Protocol Timing Analysis

This was assessed using Doppler echocardiography measurement of mitral inflow and pulmonary venous flow velocities

4.16.1 Doppler Echocardiography Measurement of mitral inflow velocities

The apical four chamber view was optimized with the use of spectral gain and wall filter in order to clearly display the onset and cessation of left ventricular inflow and to visualize the left ventricular cavity. The sample volume was positioned through a plane traversing the LV from apex to mitral valve annulus and between the tips of mitral valve leaflets at maximal excursion with care taken in obtaining the smallest possible angle between the direction of diastolic blood flow and orientation of the ultrasonic beam, this was achieved with the use of colour flow Doppler³⁵.

Spectral sweep speeds of 25-50 mm/s was initially used to obtain the pulse wave (PW) Doppler signal of mitral flow velocity and it was increased to 100 mm/s to take the measurement. The spectral tracings of the pulse wave signal was frozen. The best pair of spectral tracing was selected for measurements. The spectral waveform represent a graph where the y- axis is the velocity and the x-axis represent the time.

Mitral inflow peak early filling (E-wave) velocity:

The measurement was taken with the aid of the machine in-built caliper at the peak of the first waveform from the pair of spectral waveform selected in centimeter per second.

Mitral inflow atrial late filling (A-wave) velocity:

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The measurement was taken at the peak of the second waveform from the pair of spectral waveform selected with the aid of machine in-built caliper. E/A ratio was then calculated.

Deceleration time of early filling velocity:

Using the same pair of spectral waveform as above, time elapsed between mitral inflow peakE velocity and the point where the extrapolation of the deceleration slope of the E velocity crosses the zero baseline was measured in milliseconds.

Isovolumic Relaxation Time ( IVRT):

This is the time from the closure of aortic valve (end of left ventricular outflow) to the opening of mitral valve (begining of transmitral blood flow). It was measured in the apical five-chamber (A5Ch) view. A5Ch view was obtained from apical four-chamber view, by slightly tilting the transducer superiorly at the apex.

The apical five chamber view showed all the four chambers, the mitral valve, the tricuspid valve and the aortic valve. The sample volume of PW Doppler was placed in between the LV outflow and in-flow tracts. The PW spectral Doppler signals of aortic outflow and mitral inflow were simultaneously displayed and frozen on the screen. IVRT was measured with the use of an in-built caliper as the linear approximation of the time from closure of aortic valve to opening of mitral valve. The mean of measurements from 3 consecutive cycles was recorded for each of the variables that was measured³⁵.

4.16.2 Doppler Echocardiography Measurement of pulmonary venous flow velocities

The pulmonary venous flow in the right upper pulmonary vein was identified by colour Doppler in apical four chamber view. The transducer was adjusted slightly to ensure that flow

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from the pulmonary vein into the left atrium was nearly parallel with the ultrasound beam. The sample volume was located 1-2 cm into the pulmonary vein, proximal to its insertion into the left atrium.

The spectral recordings of the pulse wave Doppler signal was obtained at a sweep speed of 50 to 100 mm/s. The picture was frozen on the screen, the best spectral waveforms of at least two above and one below baseline was selected for measurement and the following measurements were carried out.

Pulmonary forward S wave in systole:

Peak S wave velocity of pulmonary venous forward flow during atrial relaxation and ventricular systole in centimeters per second. This was measured from the peak of the first waveform above the baseline or second phase (if the first waveform is basic) with the use of in-built caliper.

Pulmonary forward D wave in diastole:

Peak D wave velocity of pulmonary venous forward flow during ventricular diastole in centimeters per second. D wave was measured from the peak of last waveform above the baseline with the use of in-built caliper.

Pulmonary retrograde Ar wave caused by atrial contraction:

Peak Ar wave velocity of retrograde flow into pulmonary vein during atrial contraction was measured in centimeters per second. Ar was measured from the depth of the waveform below baseline with in-built caliper. The ratio of S to D wave (S/D) was then calculated.

Diastolic function was categorized into grades using the table below:

Table 3: Grading of left ventricular diastolic function¹⁷⁸.

GRADE E/A DT(ms) IVRT(ms) PVF S/D

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Normal 1– 2 160– 240 60– 100 ≥1

Impaired relaxation < 1 >240 >100

Pseudonormalization 1 – 2 150 – 220 60 – 100 < 1 Restrictive pattern >2 <160

E/A: ratio of transmitral peak early velocity to late atrial velocityDT: deceleration time;

IVRT isovolumic relaxation time

PVF S/D: ratio of pulmonary venous flow peak systolic velocity to diastolic velocity

Colour flow Doppler was used to assess presence of valvular abnormality, interatrial and interventricular shunt. Left ventricular wall motion was inspected in each of the 16 segments defined by the American Society of Echocardiography.

4.17 Doppler Echocardiograpy Assessment of pulmonary artery systolic pressure (PASP)