Aortic Valve Area Calculation

There are 3 measurements required to calculate the aortic valve area

a. Aortic jet velocity using CW doppler VTIAV
b. LVOT diameter to calculate LVOT cross-sectional area (CSALVOT)
c. LVOT velocity with PW doppler (VTILVOT)

The aortic valve area (AVA) = (CSALVOT x VTILVOT) / VTIAV

Valve Motion In Normal Subjects

The mitral valve closes a few milliseconds before the tricuspid valve. Also remember, the tricuspid valve is located slightly more apically than the mitral valve.

The cardiac cycle is a complex set of events. It has been summarised in the table below -

Phase of contraction	Physiological features	Duration of phase (seconds)	Corresponding ECG wave
Diastasis	Passive ventricular filling prior to atrial systole	0.19	P wave
Atrial contraction	Ejection of blood into ventricle	0.11	Beginning of QRS complex
Isometric ventricular contraction	Onset of ventricular contraction. Semilunar valves are closed and AV valves are just about closed.	0.50	Just after the onset of QRS complex
Rapid ventricular ejection	Increased pressure in ventricles causes opening of semilunar valves.	0.09	Onset of T wave
Slow ventricular ejection	This is the end of ventricular ejection. Atria start to fill up.	0.13	End of T wave
Isovolumetric relaxation	Closure of semilunar valves. AV valves closed as well. Ventricles relaxed.	0.08	Between the end of T wave and the start of P wave
Ventricular filling	AV valves open, ventricles fill with blood.	0.11	Between the end of T wave and the start of P wave

Based on this, the isovolumetric relaxation time is the time when both the mitral and aortic valves are closed and ends when the mitral valve opens. The ventricle is empty during this period. The atrium passively fills the ventricle by emptying 80% of its volume and only requires to contract to empty the remaining 20%.

Keep this table in mind, it is possible there will be a question based on this.

Main Points in Doppler Assessment of Valve Regurgitation

Main points in doppler assessment of valve regurgitation (1)

1. Colour doppler 

• The ideal Nyquist limit is 50 - 60cm
• Reducing the Nyquist limit can increase the size of the jet, and can result in overestimation of the severity of the regurgitation
• Due to this reason, the color flow area of the regurgitant jet is not recommended to assess and quantify how severe valve regurgitation is.

2. Vena Contracta

• This is the narrowest part of the regurgitant jet below the level of the regurgitant valve orifice (2)
• It is essential to focus on jet alone, so the size of the color jet and the imaging depth must be reduced. 
• It is difficult to accurately assess vena contracta in the presence of multiple jets and an irregular orifice

Nevertheless, it still remains a very useful method to assess the severity of valve regurgitation

3. Proximal Isovelocity Surface Area (PISA)

• Also called flow convergence
• The main principle here is that as blood flows across a regurgitant valve, convergence at this level results in the formation of ‘concentric isovelocity shells’, which can be visualized with color flow doppler at an optimal aliasing velocity
• The product of the the size of this shell and the aliasing velocity provides the flow rate. 
• The regurgitant orifice area can then be calculated by dividing this value by peak velocity of the regurgitant jet obtained on continuous wave doppler.

Advantages

• Reproducible
• Can be used for eccentric jets as well (3)
• Unaffected by the cause of regurgitation

References

1. Patrizio Lancellotti, Christophe Tribouilloy, Andreas Hagendorff, Luis Moura,Bogdan A. Popescu, Eustachio Agricola, Jean-Luc Monin, Luc A. Pierard, Luigi Badano,Jose L. Zamorano, Rosa Sicari, Alec Vahanian, and Jos R.T.C. Roelandt. European Association of Echocardiography recommendations for the assessment of valvular regurgitation. Part 1: aortic and pulmonary regurgitation (native valve disease)Eur J Echocardiogr (2010) 11(3): 223-244
2. Roberts BJ, Grayburn PA. Color flow imaging of the vena contracta in mitral regurgitation: technical considerations. J Am Soc Echocardiogr 2003;16:1002-6.
3. Enriquez-Sarano M, Tajik AJ, Bailey KR, Seward JB. Color flow imaging compared with quantitative Doppler assessment of severity of mitral regurgitation: influence of eccentricity of jet and mechanism of regurgitation. J Am Coll Cardiol 1993;21:1211-9.

