Vessel diameter changes during the cardiac cycle
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Cardiac cycle
Vasomotion
Systole
Fundus (uterus)
Abstract Myocardial blood flow varies during the cardiac cycle in response to pulsatile changes in epicardial circulation and cyclical variation in myocardial tension. First‐pass assessment of myocardial perfusion by dynamic contrast‐enhanced MRI is one of the most challenging applications of MRI because of the spatial and temporal constraints imposed by the cardiac physiology and the nature of dynamic contrast‐enhanced MRI signal collection. Here, we describe a dynamic contrast‐enhanced MRI method for simultaneous assessment of systolic and diastolic myocardial blood flow. The feasibility of this method was demonstrated in a study of 17 healthy volunteers at rest and under adenosine‐induced vasodilatory stress. We found that myocardial blood flow was independent of the cardiac phase at rest. However, under adenosine‐induced hyperemia, myocardial blood flow and myocardial perfusion reserve were significantly higher in diastole than in systole. Furthermore, the transmural distribution of myocardial blood flow and myocardial perfusion reserve was cardiac phase dependent, with a reversal of the typical subendocardial to subepicardial myocardial blood flow gradient in systole, but not diastole, under stress. The observed difference between systolic and diastolic myocardial blood flow must be taken into account when assessing myocardial blood flow using dynamic contrast‐enhanced MRI. Furthermore, targeted assessment of systolic or diastolic perfusion using dynamic contrast‐enhanced MRI may provide novel insights into the pathophysiology of ischemic and microvascular heart disease. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
Cardiac cycle
Systole
Pulsatile flow
Reactive hyperemia
Coronary circulation
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Phasic coronary artery compression is typically associated with spasm or myocardial bridging. Compression caused by acquired anatomic changes to the surrounding heart chambers has been reported only infrequently. We present a possibly unique case of phasic compression of the proximal left circumflex coronary artery during atrial contraction in association with a dilated left atrium. A 55-year-old man with multiple cardiac risk factors presented with worsening exertional dyspnea. An electrocardiogram and echocardiogram revealed marked left atrial dilation and a left ventricular ejection fraction of 0.15 to 0.20 with elevated filling pressures. Angiograms showed compression of the proximal segment of the left circumflex coronary artery during late ventricular diastole: the compression occurred in phase with atrial systole, whereas good flow without compression was present during atrial diastole. We attributed this phenomenon to ballooning of the lateral region of the atrial wall toward the atrioventricular groove during atrial systole. The patient complied with antihypertensive therapy, and his status improved after one year. To identify coronary artery compression in the presence of abnormal chamber geometry and to guide the treatment of the contributing medical conditions, we recommend careful analysis of angiographic results.
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Cardiac cycle
Circumflex
Myocardial Bridging
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To assess non-invasively the effect of verapamil treatment on coronary blood flow velocity in asymptomatic and mildly symptomatic patients with hypertrophic cardiomyopathy.High frequency transthoracic Doppler echocardiography was used to compare resting phasic coronary blood flow velocity before and after a one month period of verapamil treatment in 17 patients (14 men and three women) with non-obstructive hypertrophic cardiomyopathy. Eighteen healthy subjects formed an age and sex matched control group. Systolic and diastolic coronary blood flow velocity was measured in the distal portion of left anterior descending coronary artery using high frequency transthoracic Doppler echocardiography. Blood flow velocity before and after verapamil was compared in the patients with cardiomyopathy and with the results in the control group.Compared with the controls, patients with hypertrophic cardiomyopathy had increased diastolic coronary blood flow velocity (41.8 (8.1) v 59.9 (21.9) cm/s, p < 0.01) and a lower mean systolic coronary blood flow velocity (18.7 (10.8) v -11.2 (27.5) cm/s, p < 0. 01) before verapamil treatment. A backward pattern of systolic flow, manifested by negative values of coronary blood flow velocity, was recorded in eight of the patients, while no negative values were found in the controls. After verapamil treatment the retrograde systolic blood flow was restored to an anterograde pattern in only one patient. The mean value of systolic coronary blood flow velocity did not change significantly and remained lower than the systolic forward flow velocity in the controls (-3.6 (31.8) v 18.7 (10.8) cm/s, p < 0.05). However, diastolic coronary blood flow velocity decreased significantly after verapamil (59.9 (21.9) v 50.7 (19.5) cm/s p < 0.05), reaching a level comparable with that in the controls (50.7 (19.5) v 41.8 (8.1) cm/s, p > 0.05).In contrast to healthy subjects, in non-obstructive hypertrophic cardiomyopathy the systolic pattern of coronary blood flow was heterogeneous (both retrograde and anterograde), and diastolic coronary blood flow velocity was abnormally increased, despite a lack of significant symptoms. Verapamil treatment did not restore the forward pattern of systolic blood flow but decreased diastolic blood flow velocity to a level comparable with that in healthy subjects.
