Clinical application of coronary flow reserve using an intracoronary Doppler guide wire

Diagnostic approach for coronary microvascular dysfunction in patients with chest pain and no obstructive coronary artery disease

A large number of studies has demonstrated that abnormalities of coronary microcirculation may be responsible for both acute and chronic cardiac ischemic syndromes. In clinical practice the microvascular origin of myocardial ischemia and angina is usually considered in patients who are found to have normal or near-normal coronary arteries at angiography. In this article, we review the diagnostic approach to patients with suspected coronary microvascular dysfunction as a cause of ischemic syndromes and also suggest a classification of chronic and acute microvascular coronary ischemic syndrome, including myocardial infarction with normal coronary arteries.

Cardiac Rehabilitation and Endothelial Function

Endothelial dysfunction is an early abnormality in the process of atherosclerosis and cardiovascular disease and has been associated with worse clinical outcome. Cardiac rehabilitation (CR) has been reported to be helpful to reduce cardiovascular events in various types of cardiac disease, but the mechanisms of its beneficial effects remain only partially known. In this article, we review the studies that assessed the effect of CR on endothelial function in patients with various cardiac conditions. Available data show that CR significantly improves impaired endothelial function in these patients, which may contribute to the beneficial effects of CR on clinical outcome.

Diagnostic Approach to Patients with Stable Angina and No Obstructive Coronary Arteries

The diagnosis of microvascular angina (MVA) is usually considered in patients presenting with angina symptoms and evidence of MI on non-invasive stress tests but normal coronary arteries at angiography. A definitive diagnosis of MVA, however, would require the presence of coronary microvascular dysfunction. Several invasive (e.g. intracoronary Doppler wire recording and thermodilution) and non-invasive (e.g. PET, cardiac MRI, transthoracic Doppler echocardiography) methods can be applied to obtain a diagnosis. Both endothelium-dependent and -independent coronary microvascular dilator function, as well as increased microvascular constrictor activity, should be investigated. The main issues in the assessment of clinical and diagnostic findings in patients with suspected MVA are discussed and a diagnostic approach is suggested.

Coronary endothelial dysfunction in non-obstructive coronary artery disease: Risk, pathogenesis, diagnosis and therapy

Up to half of patients with signs and symptoms of stable ischemic heart disease have non-obstructive coronary artery disease (NoCAD). Recent evidence demonstrates that two-thirds of patients with NoCAD have demonstrable coronary endothelial dysfunction represented by microvascular or diffuse epicardial spasm following acetylcholine challenge. Patients with coronary endothelial dysfunction are recognized to have significant health services use and morbidity as well as increased risk of developing flow-limiting coronary artery disease and myocardial events, including death. Currently, there are few centers that test for this etiology owing to lack of knowledge, limited evidence for treatment options and invasive diagnostic strategies. This article reviews the pathophysiology, epidemiology, diagnosis and treatment of coronary endothelial dysfunction as a subgroup of NoCAD.

New method to measure coronary velocity and coronary flow reserve

Coronary flow reserve (CFR) is an important index of coronary microcirculatory function. The objective of this study was to validate the reproducibility and accuracy of intravascular conductance catheter-based method for measurements of baseline and hyperemic coronary flow velocity (and hence CFR). The absolute coronary blood velocity was determined by measuring the time of transit of a saline injection between two pairs of electrodes (known distance) on a conductance catheter during a routine saline injection without the need for reference flow. In vitro validation was made in the velocity range of 5 to 70 cm/s in reference to the volume collection method. In 10 swine, velocity measurements were compared with those from a flow probe in coronary arteries at different CFR attained by microsphere embolization. In vitro, the mean difference between the proposed method and volume collection was 0.7 ± 1.34 cm/s for steady flow and −0.77 ± 2.22 cm/s for pulsatile flow. The mean difference between duplicate measurements was 0 ± 1.4 cm/s. In in vivo experiments, the flow (product of velocity and lumen cross-sectional area that is also measured by the conductance catheter) was determined in both normal and stenotic vessels and the mean difference between the proposed method and flow probe was −1 ± 12 ml/min (flow ranged from 10 to 130 ml/min). For CFR, the mean difference between the two methods was 0.06 ± 0.28 (range of 1 to 3). Our results demonstrate the reproducibility and accuracy of velocity and CFR measurements with a conductance catheter by use of a standard saline injection. The ability of the combined measurement of coronary lumen area (as previously validated) and current velocity and CFR measurements provides an integrative diagnostic tool for interventional cardiology.

