2.0 (n = 28), group C; FFR 0.75 and CFR >or= 2.0 (n = 23) and group D; FFR 0.75 and CFR 2.0 (n = 6). Patients were followed for one year to document major adverse cardiac events (MACE).

RESULTS

Nineteen MACEs (0 deaths, 4 myocardial infarctions, 1 CABG, and 14 PCIs) occurred during a follow up of 323 +/- 88 days. MACE rate was lowest (4.7%) when FFR, CFR, and HSR were normal. A higher MACE rate was observed when concordant abnormal (group D) or discordant results between FFR and CFR (group B and C) were compared to concordant normal values (group A, 33.3% vs. 19.7% vs. 5.4%, P = 0.008). Multivariate regression analysis showed a higher predictive power for HSR than for FFR and CFR.

CONCLUSIONS

Abnormal FFR or abnormal CFR was documented in 31% of intermediate coronary lesions. Deferral of PCI in this group was associated with a high MACE rate, which underscores the rationale of combined pressure and flow measurements providing a stenosis resistance index that is better suited for clinical decision making in these lesions.

Electrocardiographic exercise stress testing: an update beyond the ST segment

Routine exercise testing is frequently ordered to evaluate a patient's cardiovascular performance. The test is more direct and less expensive than imaging technology, and derives valuable information. New variables such as dyspnea and heart rate recovery, as well as integrated scores, provide incremental value to conventional analysis of exercise-induced angina or electrocardiographic changes. Considerations relating to test accuracy in women need to be weighed. This paper seeks to make physicians aware of the current status of the test, and improve their understanding of and ability to integrate new variables and scores to more effectively manage their patients.

Turbulent flow as a cause for underestimating coronary flow reserve measured by Doppler guide wire

Background

Doppler-tipped coronary guide-wires (FW) are well-established tools in interventional cardiology to quantitatively analyze coronary blood flow. Doppler wires are used to measure the coronary flow velocity reserve (CFVR). The CFVR remains reduced in some patients despite anatomically successful coronary angioplasty. It was the aim of our study to test the influence of changes in flow profile on the validity of intra-coronary Doppler flow velocity measurements in vitro. It is still unclear whether turbulent flow in coronary arteries is of importance for physiologic studies in vivo.

Methods

We perfused glass pipes of defined inner diameters (1.5 – 5.5 mm) with heparinized blood in a pulsatile flow model. Laminar and turbulent flow profiles were achieved by varying the flow velocity. The average peak velocity (APV) was recorded using 0.014 inch FW. Flow velocity measurements were also performed in 75 patients during coronary angiography. Coronary hyperemia was induced by intra-coronary injection of adenosine. The APV maximum was taken for further analysis. The mean luminal diameter of the coronary artery at the region of flow velocity measurement was calculated by quantitative angiography in two orthogonal planes.

Results

In vitro, the measured APV multiplied with the luminal area revealed a significant correlation to the given perfusion volumes in all diameters under laminar flow conditions (r² > 0.85). Above a critical Reynolds number of 500 – indicating turbulent flow – the volume calculation derived by FW velocity measurement underestimated the actual rate of perfusion by up to 22.5 % (13 ± 4.6 %). In vivo, the hyperemic APV was measured irrespectively of the inherent deviation towards lower velocities. In 15 of 75 patients (20%) the maximum APV exceeded the velocity of the critical Reynolds number determined by the in vitro experiments.

Conclusion

Doppler guide wires are a valid tool for exact measurement of coronary flow velocity below a critical Reynolds number of 500. Reaching a coronary flow velocity above the velocity of the critical Reynolds number may result in an underestimation of the CFVR caused by turbulent flow. This underestimation of the flow velocity may reach up to 22.5 % compared to the actual volumetric flow. Cardiologists should consider this phenomena in at least 20 % of patients when measuring CFVR for clinical decision making.

