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Ultrasound in Mice and Rats for Cardiovascular Disease Research (Part 2) — Application in Cardiovascular Models and Quality Control Standards
2026 Cardiovascular

In the previous four installments of this series, our team has systematically established a comprehensive theoretical framework for small animal ultrasound, covering ultrasound equipment imaging principles, core imaging modules, anatomical features of the mouse and rat heart, physiological differences between humans and rodents, hemodynamic mechanisms of the cardiac cycle, and a full set of basic and advanced ultrasound evaluation indicators. We have thoroughly deconstructed the underlying scientific rationale for cardiac ultrasound detection in mice and rats. A solid theoretical foundation is a prerequisite for accurate and reliable experimental data. For researchers, the practical implementation of theory, standardized operations, error prevention, and high-quality data output are the critical factors driving project progress, academic publication, and the translation of research results into practical applications.

Currently, most research groups face common technical challenges in cardiovascular ultrasound experiments using mice and rats: under identical animal models and detection parameters, data within groups show high dispersion, and experimental results between groups suffer from poor reproducibility. Beginners are prone to issues such as imaging plane deviation, misjudgment of endocardial borders, and distortion of ultrasound indicators. Conventional detection methods often fail to capture early subclinical myocardial injury, making it difficult to meet the data requirements of high-level academic research. Furthermore, the lack of a standardized quality control system in experiments leaves them vulnerable to reviewers' questioning of data reliability. Most of these problems are not caused by equipment or model defects, but rather stem from non-standardized operational procedures, unclear model detection protocols, inadequate quality control details, and insufficient application of advanced detection technologies.

In response to these research pain points, this installment, as the second part of the series, focuses on the practical application of small animal ultrasound. It systematically elaborates on standardized detection protocols for high-frequency small animal ultrasound in mainstream cardiovascular disease animal models, full-process experimental quality control systems, and strategies for avoiding common errors. Additionally, it reviews cutting-edge advanced ultrasound detection techniques commonly used in high-impact journals, aiming to comprehensively enhance the data standardization, rigor, and academic value of cardiovascular animal experiments.

I. Core Application Value of Cardiac Ultrasound in Mice and Rats in Cardiovascular Disease Research

The pathological evolution of cardiovascular diseases exhibits clear stage-specific characteristics, sequentially presenting as early-stage functional myocardial abnormalities, mid-stage structural cardiac remodeling, and late-stage irreversible organic damage. Traditional research detection methods have significant limitations. Histopathological sections only allow static structural observation at the experimental endpoint, and serological assays can only reflect the overall level of systemic injury, failing to dynamically capture early myocardial microfunctional changes, hemodynamic fluctuations, or stage-specific pathological evolution features.

High-frequency small animal ultrasound, with its technical advantages of non-invasive in vivo monitoring, multi-dimensional quantitative assessment, long-term time-series follow-up, and stratified precision analysis, can adapt to the full-cycle research needs of various mouse and rat cardiovascular models. It covers all research scenarios, including disease model validation, pathological mechanism investigation, targeted drug screening, intervention efficacy evaluation, and prognostic dynamic assessment. Combined with the previously established anatomical and physiological theories, mice and rats are characterized by high heart rates, high myocardial metabolic activity, high susceptibility to myocardial injury, and rapid disease progression. Therefore, their ultrasound detection systems cannot simply adopt clinical human ultrasound protocols; a dedicated standardized practical system tailored to rodents must be established. Different cardiovascular disease models have distinct injury targets, pathological processes, and core observational indicators. Therefore, targeted scanning protocols and detection priorities are the fundamental prerequisites for accurately determining model phenotypes and obtaining effective research data.

II. Standardized Ultrasound Detection Protocols for Mainstream Cardiovascular Disease Models

At the current stage of basic cardiovascular research, the six most widely used mouse and rat models include: the acute myocardial infarction model, the pressure-overload myocardial hypertrophy and heart failure model, the diabetic cardiomyopathy model, the hypertensive secondary myocardial injury model, and the pulmonary hypertension complicated by right heart failure model. This chapter addresses the pathological characteristics of each model by standardizing the scanning planes, core evaluation indicators, and key research observation points, thereby forming a directly reusable experimental protocol.