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Transmural myocardial blood flow was measured with microspheres in systole and in diastole, along with intramyocardial pressure, in seven anaesthetised horses. Intramyocardial pressures were measured with a miniature manometer implanted in the tip of a 16-gauge needle. Peak systolic intramyocardial pressure decreased from subendocardium to subepicardium and never exceeded intraventricular pressure. Systolic blood flow decreased from epicardium to endocardium where it did not differ from zero. Diastolic blood flow increased from epicardium to subendocardium, but then decreased in the most endocardial layer to a level not different from the immediate subepicardial layer. The horse was a useful model for studying these parameters because the ventricular walls are so thick and the heart rate is so slow that injections may be made during various phases of the cardiac cycle. These results of transmural myocardial blood flow and intramyocardial pressure measured in the same animal are identical with those of others, except for the reduction in subendocardial blood flow compared with the layers just epicardial to that.
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Objective: To test the hypothesis that, when measured in the long axis, left ventricular systolic function is abnormal in patients with diastolic heart failure. Design: A case–control study. Setting: University teaching hospital (tertiary referral centre). Patients: 68 patients with heart failure, 29 with a left ventricular ejection fraction (LVEF) of > 0.45 and diastolic dysfunction (diastolic heart failure), 39 with an LVEF of ≤ 0.45 (systolic heart failure), and 105 normal subjects, including 33 age matched controls. Methods: LVEF was measured by cross sectional Simpson9s method, and mitral annular amplitudes and velocities by M mode and tissue Doppler echocardiography, respectively, along with mitral Doppler inflow velocities. Results were compared between the three groups. Main outcome measures: Peak systolic mitral annular velocity and amplitude between the different groups. Results: The mitral annular peak mean velocity and amplitude in systole were lower in the patients with diastolic heart failure (mean (SEM), 4.8 (0.2) cm/s) than in the age matched normal controls (6.1 (0.14) cm/s), but higher than those with systolic heart failure (2.8 (0.13) cm/s) (all p < 0.001). Similar changes were seen the mitral annular amplitude during systole. Peak early diastolic velocity and amplitude were also significantly reduced in the group with diastolic heart failure. Left ventricular hypertrophy was evident in over 95% patients in both diastolic and systolic heart failure groups, with a comparable left ventricular mass index. Conclusions: In patients with diastolic heart failure and evidence of left ventricular hypertrophy, there is systolic left ventricular impairment as measured by myocardial Doppler imaging of the longitudinal axis. Thus subtle abnormalities of systolic function are present in patients with heart failure and a normal left ventricular ejection fraction, and there appears to be a continuum of systolic function between those with truly normal, mildly impaired (labelled diastolic heart failure), and obviously abnormal left ventricular systolic function. Isolated diastolic dysfunction is uncommon.
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Diastolic heart failure
Cardiac cycle
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Cardiac cycle
Vasomotion
Systole
Fundus (uterus)
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Cardiac cycle
Systole
Dilated Cardiomyopathy
Doppler imaging
Isovolumetric contraction
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