Assessment of LV diastolic function and filling pressures
Diastolic LV dysfunction is common in the intensive care unit. A knowledge of the prescence of diastolic dysfunction and its severity is useful in the optimising volume status and hemodynamics of critically ill patients. Similar to earlier assessments, a composite of different indices are used to make an assessment of diastolic function. These indices are:
1.Mitral inflow patterns : E/A, decceleration time, IVRT
2.Mitral annulus velocities on tissue doppler: E/e' ratio
3.Pulmonary venous inflow patterns
Mitral inflow patterns
The flow from the left atrium to the left ventricle occurs in 3 phases:
An initial rush of blood as soon as the valve opens causes a peaking of velocity in early diastole, the E wave. This is followed by a period of low or no flow, also known as diastasis. In end-diastole, atrial contraction produces a final rush of blood into the ventricle, the A wave. While these waves can be analyzed by studying the movement of the anterior mitral leaflet in M-mode, it is best done with Pulsed wave Doppler.
The PWD cursor is placed between the tips of the open mitral leaflets in the A2C or A4C views. The typical flow pattern obtained is seen below (Fig1.)
Obtain the mitral inflow wave pattern on PWD and freeze the image. After selecting "E" under "mitral valve" in the calculations menu, the height of the E wave is measured to get the E velocity (see above). Similarly the A wave velocity is also measured. The E/A ratio will be calculated by most echo machines automatically.
Decceleration time (Dct)
Obtain the mitral inflow wave pattern on PWD and freeze the image. After selecting Dct under "Mitral Valve" in the calculations menu, the cursor is first placed at the peak of the E wave. On pressing select, another cusor point appears, connected to the first with a line. Pull this cursor point to the baseline and move it around till the line connecting the two points aligns itself along the downslope of the E wave. Sometimes, only the upper part of the line may actually be in contact with the E waveform. This is acceptable as long as the slope of the line faithfully reflects the slope of the E wave. The machine automatically calculates the decceleration time from this.
In this the diastolic peak velocities of the mitral annulus, are measured both medially and laterally using tissue doppler. These peak velocities are designated e' (medial) and e' (lateral).
This is done by first acquiring an A4C view. PWD is selected and the tissue doppler imaging (TDI) is switched on. A 2mm to 5mm sample volume is placed over the medial mitral annulus, at the base of the mitral leaflet, as shown below (fig.5)
Typically, 2 negative waves in diastole and 1 positive wave in systole is seen. The first of the diastolic waves is the result of movement of the annulus towards the left atrium during initial filling of the LV. This wave is referred to as e'. The second diastolic wave is referred to as a'. The systolic wave is labelled s'.
Once the waveform is acquired, freeze it and choose "e' (medial)" under "TDI" in the calculations menu. Measure the peak e' velocity with the cursor. Then, unfreeze and place the TDI cursor over the lateral mitral annulus in the A4C view, at the base of the posterior mitral leaflet.
Repeat the above procedure for the measurement of e' (lateral). Since E is already known from earlier measuremants of the mitral inflow, E/e' ratio- medial and lateral can be calulated. Many of the newer echo machines offer this calculation automatically.
Normally the e' velocities from the lateral mitral annulus are higher(15cm/sec) than those from the medial annulus.
Pulmonary vein inflow
This is studied by placing a pulsed doppler cursor at the entry of the pulmonary veins into the left atrium identified on an apical 4 chamber view. The use of colour flow imaging may help to locate this as a jet of flow can be seen entering the left atrium from the pulmonary veins. The opening of the pulmonary veins are often difficult to identify clearly on a transthoracic examination. Once identified, a PWD trace is obtained and the trace is frozen.
The normal pulmonary vein flow profile is usually biphasic with a predominant systolic forward flow (S wave) and a less prominent diastolic forward flow wave (D wave). Occasionally, there may be a triphasic flow pattern with two distinct systolic flow waves of which the initial flow into the left atrium results from atrial relaxation followed by a further inflow due to the increase in pulmonary venous pressure. The D-wave occurs when there is an open conduit between the pulmonary vein, LA and LV and reflects the transmitral E wave. A retrograde flow wave into the pulmonary vein (AR wave) occurs during atrial contraction and its amplitude and duration are related to LV diastolic pressure, LA compliance and heart rate.
See fig.8 for the timing correlates of this waveform
Interpretation of measured variables
Mitral inflow patterns:
The normal E/A ratio is between 1 and 2. This gradually reduces with age and a E/A ratio >0.75 may be considered normal above 75 years. The normal decceleration time of the E wave is 160 - 240ms.
The normal E/e' ratio from the medial annulus is <8 and suggests a normal left atrial pressure. While values between 8 and 12 are indeterminate, a value >12 is indicative of an elevated left atrial pressure or PCWP (>18mmHg). The ranges for E/e' from the lateral mitral annulus are <5, 5 -10 and >10 respectively.
