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Specialized Circulations in Susceptible Tissues
Published in Wilmer W Nichols, Michael F O'Rourke, Elazer R Edelman, Charalambos Vlachopoulos, McDonald's Blood Flow in Arteries, 2022
Coronary flow (or vascular) reserve (CFR) is the ability of the coronary arteries to supply blood (and oxygen) to the heart in excess of basal (resting) requirements. All other factors being equal, coronary flow reserve is determined by severity of coronary artery stenosis. The term “CFR” is usually generic and does not refer to any particular protocol, whereas FFR usually refers to a specific protocol (Pijls et al., 1996) that entails infusion of adenosine to dilate coronary arteries in the circulation beyond the stenosis. We have previously discussed the factors other than structural mechanical stenosis that can restrict coronary flow and cause myocardial ischemia. In clinical practice, one is faced with the problem of known coronary stenosis (or stenoses) after angiography has been done but uncertainty as to how hemodynamically significant the stenosis is—i.e. what loss of coronary flow reserve exists as a consequence of the stenosis, and what benefit can be achieved by angioplasty/stenting or by coronary bypass surgery? The problem often presents as an acute coronary syndrome, where perfusion challenges such as exercise stress testing are not available or are contraindicated and out-of-hours, with maximal benefit achieved through urgent intervention by on-site staff.
The Role of Cardiac Magnetic Resonance in Hypertrophic Cardiomyopathy
Published in Srilakshmi M. Adhyapak, V. Rao Parachuri, Hypertrophic Cardiomyopathy, 2020
Gulhane Avanti, Lakhani Zeeshan, Raj Vimal
Patients with HCM have a significantly prolonged myocardial transit time due to coronary microvascular dysfunction. The two CMR techniques that are currently used to assess coronary microvascular dysfunction (MVD) through myocardial perfusion reserve (MPR) are velocity encoded coronary sinus flow measurements (CSF-MPR) and semi-quantitative myocardial first-pass perfusion [62]. The presence of MVD is generally associated with an increased risk of adverse events such as rapid progression and decompensation of heart failure, severe MVD, ventricular arrhythmias, and/or appropriate ICD therapy, as well as mortality [63–65]. The CMR parameter of the myocardial transit time (MyoTT) may contribute to the appropriate diagnosis and subsequent monitoring of MVD (not only in HCM patients) in a simple and non-invasive way – without requiring exposure to ionizing radiation or use of a pharmacologic stress agent. The myocardial transit time (cut-off of 7.85 s for HCM) can be defined as the blood circulation time from the orifice of the coronary arteries to the pooling in the coronary sinus (CS), and accordingly measured as the temporal difference between the appearances of the CMR contrast agent in the aortic root and the CS reflecting the transit time of gadolinium in the myocardial microvasculature. Robust correlation is present between MyoTT and LV global longitudinal strain in HCM patients [66]. Cardiac magnetic resonance-based measurement of coronary flow reserve can be achieved by calculating the ratio of flows in the CS during rest and maximal vasodilator stress [67].
Orthotopic Cardiac Transplantation
Published in David Robertson, Italo Biaggioni, Disorders of the Autonomic Nervous System, 2019
Hodgson et al. (1989) used quantitative angiography, subselective Doppler catheterization and regional a- and β-blockade in a large number of heart transplant patients and innervated controls to assess the role of adrenergic tone in the coronary circulation under resting conditions. The methodological problems associated with measuring coronary blood flow in small resistance vessels is considerable. Nonetheless, the data acquired by Hodgson et al. (1989) strongly suggests that in resting patients, α-mediated coronary vascular tone is negligible in both transplanted and in control hearts. No change in coronary vascular resistance or in coronary flow reserve was seen in either group after α-blockade or selective β-blockade, although non-selective β-blockade did increase vascular resistance, presumably via β2-receptor inhibition. The effect of adrenergic innervation on coronary flow reserve under stress conditions was not studied, however.
Determinants and impact of masked hypertension in offspring of patients with diabetes: relation with coronary flow and cardiac function
Published in Blood Pressure, 2019
Ragab A. Mahfouz, Mohammad Gouda, Waleed Alawady
Coronary flow in the distal part of left anterior descending coronary artery was recorded with a high-resolution frequency transducer (5–7 MHz), guiding with color Doppler flow mapping, utilizing a sample volume (2.5 or 3.0 mm wide) positioned on the color signal in the left anterior descending. The resting baseline coronary flow was recorded first, followed by intra-venous adenosine, that was administered (0.14 mg/kg/min) to induce hyperemia and then spectral Doppler signals was recorded. The average of three cardiac cycles mean diastolic velocities were measured at baseline and peak hyperemic conditions from the Doppler signal recordings. Coronary flow reserve was defined as the ratio of hyperemic to basal mean diastolic velocities and a value <2.0 were considered pathological [9,10]. Inter- and intra-day variability of coronary flow reserve assessed by transthoracic color Doppler guided echocardiography has been evaluated and the variation in coronary flow reserve were 3.4% and 4.1% respectively.
The Management of Stable Coronary Artery Disease and Transcatheter Aortic Valve Replacement
Published in Structural Heart, 2021
Hussein Rahim, Nicholas J. Shea, Isaac George
A number of benefits of revascularization, particularly to AS patients with CAD, have been proposed. AS patients with normal coronaries are known to have decreased coronary flow reserve, constraining the capacity of the coronary circulation to increase flow to match myocardial oxygen demand.31 The left ventricular hypertrophy that results from chronic progressive AS leads to greater wall stress and myocardial oxygen supply-demand imbalance, a process that is exacerbated in the presence of CAD. Additionally, the TAVR implantation procedure itself often includes periods of hypotension and rapid pacing that may worsen ischemia in patients with combined CAD and AS, risks that may be mitigated by pre-TAVR coronary intervention.
Highlights of imaging heart structure and function
Published in Acta Cardiologica, 2023
Patrizio Lancellotti, Adriana Postolache, Raluca Dulgheru
Coronary flow reserve (CFR) is an integrated measure of coronary macro- and microvascular morphology and function and is defined as the ratio of hyperaemic coronary blood flow during maximum vasodilation of the coronary vascular bed to resting coronary blood flow [24,25]. Coronary flow velocity reserve is a surrogate of coronary flow reserve and offers information additive and complementary to standard regional wall motion analysis [26]. In elderly patients, Doppler coronary flow velocity scanning during routine echocardiography is a feasible and valuable tool for assessment of short-term prognosis [27]. The same group also showed that coronary velocity parameters provided long-term prognostic information in non-selected patients [28].