Cardiac hemodynamics, coronary circulation and interventional cardiology

Microcirculation is the functional end of the coronary circulation and it plays a key role in the regulation of coronary blood flow, both on the local and global scales. A good understanding of its function under physiological and pathophysiological conditions is crucial but, because of its micro-scale, access to this part of the coronary circulation is extremely difficult and requires a considerable amount of innovation and new technologies. Dynamics of the coronary circulation provide the true vehicle by which blood supply reaches the myocardium- coronary vasculature is only the conducting component of that vehicle. It is highly unlikely that the pulsatile nature of the flow, the capacitance of the conducting vessels and the constant pounding of coronary vasculature by surrounding tissue are not part of the design, regulation, and function of the coronary circulation. Interventions, whether to assess or to correct coronary stenosis, continue to be the main clinical avenue to dealing with coronary heart disease. Clinical decisions rely heavily on the ability to determine the true morphology of an occlusive lesion, to predict the future course of that lesion and to assess the functional toll on coronary blood supply which it will inflict at each stage.

Determinants of coronary flow velocity reserve in healthy young men

The objective of this study was to identify risk markers for attenuated coronary flow velocity reserve (CFVR) that exist in healthy young men without evident atherosclerotic risk factors. Coronary blood flow velocity was measured with transthoracic Doppler echocardiography at baseline and during adenosine infusion in 37 healthy nonsmoking men [mean age, 27 yr (SD 4.0)]. Body composition and distribution of fat tissue were assessed with anthropometric measures and regulation of fat metabolism by determination of adiponectin and leptin levels. Physical performance capacity was tested with ergospirometry. The mean body mass index was 23 kg/m2 (SD 1.9), waist-to-hip ratio was 0.84 (SD 0.04), and CFVR was 3.5 (SD 0.61). Obesity indexes at study outset, leptin, adiponectin, maximal load (Max load in W/kg) and maximal oxygen consumption (Vo2 peak in ml x kg(-1) x min(-1)) in ergospirometry, rate-pressure product, and heart rate at rest were significantly associated with CFVR. In multivariate analysis, Max load (in W/kg) and waist-to-hip ratio were the only independent predictors of CFVR. We found no relationship between CFVR and serum lipids or body mass index. We conclude that abdominal fat accumulation and low aerobic fitness are independently associated with CFVR in men.

Recovery of impaired microvascular function in collateral dependent myocardium after recanalisation of a chronic total coronary occlusion

OBJECTIVE

To assess the potential for recovery of impaired microvascular function in collateral dependent myocardium after recanalisation of a chronic total coronary occlusion and the determinants of this recovery.

PATIENTS AND DESIGN

120 patients underwent a successful recanalisation of a chronic total coronary occlusion (duration > 2 weeks) and a follow up angiography after a mean (SD) of 5.0 (1.2) months. The coronary flow velocity reserve (CFVR) and the fractional flow reserve were measured after recanalisation and at follow up. Global and regional left ventricular (LV) function were analysed by quantitative angiography.

RESULTS

Microvascular dysfunction, defined by a CFVR < 2.0 and a fractional flow reserve > or = 0.75, was observed in 55 (46%) patients after recanalisation. Microvascular function improved during follow up in 24 (20%). The CFVR increased during follow up from 2.01 (0.58) to 2.50 (0.79) (p < 0.001), due to a decrease in basal average peak velocity from 30.7 (14.9) cm/s to 25.5 (13.3) cm/s (p = 0.001). Improved microvascular function was associated with an improved regional LV function, shown by a correlation between increased wall motion severity index and increased CFVR (r = 0.38, p = 0.003). The major determinant of microvascular dysfunction at baseline was the presence of diabetes mellitus (odds ratio 4.3, 95% confidence interval 1.8 to 10.2), which remained so at follow up (odds ratio 4.1, 95% confidence interval 1.3 to 13.4). Improvement of LV function was not impaired by the presence of microvascular dysfunction after recanalisation.

CONCLUSIONS

The frequently observed microvascular dysfunction after recanalisation of a chronic total coronary occlusion is a transient phenomenon in most patients and is influenced by the presence of diabetes mellitus. It does not impede the recovery of LV function. Improved regional LV function is associated with improved microvascular function.

