|Year : 2012 | Volume
| Issue : 2 | Page : 21-26
Intraoperative applications of tissue Doppler imaging
Mohamed Elsayed Abd Elhay
Department of Anesthesia and Critical Care, Aswan Heart Center, Aswan, Egypt
|Date of Submission||11-Sep-2012|
|Date of Acceptance||22-Sep-2012|
|Date of Web Publication||30-Jun-2014|
Mohamed Elsayed Abd Elhay
Department of Anesthesia and Critical Care, Aswan Heart Center, P.O. Box 81512 Aswan
Source of Support: None, Conflict of Interest: None
Intraoperative Doppler tissue imaging with pulsed wave Doppler is a rapid method to determine the direction, timing, and velocity of regional longitudinal myocardial motion and quantify systolic and diastolic function. Although DTI provides regional measurements, sampling from different sites will help compensate for any differences, facilitating the evaluation of global EF and diastolic function and the calculation of filling pressures. Repeated DTI observations in the same patient enable the detection of regional ischemia, and the appearance or detection of postsystolic shortening is a sensitive index of ischemic but viable myocardium. DTI has also been used to detect subclinical ventricular dysfunction in asymptomatic patients with valvular disease and differentiate physiologic from pathologic hypertrophy and distinguish constrictive pericarditis from cardiomyopathy.
Keywords: anesthesia, echocardiography, tissue Doppler imaging
|How to cite this article:|
Abd Elhay ME. Intraoperative applications of tissue Doppler imaging. Egypt J Cardiothorac Anesth 2012;6:21-6
| Introduction|| |
Since its introduction in the 1980s, transesophageal echocardiography (TEE) has become an indispensible tool in every echocardiographic laboratory as well as in every center performing cardiac surgery 1. Doppler tissue imaging (DTI) is a novel ultrasound modality used less frequently by anesthesiologists that measures regional myocardial velocities in systole and diastole, and may be less operator-dependent than two-dimensional (2D) or conventional Doppler 2. DTI is easy to perform and comprehend and provides objective information that can readily be used intraoperatively [Table 1].
| Aim|| |
This review will include the intraoperative clinical applications of DTI measurements, practical aspects, and limitations.
| Review of literature|| |
Data of clinical interest to anesthesiologists or intensive care physicians are summarized in [Table 2].
DTI velocities can detect alterations in regional and global left ventricular (LV) contractility that compare favorably with sonomicrometry and pressure–volume measurement.
The clinical utility of S′ to track changes in LV systolic function was indicated in a rapid pacing-induced heart failure model, where S′ was closely related to the left ventricular ejection fraction (LVEF) at all levels of function 3. Longitudinal S′ correlates better than EF with LV+dP/dt in healthy and diseased individuals without regional wall motion abnormalities (RWMA) 4.
Estimation of the ejection fraction
The S′ velocity is a quick and easy means of estimating LVEF. TTE S′ measurements from a single 5 or average S′ from two or more, usually opposite, basal segments have been found to correlate well with LVEF 6. Cutoff values or calculation formulae are shown in [Table 3] 9 If RWMA are present, the estimation or the calculation of LVEF should be carried out using the average S′ of as many segments as possible 8. The association between S′ and clinical performance has not been evaluated extensively in patients receiving a general anesthetic. S′ from the mid-anterior LV segment (transgastric mid-LV short axis using TEE) correlated well with the fractional area change before and after coronary artery surgery 10.
|Table 3: Estimation of the ejection fraction by Doppler tissue imaging systolic velocity using transthoracic echocardiography|
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Detection of ischemia
DTI is a promising tool for the real-time detection and quantification of ischemia-induced regional myocardial dysfunction. DTI of the longitudinal axis is able to detect ischemia-induced changes earlier 11 and more consistently than epicardial electrocardiogram, myocardial lactate extraction, or global hemodynamic changes 12, even in the presence of normal LVEF and unchanged transmitral flow patterns 13. In an animal model of regional ischemia, S′, E′, and E′/A′ decreased within 5 s of the onset of ischemia, in proportion to the reduction in regional myocardial blood flow (as quantified with microspheres). These changes correlated closely to the myocardial shortening decline (recorded with sonomicrometry) and appeared in advance of 2D echocardiographic changes (such as a reduction of systolic excursion and passive paradoxic motion) 14.
