Kathryn Statham, Genevieve Carbonatto
AR is rarely physiological. If it is present then a cause needs to be found. ECHO is used to determine
- Estimate severity
- Assess chronicity
This is done first by imaging the heart with 2D echo and looking at:
- aortic root size
- LV cavity size (chronic vs acute)
- LV wall thickness
- LV function
Colour and spectral Doppler
- Jet size
- Vena contracta width
- Jet/height ratio
- Deceleration time of regurgitant flow
- Intensity of AR signal
- AR pressure half time
- Diastolic flow reversal in the descending thoracic, and abdominal aorta
Note that AR is dependent on afterload or systemic pressures. The higher the afterload, the greater the regurgitation which is why therapy is aimed at reducing afterload
Clinical manifestations/signs of severe chronic aortic regurgitation
Patients with AR remain asymptomatic for a long time as the left ventricle adapts to the increased LV volume. It hypertrophies and dilates slowly over time. Normal LV pressures are maintained despite significantly high LV volumes. End diastolic pressures rise causing high pulmonary pressures in the context of low cardiac output. Pulmonary oedema develops and eventually right heart failure. Patients get exertional dyspnea and angina.
Clinical manifestations/signs of severe acute aortic regurgitation
The most common causes of acute, severe aortic regurgitation are type A aortic dissections and infective endocarditis. Unlike patients with chronic AR who are not symptomatic for a very long time, patients with acute ,significant AR present with cardiogenic shock. The LV is unable to cope with the abrupt increase in end diastolic volume.
Echo will show an LV cavity which is neither dilated nor hypertrophied.
The regurgitant jet
The regurgitant jet is made up of a flow convergence zone and a narrow “ neck” which is called the vena contracta.
The jet as it flows back into the LVOT has a width proximal to the AV. This width is used to assess the jet height ratio or the ratio of the jet width with the height of the LVOT
The jet length refers to how far the jet flows back into the LV
The jet length is not used to assess severity as it is dependent of LVED pressures and LV function. The worse the LV function and the higher the pressures the shorter the jet length
Indirect Assessment of AR Severity- Colour Doppler Imaging
Regurgitant jet size represents the ratio of the aortic regurgitation jet diameter just below the leaflets of the aortic valve to the size of the LV outflow diameter. Another way of describing it is the colour jet height compared to the LVOT height A ratio of less than 25% is mild, between 25 and 65% moderate and higher than 65 severe. The AR jet height is measured about 0.5 to 1.0 cm proximal to the aortic valves.
Indirect Assessment of AR severity – colour Doppler imaging
The Vena Contracta is the narrowest part of the jet downstream from the flow convergence zone
Indirect assessment of AR severity: spectral Doppler
Assessment of the regurgitant jet with CW Doppler is performed using the 3 or 5 chamber views. Use colour Doppler to visualise the direction of flow, then place the CW Doppler through the regurgitant flow as parallel as possible to the flow to get the best trace possible
Since the regurgitant flow is towards the probe, the regurgitant flow will appear above the baseline. The density of the signal , and the clarity of it’s envelope is proportional to the severity of the regurgitation
The slope is called the pressure half time. It reflects the rate of decline in the pressure gradient between the aorta and the LV. The steeper the slope, the more severe the regurgitation.
The denser the Spectral Doppler signal, the more severe the regurgitation.
A pressure ½ time of more than 500 indicates mild regurgitation, between 200 and 500 moderate regurgitation and less that 200 severe regurgitation.
PW Doppler has a number of drawbacks. It may be technically difficult in some patients to get the beam aligned through the regurgitant jet in which case the Doppler signal is inaccurate. Jets may be eccentric or multiple and poor gain settings will either under or overestimate the signal density.
The pressure ½ time ( PHT) can also be misleading. The rate of deceleration and the derived pressure half‐time correspond to the rate of equalisation of the pressures between the aorta and the LV which is dependent on afterload and LV compliance. The pressure 1/2 time will appear short if LV compliance is poor in the absence of severe AR. On the other hand, in patients with chronic severe AR with good LV compliance, it will appear long despite severe AR
Using PW Doppler, flow reversal can be seen in the proximal abdominal aorta and the descending thoracic aorta.
Normally, flow in the descending thoracic aorta is systolic with little diastolic flow. The more the aortic regurgitation the longer the diastolic reverse flow.
Pan-diastolic flow reversal in the proximal abdominal aorta (below baseline) & the descending thoracic aorta (above baseline) strongly support the diagnosis of severe aortic regurgitation (PW).
Limitations/Caveats to indirect assessment of AR
- The length of the regurgitant jet does not correspond to the severity of the regurgitation
- Colour Doppler : eccentric jets can be missed, underestimated or difficult to assess. This is why panning through the valves is important
- The vena contracta is limited by
- the assumption that the regurgitant orifice is almost circular
- the small size of the measurement
- cannot be used if there are multiple jets
- The density of the spectral Doppler is affected if the Doppler gains are too high or low or there is poor alignment of the jet
- Pressure ½ time (PHT) is greatly affected by systemic vascular resistance and LV compliance
Therefore use multiple methods to assess regurgitation
The assessment of AR using colour and spectral Doppler are all indirect and qualitative measures
Quantifying the regurgitant volume is achieved using the stroke volume and PISA methods which have little value in the acute critical care setting