Effectiveness of sirolimus-Eluting stent implantation for coronary narrowings <50% in diameter

The long-term efficacy of percutaneous coronary intervention for mildly obstructive coronary narrowings is limited by the occurrence of restenosis, limiting the applicability of this therapy for these lesions. The present study reports on a consecutive series of 20 patients treated with sirolimus-eluting stent implantation for 23 angiographically mild de novo lesions (defined as a diameter stenosis <50% by quantitative coronary angiography). At a mean follow-up of 399 +/- 120 days, the survival-free of major adverse events was 95%, with no patient requiring target lesion revascularization.

Impaired left ventricular function after arterial switch operation: exclusion of significant coronary artery stenosis with an intravascular Doppler guidewire

Patients after arterial switch operation for transposition of the great arteries are at risk for coronary artery stenosis or obstruction due to intraoperative manipulation. This case describes an infant with impaired left ventricular function 8 months after arterial switch operation. A hemodynamically significant left coronary artery stenosis was excluded by determination of coronary flow reserve using an intravascular Doppler guidewire.

Frame count reserve

BACKGROUND

The Doppler wire-derived (relative) coronary flow velocity reserve (CVR) that is used to evaluate functional significance of a coronary stenosis is a method performed only by interventional cardiologists. An angiographic method would be useful in the diagnostic catheterization laboratory. For this purpose, we investigated the relation between TIMI frame count reserve (FCR) and CVR.

METHODS AND RESULTS

In 38 patients, (relative) FCR of left anterior descending (LAD) and left circumflex coronary artery (LCx) was calculated by using manual, synchronized contrast agent injections and compared with (relative) CVR. In addition, vessel length was measured with an intracoronary guidewire and frame count flow velocity was calculated and compared with average peak velocity. There was a strong correlation between FCR and CVR (r=0.62, P<0.001) and between relative FCR and relative CVR (r=0.84, P<0.001). The LAD was significantly longer than the LCx (mean, 14.3+/-1.6 cm versus 11.4+/-1.8 cm, P<0.001), and, therefore, TIMI frame count of LAD was significantly higher than of LCx (mean basal 32.5+/-15.1 versus 23.6+/-9.1 and hyperemic 12.1+/-6.6 versus 8.7+/-3.2, both P<0.02). However, all flow velocity measurements and estimations of volume flow were not different for LAD compared with LCx. There were also no differences between mean FCR and CVR of LAD or LCx, of both vessels compared with each other and between mean relative FCR and relative CVR.

CONCLUSIONS

The (relative) frame count reserve can be used to estimate (relative) coronary flow velocity reserve.

Assessment of intermediate stenosis in the left anterior descending coronary artery with contrast-enhanced transthoracic Doppler echocardiography

BACKGROUND

Visual or quantitative assessment of coronary angiography may not exactly predict the physiological significance of intermediate (40-70%) coronary stenosis. Coronary flow reserve is a well-established marker of the functional significance of coronary stenosis.

OBJECTIVES

The aim of this study was to compare the coronary flow velocity reserve (CFVR) using contrast-enhanced transthoracic Doppler echocardiography (CE-TTDE) with thallium-201 imaging in assessment of intermediate lesions in the left anterior descending coronary artery (LAD).

METHODS

A consecutive series of 50 patients with intermediate stenosis in the LAD underwent pharmacological stress thallium-201 imaging and CFVR measured by CE-TTDE.

RESULTS

CFVR could be measured in 49 of 50 patients by the present method. A CFVR <2.0 predicted the presence of a stress thallium defect in 12 of 14 patients (agreement=90%, kappa=0.76, P < 0.001). The sensitivity and specificity of CFVR for stress thallium-201 results were 86 and 91%, respectively. In contrast, significant stenosis (>50% by diameter) showed fair agreement for stress thallium defects (agreement=59%, kappa=0.28, P < 0.05).

CONCLUSIONS

In the evaluation of intermediate lesions in the LAD, CFVR as assessed by CE-TTDE could accurately predict the presence of ischemia on stress thallium imaging, whereas angiographic stenosis did not yield reliable results.