2.1 Acute Myocardial Infarction Model (Coronary Artery Ligation, AMI)

The Acute Myocardial Infarction (AMI) model is primarily established by ligating the Left Anterior Descending (LAD) coronary artery. It is a classic animal model for studying ischemic cardiomyopathy, myocardial ischemia-reperfusion injury, post-infarction ventricular remodeling, and heart failure. The core pathological features of this model include localized myocardial ischemic necrosis, regional wall motion abnormalities, ventricular cavity dilation, and significant deterioration of global left ventricular systolic function.

Standardized Scanning Protocol: The parasternal long-axis (PLAX) and parasternal short-axis (PSAX) views serve as the core imaging planes. Equipment parameters such as ultrasound scanning depth, gain, and frame rate are fixed throughout the procedure to ensure consistent detection conditions across baseline (pre-surgery), post-modeling, and various post-drug intervention time points. M-mode sampling is positioned at the mid-ventricular level at the papillary muscle level to stably track the dynamic motion changes of the interventricular septum, left ventricular anterior wall, and left ventricular posterior wall. Color Doppler Flow Imaging (CDFI) and Pulsed Wave (PW) Doppler are used to assess aortic ejection flow parameters. Advanced detection incorporates Speckle Tracking Imaging (STI) to evaluate regional myocardial motion synchrony and myocardial strain function.

Core Observational Indicators and Research Priorities: Left ventricular systolic function indicators are the core evaluation criteria for this model, primarily including Left Ventricular Ejection Fraction (EF), Fractional Shortening (FS), and Stroke Volume (SV). In the AMI model, these indicators show a persistent and significant decrease post-surgery. Structural indicators focus on Left Ventricular End-Diastolic Diameter (LVEDD) and Left Ventricular End-Systolic Diameter (LVESD) to assess ventricular cavity dilation and pathological remodeling progression. Functionally, the model allows for the identification of areas of hypokinesis, akinesis, and dyskinesis of the myocardial wall, precisely distinguishing between the infarcted region, the ischemic border zone, and normal myocardial areas. Long-term follow-up can observe characteristic imaging changes such as wall thinning and increased echogenicity due to myocardial fibrosis.

Research Application Scenarios: Primarily used to verify the reparative effects of cardioprotective drugs, stem cell therapies, and targeted gene interventions on ischemic myocardial injury, and to quantitatively evaluate the improvement in cardiac function and the inhibitory effect on pathological ventricular remodeling resulting from these interventions.

Figure 1: Schematic diagram of the LAD model. 1: Infarct area; 2: Left coronary artery ligation.

 

2.2 Pressure-Overload Myocardial Hypertrophy and Heart Failure Model (TAC)

The Transverse Aortic Constriction (TAC) model establishes pressure overload by constricting the aortic arch, simulating the chronic cardiac pressure overload seen in clinical hypertension and aortic stenosis. The pathological progression of this model exhibits distinct stage-specific characteristics: the early stage is marked by compensatory myocardial hypertrophy, with normal or mildly enhanced cardiac function; the mid-stage is predominantly characterized by impaired diastolic function; and the late stage progresses to the decompensated phase, featuring ventricular dilation and systolic heart failure. This model is the gold standard for studying pressure-overload-mediated myocardial hypertrophy and heart failure.

Standardized Scanning Protocol: The parasternal short-axis view serves as the core plane, with precise localization and fixation of the sampling position to avoid measurement errors in wall thickness caused by plane deviation. This is combined with the apical four-chamber view to evaluate global cardiac function and filling status. A dedicated aortic arch view is added to clearly visualize the constricted segment of the aorta and acquire flow velocity spectra at the stenosis site, which are used for confirming successful pre-surgical modeling and for long-term postoperative hemodynamic follow-up.

Core Observational Indicators and Research Priorities

Model Validation Indicators: Peak flow velocity at the aortic constriction site and trans-stenotic pressure gradient. An increase in flow velocity and pressure gradient at the stenosis site serves as a direct quantitative basis for confirming effective luminal narrowing. These parameters are used to determine the success rate of the surgical model and to exclude animals with insufficient ligation that fail to establish effective pressure overload.