Assessment of the arterial input function for estimation of coronary flow reserve by single photon emission computed tomography: comparison of two different approaches

PURPOSE

Attempts to estimate coronary flow reserve (CFR) with single photon emission computed tomography (SPECT) tracers have been recently made. We compared two different methods for the estimation of CFR by SPECT imaging.

METHODS

Fourteen patients with coronary artery disease underwent dipyridamole 99mTc-sestamibi SPECT and intracoronary Doppler within 5 days. Myocardial blood flow (MBF) was estimated by measurement of first transit counts in the right pulmonary artery (PA) and left ventricular (LV) chamber, and myocardial counts from SPECT images. Estimated CFR was expressed as the ratio of stress MBF to rest MBF.

RESULTS

Rest and stress MBF obtained using first transit counts from PA were higher compared to that from LV chamber (rest: 1.05 ± 0.38 vs 0.87 ± 0.34 counts/pixel per s, respectively, p < 0.01 and stress: 1.34 ± 0.45 vs 0.91 ± 0.20 counts/pixel per s, respectively, p < 0.05). In the study vessels, CFR by Doppler was 1.39 ± 0.42, and SPECT CFR obtained using first transit counts from PA and LV chamber were 1.36 ± 0.43 and 1.16 ± 0.39, respectively (p across categories NS). A significant relationship between SPECT CFR obtained using first transit counts from PA and CFR by Doppler was found (r = 0.85, p < 0.001). No relationship between SPECT CFR obtained using first transit counts from LV chamber and CFR by intracoronary Doppler was OBSERVED (R = 0.43, P = NS).

CONCLUSION

SPECT-estimated CFR obtained using first transit counts from right PA is more accurate and correlates better with the results of intracoronary Doppler than estimated CFR obtained using arterial input function from LV chamber.

Correlation between noninvasive and endovascular Doppler in patients with atherosclerotic renal artery stenosis: A pilot study

Considerable interest exists in using endovascular techniques for assessing the renal circulation. The vasomotor response of the renal circulation in patients with hypertension and severe atherosclerotic renal artery stenosis was evaluated. Sixteen patients (5 men and 11 women) with a mean age of 73.2+/-7.1 years (range, 59-82 years) underwent noninvasive renal duplex ultrasonography and endovascular flow wire evaluation. The flow wire was positioned in the main renal artery distal to the stenosis and used to examine the reactivity of the renal circulation in response to intra-arterial papaverine before and after percutaneous revascularization. Resistive index was computed as (MPV - EDV)/MPV, where MPV is the maximum peak velocity and EDV is the end-diastolic velocity. Renal flow reserve was defined as the ratio of peak hyperemic response to baseline flow. Intervention was technically successful in 18/18 arteries. Heart rate (69+/-11 vs. 65+/-10 beats/min; P=NS) and systolic blood pressure (168+/-19 vs. 163+/-24 mm Hg; P=NS) remained constant following injection of intrarenal papaverine, while diastolic blood pressure decreased (77+/-13 vs. 65+/-11 mm Hg; P<0.006). Papaverine injection resulted in significant increases in average peak velocity (APV; 148% of baseline; P=0.0003), MPV (146% of baseline; P=0.001), and EDV (161% of baseline; P=0.0026), but had no effect on the endovascular resistive index (0.81+/-0.12 vs. 0.84+/-0.08; P=NS). Renal artery stenting produced no effect on APV or EDV, but a small increase in MPV (123% of baseline; P<0.05). In contrast, renal stenting resulted in a significant increase in the endovascular resistive index (0.77+/-012 vs. 0.84+/-0.08; P=0.003), pulsatility index (1.84+/-0.61 vs. 2.23+/-0.70; P<0.014), and renal flow reserve (1.49+/-0.44 vs. 1.86+/-0.73; P<0.0071). A correlation was found between the noninvasive and endovascular measures diastolic/systolic ratio (r=0.73; P<0.0009) and resistive index (r=0.63; P<0.0053). Patients with atherosclerotic renal artery stenosis have preserved vasomotor response to papaverine, as well as marked increases in renal flow and resistive index following successful renal artery stenting. Endovascular flow wire measurements are safe, easy to perform, and correlate well with noninvasive Doppler measurements.