Measuring pressure-derived fractional flow reserve through four French diagnostic catheters

Measurement of fractional flow reserve (FFR) with a pressure wire is used to discriminate between patients with and without functionally significant lesions. FFR can be assessed through a conventional 4Fr diagnostic catheter, which is a more convenient method of assessment. The aim of this study was to assess the feasibility, safety, repeatability, and reliability of routine FFR measurements through 4Fr diagnostic catheters. From a single-center prospective registry, results of FFR assessment through a 4Fr catheter were used to determine: (1) feasibility and safety, by the procedural success rate and immediate and 30-day clinical outcome; (2) repeatability, by the intraclass correlation coefficient and comparison of the difference (means +/- 2 SDs); and (3) reliability, by comparison of results obtained using 4Fr versus 7Fr guiding catheters. During the study period, FFR was measured in 190 patients, in 122 using a diagnostic 4Fr catheter (study population) and in 68 using a 7Fr guiding catheter. Measurement of FFR wa successful in 115 of 122 patients (94%). No complications related to the use of the 4Fr catheter occurred. Repeatability was determined from 108 repeated measurements: the intraclass correlation coefficient was 0.942 and the mean difference between repeated FFR measurements was -0.001 +/- 0.038. Reliability was determined from 15 unselected patients; there was no systematic error and only 1 value was out of the range of 2 SDs of the mean difference. Using a threshold value of 0.75, the Kappa coefficient for the qualitative agreement was 0.84. Thus, pressure-derived FFR assessment can safely be performed through 4Fr diagnostic catheters, with similar repeatability and reliability as 7Fr guiding catheters, resulting in a simplification of the measurement procedure.

Noninvasive coronary flow reserve assessed by transthoracic coronary Doppler ultrasound in patients with left anterior descending coronary artery stents

Noninvasive measurement of coronary flow reserve (CFR) (hyperemic/flow velocity ratio at rest) by transthoracic Doppler echocardiography showed normalization of flow in the left anterior descending (LAD) coronary artery early after stenting. We hypothesized that noninvasive CFR may reveal in-stent restenosis at follow-up. Therefore, we studied 134 patients, 0 to 72 months after successful proximal-middle LAD stenting, and 38 controls. LAD flow velocity was measured by transthoracic Doppler echocardiography during 90 seconds venous adenosine infusion (140 microg/kg/min). CFR was measured in diastole. According to angiography, patients who received stents were divided into 3 groups: group I, <50% LAD in-stent restenosis (n = 83); group II, nonsignificant (50% to 69%) LAD in-stent restenosis (n = 17); and group III, significant (> or = 70%) LAD in-stent restenosis (n = 34). LAD CFR was similar in group I and controls (2.90 +/- 0.58 vs 3.05 +/- 0.81; p = NS), it was slightly lower in group II (2.42 +/- 0.33) compared with controls and group I (p <0.001 vs both), and clearly abnormal (<2) in group III (1.38 +/- 0.48) compared with controls, and groups I and II (p <0.001). A CFR <2 had 91% sensitivity, 95% specificity, and 96% positive and 97% negative predictive values to detect significant stenosis in patients with LAD stents. Our data show that noninvasive Doppler assessment of CFR allows identification of significant LAD in-stent restenosis, based on a cut-off value of <2.

Evaluación y guía terapéutica de las lesiones coronarias intermedias en el laboratorio de hemodinámica

Contrast angiography has been used for nearly five decades to evaluate the severity of coronary lesions. However, when attempting to distinguish between intermediate coronary lesions able or unable to produce ischemia, the technique has several limitations. A large number of patients undergo cardiac catheterization without prior evaluation of coronary perfusion by non-invasive tests. This number is likely to increase in the coming years, because current recommendations favor the invasive treatment of acute coronary syndromes. This has triggered marked interest in new diagnostic techniques capable of assessing the physiological significance of intermediate lesions in the catheterization room. This paper reviews the different techniques currently available for scientifically assessing the significance of such lesions. The advantages and limitations of each are discussed.

Assessment of coronary flow reserve: comparison between contrast-enhanced magnetic resonance imaging and positron emission tomography

OBJECTIVES

The study compared flow reserve indices by magnetic resonance imaging (MRI) with quantitative measures of coronary angiography and positron emission tomography (PET).

BACKGROUND

The noninvasive evaluation of myocardial flow by MRI has recently been introduced. However, a comparison to quantitative flow measurement as assessed by PET has not been reported in patients with coronary artery disease (CAD).