Early Compensatory Stage: The focus is on measuring Interventricular Septal Thickness at Diastole (IVSd), Interventricular Septal Thickness at Systole (IVSs), Left Ventricular Posterior Wall Thickness at Diastole (LVPWd), Left Ventricular Posterior Wall Thickness at Systole (LVPWs), and the mean wall thickening rate to assess the degree of compensatory myocardial hypertrophy.

Disease Progression Stage: The core observational target is diastolic dysfunction. Key parameters assessed include mitral E-wave velocity, A-wave velocity, E/A ratio, mitral annular early diastolic velocity (e'), E/e' ratio, and Isovolumic Relaxation Time (IVRT). The E/e' ratio is particularly valuable as it effectively mitigates interference from heart rate fluctuations and ventricular volume loading, accurately distinguishing between early occult diastolic dysfunction and pseudonormalized filling patterns. It is a core advanced indicator for high-level research using this model.

Decompensated Stage: The focus shifts to monitoring the decline in EF and FS, as well as increases in LVEDD and LVESD, to quantitatively evaluate the progression of heart failure. The trans-stenotic pressure gradient dynamically reflects the sustained level of cardiac pressure overload and correlates with the rates of myocardial hypertrophy and heart failure progression, thereby enriching the hemodynamic evaluation system of the model.

Figure 2: Pressure-overload myocardial hypertrophy and heart failure model (TAC)

 

2.3 Diabetic Cardiomyopathy Model (DCM)

Diabetic Cardiomyopathy (DCM) can be induced by feeding a high-sugar, high-fat diet or by injecting streptozotocin (STZ). This model lacks significant coronary artery stenosis or hypertensive pathological features. Its core characteristics are chronic, insidious myocardial injury mediated by glycolipid metabolic disorders. In the early stage, there are no obvious structural cardiac abnormalities, making it highly suitable for simulating the pathological progression of clinically relevant diabetes-associated myocardial injury.

Standardized Scanning Protocol: This protocol utilizes two-dimensional echocardiography, M-mode echocardiography, and Tissue Doppler Imaging (TDI) in combination, focusing on capturing subclinical myocardial micro-injury that is difficult to detect with conventional ultrasound. Through time-series monitoring at multiple time points, it tracks the dynamic evolution of early subtle functional abnormalities.

Core Observational Indicators and Research Priorities: The most typical pathological feature of the DCM model is early isolated diastolic dysfunction, without significant abnormalities in systolic function or chamber structure. Key observational indicators include diastolic function parameters such as a decreased E/A ratio, an elevated E/e' ratio, and prolonged IVRT. TDI enables precise detection of microfunctional abnormalities, including reduced myocardial diastolic velocity and regional myocardial dyssynchrony. In the late stages, organic damage such as myocardial hypertrophy, ventricular dilation, and decreased systolic function may gradually appear. This model is primarily used to evaluate the protective effects of metabolic interventions and glucose-lowering cardioprotective drugs on early diabetic myocardial injury.

Figure 3: Diabetic cardiomyopathy model (DCM)

 

2.4 Hypertensive Secondary Myocardial Injury Model

This model category primarily includes spontaneously hypertensive rats (SHR) and angiotensin II (Ang II) infusion mice. The core pathological mechanism is long-term arterial hypertension inducing cardiac pressure overload, which subsequently triggers myocardial hypertrophy, myocardial fibrosis, and ventricular remodeling, ultimately progressing to heart failure. This pathophysiological progression closely mirrors clinical hypertensive heart disease.

Standardized Scanning Protocol: The protocol employs parasternal long-axis and short-axis views combined with PW and CDFI flow measurements to simultaneously assess cardiac structural morphology, global pump function, and macrovascular hemodynamic status. Emphasis is placed on comparing indicator differences between baseline and various post-modeling time points to delineate the dynamic evolution of myocardial injury.