Estimation of coronary flow reserve by Tc-99m sestamibi imaging in patients with coronary artery disease: comparison with the results of intracoronary Doppler technique

BACKGROUND

This study compared coronary flow reserve (CFR) estimated by technetium 99m sestamibi imaging with the results obtained with intracoronary Doppler in patients with coronary artery disease. Intraobserver and interobserver reproducibility of the radionuclide-estimated CFR was also assessed.

METHODS AND RESULTS

Fourteen consecutive patients (mean age, 54 +/- 7 years) with documented coronary artery disease in whom percutaneous coronary intervention was planned underwent dipyridamole (0.74 mg/kg) sestamibi imaging and intracoronary Doppler within 5 days. Myocardial blood flow (MBF) was estimated by measurement of first transit counts in the pulmonary artery and myocardial counts from single photon emission computed tomography images. Estimated CFR was expressed as the ratio of stress MBF to rest MBF. In the study vessels, CFR was 1.36 +/- 0.43 as estimated by sestamibi and 1.39 +/- 0.42 by intracoronary Doppler ( P = .69). A significant relationship between CFR estimated by sestamibi and CFR obtained by intracoronary Doppler was observed ( r = 0.85, P < .001). On Bland-Altman analysis, the mean difference between CFR by sestamibi and by Doppler was 0.03 and the intraclass correlation coefficients for intraobserver and interobserver reproducibility were high (all P < .001) for both global and regional CFR.

CONCLUSIONS

This study demonstrates a good agreement between CFR estimated by sestamibi imaging and by intracoronary Doppler results and a lack of intraobserver and interobserver variability of this noninvasive approach.

How to prevent unnecessary coronary interventions: identifying lesions responsible for ischemia in the cath lab

PURPOSE OF REVIEW

Coronary angiography is limited by the inability to identify intermediate coronary lesions responsible for ischemia. In the catheterization laboratory three techniques can be used for the evaluation of the physiologic significance of intermediate or borderline significant coronary stenoses: (1) pressure wire-derived coronary fractional flow reserve (FFR), (2) Doppler wire-derived measurement of coronary flow reserve (CFR), and (3) intravascular ultrasound (IVUS).

RECENT FINDINGS

All of these techniques have been validated for assessing the functional significance of intermediate stenoses, but also have inherent limitations.

SUMMARY

Overall, measurement of FFR appears to be the best method for interrogating intermediate coronary lesions. This review discusses the strengths and limitations of each of these techniques.

Estimation of coronary flow reserve with the use of dynamic planar and SPECT images of Tc-99m tetrofosmin

BACKGROUND

We developed a noninvasive method to examine coronary flow reserve with technetium 99m tetrofosmin based on the microsphere model. According to the microsphere model, myocardial blood flow (MBF) can be calculated by MBF = q / integral C(t)dt, where q is myocardial activity and C(t) is tracer concentration in blood. Because the ratio of integral C(t)dt at stress to rest is equal to the ratio of the first transit count in the pulmonary artery (PA) and attenuation factors were canceled out, we calculated the increase ratio of MBF (MBF(IR)).

METHODS AND RESULTS

After injection of dipyridamole, tetrofosmin was injected as a bolus and serial dynamic planar images were obtained to measure the first transit count in PA (PAC). Myocardial single photon emission computed tomography was performed to measure the regional myocardial count (RMC). MBF(IR) was calculated as [(RMCs x PACr)/(RMCr x PACs) - 1] x 100, where r and s denote resting and stress conditions, respectively. In contrast, the increase in the myocardial uptake ratio (MUR(IR)) was defined as (RMCs x SCr/RMCr x SCs - 1) x 100, where SC is syringe count of tracer. The results were as follows: (1) The mean MBF of healthy subjects was 46.9% +/- 22.8%. (2) MBF(IR) of the infarcted region and ischemic region was significantly decreased (8.3% +/- 12.2% and 11.2% +/- 11.9%, respectively; P <.001). (3) MUR(IR) was significantly lower than MBF(IR) (14.1% +/- 21.2%; P <.001). (4) MBF(IR) decreased according to the heart rate at rest (r = 0.47; P <.05).

CONCLUSIONS

MBF(IR) is a potential parameter with which to evaluate coronary flow reserve when the changes of arterial input function during stress are considered.