METHODS

Two groups of healthy volunteers and 25 patients with angiographically documented CAD were examined by MRI and PET at rest and during adenosine stress. Dynamic MRI was performed using a multi-slice ultra-fast hybrid sequence and a rapid gadolinium-diethylenetriaminepenta-acetic acid bolus injection (0.05 mmol/l). Upslope and peak-intensity indices were regionally determined from first-pass signal intensity curves and compared to N-13 ammonia PET flow reserve measurements.

RESULTS

In healthy volunteers, the upslope analysis showed a stress/rest index of 2.1 plus minus 0.6, which was higher than peak intensity (1.5 plus minus 0.3), but lower than flow reserve by PET (3.9 plus minus 1.1). Localization of coronary artery stenoses (> 75%, MRI < 1.2), based on the upslope index, yielded sensitivity, specificity and diagnostic accuracy of 69%, 89% and 79%, respectively. Upslope index correlated with PET flow reserve (r = 0.70). A reduced coronary flow reserve (PET < 2.0, MRI < 1.3) was detected by the upslope index with sensitivity, specificity and diagnostic accuracy of 86%, 84% and 85%, respectively.

CONCLUSIONS

Magnetic resonance imaging first-pass perfusion measurements underestimate flow reserve values, but may represent a promising semi-quantitative technique for detection and severity assessment of regional CAD.

Prognostic value of coronary blood flow velocity and myocardial perfusion in intermediate coronary narrowings and multivessel disease

OBJECTIVES

This study aimed to investigate the roles of intracoronary derived coronary flow velocity reserve (CFVR) and myocardial perfusion scintigraphy (single photon emission computed tomography, or SPECT) for management of an intermediate lesion in patients with multivessel coronary artery disease.

BACKGROUND

Evaluation of the functional significance of intermediate coronary narrowings (40% to 70% diameter stenosis) is important for clinical decision making and risk stratification.

METHODS

In a prospective, multicenter study, SPECT was performed in 191 patients with stable angina and multivessel disease and scheduled for angioplasty (percutaneous transluminal coronary angioplasty, or PTCA) of a severe coronary narrowing. Coronary flow velocity reserve was determined selectively distal to an intermediate lesion in another artery using a Doppler guidewire. Percutaneous transluminal coronary angioplasty of the intermediate lesion was deferred when SPECT was negative or CFVR greater-than-or-equal 2.0. Patients were followed for one year to document major cardiac events (death, infarction, revascularization), related to the intermediate lesion.

RESULTS

Reversible perfusion defects were documented in the area of the intermediate lesion in 30 (16%) patients; CFVR was positive in 46 (24%) patients. Percutaneous transluminal coronary angioplasty of the intermediate lesion was deferred in 182 patients. During follow-up, 19 events occurred (3 myocardial infarctions, 16 revascularizations). Coronary flow velocity reserve was a more accurate predictor of cardiac events than was SPECT; relative risk: CFVR 3.9 (1.7 to 9.1), p < 0.05; SPECT 0.5 (0.1 to 3.2), p = NS. Multivariate analysis revealed CFVR as the only significant predictor for cardiac events.

CONCLUSIONS

Deferral of PTCA of intermediate lesions in multivessel disease is safe when CFVR greater-than-or-equal 2.0 (event rate 6%). This selective evaluation of coronary lesion severity during cardiac catheterization allows a more accurate risk stratification than does SPECT, which is important for clinical decision making in this patient cohort.

[Physiologic evaluation of coronary circulation. Role of invasive and non invasive techniques]

For many years, the evaluation of the extent and severity of coronary artery disease has been mainly anatomical, carried out by coronary angiography. However, this technique has methodological limitations and interobserver variability is considerable. Quantification of coronary reserve with pressure guidewires and intracoronary Doppler now provides more precise physiologic evaluation of coronary circulation. Myocardial perfusion single proton emission computed tomography and echocardiography, combined with stress and/or pharmacological challenge testing, though they are only semiquantitative techniques, also offer appropriate complements to coronary angiography in the functional evaluation of coronary patients. The aim of this paper is to discuss the clinical value of these techniques.

