Name: noninvasive determination of vortex formation time using transesophageal echocardiography during cardiac surgery
Uploaded: 2018-11-28T12:30:00
Description: Watch this Scientific Journal Video about Noninvasive Determination of Vortex Formation Time Using Transesophageal Echocardiography During Cardiac Surgery at JoVE.com

This material is the result of work supported with resources and the use of the facilities at the Clement J. Zablocki Veterans Affairs Medical Center in Milwaukee, Wisconsin.

The Institutional Review Board of the Clement J. Zablocki Veterans Affairs Medical Center approved the protocols. Written informed consent was waived because invasive cardiac monitoring and TEE are routinely used in all patients undergoing cardiac surgery in our institution. Patients with relative or absolute contraindications for TEE, those undergoing repeat median sternotomy or emergency surgery, and those with atrial or ventricular tachyarrhythmias were excluded from participation.
1. Anesthe...

The current results illustrate that VFT can be reliably measured during cardiac surgery using the TEE techniques described here. Previous descriptions of VFT used transthoracic echocardiography in conscious subjects, but this approach cannot be utilized when the chest is open. We used intraoperative TEE to determine VFT in the anesthetized patients undergoing cardiac surgery during which changes in LV filling dynamics are often encountered as a result of ischemia-reperfusion injury or surgical interventions. Our findings...

Fluid mechanics is a critical yet often underappreciated determinant of left ventricular (LV) filling. A three-dimensional rotational body of fluid, known as a vortex ring, is generated whenever a fluid traverses an orifice1,2,3. This vortex ring improves the efficiency of fluid transport compared with a continuous linear jet4. Movement of blood through the mitral valve during early LV filling causes a vortex ring to form5,6,7,8 and facilitates its propagation into the chamber by preserving fluid momentum and kinetic energy9. These actions enhance LV filling efficiency4,10,11,12,13. The ring not only inhibits blood flow stasis in the LV apex14,15,16,17 but also directs flow preferentially beneath the anterior mitral leaflet7,18, effects that decrease the risk of apical thrombus formation and facilitate filling of the LV outflow track19, respectively. Contrast echocardiography17, Doppler vector flow mapping6,20,21, magnetic resonance imaging7, and particle imaging velocimetry9,22,23,24 have been used to demonstrate the appearance and behavior of trans-mitral vortex rings under normal and pathological conditions. The left atrial-LV pressure gradient, the degree of diastolic mitral annular excursion, the minimum LV pressure achieved during diastole, and the rate and extent of LV relaxation are the four major determinants of the duration, size, flow intensity, and position of the trans-mitral ring2,12,25,26,27,28,29.
Vortex ring development is most often quantified with a dimensionless parameter (vortex formation time; VFT) based on fluid ejection from a rigid tube3, where VFT is defined as the product of the time-averaged fluid velocity and the duration of ejection divided by the orifice diameter. The optimal size of a vortex ring is achieved when VFT is 4 in vitro because trailing jets and energetic limitations prevent it from attaining a larger size3,4. Mitral valve VFT has been approximated clinically using transthoracic echocardiography8,30,31. Based on analysis of trans-mitral blood flow velocity and mitral valve diameter (D), it can be easily shown8 that VFT = 4 &#215; (1-&#946;) &#215; EF &#215;&#945;3, where &#946; = atrial filling fraction, EF = LV ejection fraction, and &#945; = EDV1/3/D, where EDV = end-diastolic volume. Ejection fraction is the ratio of stroke volume (SV) and EDV, allowing this equation to be simplified to VFT = 4 &#215; (1-&#946;) &#215; SV/(&#960;D3). Because VFT is dimensionless (volume/volume), this index allows direct comparison between patients of varying size without adjustment for weight or body surface area8. Optimal VFT ranges between 3.3 and 5.5 in healthy subjects8, and results are consistent with those obtained in fluid dynamics models3,32. VFT was shown to be &#8804; 2.0 in patients with depressed LV systolic function, findings that are also supported by theoretical predictions8. Reductions in VFT independently predicted morbidity and mortality in patients with heart failure30. Elevated LV afterload33, Alzheimer&#39;s disease34, abnormal diastolic function19, and replacement of the native mitral valve with a prosthesis35 have also been shown to decrease VFT. Measurement of VFT may also be useful to identify blood flow stasis or thrombosis in patients with acute myocardial infarction36,37.
Our group is interested in factors that affect LV filling efficiency during cardiac surgery38,39,40,41. We use standard two-dimensional and Doppler transesophageal echocardiography (TEE) to noninvasively derive the variables required to calculate VFT. In this report, we describe this methodology in detail and review our findings to date.

