Noninvasive Determination of Vortex Formation Time Using Transesophageal Echocardiography During Cardiac Surgery
November 28th, 2018
We describe a protocol to measure vortex formation time, an index of left ventricular filling efficiency, using standard transesophageal echocardiography techniques in patients undergoing cardiac surgery. We apply this technique to analyze vortex formation time in several groups of patients with differing cardiac pathologies.
This method can help answer key questions about left ventricular filling efficiency during cardiac surgery. The main advantage of this technique is that the vortex formation time can be calculated during cardiac surgery using conventional transesophageal echocardiography techniques. To perform a comprehensive Transesophageal Echocardiography Examination or TEE, gently insert the probe into the patient's esophagus by lifting the patient's jaw.
The probe should not be forced or injury may occur. Identify the early left ventricle filling and atrial systole blood flow waveforms of transmitral blood flow velocity and measure their corresponding peak velocities and velocity time integrals using the integrated software package of the echocardiography equipment. Measure the maximum diameter of the left ventricle outflow tract immediately below the aortic valve in the mid-esophageal aortic valve long axis TEE view during mid-systole and calculate the area of the left ventricle outflow tract.
Obtain a deep transgastric long axis TEE view and place a pulse wave Doppler sample volume in the distal left ventricle outflow tract to record a blood flow velocity envelope at the same level where the diameter was measured. To obtain the velocity time integral, use the TEE software package to integrate the area of the waveform. Multiply the resulting velocity time integral of the left ventricle outflow tract blood flow velocity waveform by the area of the outflow tract to obtain the stroke volume.
Record the video clips of the mid-esophageal bi-commissural and the left ventricle long axis TEE imaging planes, taking care to include several cardiac cycles in each recording. Then manually inspect the slow motion images of the video clips after the echocardiography T-wave to select the maximum opening of the mitral valve leaflets and use the caliper function in the echocardiography equipment to measure the distance between the mitral leaflets. To calculate the atrial filling fraction, a pulse wave Doppler sample volume can be placed at the tips of the mitral leaflets in the mid-esophageal four chamber view to obtain the transmitral blood flow velocity profile.
The left ventricle outflow tract diameter can be measured in the mid-esophageal left ventricle long axis view whereas the blood flow through the outflow tract can be determined in the deep transgastric short axis imaging plane. The average mitral valve diameter is calculated as the average of the major and minor axis diameters measured in the mid-esophageal bi-commissural and left ventricle long axis planes respectively. Exposure to cardiopulmonary bypass reduces the vortex formation time in patients undergoing coronary artery surgery with the vortex formation time recovering to baseline values within 60 minutes after bypass.
The greater atrial contribution to left ventricle filling is primarily responsible for the decline in vortex formation time as the stroke volume and mitral valve diameter remain unchanged. A decrease in vortex formation time also occurs in patients with severe aortic valve stenosis and left ventricle pressure overload hypertrophy compared to those with normal left ventricle wall thickness. Moderate aortic insufficiency invalidates the use of vortex formation time in the presence of aortic stenosis.
Further, the vortex formation time is lower in octogenarians compared to younger patients coincident with an impaired relaxation pattern of the left ventricle diastolic dysfunction. Noninvasive measurement of vortex formation time using standard two-dimensional and Doppler TEE techniques is straightforward and may allow assessment of the impact of pathologic conditions and surgical interventions on left ventricular filling efficiency in real-time.
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Overview
This article describes a protocol for measuring vortex formation time, which indicates left ventricular filling efficiency, using transesophageal echocardiography during cardiac surgery. The technique is applied to analyze vortex formation time across various patient groups with different cardiac conditions.
Key Study Components
Area of Science
- Cardiology
- Echocardiography
- Cardiac Surgery
Background
- Vortex formation time is a critical measure of left ventricular filling efficiency.
- Transesophageal echocardiography is a standard technique used in cardiac assessments.
- Understanding filling efficiency can improve surgical outcomes.