Valve Regurgitation Assessment

For the purposes of echo exams, it is important to familiarise yourself with current guidance on the assessment of valve regurgitation. We have listed a few as references to the statements below.

Carpentier classification (1) is used to classify dysfunction in leaflet mobility as follows

Type I - Normal leaflet motion
Type II - Increased leaflet mobility
Type III - Reduced leaflet mobility (IIIa in systole and diastole, IIIb in systole alone)

It is not used to grade LV dysfunction.

It has been discussed in other sections of this course, but to quickly reiterate that acute regurgitation of any sort does not cause ventricular hypertrophy or dilatation, as these processes are time-dependent and are seen in chronic ventricular overload. In chronic overload of the ventricle due to mitral or tricuspid regurgitation, the amount of blood entering the ventricle from the atrium is increased, implying an increased preload.

In the case of aortic or pulmonary regurgitation, the ventricle has to pump more blood as most of it has returned back to it from the aorta or pulmonary artery, implying an increase in afterload. Both of these cases will result in a degree of ventricular hypertrophy, and over time, dilatation.

Imaging of the left heart with transthoracic echo is best obtained in end-expiration. Valsalva should be avoided as image quality will be poor. At least 3 cardiac cycles of LV contraction should be obtained in sinus, and 5 in atrial fibrillation (2).

Just of note, the ESC recommends using contrast imaging if <80% of the endocardial border is visible clearly. (2,3)

References

1. Carpentier A, Chauvaud S, Fabiani JN, Deloche A, Relland J, Lessana A, et al. Reconstructive surgery of mitral valve incompetence: ten-year appraisal. J Thorac Cardiovasc Surg 1980;79:338-48.
2. Patrizio Lancellotti, Christophe Tribouilloy, Andreas Hagendorff, Luis Moura,Bogdan A. Popescu, Eustachio Agricola, Jean-Luc Monin, Luc A. Pierard, Luigi Badano,Jose L. Zamorano, Rosa Sicari, Alec Vahanian, and Jos R.T.C. Roelandt. European Association of Echocardiography recommendations for the assessment of valvular regurgitation. Part 1: aortic and pulmonary regurgitation (native valve disease)Eur J Echocardiogr (2010) 11(3): 223-244
3.  Roxy Senior, Harald Becher, Mark Monaghan, Luciano Agati, Jose Zamorano,Jean Louis Vanoverschelde, and Petros Nihoyannopoulos. Contrast echocardiography: evidence-based recommendations by European Association of Echocardiography. Eur J Echocardiogr (2009) 10(2): 194-212

Image Resolution

Image resolution or spatial resolution is the ability of the ultrasound wave to define 2 points as separate in space. This includes axial and lateral resolution. Also included is temporal resolution.

Axial resolution (azimuthal resolution) is the resolution of the objects along the line of the ultrasound beam. The axial resolution is directly proportional to the pulse resolution. This means that an increase in the frequency of the ultrasound waves reduces the wavelength, and thus the spatial pulse length. In short, the axial resolution depends on the wave frequency and spatial pulse length. It is not affected by altering the focus.

Lateral resolution is the resolution of structures at 90 degrees to the line of ultrasound waves propagation. It is a cause for artifact formation in imaging. It can be corrected by altering the focus. In addition, increasing the width of the bean and the frequency also increases lateral resolution.

Temporal resolution is the resolution of images over time. It is also called the frame rate. It is directly related to the pulse repetition frequency.

As discussed previously, backscatter is the reason why images are generated on the echo machine. It is not the cause for distortion of images, but in fact, required for normal image generation.