Core Observational Indicators and Research Priorities: At the structural level, key parameters include wall thickness and left ventricular chamber volume indices to evaluate the degree of myocardial hypertrophy and ventricular remodeling. At the functional level, both systolic and diastolic function parameters are analyzed concurrently. At the hemodynamic level, aortic peak flow velocity, cardiac valve regurgitation velocity, and regurgitation area are measured to assess the impact of pressure overload on myocardial pump function and macrovascular compliance. This model is primarily used to validate the efficacy of interventions aimed at lowering blood pressure, anti-fibrotic therapies, and strategies to inhibit ventricular remodeling.

Figure 4: Secondary hypertension phenotype

 

2.5 Pulmonary Arterial Hypertension and Right Heart Failure Model (PAH)

The Pulmonary Arterial Hypertension (PAH) model can be established through chronic hypoxia exposure, monocrotaline injection, or other methods. The core pathogenic factor is a sustained elevation of pulmonary circulatory pressure, which primarily affects the right heart system, predisposing it to right ventricular volume and pressure overload, right ventricular hypertrophy, and right ventricular systolic failure. This is the core animal model for simulating clinical cor pulmonale (pulmonary heart disease).

Standardized Scanning Protocol: This protocol optimizes dedicated right-heart imaging planes, with emphasis on acquiring the parasternal right ventricular view, the pulmonary artery flow view, and the apical right ventricular optimized view, thereby addressing the detection blind spot of conventional experiments that focus only on left ventricular function. TDI spectra at the tricuspid annulus are acquired in a standardized manner, with the sample volume fixed at the lateral tricuspid annulus to stably obtain core right ventricular functional parameters.

Core Observational Indicators and Research Priorities: Key parameters include right ventricular internal diameter, right ventricular wall thickness, pulmonary artery peak flow velocity, and pulmonary valve transvalvular pressure gradient, which are used to assess the severity of pulmonary hypertension and the degree of right heart structural remodeling. Tricuspid Annular Systolic Excursion (TAPSE) and tricuspid annular peak systolic velocity (S') are the gold-standard parameters for evaluating global right ventricular longitudinal systolic function. These parameters are less susceptible to interference from right ventricular loading conditions and ventricular geometry, enabling early detection of occult right ventricular systolic impairment and effectively distinguishing between compensatory right ventricular hypertrophy and early functional decline. They are essential advanced quantitative indicators for PAH model research.

Figure 5: Pulmonary arterial hypertension and right heart failure model (PAH)

 

III. Full-Process Standardized Quality Control System for Cardiac Ultrasound in Mice and Rats

The core causes of poor experimental data reproducibility, non-replicable results, and academic reviewer skepticism — 90% of them — originate from non-standardized practical quality control. The cardiac structures of mice and rats are minute, their heart rates are extremely rapid, and their neurohumoral regulation is highly sensitive. They are acutely responsive to environmental stimuli, anesthetic state, and operational pressure. Any minor experimental deviation can lead to systematic distortion of ultrasound indicators. This chapter establishes a full-process standardized quality control system covering pre-experimental preparation, animal state management, imaging scanning, parameter measurement, and data screening, comprehensively mitigating both systematic and random errors.

3.1 Pre-Experimental Quality Control: Standardization of Environment, Equipment, and Consumables

Environmental Quality Control: Maintain a constant temperature and humidity environment in the experimental area, with ambient temperature stable at 22–25°C. Avoid stress-inducing factors such as airflow disturbances, noise stimulation, and intense light exposure. Animal stress can directly trigger heart rate fluctuations and myocardial contractile disturbances, significantly increasing data dispersion, and is the most commonly overlooked source of error for beginners.

Equipment Quality Control: Standardize core equipment parameters including frame rate, gain, scanning depth, and contrast. All experimental groups and all follow-up time points must use identical settings to prevent data deviations caused by arbitrary parameter adjustments. Perform regular self-checks, probe calibration, and maintenance to avoid imaging blurring and artifacts caused by probe aging or reduced resolution.

Consumables Quality Control: Pre-warm ultrasound coupling gel to 37°C to match the experimental animal's body temperature, avoiding animal stress and heart rate fluctuations induced by cold stimulation. Apply a thin, uniform layer of coupling gel to the scanning area, avoiding excessive amounts that could compress the thorax and restrict cardiac motion, as well as insufficient amounts that could cause abnormal acoustic wave transmission or imaging blind spots.