The reduction of S′ and E′ during ischemia was accompanied by increased isovolumic relaxation velocity, whereas reperfusion was associated with a transient increase in S′ to a value higher than that at baseline, followed by a decrease, indicating myocardial stunning [Figure 1] 15. Consequently, although DTI may be more sensitive than visual evaluation of RWMA in detecting regional ischemia, it is unable to distinguish active ischemia from reperfusion-induced contractile dysfunction. The isovolumic contraction velocity decreases during milder degrees of myocardial ischemia (reduction in coronary artery flow by 50%) 16 and precedes the development of infarction. Because it disappeared in those segments that eventually developed more than 20% infarcted tissue, it remained unchanged in smaller infarcts 17.
|Figure 1: Detection of ischemia with spectral Doppler tissue imaging in a patient undergoing an off-pump coronary artery bypass surgery. (a) Baseline myocardial velocities. (b) Occlusion of the left anterior descending (LAD) coronary artery led to the appearance of postsystolic shortening (PSS) and reversal of the E′/A′ ratio. PSS is in the same direction as S′. (c) After reperfusion of the left internal mammary artery (LIMA) to the LAD graft, persistence of PSS is characteristic of stunned myocardium. S′ is increased. Recordings were made from the basal anterolateral left ventricular wall (mid-esophageal four-chamber view). A′, late diastolic myocardial velocity; E′, early diastolic velocity; S′, systolic velocity.|
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After a first myocardial infarction, S′ is significantly reduced in all basal LV segments, even when the 2D echocardiographic function is normal 18. The infracted segments show the largest reduction in velocity, prolongation of the Q-to-peak-S′ time interval, and a reduction in E′ without A′ changes, resulting in E′/A′<1 7,19. In myocardial segments remote from ischemia, DTI velocities will remain the same or even decrease, depending on the presence or absence of functional reserve 14. Prolongation of intervals or velocity ratios are easy to measure, are not influenced by the Doppler angle of incidence, and provide additional information in identifying ischemic LV segments. A longer Q-to-peak-S′ interval in the ischemic area delays regional relaxation and leads to systolic tension persisting in diastole. This manifests as systolic velocity during isovolumic relaxation (appearing in the same direction with S′). This represents postsystolic shortening of the ischemic area 20 [Figure 1] and is associated with adverse effects on overall systolic and diastolic LV function. Postsystolic shortening is a marker of myocardial viability, as it predicts the recovery of function after coronary reperfusion 21. An isovolumic relaxation period (S′-end-to-E′ onset) greater than 85 ms 22 or an earlier onset of transmitral flow early velocity, compared with DTI E′ 22, also aid in identifying LV ischemic segments. The E′/A′ ratio is easy to recognize visually, and a ratio E′/A′′<1 is found in the majority of akinetic and hypokinetic segments 23.
Regional DTI diastolic abnormalities relate to the global LV diastolic filling pattern, as patients with an abnormal transmitral E/A ratio <1 have more LV segments with DTI E′/A′<1 than patients with normal transmitral E/A>1 23.
The recognition of wall motion abnormalities on 2D echocardiography during stress echocardiography remains difficult and uncertain, especially if endocardial definition is suboptimal. There is a need for an objective method to quantify myocardial function. DTI S′ velocities recorded from the mitral annulus are more sensitive than 2D observation in detecting the myocardial response to dobutamine stress echocardiography. Coronary artery disease can be diagnosed accurately and objectively from off-line measurements of S′ velocities during dobutamine stress. S′ increased at a dose of 1 μg/kg/min, whereas 2D changes did not become apparent until 3 μg/kg/min 24. The characteristic features of the ischemic myocardial response to dobutamine stress are reduced (⩽50–75% increase from the baseline) 25 or show a lack of increase 26 of S′, development of prominent postsystolic shortening 27, and unchanged or slightly decreased E′ 27. At peak stress, S′ increases by at least 100% in normal individuals 28. The utility of DTI in unmasking coronary artery disease in the anesthetized, mechanically ventilated cardiac patient is worth studying, as S′ changes occur at a relatively low-dose infusion of dobutamine.