Adequate patient selection for coronary revascularization: an overview of current methods used in daily clinical practice

Widely used non-invasive stress modalities, like exercise ECG, MPS and stress-echocardiography, are the tests of first choice for the diagnosis of CAD. It has been shown in numerous studies that non-invasive assessment of perfusion abnormalities is an adequate strategy for risk stratification. Moreover, non-invasive stress testing should be performed before a diagnostic cardiac catheterization to document the presence of myocardial ischemia, as a prerequisite for coronary revascularization. Coronary angiography is the gold standard for identifying CAD; however this technique is limited in assessing functional severity of coronary narrowings ('illusion of luminology'; see also Figure 5). The recently introduced i.c. hemodynamic parameters (CFVR and FFR) can identify functional severity of specific lesions and have shown a good agreement with the results of non-invasive stress test in validation studies. Furthermore, there is accumulating evidence that it is safe to defer a PTCA procedure, based on normal FFR and CFVR values. As these indices are derived during an invasive cardiac catheterization procedure, its use is recommended during a so called 'ad hoc' PTCA setting. Furthermore, they are particularly useful for clinical decision making in patients with documented multivessel CAD, as both indices allow selective evaluation of coronary narrowings in different arteries. Revascularization procedures are costly and always have a potential risk. It is important to be aware that, using above mentioned methods, unnecessary interventions (lacking potential benefit) may be avoided.

Assessing coronary sinus blood flow in patients with coronary artery disease: a comparison of phase-contrast MR imaging with positron emission tomography

OBJECTIVE

This study was performed to determine whether MR imaging can be used to reliably measure global myocardial blood flow and coronary flow reserve in patients with coronary artery disease as compared with such measurements obtained by positron emission tomography (PET).

SUBJECTS AND METHODS

We measured myocardial blood flow first at baseline and then after dipyridamole-induced hyperemia in 20 patients with coronary artery disease. Myocardial blood flow as revealed by MR imaging was calculated by dividing coronary sinus flow by the left ventricular mass. Coronary flow reserve was calculated by dividing the rate of hyperemic flow by the rate of baseline flow.

RESULTS

Using MR imaging, myocardial blood flow at baseline was 0.73 +/- 0.23 mL x min(-1) x g(-1), and at hyperemia the blood flow was 1.43 +/- 0.37 mL x min(-1) x g(-1), yielding an average coronary flow reserve of 1.99 +/- 0.47. Using PET, myocardial blood flow was 0.89 +/- 0.21 mL x min(-1) x g(-1) at baseline and 1.56 +/- 0.42 mL x min(-1) x g(-1) at hyperemia, yielding an average coronary flow reserve of 1.77 +/- 0.36. The correlation of myocardial blood flow and coronary flow reserve measurements for these two methods was an r of 0.80 (p < 0.01) and an r of 0.50 (p < 0.05), respectively.

CONCLUSION

This study shows that myocardial blood flow measurements obtained using MR imaging have a good correlation with corresponding PET measurements. Coronary flow reserve measurements obtained using MR imaging had only moderate correlation with PET-obtained measurements. Our results suggest that MR imaging flow quantification could potentially be used for measuring global myocardial blood flow in patients in whom interventional treatment for coronary artery disease is being evaluated.

Clinical management of patients with coronary syndromes and negative fractional flow reserve findings

AIMS

New interventional techniques to diagnose coronary artery stenosis, such as calculation of myocardial fractional flow reserve (FFR) with a guidewire and pressure transducer, provide a functional assessment of coronary lesions. The present study was designed to investigate the occurrence of cardiac events in patients with coronary syndromes and negative FFR findings in moderately severe coronary stenosis in order to determine the usefulness of this technique in predicting coronary events during follow-up for problems commonly encountered in clinical practice. A further objective was to evaluate the safety of deferring angioplasty in patients with a negative FFR result.

METHODS

We studied 43 patients with 44 moderately severe coronary artery stenoses on angiography and FFR > or = 0.75. Mean age of the patients was 58 +/- 11.4 years. The indications for coronary angiography included recent unstable angina in 24 (55.8%) patients, recent acute myocardial infarction in 10 (23.2%) patients, 5 (11.6%) patients with a coronary stent who had symptoms of uncertain cause, and stable angina in 4 (9.3%) patients.