- Different cardiac pathologies may influence vortex formation time.
Purpose of Study
- To establish a reliable method for measuring vortex formation time during surgery.
- To assess the impact of various cardiac conditions on filling efficiency.
- To enhance the understanding of left ventricular dynamics in surgical patients.
Methods Used
- Insertion of a transesophageal echocardiography probe into the esophagus.
- Identification of early left ventricle filling and atrial systole blood flow waveforms.
- Measurement of peak velocities and velocity time integrals using echocardiography software.
- Calculation of the left ventricle outflow tract area during mid-systole.
Main Results
- Vortex formation time can be effectively measured during cardiac surgery.
- Variations in vortex formation time were observed across different patient groups.
- The technique provides valuable insights into left ventricular filling efficiency.
- Results may inform surgical strategies and patient management.
Conclusions
- The protocol offers a practical approach to assess cardiac function intraoperatively.
- Understanding vortex formation time can enhance surgical outcomes.
- Further studies may explore the implications of these findings in clinical practice.
Frequently Asked Questions
Executive Industry Relevance
Assessing left ventricular filling efficiency during cardiac surgery provides critical hemodynamic insights that can inform real-time surgical decision-making. Noninvasive measurement of vortex formation time via transesophageal echocardiography enables rapid evaluation of diastolic function under varying pathophysiological and interventional conditions. This capability supports mechanistic de-risking in preclinical and translational cardiovascular research by linking functional outcomes to structural interventions.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of therapeutic hypotheses related to diastolic dysfunction and ventricular-vascular coupling in disease models.
- Operational Value: Provides a quantitative, dimensionless parameter (VFT) for functional target validation in large animal or clinical surrogate systems.
Screening & Assay Development
- Scientific Value: Supports development of standardized echocardiographic assays for assessing compound effects on ventricular filling dynamics.
- Operational Value: Facilitates reproducible, noninvasive longitudinal monitoring of cardiac function in conscious or anesthetized models.
Translational & Preclinical Research
- Scientific Value: Bridges mechanistic findings in ventricular filling to clinical relevance through direct parameter translation.
- Operational Value: Enables continuous assessment of LV filling efficiency during simulated surgical stress or pharmacologic challenge.
Pipeline & Workflow Integration
The method integrates into discovery workflows by providing functional hemodynamic readouts that complement molecular and histological endpoints in cardiovascular target validation.
- Discovery Biology: Supports hypothesis testing of pathways regulating diastolic relaxation and atrial contribution to ventricular filling.
- Screening: Delivers quantitative, reproducible outputs for evaluating pharmacologic modulation of preload and afterload.
- Analytics: Generates dimensionless VFT values enabling cross-study comparison and normalization across models.
- Translational Research: Aligns with clinical echocardiography practices, enhancing predictive confidence in preclinical-to-clinical translation.
- Enterprise Reuse: Represents a reusable core capability for cardiovascular safety pharmacology and efficacy assessment programs.
Operational & Enterprise Impact
- Scientific Value: Increases predictive confidence in target validation by reducing ambiguity in functional cardiac phenotypes.
- Operational Value: Leverages existing clinical imaging infrastructure, minimizing need for specialized equipment.
- Strategic Value: Improves go/no-go decisions by identifying compounds that adversely affect diastolic function early in development.
- Portfolio Impact: Enables risk-adjusted prioritization of candidates based on ventricular filling efficiency profiles.
Implementation Considerations
- Requires expertise in transesophageal echocardiography image acquisition and Doppler signal interpretation.
- Dependent on access to echocardiography systems with integrated software for velocity-time integral and diameter measurements.
- Necessitates standardized imaging planes and timing relative to cardiac cycle for reproducible VFT calculation.
- Limited by acoustic windows and patient-specific factors affecting image quality in intraoperative settings.
- Assumes mitral valve geometry approximates a circular orifice, which may introduce error in pathologic remodeling.
