Ultrasound Based Assessment of Coronary Artery Flow and Coronary Flow Reserve Using the Pressure Overload Model in Mice
April 13th, 2015
Coronary flow reserve (CFR) is useful for assessment of myocardial oxygen demand and evaluation of cardiovascular risk. This study establishes a step-by-step transthoracic Doppler echocardiographic (TTDE) method for longitudinal monitoring of the changes in CFR, as measured from coronary artery in mice, under the experimental pressure overload of aortic banding.
The overall goal of this procedure is to non-invasively and longitudinally monitor fluctuations in the coronary flow dynamics that occur in response to changes in the coronary artery flow. This is accomplished by first capturing long and short axis images of the septal coronary artery, or SCA on aortic banded adult male mice. Color doppler images of the SCA then are obtained before and after the application of a pulse wave to acquire the baseline and peak flow velocities.
Ultimately, the systolic to diastolic coronary flow velocities are compared under hyperemia and at baseline to determine the coronary flow reserve. The implications of this technique extend toward imaging based diagnostics as real-time detection that utilizes high resolution imaging allows the detection of small but significant changes in the coronary flow before the full onset of disease. Through this method can provide insight into the coronary growth dynamics of mice.
It can also be applied to other MAR systems such as rats and the large mammals, including humans. Begin by using a medical grade depilatory cream to remove the chest hair from an eight to 10 week old male, C 57 BL six mouse. Next, connect a probe with a center frequency of 40 megahertz to the active port of the ultrasound machine and set the application preset to the cardiac imaging setting.
Then to acquire long and short axis images of the SCA in the B mode, place the animal supine on the imaging platform and use the rail system to position the probe to obtain a parasternal long axis view of the animal. Rotate the probe clockwise with a notch pointing coddly such that the probe angle is 15 degrees to the left of the parasternal line. Then tilt the probe slightly along the Y axis to obtain a full length longitudinal view of the SCA in the center of the screen.
Once the aortic valve and pulmonary artery are in view, cine store the image using the highest frame rate possible. Next, use the XY axes, microm manipulators to adjust the probe position and obtain the clearest image of the SCA. Then rotate the probe 90 degrees clockwise with a notch pointing coddly such that the notched end of the probe is to the left of midline.
By switching to color doppler, the anatomic heartland mark can be viewed in color such a L in the SEP coronary artery, which can help to determine the exact position of the coronary artery To obtain long and short axis color images of the SCA Once a B mode image has been captured. Click the color Doppler key key on the keyboard to open the color Doppler acoustic window. Next, ensure that the focus depth, which is indicated by the yellow arrowhead, lies in the center of the coronary artery.
Then using the cine store key confirmed that the data is recorded at the highest possible frame rate to image the SCA in the pulse wave mode. While using the color doppler, click on the pulse wave key to bring up a yellow indicator line on the coronary artery. Place the yellow pulse wave line in the middle of the coronary artery at an angle that parallels the directionality of the flow.
Next, use the pulse wave angle key to adjust the angle of the flow to 60 degrees or less, and the sample volume key to capture the flow in the center of the SCA. Then using one and 2.5%iso fluorine cine store the waveforms that indicate the velocity of the coronary flow at peak systole and diastole. Finally, to analyze the data, use the velocity time integral tool to obtain the peak systolic and diastolic velocities.
In this representative experiment, the coronary flow reserve was calculated. Unlike the sham group, the banded mice exhibited a marked continuous decline starting early after surgery and persisting through the 13 day study period. This steady reduction in the coronary flow reserve suggests a progressive coronary dysregulation responsible for the reduction in the myocardial perfusion, the systolic to diastolic coronary velocity ratio.
Another indicator of coronary dysfunction also increased significantly in the bandit group at both the baseline and hyperemia benchmarking. The echo data against the histology revealed a tight correlation with the histopathological changes observed in the coronary artery. Finally, neither the intra nor inter observer variabilities were determined to be significant, nor were any significant changes observed in the traditional echocardiographic parameters of the left ventricle function After its development.
This technique paved the way for researchers in the fields of clinical diagnostic and molecular imaging to the high resolution visualization of smaller vessels and small animal models that accurately mimic human disease conditions such as aortic stenosis or hypertensive cardiomyopathy. After watching this video, you should have a good understanding of how to perform geo tie imaging and the analysis of coronary artery flow in mice that have undergone surgical intervention or are under all defined conditions such as hyperemia that affect coronary flow dynamics.
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Overview
This study presents a non-invasive method for longitudinal monitoring of coronary flow reserve (CFR) in mice using transthoracic Doppler echocardiography. The technique allows for the assessment of myocardial oxygen demand and cardiovascular risk under experimental conditions.
Key Study Components
Area of Science
- Cardiovascular physiology
- Non-invasive imaging techniques
- Experimental models in mice
Background
- Coronary flow reserve (CFR) is critical for evaluating heart health.
- Understanding CFR can help in assessing cardiovascular risk.
- Transthoracic Doppler echocardiography (TTDE) is a valuable imaging tool.
- Monitoring CFR changes can provide insights into heart disease progression.
Purpose of Study
- To establish a method for monitoring CFR in response to aortic banding in mice.
- To evaluate changes in coronary flow dynamics.
- To enhance imaging-based diagnostics for early disease detection.
Methods Used
- Capture long and short axis images of the septal coronary artery (SCA).
