Valtteri Uusitalo

Relative Flow Reserve Derived From Quantitative Perfusion Imaging May Not Outperform Stress Myocardial Blood Flow for Identification of Hemodynamically Significant Coronary Artery Disease

Background—Quantitative myocardial perfusion imaging is increasingly used for the diagnosis of coronary artery disease. Quantitative perfusion imaging allows to noninvasively calculate fractional flow reserve (FFR). This so-called relative flow reserve (RFR) is defined as the ratio of hyperemic myocardial blood flow (MBF) in a stenotic area to hyperemic MBF in a normal perfused area. The aim of this study was to assess the value of RFR in the detection of significant coronary artery disease. Methods and Results—From a clinical population of patients with suspected coronary artery disease who underwent oxygen-15–labeled water cardiac positron emission tomography and invasive coronary angiography, 92 patients with single- or 2-vessel disease were included. Intermediate lesions (diameter stenosis, 30%–90%; n=75) were interrogated by FFR. Thirty-eight (41%) vessels were deemed hemodynamically significant (>90% stenosis or FFR ⩽0.80). Hyperemic MBF, coronary flow reserve, and RFR were lower for vessels with a hemodynamically significant lesion (2.01±0.78 versus 2.90±1.16 mL·min−1·g−1; P<0.001, 2.27±1.03 versus 3.10±1.29; P<0.001, and 0.67±0.23 versus 0.93±0.15; P<0.001, respectively). The correlation between RFR and FFR was moderate (r=0.54; P<0.01). Receiver operator characteristic curve analysis showed an area under the curve of 0.82 for RFR, which was not significantly higher compared with that for hyperemic MBF and coronary flow reserve (0.76; P=0.32 and 0.72; P=0.08, respectively). Conclusions—Noninvasive estimation of FFR by quantitative perfusion positron emission tomography by calculating RFR is feasible, yet only a trend toward a slight improvement of diagnostic accuracy compared with hyperemic MBF assessment was determined.

The Functional Effects of Intramural Course of Coronary Arteries and its Relation to Coronary Atherosclerosis

OBJECTIVES This study observed hemodynamic consequences of myocardial bridging and its relation to coronary atherosclerosis. BACKGROUND Myocardial bridging is seen as intramural course by computed tomography angiography (CTA) or systolic compression by invasive coronary angiography. Segments with myocardial bridging are in previous studies closely associated with proximal atherosclerotic plaques. METHODS We prospectively studied 100 patients 63 ± 7 years of age with intermediate likelihood of coronary artery disease. Segments with superficial (>1 mm) or deep (>2 mm) intramural course were identified using CTA. Myocardial perfusion was studied by 15-Oxygen water positron emission tomography and systolic compression by invasive coronary angiography. RESULTS Myocardial bridging was detected in 34 (34%) patients in 48 different vascular segments. Of these, 24 (50%) were deep and systolic compression was present in 14 (29%). In patients without obstructive coronary artery disease, myocardial stress perfusion distal to myocardial bridging was comparable with remote control regions (3.3 ± 0.9 ml/g/min vs. 3.3 ± 0.7 ml/g/min, n = 24, p = 0.88). Stress perfusion was comparable in segments with and without systolic compression (3.0 ± 0.9 vs. 2.7 ± 1.0 ml/g/min, p = 0.43). Atherosclerotic plaques were more frequent in proximal (71%) than myocardial bridging (7%) or distal (21%) segments. The presence of atherosclerosis and the average number of plaques were comparable in coronary arteries with and without myocardial bridging (73% vs. 60%, p = 0.14 and 2.0 ± 1.7 vs. 1.5 ± 1.6, p = 0.06). Median Agatston coronary calcium score was not elevated in vessels with myocardial bridge (15 [interquartile range: 0, 129] vs. 50 [interquartile range: 0, 241], p = 0.21). CONCLUSIONS Myocardial bridging of coronary arteries is common on CTA, but only approximately one-third of these show systolic compression. Myocardial bridging is not associated with reduced myocardial perfusion during vasodilator stress. Atherosclerosis is located predominantly proximal to myocardial bridging but atherosclerotic burden and presence of vulnerable plaques were comparable.

The association between coronary flow reserve and development of coronary calcifications: a follow-up study for 11 years in healthy young men

AIMS We studied whether a reduced coronary flow reserve (CFR) in healthy young men independently predicts the presence of coronary artery disease as assessed by coronary artery calcification after 11 years of follow-up. METHODS AND RESULTS Coronary microvascular dysfunction in early stages of coronary artery disease can be detected as a reduced CFR by positron emission tomography (PET). Seventy-seven healthy, lean, normotensive, non-smoking and non-diabetic men underwent 15-Oxygen ((15)O) water myocardial perfusion PET at rest and during vasodilator stress at the age of 35 ± 4 years at baseline. The subjects were followed-up for 11 ± 1 years and the coronary artery calcium score (CCS) was measured with computed tomography at the end of the follow-up. At the end of the follow-up, 30 (39%) individuals had CCS >0 (average 65 ± 93), but none had clinical symptoms or evidence of ischaemia in stress echocardiography. At baseline, the average CFR was comparable in individuals with CCS >0 and CCS = 0 (4.2 ± 1.4 vs. 4.0 ± 1.2, P = 0.4). Logistic regression analysis showed no associations between CFR, serum glucose, cholesterol levels, systolic blood pressure or body mass index at baseline and CCS at the end of the follow-up (P always >0.05). The presence of CCS (CCS >0) was associated with higher systolic and diastolic blood pressures at the end of the follow-up (137 ± 18 vs. 128 ± 11 mmHg, P = 0.04 and 86 ± 12 vs. 78 ± 11 mmHg, P = 0.01). CONCLUSIONS Coronary reactivity to vasodilator-induced hyperaemia as assessed by perfusion PET was not predictive of the presence of coronary calcification after 11 years of follow-up in asymptomatic men with very low likelihood of coronary artery disease.

Multimodality Imaging in the Assessment of the Physiological Significance of Myocardial Bridging

In myocardial bridging (MB) a segment of the coronary artery is covered by the myocardium. MB can be seen as a systolic compression by invasive coronary angiography (ICA) or as an intramural course by computed tomography angiography (CTA). Intramural course is a common incidental finding in CTA studies. Only minority of the bridging segments are associated with systolic compression causing a possible impairment of myocardial perfusion. The relationship between myocardial blood flow and MB is complex and poorly evaluated by anatomic imaging. Furthermore, provocation tests are frequently needed to uncover systolic compression. Fractional flow reserve can be used to assess the hemodynamic significance of MB. Nuclear perfusion imaging can demonstrate flow abnormalities associated with MB. Stress echocardiography can demonstrate ischemic wall motion abnormalities. They can be complemented by hybrid imaging with CTA to distinguish epicardial coronary artery disease and MB. This article will review different imaging modalities for the evaluation of the physiologic significance of MB.