Echocardiography (Non-invasive diagnostic technique)

1. The evaluation of cardiac structure and function with images and recordings produced by ultrasound

2. There are many echocardiographic modalities:

- M-mode

- 2D

- 3D

- Doppler

3. Echocardiographic findings in aortic stenosis case:

a. 2D echocardiographer

- Thickened Aortic Valve Leaflets

1. leaflet is more reflective and can be seen in systole and diastole
2. best visualized in 2D
3. right coronary cusp most affected
4. left coronary cusp least affected

* It is thickened as a result of calcification or fibrosis. However, the older patient without valve stenosis may also have thickened cusps

- Restricted Leaflet Motion

1. systolic separation of right coronary cusp (anterior) and noncoronary cusp (posterior) falls below 1.5 cm in adults
2. fused commissures results in systolic doming of the valve

* However, the aortic valve may also have a reduced opening in which the cardiac output is reduced. Hence, we can use Pulsed-wave (PW) Doppler echocardiography to estimate the cardiac output by recording the distance between the left ventricular outflow tract (LVOT) and right ventricular outflow tract.

- Narrowed orifice

1. acquired - advanced valvular obstruction with calcification
2. congenital – unicuspid or bicuspid aortic valve with/without calcification

b. M-mode (Not reliable technique for assessing the severity of aortic stenosis) Note: thickened leaflets and decreased aortic cusp separation. The vertical axis gives the distance of each point from the transducer while horizontal axis gives the time period

* However, when we find a normal movement of thin aortic leaflets on this echocardiogram, it is strong evidence against severe AS

Doppler (Very reliable)

c. Spectral Doppler (Very reliable)

- Increased Peak systolic velocity (more than 3.5 m/sec)

- Peak systolic velocity ranged from 1.2 to 3.3 cm/s, and peak diastolic velocity ranged from 1.6 to 4.5 cm/s (http://www.ajnr.org/cgi/content/abstract/24/2/169)

- Increased Pressure Gradient (Bernoulli). Bernoulli principle can be used to calculate AVA

- Decreased Valve Orifice

d. Color Flow Doppler

- Use one color for blood flowing towards the transducer and another color for blood flowing away

- High velocity systolic jet

* Transesophageal echo/Doppler ultrasound and transthoracic technique are very useful

Cardiac catheterization

- Introduce a thin radio-opaque tube (catheter) into the circulation

- Used to record the systolic pressure difference (gradient) between the aorta and the left ventricle and assess left ventricular function

- This is done by measuring simultaneous LV and ascending aortic pressures and measuring cardiac output

- Data that can be obtained:

a. Left ventricular pressure

- Elevated because the ventricle has to force blood through the narrowed opening of the aortic valve

- Elevated end diastolic pressure occur as ventricle adapts to the pressure overload condition

b. Left atrial pressure

- Increase as atrium adapts to changes in left ventricular pressures

c. Aortic Valve Gradient

- Measure the peak left ventricular pressure minus the peak aortic systolic pressure

Provocative Diagnostic Test

1. As mentioned above, the severity of AS may be in doubt due to small mean aortic valve gradient. The calculated AVA can be small because of severe stenosis or small stroke volume.

2. In this test, an inotropic agent such as dobutamine, which will cause an increase in cardiac output (stroke volume) and heart rate (shortening of systolic ejection time), will be used.

3. Then, measure cardiac output and LV and aortic pressures simultaneously, both before and during dobutamine infusion because it will cause systemic vascular resistance either increase or decrease.

4. Whether the AS is mild or severe, the gradient increases with dobutamine infusion.

However, in mild AS, the AVA increases significantly but in severe AS the AVA does not increase or increase minimally (~10%).

Gated Blood Pool Radionuclide Scans

1. It uses radioisotope dye that shows how blood pools in the heart during rest, exercise, or both. It gives information on how well the heart is pumping blood and if it is working harder to make up for one or more blocked arteries.

2. It can also find ejection fraction, which is the percentage of blood that is pumped out of the heart’s left ventricle.

3. A radioactive substance is injected into the bloodstream. The radioactive substance tags or labels the red blood cells in the blood. This substance is safe and will not cause any harm. A gamma-ray camera is used to take pictures of the heart as the tagged red blood cells circulate.

Hence, in AS, it can shows how well the heart is functioning to pump the blood out. Ejection fraction can be used to assess the presence of obstruction in the heart.