- Obtain color Doppler images before and after applying a pulse wave.
- Measure baseline and peak flow velocities to calculate CFR.
- Compare systolic and diastolic flow velocities under hyperemia and baseline conditions.
Main Results
- The method successfully captures fluctuations in coronary flow dynamics.
- Significant changes in flow velocities were detected before disease onset.
- Real-time imaging allows for early detection of coronary issues.
- Insights into coronary growth dynamics were obtained from the study.
Conclusions
- The TTDE method is effective for monitoring CFR in mice.
- This technique can aid in understanding cardiovascular health and disease.
- Future applications may enhance diagnostic capabilities in clinical settings.
Frequently Asked Questions
Executive Industry Relevance
Non-invasive longitudinal monitoring of coronary flow reserve (CFR) in murine models enables early detection of coronary dysregulation preceding functional decline, supporting mechanistic de-risking in cardiovascular drug discovery. This approach provides predictive confidence for target validation by correlating functional hemodynamics with histopathological endpoints, reducing reliance on terminal assays. The method enhances translational continuity by identifying perfusion defects at stages amenable to intervention, informing go/no-go decisions in preclinical pipelines.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of therapeutic hypotheses by quantifying coronary flow dynamics in response to pressure overload, clarifying pathway-specific effects on myocardial perfusion.
- Operational Value: Supports biological de-risking through repeated, non-terminal assessments of coronary function, reducing animal usage and increasing data density per model.
- Predictive Value: Facilitates portfolio triage by detecting early coronary dysregulation before left ventricular dysfunction, improving confidence in target-mediated vascular effects.
Screening & Assay Development
- Assay Readiness: Establishes standardized protocols for acquiring reproducible septal coronary artery flow velocity measurements under baseline and hyperemic conditions induced by isoflurane.
- Quantitative Outputs: Generates coronary flow reserve (CFR) and systolic-to-diastolic (S/D) ratio metrics via Doppler echocardiography, enabling compound-induced changes in vascular function to be tracked over time.
- Scalability: Demonstrates intra- and inter-observer reliability, supporting platform adaptation across laboratories for consistent preclinical screening.
Translational & Preclinical Research
- Disease Relevance: Models coronary microvascular dysfunction in pressure overload, aligning with human hypertensive cardiomyopathy and aortic stenosis pathophysiology.
- Translational Continuity: Links non-invasive CFR measurements to histopathological validation (peri-coronary fibrosis), strengthening biomarker qualification for preclinical efficacy studies.
- Risk-Adjusted Advancement: Provides early functional readouts that inform dose selection and timing of intervention in preclinical cardiovascular programs.
Pipeline & Workflow Integration
The method integrates into discovery biology workflows by providing hemodynamic phenotyping that bridges genetic or pharmacological modulation with functional vascular outcomes, preceding structural remodeling.
- Discovery Biology: Supports hypothesis testing of coronary flow regulation by measuring CFR and S/D ratio changes in response to aortic banding, enabling mechanistic insight into vascular stress responses.
- Screening: Delivers assay-ready, quantitative flow velocity data under controlled hyperemia, facilitating evaluation of compounds targeting coronary microvascular function.
- Analytics: Produces CFR as a ratio of hyperemic to baseline flow and S/D ratio as systolic-to-diastolic velocity comparison, offering normalized metrics for cross-group comparison and temporal tracking.
- Translational Research: Connects functional coronary assessments to histopathological endpoints, validating echocardiography as a surrogate for microvascular fibrosis in preclinical models.
- Enterprise Reuse: Establishes a reusable imaging platform applicable across strains, interventions, and timepoints, maximizing resource efficiency in cardiovascular discovery pipelines.
Operational & Enterprise Impact
- Scientific Value: Increases predictive confidence in target validation by detecting coronary perfusion changes prior to overt dysfunction, reducing false negatives in vascular safety assessment.
- Operational Value: Enhances reproducibility through standardized image acquisition and dual-observer analysis, minimizing variability in longitudinal hemodynamic tracking.
- Strategic Value: Improves capital efficiency by enabling early go/no-go decisions based on coronary flow reserve trends, reducing investment in targets with adverse vascular effects.
- Portfolio Impact: Supports risk-adjusted prioritization by identifying compounds that preserve or improve CFR, informing advancement decisions in cardiovascular portfolios.
Implementation Considerations
- Requires expertise in murine echocardiography and Doppler signal acquisition to ensure accurate septal coronary artery visualization and angle correction.
- Dependent on high-frequency ultrasound systems (40 MHz) and specialized software for velocity time integral analysis to derive peak systolic and diastolic flow metrics.
- Necessitates standardized hyperemia induction via isoflurane and consistent baseline conditions to ensure reproducible CFR calculations across study groups.
- Involves adaptation considerations for different murine strains or surgical models, as septal coronary artery accessibility may vary with anatomy or pathology.
- Limited by the inability to distinguish epicardial from microvascular contributions to flow changes, requiring complementary assays for mechanistic specificity.
Biopharma FAQs
Chapters in this video
0:05
Title
1:24
Long and Short Axis Septal Coronary Artery (SCA) Imaging (B-mode)
2:51
Long and Short Axis SCA Imaging (Color Doppler Mode)
3:38
Pulse Wave (PW) Doppler Imaging of SCA (Pulsed Wave or PW Mode)
4:34
Results: Representative Coronary Flow Analyses
5:45
Conclusion
