Novel Uses of DTI
In addition to assessing diastolic function, Ea velocities can be used to estimate LV filling pressures, to discriminate between constrictive pericarditis and restrictive cardiomyopathy, and to differentiate athlete's heart from hypertrophic cardiomyopathy (HCM).
Several investigators have performed simultaneous cardiac catheterization and echocardiography studies to estimate LV filling pressures using the ratio of the mitral inflow E-wave and the tissue Doppler Ea-wave. Different regression formulas have been proposed to calculate either LV end diastolic pressure (LVEDP) or pulmonary capillary wedge pressure. Perhaps more practical than specific regression formulae is the correlation with the ratio of E/E alone.
E/Ea more than 10-15 correlates with an elevated LVEDP (>12 mmHg).
E/E less than 8 correlates with a normal LVEDP.
Differentiation Between Constrictive and Restrictive Physiology
With both constrictive pericardititis and restrictive cardiomyopathy, there is abnormal LV filling. With constrictive physiology, extrinsic factors (pericardial constraint) impede normal filling of the LV. In the case of restrictive cardiomyopathy, abnormal filling is secondary to factors intrinsic to the myocardium that cause impaired relaxation and decreased compliance. Ea velocities with constrictive pericarditis in the absence of coexistant myocardial pathology are typically normal. In contrast, Ea velocities in restrictive cardiomyopathy are typically reduced (see Chapter 9, Fig. 13).
Differentiation of Athletes' Hearts From HCM
Approximately 2% of elite athletes may have an increased LV wall thickness, raising the potential diagnosis of HCM. It can be clinically challenging to discriminate the physiologic hypertrophy that results from intense athletic conditioning from pathological hypertrophy. Recent studies incorporating measurement of Ea velocities may be helpful in making this differentiation. Athletes typically have brisk Ea velocities, reflective of a highly compliant LV, whereas individuals with HCM typically have reduced Ea velocities owing to decreased LV compliance and impaired LV relaxation (see Chapter 9, Table 14).
Color M-mode Doppler imaging from the apical four-chamber window is an alternative method to relate mitral inflow to LV relaxation, again in a less load-dependent manner than standard transmittal Doppler. The velocity of propagation of flow (Vp) from the LV base toward the apex is measured in early diastole. The slope of this flow signal is thought to represent the LV intraventricular gradient, influenced by active recoil (suction forces) and relaxation. This is accomplished by measuring the slope of the leading edge of flow (the transition from black to color) or an isovelocity line (e.g., the first aliasing velocity line). Normal Vp exceeds 55 cm per second. Vp less than 45 cm per second is thought to indicate impaired relaxation. In real practice, precise measurement of Vp has proven challenging, thus the most common application of this technology is as a qualitative measure of diastolic function. If the Vp slope appears nearly upright by visual estimate, this is an indication of preserved diastolic function. If the Vp slope appears quite blunted, this indicates impaired diastolic function (Fig. 14).
comprehensive echocardiography assessment of diastolic function
Accurate assessment of diastolic function requires the assessment of multiple parameters. By integrating information gleaned from mitral inflow patterns, PV flow, and TDI, as well as looking for surrogate evidence of decreased LV compliance, such as left ventricular hypertrophy or LA enlargement, the overall state of LV diastolic function may be best evaluated (Table 3).
Diastolic Function Assessment Algorithm
1. Assess overall LV and RV systolic function from two-dimensional images. "Yes" answers increase the likelihood of diastolic dysfunction.
a. Are chamber sizes normal?
i. Is LA enlargement seen?
ii. Is LVH present?
iii. Is LV systolic function abnormal?
b. Standard Doppler interrogation of mitral inflow and PV flow.
i. If mitral inflow appears normal, integrate the above information and assess the PV flow pattern to differentiate from a pseudonormal pattern.
a d. Color M-mode of mitral inflow with qualitative assessment of Vp.
e. If further investigation is required, consider:
i. Assessment of mitral filling patterns in response to alterations in loading conditions (administration of sublingual nitroglycerin to decrease preload or passive leg raising to increase preload).
ii. Response to exercise.
iii. Estimation of LV filling pressures using E/Ea.
iv. Measurement of IVRT.
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