Pulmonary venous flow profile:
The 2 components to note are the diastolic forward flow (D) and the diastolic flow reversal (AR). The D wave is normally equal to or smaller than the S wave. Changes in the D wave with increases in LA pressure parallel changes in the transmitral E wave, initially decreasing and then increasing to become much larger than the S wave. A S/D ratio of < 40% suggests a LA pressure more than 20mmHg. The decceleration time of the D wave also shortens with increasing LA pressures.
The atrial reversal wave increases in amplitude and duration with increasing LA pressures. An AR amplitude more than 25cms/sec and a AR duration 30ms more than the transmitral A wave duration suggest a LA pressure more than 20mmHg.
Hepatic venous flow profile is similar to the pulmonary venous flow profile and is an indicator of Right Ventricular filling patterns. (see fig.9)
Grading of diastolic dysfunction or diastolic filling pattern
Diastolic filling abnormalities can be graded as follows:
Grade 1: Impaired relaxation pattern with normal filling pressures
Grade 1a: Impaired relaxation pattern with elevated filling pressures
Grade 2: Psuedonormalized pattern
Grade 3: Reversible restrictive pattern
Grade 4: Irreversible restrictive pattern
Grade 1 diastolic dysfunction (Impaired myocardial relaxation)
In diastolic dysfunction from any cause, the initial abnormality is impaired myocardial relaxation. The common causes are increasing age, LV hypertrophy and myocardial ischemia.
The E/A ratio is < 1, with a prolonged Dct (>240ms).
In the tissue doppler assessment, e' is also reduced with a resultant E/e' ratio (medial) <8, suggesting a normal LA pressure.
The D wave of the pulmonary venous inflow is smaller than the S wave and the AR wave is normal.
Grade 1a diastolic dysfunction (Impaired myocardial relaxation with elevated filling pressures)
The pattern is similar to Grade 1, with the exception of the E/e' ratio (medial) which is > 15, suggestive of a high LA pressure. See fig.10 and 11
Grade 2 diastolic dysfunction (Psuedonormalized pattern)
When diastolic LV function deteriorates, LV compliance progressively decreases and there is an increase of LA pressure and the diastolic filling pressure. The transmitral E wave velocity progressively increases and the Dct decreases. As it does so, it goes through a phase that resembles a normal filling pattern. The E/A ratio is between 1 and 2 and the Dct between 160 and 240ms. This pseudo-normal pattern is a transition pattern from impaired relaxation to restrictive filling and is a result of a moderately increased LA pressure superimposed on a relaxation abnormality. The following clues help distinguish this from a normal filling pattern
E/e' ratio (medial) >15
Pulmonary venous flow AR >25cm/sec and longer than transmitral A wave
Presence of LA enlargement or LV hypertrophy
Grade 3 and 4 diastolic dysfunction (restrictive pattern)
With more severe diastolic dysfunction, LV compliance reduces and LA pressures rise. The low compliance of the LV causes a rapid increase in the early LV pressure and a shortened inflow and DT. The E/A ratio is > 2. Dct is < 160ms. The high LA pressure manifests as a E/e' ratio >15 at the medial annulus. Forward diastolic pulmonary vein flow stops in mid-late diastole and during atrial contraction there is a significant flow reversal resulting in a prolonged AR.
A reversal to grade 1 or 2 on reducing the preload by performing Valsalva manouvre or administering nitroglycerine suggests reversibility of the cardiac restriction and is termed grade 3. Diastolic filling should be graded as irreversible (grade 4) in the absence of such a reversal.
Assessment of diastolic function in atrial fibrillation and fused EA waves
Atrial fibrillation is common in the critically ill and eliminates the use of the E/A ratio as the A wave is absent. The decceleration time varies as it is dependent on the cardiac cycle length. The only parameter that can be used with confidence is the E/e' ratio.
In sinus tachycardia, the E and A waves frequently fuse, making assessment of diastolic filling pattern based on transmitral flows difficult. In this situation, the E/e' ratio correlates with filling pressures well.
Estimation of LV filling pressures
Other than in the grading of diastolic dysfunction, estimation of LV filling pressures also influence desicions on fluid resuscitation in hemodynamically unstable patients and in titrating diuretics and fluids in patients with diastolic heart failure. While the markers of an elevated LV filling pressure have been mentioned earlier and tabulated below, several formulae have been evaluated to arrive at a numerical value.
Markers of elevated LV filling pressure:
E/A > 2
Dct < 160ms
E/e' (medial) >15
E/e' (lateral) >10
PFV S/D <40%
PFV AR amplitude >25 cm/sec
PFV AR duration > 30ms more than A wave
Formulae to calculate LA pressure
The E/e' included in the above calculations indicates that obtained from the medial mitral annulus.