RESULTS

During a mean follow-up period of 10.7 +/- 5.9 months, clinical events (unstable angina) occurred in five patients. In three patients, the initially investigated artery was involved, and in the two patients who required coronary revascularization, unstable angina was related with an artery different from the one studied initially.

CONCLUSIONS

Patients with recent coronary syndromes and negative FFR findings in moderately severe coronary stenosis were unlikely to have cardiac events during a 10-month follow-up period. Our findings suggest that FFR is a potentially useful indicator of the likelihood of cardiac events and thus represents a useful aid in clinical decision-making in the hemodynamics laboratory. This diagnostic technique also is potentially useful in identifying patients for whom angioplasty can be safely deferred.

Reproducibility of intravascular ultrasound and intracoronary Doppler measurements

The aim of this study was to evaluate the reproducibility of intravascular ultrasound (IVUS) and intracoronary (IC) Doppler flow velocity measurements. The use of IVUS and IC Doppler has been suggested as a means for percutaneous coronary intervention (PCI) guidance in a series of studies. This would require an acceptable level of accuracy and reproducibility of these two methods for lesion evaluation. In this study, the main focus was on the issue of reproducibility. One hundred and eight patients referred for PCI entered into the study. Inter- and intraobserver variability was measured. Catheter difference was assessed. On-line and off-line measurements were compared. MUSIC criteria were assessed off-line, twice. Calculated and measured diameters were compared. After having obtained initial IC Doppler measurements, the Doppler wire was immediately withdrawn and repositioned for reacquisition of Doppler measurements. IVUS measurements are reproducible and reliable off-line and, to a slightly lesser degree, on-line. Area measurements should be performed more than once and the mean used for vessel description. Lumen diameters should be calculated from the mean of the area measurements. A measuring technique consensus should be reached and adhered to. CFR measurements can be used to determine reduced vs. normal flow reserve. In this study, it was found that proximal to distal velocity ratio and diastolic to systolic velocity ratio variability made these parameters unsuitable for PCI guidance.

Stratification of single-vessel coronary stenosis by ischemic threshold at the onset of wall motion abnormality during continuous monitoring of left ventricular function by semisupine exercise echocardiography

We studied the relation between the ischemic threshold at the onset of wall motion abnormality on exercise echocardiography (EE) and the severity of coronary stenosis in patients with 1-vessel coronary artery disease (CAD). We screened 216 consecutive patients who underwent coronary angiography and EE for suspected CAD. Ninety-five (74 men; age, 56 +/- 12 years) satisfied the study criteria, that is, the presence of 1-vessel disease or no evidence of CAD on angiography and a normal baseline echocardiogram. Eighty-seven patients had 1-vessel CAD on angiography, and exercise-induced wall motion abnormality occurred in 73 (77%). Optimal cutoff values of percent diameter stenosis and minimal lumen diameter for predicting a positive EE were 61% (sensitivity and specificity of 76%) and 1.12 mm (sensitivity and specificity of 74%). Among patients with positive EE, heart rate-blood pressure product at ischemic threshold was correlated with quantitative coronary stenosis (r = -0.72, P <.001). The ischemic threshold from continuous monitoring of left ventricular function during semisupine EE is correlated with the severity of coronary stenosis among patients with 1-vessel disease and a normal resting echocardiogram.

Fractional flow reserve, absolute and relative coronary blood flow velocity reserve in relation to the results of technetium-99m sestamibi single-photon emission computed tomography in patients with two-vessel coronary artery disease

OBJECTIVES

We sought to perform a direct comparison between perfusion scintigraphic results and intracoronary-derived hemodynamic variables (fractional flow reserve [FFR]; absolute and relative coronary flow velocity reserve [CFVR and rCFVR, respectively]) in patients with two-vessel disease.

BACKGROUND

There is limited information on the diagnostic accuracy of intracoronary-derived variables (CFVR, FFR and rCFVR) in patients with multivessel disease.

