Intramyocardial Coronary Arteries Research Articles

Cardiac Allograft Vasculopathy: Challenges and Advances in Invasive and Non-Invasive Diagnostic Modalities.

Cardiac allograft vasculopathy (CAV) is a distinct form of coronary artery disease that represents a major cause of death beyond the first year after heart transplantation. The pathophysiology of CAV is still not completely elucidated; it involves progressive circumferential wall thickening of both the epicardial and intramyocardial coronary arteries. Coronary angiography is still considered the gold-standard test for the diagnosis of CAV, and intravascular ultrasound (IVUS) can detect early intimal thickening with improved sensitivity. However, these tests are invasive and are unable to visualize and evaluate coronary microcirculation. Increasing evidence for non-invasive surveillance techniques assessing both epicardial and microvascular components of CAV may help improve early detection. These include computed tomography coronary angiography (CTCA), single-photon emission computed tomography (SPECT), positron emission tomography (PET), and vasodilator stress myocardial contrast echocardiography perfusion imaging. This review summarizes the current state of diagnostic modalities and their utility and prognostic value for CAV and also evaluates emerging tools that may improve the early detection of this complex disease.

Signaling and structures underpinning conducted vasodilation in human and porcine intramyocardial coronary arteries.

BackgroundAdequate blood flow into coronary micro-arteries is essential for myocardial function. Here we assess the mechanisms responsible for amplifying blood flow into myogenically-contracting human and porcine intramyocardial micro-arteries ex vivo using endothelium-dependent and -independent vasodilators.MethodsHuman and porcine atrial and ventricular small intramyocardial coronary arteries (IMCAs) were studied with pressure myography and imaged using confocal microscopy and serial section/3-D reconstruction EM.Results3D rendered ultrastructure images of human right atrial (RA-) IMCAs revealed extensive homo-and hetero-cellular contacts, including to longitudinally-arranged smooth muscle cells (l-SMCs) found between the endothelial cells (ECs) and radially-arranged medial SMCs (r-SMCs). Local and conducted vasodilatation followed focal application of bradykinin in both human and porcine RA-IMCAs, and relied on hyperpolarization of SMCs, but not nitric oxide. Bradykinin initiated asynchronous oscillations in endothelial cell Ca2+ in pressurized RA-IMCAs and, as previously shown in human RA-IMCAs, hyperpolarized porcine arteries. Immunolabelling showed small- and intermediate-conductance Ca2+-activated K+ channels (KCa) present in the endothelium of both species, and concentration-dependent vasodilation to bradykinin followed activation of these KCa channels. Extensive electrical coupling was demonstrated between r-SMCs and l-SMCs, providing an additional pathway to facilitate the well-established myoendothelial coupling. Conducted dilation was still evident in a human RA-IMCA with poor myogenic tone, and heterocellular contacts were visible in the 3D reconstructed artery. Hyperpolarization and conducted vasodilation was also observed to adenosine which, in contrast to bradykinin, was sensitive to combined block of ATP-sensitive (KATP) and inwardly rectifying (KIR) K+ channels.ConclusionsThese data extend our understanding of the mechanisms that coordinate human coronary microvascular blood flow and the mechanistic overlap with porcine IMCAs. The unusual presence of l-SMCs provides an additional pathway for rapid intercellular signaling between cells of the coronary artery wall. Local and conducted vasodilation follow hyperpolarization of the ECs or SMCs, and contact-coupling between l-SMCs and r-SMCs likely facilitates this vasodilation.

Extension of Endocardium-Derived Vessels Generate Coronary Arteries in Neonates.

Unraveling how new coronary arteries develop may provide critical information for establishing novel therapeutic approaches to treating ischemic cardiac diseases. There are 2 distinct coronary vascular populations derived from different origins in the developing heart. Understanding the formation of coronary arteries may provide insights into new ways of promoting coronary artery formation after myocardial infarction. To understand how intramyocardial coronary arteries are generated to connect these 2 coronary vascular populations, we combined genetic lineage tracing, light sheet microscopy, fluorescence micro-optical sectioning tomography, and tissue-specific gene knockout approaches to understand their cellular and molecular mechanisms. We show that a subset of intramyocardial coronary arteries form by angiogenic extension of endocardium-derived vascular tunnels in the neonatal heart. Three-dimensional whole-mount fluorescence imaging showed that these endocardium-derived vascular tunnels or tubes adopt an arterial fate in neonates. Mechanistically, we implicate Mettl3 (methyltransferase-like protein 3) and Notch signaling in regulating endocardium-derived intramyocardial coronary artery formation. Functionally, these intramyocardial arteries persist into adulthood and play a protective role after myocardial infarction. A subset of intramyocardial coronary arteries form by extension of endocardium-derived vascular tunnels in the neonatal heart.

