Noninvasive Measurement of Left Coronary Blood Flow Reserve by Transthoracic Doppler Echocardiography: Comparison with Doppler Guidewire Ultrasonography

Doppler Echocardiography Assessment of Coronary Microvascular Function in Patients With Angina and No Obstructive Coronary Artery Disease

Echocardiographic evaluation is an essential part of the diagnostic work-up in patients with known or suspected cardiovascular disease. Transthoracic Doppler echocardiography (TTDE) enables straightforward and reliable visualization of flow in the left anterior descending artery. In the absence of obstructive coronary artery disease, low TTDE-derived coronary flow velocity reserve (CFVR) is considered a marker of coronary microvascular dysfunction (CMD). TTDE CFVR is free from ionizing radiation and widely available, utilizing high-frequency transducers, pharmacologic vasodilator stress, and pulsed-wave Doppler quantification of diastolic peak flow velocities. European Society of Cardiology guidelines recommend TTDE CFVR evaluation only following preceding anatomic invasive or non-invasive coronary imaging excluding obstructive CAD. Accordingly, clinical use of TTDE CFVR is limited and CMD frequently goes undiagnosed. An evolving body of evidence underlines that low CFVR is an important and robust predictor of adverse prognosis and continuing symptoms in angina patients both with and without obstructive CAD. The majority of angina patients have no obstructive CAD, particularly among women. This has led to the suggestion that there may be a gender-specific female atherosclerotic phenotype with less epicardial obstruction, and a low CFVR signifying CMD instead. Nevertheless, available evidence indicates low CFVR is an equally important prognostic marker in both men and women. In this review, TTDE CFVR was evaluated regarding indication, practical and technical aspects, and interpretation of results. Association with symptoms and prognosis, comparison with alternative invasive and non-invasive imaging modalities, and possible interventions in angina patients with low CFVR were discussed, and key research questions were proposed.

Disproportionally impaired microvascular structure in essential hypertension

BACKGROUND

Increased microvascular resistance and small artery remodelling are key abnormalities in the pathophysiology of essential hypertension. We investigated the relation between the impairment of coronary and forearm minimum vascular resistances (C-Rmin and F-Rmin) and the degree of hypertension.

METHOD

Seventy-five never-treated essential hypertension patients with 24-h systolic blood pressure (BP) at least 130 mmHg or diastolic BP at least 80 mmHg were assigned into grade 1 (office BP 140/90-159/99 mmHg) and grade 2 (office BP 160/100-179/109 mmHg) hypertension and compared to normotensive controls (n = 25). The patients were (48 years, 60% men) without cardiovascular disease. C-Rmin and coronary flow reserve (CFR) were derived from flow measurements in the left anterior descending artery using transthoracic echocardiography. F-Rmin was measured using venous occlusion plethysmography. Resting systemic vascular resistance index (SVRI) was measured with a gas rebreathing technique.

RESULTS

Compared to normotensive controls: 24-h mean BP was raised 14% in grade 1 essential hypertension and 28% in grade 2 essential hypertension, whereas F-Rmin and C-Rmin were elevated by 58 and 87% in grade 1 essential hypertension and 72 and 125% in grade 2 essential hypertension. C-Rmin and F-Rmin were thus both increased more than expected from the BP level. SVRI and left-ventricular mass were increased proportionally to the BP. CFR was decreased by approximately 30% in both essential hypertension groups.

CONCLUSION

The results demonstrate excessive microvascular structural abnormalities in hypertension suggesting microvascular alterations occur early and not just as an adaptation to the BP level. Thus the level of BP elevation does not give an accurate indication of the microvascular involvement and impairment in essential hypertension.

Assessment of coronary flow reserve by adenosine transthoracic echocardiography: validation with intracoronary Doppler

OBJECTIVE

Data on the accuracy of transthoracic echocardiographic (TTE) analysis of coronary flow reserve are scarce. We compared coronary flow reserve measurements assessed using TTE with those achieved using the gold standard of intracoronary Doppler.

METHODS

Twenty-one patients admitted for elective coronary angioplasty to the circumflex or left anterior descending (LAD) coronary artery underwent TTE immediately before angioplasty, both at rest and during intravenous administration of adenosine 140 microg/kg/min. Transthoracic images of distal LAD coronary diameter and coronary flow were obtained in 14 patients (66%). These patients then underwent intracoronary Doppler analysis of coronary flow reserve in the distal LAD coronary artery. In 1 patient with a proximal LAD artery lesion, the narrowing could not be crossed with the Doppler guidewire. Paired data on coronary flow reserve were therefore available in 13 patients.

RESULTS

Patients were aged 61.7 +/- 8.3 years. Ten were men. Body mass index was 26.3 +/- 4.6 kg/m(2). Resting distal LAD artery blood flow was 18.4 +/- 9.0 mL/min assessed by TTE versus 17.6 +/- 8.1 mL/min by intracoronary Doppler. Hyperemic flow was 36.3 +/- 23.4 versus 33.1 +/- 19.2 mL/min, respectively. Coronary flow reserve was therefore 1.89 +/- 0.66 by TTE compared with 1.83 +/- 0.62 by intracoronary Doppler. Limits of agreement for coronary flow reserve were -0.28 to +0.44, well within boundaries of clinical acceptability.

CONCLUSION

Transthoracic echocardiography is capable of providing accurate data on coronary flow reserve in the distal LAD coronary artery. As a truly noninvasive modality, this technique offers advantages over traditional invasive procedures.