Diastolic function and estimation of filling pressures
The Doppler patterns of transmitral and pulmonary venous flow are influenced by loading conditions and do not always represent actual LV diastolic properties, such as relaxation 29. E′ is related to LV diastolic properties, such as elastic recoil and relaxation, irrespective of filling pressures or systolic function 30. E′ changes in the same direction with preload when the diastolic function is normal. This effect is less pronounced in ventricles with impaired relaxation, where E′ decreases and remains low even when ventricular filling pressure is high, as in patients with advanced diastolic dysfunction (pseudonormal and restrictive filling pattern) [Figure 2] 31.
|Figure 2: Evaluation of diastolic function with Doppler tissue imaging (DTI). A DTI ratio E′/A′<1 is abnormal and used to differentiate between normal and pseudonormal transmitral flow (TMF) patters. (a) Normal diastolic function: E/A>1 and E′/A′>1. (b) Impaired relaxation: E/A<1 and E′/A′<1. (c) ‘Pseudonormal’ pattern: E/A>1 and E′/A′<1. (d) Restrictive pattern: E/A>2 and E′/A′<1. A′, late diastolic myocardial velocity; E′, early diastolic velocity; S′, systolic velocity.|
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This disassociation between preload and E′ is used to diagnose the different stages of diastolic dysfunction and to estimate filling pressures by evaluating the transmitral E/A and DTI E′/A′ ratios together 32.
The best evidence of normal diastolic function is a ratio E′/A′>1 during a Valsalva maneuver (which decreases preload and minimizes its effect on E′) 33. Abnormal relaxation is the first stage of diastolic dysfunction, and the ratio E′/A′ inverts (E′/A′<1) [Figure 2]. This occurs at an early age (fifth decade), even in the presence of a normal transmitral flow pattern 34. As diastolic dysfunction progresses, E′ decreases and E′/A′ remains less than 1, despite any normalization of transmitral flow E/A because of augmented preload (E/A≥1.5) 35. In the last stage of diastolic dysfunction (restrictive transmitral flow pattern E/A>2), an A′>5 cm/s may predict a favorable response to afterload reduction 36.
The combination of transmitral flow E (affected by both volume and relaxation) and DTI E′ (expressing relaxation but not volume) can be used to assess LV filling pressures [Figure 3]. The ratio E/E′ (measured in the same units) was associated with pulmonary capillary wedge pressure (PCWP) independent of the underlying pathology 5,30 or LV systolic function. The mean PCWP can be calculated as
|Figure 3: Estimation of filling pressures with Doppler tissue imaging (DTI). The mean capillary wedge pressure is calculated using the ratio of the transmitral flow early velocity (E) and the average early diastolic myocardial velocity (E′): mean wedge pressure=(1.3×E/E′)+2 mmHg. Transmitral flow is recorded with pulsed wave Doppler at the tips of mitral valve leaflets, and spectral DTI velocities from basal myocardial segments, next to the mitral annulus. The anteroseptal myocardial velocity was not recorded because of increased Doppler angle.|
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This ratio has been validated in awake patients in either atrial fibrillation 37 or sinus tachycardia 38. The ratio E/E′ may be less predictive of LV filling pressures in the presence of normal LV function 39, when both transmitral flow E and E′ are preload dependent. In older patients with normal LV function, age and hypovolemia may together decrease E′ and increase the ratio E/E′ disproportionately to the filling pressures. The site of DTI recording will have an impact on the ratio E/E′ as well 31.
In a small number of cardiac surgical patients, the septal DTI velocities decreased postoperatively, whereas the lateral mitral annulus velocities did not 40. As DTI measures regional velocity, any particular E′ should not be considered a direct measurement of global myocardial relaxation, especially in patients with coronary artery disease where LV relaxation is not uniform at baseline. However, the lateral mitral annulus site is rarely involved in ischemic heart disease, and E′ recording at this location usually will represent LV relaxation 31.
Therefore, to estimate LV filling pressures using the E/E′ ratio, the mid-esophageal four-chamber view should probably be used to record the lateral mitral annulus site E′. The application of the E/E′ ratio in the anesthetized patient in the operating room merits further investigation.
Valvular heart disease
DTI can be useful in detecting LV dysfunction in patients with regurgitant valvular lesions, who may be asymptomatic despite the presence of LV dilation and increased wall stress. Among asymptomatic patients with variable severities of aortic 41 or mitral 42 regurgitation, myocardial contractile reserve (diagnosed as an increase of LVEF>5% during exercise) was present if longitudinal S′ (measured from the lateral or septal mitral annulus) was normal at rest. Among patients with stenotic valvular lesions, there is a significant inverse relationship between S′, E′, and E′/A′ ratio and the severity of aortic and mitral stenosis 43.
Heart failure prognosis
Significantly decreased DTI velocities (S′⩽3 cm/s, E′⩽3 cm/s, A′⩽4 cm/s) and E/E′> 20 independently identified those heart failure patients at risk of cardiac death 44.