Recognition of acute myocardial infarction caused by spontaneous coronary artery dissection of first septal perforator.

Spontaneous coronary artery dissection (SCAD) diagnosis is challenging as angiographic findings are often subtle and differ from coronary atherosclerosis. Herein, we describe characteristics of patients with acute myocardial infarction (MI) caused by first septal perforator (S1) SCAD. Patients were gathered from SCAD registries at Minneapolis Heart Institute and Vancouver General Hospital. First septal perforator SCAD prevalence was 11 of 1490 (0.7%). Among 11 patients, age range was 38-64 years, 9 (82%) were female. Each presented with acute chest pain, troponin elevation, and non-ST-elevation MI diagnosis. Initial electrocardiogram demonstrated ischaemia in 5 (45%); septal wall motion abnormality was present in 4 (36%). Angiographic type 2 SCAD was present in 7 (64%) patients with S1 TIMI 3 flow in 7 (64%) and TIMI 0 flow in 2 (18%). Initial angiographic interpretation failed to recognize S1-SCAD in 6 (55%) patients (no culprit, n = 5, septal embolism, n = 1). First septal perforator SCAD diagnosis was established by review of initial coronary angiogram consequent to cardiovascular magnetic resonance (CMR) demonstrating focal septal late gadolinium enhancement with corresponding oedema (n = 3), occurrence of subsequent SCAD event (n = 2), or second angiogram showing healed S1-SCAD (n = 1). Patients were treated conservatively, each with ejection fraction >50%. First septal perforator SCAD events may be overlooked at initial angiography and mis-diagnosed as 'no culprit' MI. First septal perforator SCAD prevalence is likely greater than reported herein and dependent on local expertise and availability of CMR imaging. Spontaneous coronary artery dissection events may occur in intra-myocardial coronary arteries, approaching the resolution limits of invasive coronary angiography.

Angiographic evidence of backward compression wave: systolic compression of septal perforators in a child with hypertrophic cardiomyopathy.

Intracoronary wave intensity analysis in hypertrophic cardiomyopathy has shown a large backward compression wave due to compressive deformation of the intramyocardial coronary arteries in systole. The authors describe the angiographic evidence of this backward compression wave, which has not been described in this physiological context and can be a marker of poor prognosis.

Abstract 17038: Influence of Cardiac Workload on Vascular Pyridine Nucleotide Redox State

Introduction: Myocardial perfusion is enhanced during periods of elevated cardiomyocyte oxygen consumption. The coupling between blood flow and myocardial oxygen demand is mediated by redox-dependent signals, yet the influence of cardiac workload on arterial myocyte pyridine nucleotide redox status is unknown. Hypothesis: Increased cardiac workload acutely alters intramyocardial arterial myocyte [NADH] i :[NAD + ] i . Methods and Results: The genetically-encoded fluorescent biosensor Peredox-mCherry was used to monitor real-time changes in intracellular [NADH] i :[NAD] i in isolated arterial myocytes. Treatment of cells expressing Peredox-mCherry with a range of [lactate] o :[pyruvate] o resulted in significant changes in green (Ex,Em: 400, 510 nm): red (Ex,Em: 585,615 nm) fluorescence ratio (1.903 ± 0.010, 10 mM lactate, 1.072 ± 0.073, 10 mM pyruvate), affording accurate quantification of arterial myocyte [NADH] i :[NAD] i . Increased arterial myocyte [NADH] i :[NAD] i was observed in response to reductions in oxygen tension from 5% (0.0021 ± 0.0001) to 1% (0.0050 ± 0.0001; P<0.05). [NADH] i :[NAD] i was not altered by direct stimulation of arterial myocytes with the beta-adrenergic agonist isoproterenol (1 μM; P = .0630). Furthermore, biosensor-expressing arterial myocytes in co-culture with human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) recapitulated the effects of elevated [lactate] o :[pyruvate] o and reduced oxygen tension, exhibiting frequency-dependent increases in [NADH] i :[NAD] I following electrical pacing (e.g., ~3.3 fold increase in 3 Hz vs. unpaced; P<0.05). Consistent with these results, intramyocardial coronary arteries in mice acutely treated with dobutamine (10 mg/kg, i.p.) to drive high cardiac work exhibited significantly greater lactate:pyruvate ratio, used as a surrogate for [NADH] i :[NAD] i , compared with those in hearts treated with vehicle (3.17 ± 0.23 vs. 2.21 ± 0.11; P<0.05). Conclusions: Our results indicate that acute increases in cardiac workload promote the elevation of [NADH] i :[NAD] i in intramyocardial arterial myocytes.