3.2 Animal State Quality Control: Standardized Management of Anesthesia, Body Temperature, and Heart Rate

Animal physiological state is the core factor determining the authenticity and reliability of ultrasound data, and it is also a key focus of experimental audits in high-impact journals. Mice and rats have high myocardial metabolic activity and rapid stress responses; abnormal anesthetic depth or body temperature disturbances can directly interfere with baseline cardiac function.

Standardized Anesthesia: Isoflurane inhalation anesthesia is preferred, ensuring smooth induction and sustained stable depth, avoiding the disadvantages of intraperitoneal injection, such as slow onset and large depth fluctuations. Strictly control the heart rate range during the experiment: maintain resting heart rate at 400–600 beats/min for mice and 300–400 beats/min for rats. A heart rate that is too high indicates insufficient anesthesia depth and an animal under stress; a heart rate that is too low indicates excessive anesthetic depth and drug-induced suppression of myocardial function. Data obtained under either condition are invalid and must be excluded and remeasured. All experimental animals should receive the same anesthesia method, dosage, and duration to eliminate confounding effects of anesthesia on experimental results.

Standardized Body Temperature: Use a constant-temperature heating pad throughout the procedure to maintain animal body temperature. When conditions permit, use a rectal temperature probe for real-time monitoring, strictly maintaining the animal's core temperature at 36–37°C. Hypothermia can directly reduce heart rate and suppress myocardial contractility, causing false reductions in systolic parameters such as EF and FS, and is a major contributor to experimental data deviation.

Standardized Preoperative Preparation: Thoroughly shave the scanning area to completely remove body hair, preventing hair from blocking the ultrasound beam and causing imaging blurring or echo artifacts. Perform shaving gently to avoid skin abrasions, subcutaneous edema, or other local tissue damage that could interfere with imaging results.

3.3 Imaging Scanning Quality Control: Standardized Planes, Precise Angles, and Artifact-Free Imaging

Non-standard imaging planes are the primary cause of indicator misinterpretation. All M-mode sampling must be positioned based on standard two-dimensional B-mode imaging; blind sampling without anatomical reference is prohibited. The standard PLAX view must clearly display the left ventricular cavity, mitral valve structures, and aortic root, with symmetrical ventricular contours and no tilting distortion. The standard PSAX view is positioned at the level of the left ventricular papillary muscles, ensuring the chamber appears as a regular, symmetrical ring.

During scanning, the probe should be perpendicular to the thoracic surface. Apply gentle, consistent scanning pressure; never press forcefully on the chest wall to prevent external compression from reducing ventricular volume, deforming wall morphology, or causing abnormal heart rate fluctuations. Select cardiac cycles with stable respiration and regular rhythm for imaging and sampling, avoiding interference from respiratory and motion artifacts on image quality.

3.4 Measurement and Analysis Quality Control: Standardization of Border Delineation, Sampling Rules, and Data Screening

Standardized Border Delineation: Consistently apply fixed border delineation criteria to precisely outline the endocardial contour, preventing measurement errors in chamber diameter and wall thickness caused by subjective border offsets. M-mode motion curves must precisely match the two-dimensional anatomical structures, avoiding indicator distortion caused by curve drift or structural mismatch.

Sampling and Data Screening Rules: For each animal, continuously select 3–5 clear, artifact-free consecutive cardiac cycles with regular rhythm for measurement. Take the average as the final experimental data to offset random measurement errors. Uniformly exclude invalid data affected by arrhythmia, respiratory interference, plane deviation, or imaging blurring, ensuring the objectivity and authenticity of the experimental data.

Blinded Analysis Standards: High-level research is recommended to adopt a blinded analysis mode, separating the personnel responsible for experimental operations from those performing data analysis, to avoid subjective bias. This approach significantly enhances data credibility and aligns with the publication standards of high-impact SCI journals.

IV. Analysis of Common High-Frequency Experimental Errors and Standardized Mitigation Strategies

Drawing on extensive practical experience, this section summarizes the four most common types of standardized errors in cardiac ultrasound experiments using mice and rats, clarifies their causes, and provides directly implementable mitigation strategies to correct operational misunderstandings.