<table>
	<tbody>
		<tr>
			<td>Echocardiography Machine</td>
			<td>Philips Ultrasound, Bothall, WA</td>
			<td>iE33</td>
			<td></td>
		</tr>
		<tr>
			<td>Transesophageal Echocardiography Probe</td>
			<td>Philips Ultrasound, Bothall, WA</td>
			<td>X7-2t</td>
			<td></td>
		</tr>
		<tr>
			<td>Statistical Software</td>
			<td>AnalystSoft, Walnut, CA</td>
			<td>StatPlus:mac Pro</td>
			<td></td>
		</tr>
	</tbody>
</table>

noninvasive determination of vortex formation time using transesophageal echocardiography during cardiac surgery

Trans-mitral blood flow produces a three-dimensional rotational body of fluid, known as a vortex ring, that enhances the efficiency of left ventricular (LV) filling compared with a continuous linear jet. Vortex ring development is most often quantified with vortex formation time (VFT), a dimensionless parameter based on fluid ejection from a rigid tube. Our group is interested in factors that affect LV filling efficiency during cardiac surgery. In this report, we describe how to use standard two-dimensional (2D) and Doppler transesophageal echocardiography (TEE) to noninvasively derive the variables needed to calculate VFT. We calculate atrial filling fraction (&#946;) from velocity-time integrals of trans-mitral early LV filling and atrial systole blood flow velocity waveforms measured in the mid-esophageal four-chamber TEE view. Stroke volume (SV) is calculated as the product of the diameter of the LV outflow track measured in the mid-esophageal long axis TEE view and the velocity-time integral of blood flow through the outflow track determined in the deep transgastric view using pulse-wave Doppler. Finally, mitral valve diameter (D) is determined as the average of major and minor axis lengths measured in orthogonal mid-esophageal bicommissural and long axis imaging planes, respectively. VFT is then calculated as 4 &#215; (1-&#946;) &#215; SV/(&#960;D3). We have used this technique to analyze VFT in several groups of patients with differing cardiac abnormalities. We discuss our application of this technique and its potential limitations and also review our results to date. Noninvasive measurement of VFT using TEE is straightforward in anesthetized patients undergoing cardiac surgery. The technique may allow cardiac anesthesiologists and surgeons to assess the impact of pathological conditions and surgical interventions on LV filling efficiency in real time.

The current technique allowed us to reliably measure VFT during cardiac surgery under a variety of clinical conditions by obtaining each determinant from blood flow and dimensional recordings in standard TEE imaging planes. A pulse-wave Doppler sample volume was placed at the tips of the mitral leaflets in the mid-esophageal four-chamber view to obtain the trans-mitral blood flow velocity profile necessary to calculate atrial filling fraction (&#946;; Figure 1</strong...

Watch this Scientific Journal Video about Noninvasive Determination of Vortex Formation Time Using Transesophageal Echocardiography During Cardiac Surgery at JoVE.com

Noninvasive Determination of Vortex Formation Time Using Transesophageal Echocardiography During Cardiac Surgery

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.

Trans-mitral blood flow produces a three-dimensional rotational body of fluid, known as a vortex ring, that enhances the efficiency of left ventricular ...

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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