ACE2 (Angiotensin-Converting Enzyme 2) and TMPRSS2 (Transmembrane Serine Protease 2) Expression and Localization of SARS-CoV-2 Infection in the Human Heart.

ACE2 (Angiotensin-Converting Enzyme 2) and TMPRSS2 (Transmembrane Serine Protease 2) Expression and Localization of SARS-CoV-2 Infection in the Human Heart.

Human Coronary Micro‐artery Dysfunction is Associated with Structural and Smooth Muscle Cell Phenotypic Alterations

Autoregulation is compromised in patients with coronary heart disease. A lack of myogenic reactivity and endothelial dysfunction each contribute to a reduced ability to control blood flow within the coronary microcirculation. Little is known how coronary arterial smooth muscle structure and phenotype links to vascular reactivity.Right atrial appendage biopsies from consented patients undergoing valve replacement surgery, and from pigs were collected at clinical standards under general anesthesia. Human and porcine arteries from right atrial appendage samples were isolated and mounted for pressure myography. Confocal imaging established vasomotor responses, cellular viability, and immunohistochemical localization of proteins. The human study complies with the Helsinki Declaration and the animal study complies with the UK Animal (Scientific Procedures) Act, 1986.Here, we compared the structural features of human patient intra‐myocardial coronary arteries (IMCAs) with equivalently handled porcine IMCAs, representing healthy, juvenile controls. More than half the human IMCAs failed to develop ≥10% myogenic tone, even those in which constituent smooth muscle cells (SMCs) could adequately mobilize intracellular Ca2+required for contraction. 3D confocal revealed a novel, distinct layer of longitudinally‐arranged sub‐intimal SMCs (l‐SMCs) between the endothelium and the expected circumferentially‐arranged SMCs responsible for radial contraction (r‐SMC) in the majority of human and porcine IMCAs.Contractile function strongly correlated with SMC phenotype, with the synthetic markers L‐caldesmon and vimentin highly expressed in SMCs with poor contractile function, namely the human r‐SMCs and the porcine l‐SMCs. Thus, we propose that l‐SMCs retain an immature, synthetic phenotype in healthy vessels with functional r‐SMCs but, with loss of r‐SMC function in aged patients, l‐SMCs may play a reparative role and can adopt a contractile phenotype in an attempt to restore function and control myocardial perfusion. The role of l‐SMCs in maintaining the integrity of arterial function warrants further investigation.Support or Funding InformationThis work was supported by the British Heart Foundation (grant numbers FS/08/033/25111, FS/13/16/30199, IG/13/5/30431, PG/18/11/33552) and by the Oxford BHF Centre of Research Excellence (RE/13/1/30181).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

3273Expression of lectin-like oxidized low-density lipoprotein receptor-1 in human epicardial and intramyocardial coronary arteries of male patients undergoing coronary artery bypass grafting

3273Expression of lectin-like oxidized low-density lipoprotein receptor-1 in human epicardial and intramyocardial coronary arteries of male patients undergoing coronary artery bypass grafting

INTRAMYOCARDIAL CORONARY ARTERIES IN CHILDREN: NOT ALL ARE BENIGN BUT MOST ALLOW RETURN TO EXERCISE

Intramyocardial (IM) coronary arteries are characterized by a segment of a coronary artery (CA) that travels into the myocardium instead of the normal epicardial course. It may occur in isolation or in association with anomalous aortic origin of a CA (AAOCA). They are uncommon lesions in children

Expression of Lectin-Like Oxidized Low-Density Lipoprotein Receptor-1 in Human Epicardial and Intramyocardial Coronary Arteries of Male Patients Undergoing Coronary Artery Bypass Grafting