Error 1: Plane Tilting Leading to Distorted Wall Thickness and Chamber Diameter Measurements: Tilting of the PSAX plane can cause false thickening of one side of the ventricular wall and chamber morphological distortion, directly interfering with quantitative results in myocardial hypertrophy models. Mitigation Strategy: Use the regularity of the two-dimensional plane as the gold standard; confirm chamber symmetry and structural integrity before initiating M-mode sampling. Measurements on oblique planes are strictly prohibited.

Error 2: Excessive Anesthetic Depth Causing False Decrease in Myocardial Contractile Function: Excessive anesthesia can directly suppress myocardial contractile activity, leading to false decreases in EF, FS, and other systolic parameters, thereby interfering with the evaluation of drug intervention efficacy. Mitigation Strategy: Monitor heart rate and body temperature in real time throughout the experiment, strictly control anesthetic depth, and promptly review animal physiological status, excluding abnormal data when necessary.

Error 3: Evaluating Only Systolic Function and Missing Early Diastolic Dysfunction: Models such as diabetic cardiomyopathy, aging-related myocardial injury, and early-stage hypertensive myocardial injury often show no significant systolic abnormalities but only diastolic dysfunction. Relying solely on systolic indicators will completely miss the core pathological phenotype of early disease. Mitigation Strategy: Integrate diastolic indicators such as E/A, E/e', and IVRT into the routine evaluation system to broaden the assessment dimensions for early myocardial injury.

Error 4: Inconsistent Equipment Parameters Across Time Points, Rendering Longitudinal Data Incomparable: Adjusting ultrasound gain, scanning depth, and other parameters arbitrarily at different follow-up time points leads to inconsistent baselines in time-series data, undermining the value of longitudinal comparisons. Mitigation Strategy: Maintain fixed equipment parameters, scanning positioning, and sampling locations throughout the entire study period for each animal, ensuring the continuity and comparability of long-term follow-up data.

V. Overall Summary and Recommendations for Research Applications

Combining the theoretical content from the previous four installments with the practical system presented in this installment, this series has comprehensively established a complete cardiovascular ultrasound research framework for mice and rats, covering "cardiac anatomical and physiological theory — ultrasound imaging principles — core indicator interpretation — disease model-specific application — full-process quality control standards." Foundational theory is the cornerstone of experimental precision, while standardized practical procedures and rigorous quality control systems are the essential guarantees of credible data and reproducible results.

For basic conventional research experiments, strictly adhering to the full-process quality control standards outlined in this article can effectively resolve common problems such as high data dispersion, poor reproducibility, and data distortion, ensuring stable and reliable data for fundamental projects. For mechanistic investigations and high-impact paper studies, it is necessary to integrate advanced detection methods tailored to the pathological characteristics of the specific model, including advanced diastolic function indicators, right ventricular function parameters, and myocardial strain techniques, to uncover early, subtle, and specific myocardial pathological phenotypes, thereby enhancing research innovation and academic depth.

Cardiac ultrasound in mice and rats is not merely a single imaging observation technique, but rather a systematic, standardized, and precise cardiovascular research evaluation system. Proficiency in the adapted detection protocols, operational quality control details, and advanced technical applications for various cardiovascular models can comprehensively enhance the standardization and accuracy of cardiovascular animal experiments, providing a robust technical foundation for investigating the pathological mechanisms of cardiovascular diseases, new drug development, and optimization of intervention strategies.

The five installments of this series comprehensively cover the full spectrum of knowledge in cardiovascular ultrasound research using mice and rats — from foundational theory to practical application, from basic detection to advanced analysis — forming a complete research methodology. It serves as a systematic reference for cardiovascular researchers in experimental design, project implementation, and data support for publications.

Going forward, we will continue to delve deeply into the field of small animal ultrasound research, regularly updating practical skills, advanced technical analyses, model-specific experimental protocols, data optimization strategies, and FAQs. We will continuously refine the small animal ultrasound research framework to assist researchers in standardizing their experimental procedures, improving data quality, and producing high-level scientific outputs. We welcome your continued attention and engagement.