Cardiomyopathies and constrictive pericarditis
DTI may be the diagnostic tool of choice when conventional echocardiography cannot differentiate physiologic (the result of exercise in healthy individuals) from pathologic hypertrophy, or constrictive pericarditis from restrictive cardiomyopathy. In hypertensive patients, LV hypertrophy is pathologic if DTI shows asynchronous regional systolic contraction and relaxation, and abnormal diastolic function 45, postsystolic shortening suggestive of subendocardial ischemia 46, or decreased velocities 47. Both constrictive pericarditis and restrictive cardiomyopathy have similar clinical (heart failure) and echocardiographic presentations (restrictive transmitral flow pattern). In constrictive pericarditis, the E′ velocity is normal, indicating preserved elastic recoil, even when the respiratory variation in the transmitral E wave is blunted or absent. However, E′ is reduced in restrictive cardiomyopathy as a result of intrinsic myocardial disease 48.
Right ventricular function
The echocardiographic assessment of right ventricular (RV) function is cumbersome, and measurement of volumes and calculation of EF are inaccurate because of anatomic (irregular shape, presence of trabeculations, different embryologic origin of the inflow and outflow tracts) and physiologic (load dependency and pericardial influence) factors. DTI velocities from the free RV wall [Figure 4] lateral to the tricuspid annulus have been used to evaluate RV function 49. Although easy to perform, DTI of the tricuspid annulus represents only the longitudinal myocardial fiber function and is affected by translational motion and rotation of the entire heart 49. The excursion of the tricuspid annulus is greater when compared with the mitral annulus because of the shape of the ventricle and the DTI velocities are significantly higher in the RV 50. In contrast to the LV, only the RV E′ tissue velocities correlate with age 51. A tricuspid annulus S′<10–11.5 cm/s is associated with RVEF 45% 52. As is the case with LV velocities, TTE-recorded and TEE-recorded tricuspid annulus velocities may not be comparable because of different views, DTI modality (color vs. spectral), and/or the potential effect of general anesthesia. The RV free wall tricuspid annulus velocities of precoronary artery bypass graft patients were higher with TTE of the apical four-chamber view than with TEE of the modified deep transgastric LV view 53 and were not related to hemodynamics. Attempts to correlate the mean right atrial pressure with the E/E′ ratio derived from the transtricuspid flow and the lateral tricuspid annulus in anesthetized patients are not always successful 54. DTI can have diagnostic value in RV infarction. A low S′ identified those patients with RV myocardial infarction 55 or proximal right coronary artery involvement 55, whereas an S′<8 cm/s was predictive of cardiac death or rehospitalization at 1 year 56.
|Figure 4. Doppler tissue imaging of the right ventricle (RV). The RV inflow (top) and outflow (bottom) regions are examined with color (left) and pulsed wave (right) Doppler tissue imaging, in the deep transgastric RV view. PV, pulmonic valve; RA, right atrium; TCV, tricuspid valve. A′, late diastolic myocardial velocity; E′, early diastolic velocity; S′, systolic velocity.|
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In normal synchronous hearts, segmental S′ peaks almost simultaneously, whereas in dyssynchronous hearts, the lateral segments peak considerably later than the septal, which results in insufficient ejection. Pacing of the affected region allows synchronized mechanical activity and improves ejection 57. Mechanical dyssynchrony as determined by longitudinal DTI velocities may be superior to electrocardiography in predicting response to cardiac resynchronization therapy. The most recent guidelines suggest the use of color DTI for the identification of mechanical dyssynchrony.
| Conclusion|| |
Currently, DTI with pulsed wave Doppler is a rapid method to determine the direction, timing, and velocity of regional longitudinal myocardial motion and quantify systolic and diastolic function. Although extensively investigated in awake patients, the potential intraoperative applications need to be verified. Although DTI provides regional measurements, sampling from different sites will help compensate for any differences, facilitating the evaluation of global EF and diastolic function and the calculation of filling pressures. Repeated DTI observations in the same patient enable the detection of regional ischemia (decrease in S′ and E′ and E′/A′ 1), and the appearance or detection of postsystolic shortening is a sensitive index of ischemic but viable myocardium. DTI has also been used to detect subclinical ventricular dysfunction in asymptomatic patients with valvular disease and differentiate physiologic from pathologic hypertrophy and distinguish constrictive pericarditis from cardiomyopathy.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3]