Objectives: Atherosclerosis is almost absent in intramyocardial coronary arteries, while epicardial coronary arteries may show extensive occlusive disease. Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) expression has been implicated in atherogenesis. We aimed to investigate differences in arterial wall LOX-1 expression between human epicardial and intramyocardial coronary arteries. Methods: Epicardial and intramyocardial total artery wall specimens were obtained from 13 male patients (aged 61.9 ± 10.3 years) undergoing coronary artery bypass graft surgery due to 3-vessel coronary artery disease. LOX-1 expression was examined by reverse transcription-polymerase chain reaction. Results: LOX-1 expression was significantly higher in the arterial wall of epicardial coronary arteries compared to intramyocardial coronary arteries. The LOX-1/GAPDH ratio was 0.48 ± 0.07 vs. 0.35 ± 0.03 (p < 0.001). Conclusions: Our findings may partially explain the atheroprotective effect of the intramyocardial course since arterial wall LOX-1 expression was lower in intramyocardial arteries and higher in epicardial coronary arteries.

Speculative Considerations about Some Cardiology Enigmas.

Background:Enigmas often lead to hypotheses and speculations. For this reason, especially for the sake of the reader’s motivation, we opted for the plain discussion of some cardiology enigmas.Objective:The present text was aimed to discuss speculatively some cardiology enigmas.Method:Text was freely designed in the context of coronary artery and heart valve diseases.Results:The results were presented as the combination enigma/hypothesis. 1) The absence of arteriosclerosis in intramyocardial coronary arteries/ endothelium-myocardial interaction (crosstalk); 2) The unique and always confirmed superior evolution of the internal thoracic artery as coronary graft/ higher NO basal release 3) The prophylactic left internal thoracic artery graft in mildly-stenosed coronary lesions/need of more accurate functional imaging techniques; 4) The high incidence of perioperative atrial fibrillation in patients with coronary artery disease/atrial ischemia associated to left circumflex coronary lesions; 5) The handling of disease-free saphenous vein grafts at the time of re-operation/biological serendipity with graft vein segments; 6) The possible aortic stenosis protection against coronary artery disease/ endothelium myocardium interaction (crosstalk) improving NO release.Conclusion:The discussed topics associated with their respective speculative hypothesis remain as enigmas, but would become motivations for investigations

CXCL12 And Vascular Maturation Of The Coronary System During Heart Development

Elucidating the mechanisms involved in the patterning of coronary blood vessels in the embryo will help to improve therapies for coronary perfusion in the injured heart. In the past few years, there have been significant efforts and advances in the understanding of coronary vessel development. The major endothelial cell sources that provide coronary endothelial progenitors to the heart are the sinus venosus (the vein that delivers the venous return) and the endocardium, although the respective contribution from each source is debated. Angiogenic sprouts from the sinus venosus reach the ventricles starting at E11.5 in the mouse and form a vascular plexus in the subepicardial space. This primitive plexus undergoes a complex and incompletely understood process of vascular maturation that involves pruning, branching and reorganization into a hierarchical network of superficial veins and intramyocardial arteries. The main branches of the coronary arteries ultimately connect to the aorta through the coronary ostia by E13.5 – E14.0.CXCL12 (also known as stromal derived factor 1, SDF1) is a chemokine that acts through the G protein‐coupled receptor CXCR4. Global deficiency of Cxcl12 or Cxcr4 as well as endothelial deletion of Cxcr4 result in vascular defects in the mouse kidney and gut, but these defects do not explain the associated late gestation lethality. We hypothesized that coronary vascular defects might underlie the embryonic lethality of CXCL12 deficiency.Cxcl12 and Tie2Cre/Cxcr4 mutants form an initial coronary vascular plexus, which then fails to remodel into a hierarchical network of mature vessels, resulting in the absence of the major intramyocardial coronary arteries, hemorrhage and reduced ventricular wall perfusion. The coronary veins were mostly unaffected, and the basis of the selectivity of CXCL12 on the arterial side of the vasculature is still unclear.In vitro, CXCL12 does not induce sprouting of endothelial cells from beads embedded in a fibrin gel matrix, but instead promotes maturation of vascular sprouts preformed in response to VEGF, by increasing tube elongation, vessel branching, anastomosis and intussusception, all features of mature blood vessel networks. These features were abolished in the presence of AMD3100, a CXCR4 inhibitor. Thus, CXCL12 does not initiate vasculogenesis but rather promotes further remodeling of a plexus that is initially induced by VEGF.We conclude that failed maturation of the coronary system explains the late‐gestation lethality of Cxcl12 mutants, and highlight the role of CXCL12 as an organ‐specific arterial maturation factor of particular relevance in the coronary vasculature. Our current studies are aimed at defining the role of CXCL12 in reprogramming of venous endothelial cells from the sinus venosus into coronary arterial endothelium.Support or Funding InformationThis work was supported by NIH grant HL070123 to H.M.S. and grant 14BGIA20500059 to S.R.K. from the American Heart Association. S.C. was supported by a Postdoctoral Fellowship from the American Heart Association. H.S. was supported by a Postdoctoral Fellowship from the California Institute for Regenerative Medicine.