Exercise testing

1. It is not safe in symptomatic patients with severe AS. Hence, it is only best to use for asymptomatic patient. Indeed, patients with severe AS need to undergo aortic valve replacement (AVR).

2. In the absence of coronary disease, most patients with severe AS exhibit a normal cardiac output at rest. However, the hypertrophic left ventricle is less compliant than normal and LV end-diastolic pressure is often increased.

3. During exercise, cardiac output fails to increase normally in most of patients with severe AS.

4. The mechanical obstruction to blood flow posed by the stenotic valve limits blood flow and the reduced diastolic compliance of the hyperthrophied ventricle contributes by reducing the potential to augment end-diastolic volume and utilize the Frank Starling mechanism during exercise. As a result, stroke volume fails to rise and changes in cardiac output largely depend on changes in heart rate.

5. Blood pressure normally increases during exercise, but inadequate cardiac output or abnormal peripheral vascular response can result in hypotension.

6. Arterial and venous vasodilatation with bradycardia, mediated by sudden changes in LV pressure and baroreceptor activity (the Bezold Jarish reflex), play a role in effort-related hypotension and syncope in patients with AS.

7. Basically, exercise testing can only give prognostic information. Hence, it can be used to provide an exercise prescription and to reassure the patient who might otherwise excessively limit his or her activity.

Clinical Decision Making

It includes a complete clinical evaluation:

1. History

2. Physical examination

3. ECG

4. Chest Radiography

5. Disease of all cardiac valves, ventricular function, hemodynamic effects, as well as CAD, other cardiovascular disease, and disease of other organs, should be diagnosed and the severity assessed

6. Additional testing

Clincial examination

1. For a complete physical examination, it was presented by Joanna last week. Hence, I will focus on auscultation and pulse which is very important in diagnosing AS.

Pulse

1. The arterial pulse rises slowly, taking a longer time than normal to reach peak pressure, and the peak is reduced (parvus et tardus). Parvus et tardus pulse means an arterial pulse that is small and has a delayed systolic peak (severe AS often have it). It is easier to detect in the carotid artery than in more distal arteries.

2. The pulse pressure may be narrowed. The anacrotic notch on the upstroke is best appreciated in the carotid arteries. The more severe the valve stenosis, the lower the anacrotic notch on the arterial pulse. Anacrotic means a detectable shoulder on the upstroke of the carotid pulse. Palpable coarse vibrations often are present as a systolic thrill over the slowly rising carotid pulse.

3. Uncomplicated severe AS will have a parvus et tardus pulse but can also occur in relatively mild stenosis.

4. The JVP is normal unless there is heart failure.

Auscultation

1. There may be a palpable fourth heart sound (S₄). There is S₄ gallop sound, a midsystolic ejection murmur that peaks late in systole and a single second heart sound (S₂) because A₂ and P₂ are superimposed or A₂ is absent or soft.

2. There is often a faint early diastolic murmur of minimal aortic regurgitation (AR).

3. In the young patient with AS, a systolic ejection sound (systolic ejection click) initiates the systolic murmur but later tends to disappear as AS becomes severe.

The S₂ may be paradoxically split because of late A₂, and there may be no early diastolic murmur. In many patients, particularly the older patients, the systolic ejection murmur is atypical, may be soft, is described as a seagull sound (or musical, or cooing), and may be heard only at the apex of the heart (Gallavardin phenomenon).

References:

1. Kumar & Clarks Clinical Medicine 7^th Edition 2009, Aortic Stenosis (pg. 765), Kumar, P. & Clark, M. (eds.), Saunders Elsevier, London.

2. Rahimtoola Shahbudin H, "Chapter 75. Aortic Valve Disease " (Chapter). Fuster V, O’Rourke RA, Walsh RA, Poole-Wilson P, Eds. King SB, Roberts R, Nash IS, Prystowsky EN, Assoc. Eds.: Hurst's The Heart, 12e: http://www.accessmedicine.com.ezproxy.lib.monash.edu.au/content.aspx?aID=3062773

3. http://www.echo-web.com/asp/samples/sample5.asp

4. http://resources.metapress.com/pdf-preview.axd?code=5v4t3r760358h403&size=largest

5. http://www.ajnr.org/cgi/content/abstract/24/2/169

http://www.texasheartinstitute.org/HIC/Topics/Diag/dimuga.cfm