METHODS

Dipyridamole technetium-99m sestamibi (MIBI) single-photon emission computed tomography (SPECT) was performed in 127 patients. The presence of reversible perfusion defects in the region of interest was determined. Within one week, angiography was performed; CFVR, rCFVR and FFR were determined in 161 coronary lesions after intracoronary administration of adenosine. The predictive value for the presence of reversible perfusion defects on MIBI SPECT of CFVR, rCFVR and FFR was evaluated by the area under the curve (AUC) of the receiver operating characteristics curves.

RESULTS

The mean percentage diameter stenosis was 57% (range 35% to 85%), as measured by quantitative coronary angiography. Using per-patient analysis, the AUCs for CFVR (0.70 +/- 0.052), rCFVR (0.72 +/- 0.051) and FFR (0.76 +/- 0.050) were not significantly different (p = NS). The percentages of agreement with the results of MIBI SPECT were 76%, 78% and 77% for CFVR, rCFVR and FFR, respectively. Per-lesion analysis, using all 161 measured lesions, yielded similar results.

CONCLUSIONS

The diagnostic accuracy of three intracoronary-derived hemodynamic variables, as compared with the results of perfusion scintigraphy, is similar in patients with two-vessel coronary artery disease. Cut-offvalues of 2.0 for CFVR, 0.65 for rCFVR and 0.75 for FFR can be used for clinical decision-making in this patient cohort. Discordant results were obtained in 23% of the cases that require prospective evaluation for appropriate patient management.

Intravascular ultrasound findings in patients with abnormal coronary flow reserve after stenting

A coronary flow reserve (CFR) of 2.0 has been advocated as the endpoint for coronary intervention therapy. Experience shows, however, that CFR does indeed exceed 2.0 in many cases poststenting, while remaining below 2.0 in others. In this study, we assessed the clinical characteristics and IVUS findings of patients whose CFR remained below 2.0 after stent implantation, specifically 16 patients with CFR below 2.0 (22 lesions, 64 +/- 9 years, 4 female), and 102 patients with CFR above 2.0 (112 lesions, mean age 66 +/- 11 years, 22 female). Patient population comprised patients selected for retrospective study, but participants were selected on the basis of matching patient and lesion characteristics. The IVUS findings showed that incidence of calcified lesions and post-PTCA dissection of hard plaque were higher among patients with CFR < 2.0. Further, IVUS-obtained vascular measurements showed post-PTCA area stenosis to be 58.7 +/- 15.2% in the CFR < 2.0 group, and 45.3 +/- 12.5% among CFR > or = 2.0 patients (P < 0.05). These findings indicate that patients with diffuse calcified lesions or high post-PTCA % area stenosis, as determined by IVUS, are more likely to have lower CFR after stenting.

Global myocardial blood flow and global flow reserve measurements by MRI and PET are comparable

Coronary flow reserve (CFR) measurements have been widely used in assessing the functional significance of coronary artery stenosis because they are more sensitive in predicting major cardiac events than angiographically detected reductions of coronary arteries. Myocardial blood flow can be determined by measuring coronary sinus (CS) flow with velocity-encoded cine magnetic resonance imaging (VEC-MRI). The purpose of this study was to compare global myocardial blood flow (MBF) and CFR measured using VEC-MRI with MBF and CFR measured using positron emission tomography (PET). We measured MBF at baseline and after dipyridamole-induced hyperemia in 12 male volunteers with VEC-MRI and PET. With VEC-MRI, MBF was 0.64 +/- 0.09 (ml/min/g) at baseline and 1.59 +/- 0.79 (ml/min/g) at hyperemia, which yielded an average CFR of 2.51 +/- 1.29. With PET, MBF was 0.65 +/- 0.20 (ml/min/g) at baseline and 1.78 +/- 0.72 (ml/min/g) at hyperemia, which yielded an average CFR of 2.79 +/- 0.97. The correlation of MBFs between these two methods was good (r = 0.82, P < 0.001). The CFRs measured by MRI correlated well with those measured using PET (r = 0.76, P < 0.004). These results suggest that MRI is a useful and accurate method to measure global MBF and CFR. Therefore, it would be suitable for studying risk factor modifications of vascular function at an early stage in healthy volunteers.