Young Investigator Award session – Basic Science3433D printed models for surgical planning in complex congenital heart disease344Ultrafast doppler imaging of intramyocardial coronary arteries345Quantification of mitral regurgitation with multiple jets: in vitro comparison of two-dimensional PISA techniques346Non-invasive ultrasonic chordal cutting

Young Investigator Award session – Basic Science3433D printed models for surgical planning in complex congenital heart disease344Ultrafast doppler imaging of intramyocardial coronary arteries345Quantification of mitral regurgitation with multiple jets: in vitro comparison of two-dimensional PISA techniques346Non-invasive ultrasonic chordal cutting

Extending Flaps Lifts an Infarcted Heart Toward Repair

Normal hearts comprise 2 × 109 myocytes, but this number may be doubled in excessively hypertrophied hearts. After a heart attack caused by blockage of one of the arteries that supply the heart, approximately 20% or more of cardiomyocytes are acutely and irreversibly lost in the ischemic area. However, the damage is not limited to the acute interruption of blood flow. Reperfusion of the ischemic territory can cause additional damage due to a burst of toxic reactive oxygen species. Moreover, additional cardiomyocytes are lost in the peri-infarct area during the subacute phase, leading to extension of the infarcted area. The ensuing remodeling response, which consists of cardiomyocyte hypertrophy and collagen accumulation, is insufficient to compensate for the massive cell loss, thus leading to scar expansion, ventricular chamber dilation, and failure.

BAF200 is required for heart morphogenesis and coronary artery development.

ATP-dependent SWI/SNF chromatin remodeling complexes utilize ATP hydrolysis to non-covalently change nucleosome-DNA interactions and are essential in stem cell development, organogenesis, and tumorigenesis. Biochemical studies show that SWI/SNF in mammalian cells can be divided into two subcomplexes BAF and PBAF based on the subunit composition. ARID2 or BAF200 has been defined as an intrinsic subunit of PBAF complex. However, the function of BAF200 in vivo is not clear. To dissect the possible role of BAF200 in regulating embryogenesis and organ development, we generated BAF200 mutant mice and found they were embryonic lethal. BAF200 mutant embryos exhibited multiple cardiac defects including thin myocardium, ventricular septum defect, common atrioventricular valve, and double outlet right ventricle around E14.5. Moreover, we also detected reduced intramyocardial coronary arteries in BAF200 mutants, suggesting that BAF200 is required for proper migration and differentiation of subepicardial venous cells into arterial endothelial cells. Our work revealed that PBAF complex plays a critical role in heart morphogenesis and coronary artery angiogenesis.

Myocardium-derived angiopoietin-1 is essential for coronary vein formation in the developing heart.

The origin and developmental mechanisms underlying coronary vessels are not fully elucidated. Here we show that myocardium-derived angiopoietin-1 (Ang1) is essential for coronary vein formation in the developing heart. Cardiomyocyte-specific Ang1 deletion results in defective formation of the subepicardial coronary veins, but had no significant effect on the formation of intramyocardial coronary arteries. The endothelial cells (ECs) of the sinus venosus (SV) are heterogeneous population, composed of APJ-positive and APJ-negative ECs. Among these, the APJ-negative ECs migrate from the SV into the atrial and ventricular myocardium in Ang1-dependent manner. In addition, Ang1 may positively regulate venous differentiation of the subepicardial APJ-negative ECs in the heart. Consistently, in vitro experiments show that Ang1 indeed promotes venous differentiation of the immature ECs. Collectively, our results indicate that myocardial Ang1 positively regulates coronary vein formation presumably by promoting the proliferation, migration and differentiation of immature ECs derived from the SV.

