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NewsletterJune 2002 Newsletter: Tissue Doppler Imaging Assessment of Diastolic Function
Mark A. Chaney, MD
Congestive heart failure (CHF) is a major public health concern, the total cost of which is estimated at $15 to $40 billion annually. CHF can be caused by either abnormal systolic function or abnormal diastolic function (1). Epidemiological and case-control studies of individuals presenting with clinical CHF have estimated that 40% to 50% have normal systolic function and thus, presumed diastolic CHF. This distinction between diastolic dysfunction and systolic dysfunction is very important because diastolic CHF is associated with better long-term survival (yet still associated with a 5% - 8% annual mortality rate) and because each form requires different therapeutic approaches (for example, positive inotropic drugs should be used with caution in isolated diastolic dysfunction yet are indicated when systolic dysfunction is present). Unfortunately, to definitively diagnose diastolic dysfunction, one must rely on invasive measurements of intracardiac pressures via cardiac catheterization. Furthermore, there is continued controversy surrounding the exact definition of diastolic dysfunction and the diagnostic criteria for diastolic heart failure. Objective measurements of left ventricular diastolic function serve to confirm rather than establish the diagnosis of diastolic heart failure.
Over the last decade, many investigators have evaluated noninvasive methods of assessing diastolic function via transthoracic and/or transesophageal echocardiography, including mitral inflow velocity curves (traditional E/A ratios), pulmonary venous velocity curves, and color M-mode analysis, among others (2). These methods assess diastolic function by measuring indices of volume transients during ventricular filling. Unfortunately, all of these noninvasive methods have substantial limitations and are affected by changes in leading conditions. Recently, tissue Doppler imaging (TDI) of mitral annular motion has been proposed as an improved (load-independent) noninvasive method of assessing diastolic function via echocardiography (3-5). A recent investigation revealed that TDI of mitral annular motion via echocardiography obtained in one hundred consecutive patients undergoing cardiac catheterization was extremely useful in predicting diastolic dysfunction when compared with the "gold standard" intracardiac pressure via catheterization (5). Thus, TDI of mitral annular motion appears to be an excellent noninvasive, load-independent, method of assessing diastolic function that does not possess the substantial limitations of previous traditional noninvasive techniques.
So how does tissue Doppler echocardiography work? It is a variation of conventional Doppler flow imaging that allows quantification of the Doppler shift within the range of myocardial tissue motion. Whereas Doppler ultrasound had been traditionally utilized to measure flow velocities of red blood cells, TDI allows measurement of velocities of myocardial tissue (typically low velocities in conjunction with high amplitude) at certain points. The velocity at a variety of myocardial sites can be determined and distinguished very rapidly by using Doppler techniques. The velocity of moving tissue can be studied with pulsed-wave tissue Doppler sampling, which displays the velocity of a selected myocardial region against time, with high temporal resolution. In addition, the velocities can be calculated with time-velocity maps and displayed as color-encoded velocity maps in either an M-mode or 2D format. Whereas pulse-wave TDI allows measurements of velocities of a selected myocardial region, color TDI gives the best overview of cardiac dynamics because the entire scanned color data are displayed simultaneously. To assess diastolic function, TDI is used to evaluate mitral annular displacement during diastole. Velocity profiles are obtained (similar to traditional E/A ratios) using apical views for long-axis motion and analyzed for specific characteristics to assess diastolic function. The advantages of TDI include proposed load-independence, high reproducibility, determination of isovolumic relaxation and contraction time are simpler to assess, and it is more reliable in the presence of tachycardia.
Perioperative diastolic function in patients undergoing surgery may be altered dramatically by a wide variety of factors including anesthetic medications (inhaled and/or intravenous), intravascular volume changes, myocardial ischemia, and therapeutic interventions, among others. These extrinsic changes in diastolic function are especially important in patients undergoing cardiac surgery, whom often already possess intrinsic systolic and diastolic dysfunction. In fact, a recent clinical investigation revealed that preoperatively assessed diastolic dysfunction was associated with adverse outcome following cardiopulmonary bypass (increased use of inotropic support and delayed weaning) (6). Although accurate information regarding diastolic function in patients undergoing cardiac surgery would most certainly aid in perioperative management and potentially improve morbidity, very little work has been done in this area. A recent investigation revealed that assessment of diastolic function in patients undergoing cardiac surgery via traditional mitral inflow velocity curves obtained by echocardiography helps identify patients with diastolic dysfunction (7).
In conclusion, accurate information regarding diastolic function in patients undergoing cardiac surgery would help guide perioperative management and potentially improve morbidity. The traditional noninvasive methods of assessing diastolic function do not yield accurate information. Recently, TDI of mitral annular motion via echocardiography has been shown to yield accurate information regarding diastolic function, and thus represents a promising new technique that may eventually help guide perioperative management of patients undergoing cardiac surgery. References
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