Medicine
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Noninvasive Determination of Vortex Formation Time Using Transesophageal Echocardiography During Cardiac Surgery
Chapters
Summary 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.
Transcript
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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