Remodeling of small intramyocardial coronary arteries distal to total occlusions after myocardial infarction in pigs

The present study was designed to investigate whether microvascular remodeling could occur in hibernating myocardium and infarction regions distal to a total occluded coronary artery after acute myocardial infarction. Copper stents were implanted in the left descending coronary arteries of 64 pigs to induce anterior wall myocardial infarction. The pigs were assigned randomly to group A (n=8; killed at 1 week), group B (n=8; killed at 2 weeks), group C (n=16; killed at 4 weeks), group D (n=16; killed at 3 months), and group E (n=16; killed at 6 months). The control group included six pigs that were subjected to the same procedures but without implantation of copper stents. The wall area (WA) and lumen area (LA) of small intramyocardial coronary arteries (SIMCA) distal to occlusions were measured and the ratios of WA/LA and LA/total vessel area (%L) were calculated. The composition of the arterial wall was determined by Masson's trichrome stain, transmission electron microscope. A significant increase in WA/LA and decrease %L in SIMCA were observed in group B (P<0.05), group C (P<0.01), group D (P<0.01), and group E (P<0.01) compared with the control. There was increased area of collagen fiber in the thickened arterial wall in group C (P<0.05), group D (P<0.01), and group E (P<0.01) compared with the control group, group A, and group B. A significantly increased ratio of the synthetic phenotype vascular smooth muscle cells were found in group B (P<0.05), group C (P<0.01), group D (P<0.01), and group E (P<0.01) compared with the control group. Several weeks after occlusion of epicardial coronary, the SIMCAs distal to occlusion developed remodeling, with an increase in wall thickness and a decrease in lumen size. These structural changes may restrict blood flow to ischemic or hibernating myocardium after revascularization.

Subepicardial endothelial cells invade the embryonic ventricle wall to form coronary arteries

Coronary arteries bring blood flow to the heart muscle. Understanding the developmental program of the coronary arteries provides insights into the treatment of coronary artery diseases. Multiple sources have been described as contributing to coronary arteries including the proepicardium, sinus venosus (SV), and endocardium. However, the developmental origins of coronary vessels are still under intense study. We have produced a new genetic tool for studying coronary development, an AplnCreER mouse line, which expresses an inducible Cre recombinase specifically in developing coronary vessels. Quantitative analysis of coronary development and timed induction of AplnCreER fate tracing showed that the progenies of subepicardial endothelial cells (ECs) both invade the compact myocardium to form coronary arteries and remain on the surface to produce veins. We found that these subepicardial ECs are the major sources of intramyocardial coronary vessels in the developing heart. In vitro explant assays indicate that the majority of these subepicardial ECs arise from endocardium of the SV and atrium, but not from ventricular endocardium. Clonal analysis of Apln-positive cells indicates that a single subepicardial EC contributes equally to both coronary arteries and veins. Collectively, these data suggested that subepicardial ECs are the major source of intramyocardial coronary arteries in the ventricle wall, and that coronary arteries and veins have a common origin in the developing heart.

Imaging flow dynamics in murine coronary arteries with spectral domain optical Doppler tomography

Blood flow in murine epicardial and intra-myocardial coronary arteries was measured in vivo with spectral domain optical Doppler tomography (SD-ODT). Videos at frame rates up to 180 fps were collected and processed to extract phase shifts associated with moving erythrocytes in the coronary arteries. Radial averaging centered on the vessel lumen provided spatial smoothing of phase noise in a single cross-sectional frame for instantaneous peak velocity measurement without distortion of the flow profile. Temporal averaging synchronized to the cardiac cycle (i.e., gating) was also performed to reduce phase noise, although resulting in lower flow profiles. The vessel angle with respect to incident imaging beam was measured with three-dimensional raster scans collected from the same region as the high speed cross-sectional scans. The variability in peak phase measurement was 10-15% from cycle to cycle on a single animal but larger for measurements among animals. The inter-subject variability is attributed to factors related to real physiological and anatomical differences, instrumentation variables, and measurement error. The measured peak instantaneous flow velocity in a ~40-µm diameter vessel was 23.5 mm/s (28 kHz Doppler phase shift). In addition to measurement of the flow velocity, we observed several dynamic features of the vessel and surrounding myocardium in the intensity and phase sequences, including asymmetric vessel deformation and rapid flow reversal immediately following maximum flow, in confirmation of known coronary artery flow dynamics. SD-ODT is an optical imaging tool that can provide in vivo measures of structural and functional information on cardiac function in small animals.