Acquired aortic valve disease

[얼음심장]

Acquired aortic valve disease

<Normal aortic valve anatomy>

Aortic valve는 lt. ventricle에서 aorta로 피를 보내줌과 동시에 aorta로부터 lt. ventricle로 피가 역류하는 것을 막는 기능을 한다. 정상 aortic valve는 tricuspid로, lt. coronary, rt. coronary, noncoronary leaflets이 각각 sinuses of Valsalva 바로 아래에 붙어있다. Aortic valve는 fibrous skeleton에 의해 지지 받고 있으며, 이것은 mitral valve의 ant. leaflet과 연결되어 있다. 각각의 valve leaflet은 endothelium lining의 fibrous tissue로 구성되어 있고, 특별한 vascular supply가 없다.

<Aortic stenosis (AS)>

AS의 가장 흔한 원인은 degenerative valve calcification이다. Calcification은 atherosclerosis에 의해progressive하게 진행되며 significant calcification은 30세 이전에는 거의 발생하지 않는다. Calcification은 tricuspid보다 bicuspid에서 더 흔하며, annulus, interventricular septum, mitral valve의 ant. leaflet 으로도 흔히 침범한다.

1.Pathphysiology

1)     Aortic stenosis à elevated left ventricular afterload with secondary impairment of the left ventricular emptying during systole

2)     Pressure gradient across the aortic valve↑ à LV pressure ↑(∵ascending aorta에서 normal perfusion pressure를 유지하기 위해) à LV wall stress↑à LV hypertrophy

(∵Laplaces’ law à T= Pr/2h, r=lt. ventricular radius, h= lt. ventricular wall thickness)

3)     만약 LV hypertrophy가 ventricular wall stress를 normalize하지 못하게 되면 lt. ventricular failure(ventricular contractility↓, progressive lt. ventricular dilatation)

4)     Aortic stenosis를 교정해주면 lt. ventricular EF, lt. ventricular end-diastolic volume 등은 그 즉시 좋아진다. 그러나 aortic stenosis로 인한 lt. ventricular hypertrophy는 valve replacement 한지 6-12개월 정도가 지나야 좋아지기 시작하며, 정상까지 변하지는 못한다.

5)     EF과 wall stress는 valve replacement의 outcome을 예측하는데 도움이 되지 못한다. Low EF, low wall stress 환자들의 수술 후 결과가 종종 좋기 때문이다.

2.Clinical findings

1)     Early AS 환자들은 대부분 무증상이나, 시간이 지나면서 exertional dyspnea, angina, syncope등의 증상을 보이게 된다.

2)     Physical exam상, 대부분 systolic ejection murmur (2^nd intercostal space to the rt. of the sternum with radiation into both carotid a.)가 들린다. Severe AS 환자에서는 late systole 때 murmur가 가장 잘 들리며 thrill을 동반하기도 한다. 그러나 심한 LV failure가 동반된 환자에서는 CO의 감소로 murmur의 크기가 감소할 수도 있다.

3)     Echocardiogram상 대부분 LV hypertrophy with strain을 나타내며, 때때로 AF이나 lt. or rt. bundle branch block소견을 보이기도 한다.

4)     Chest radiography상 aortic valve calcification, LVE, dilatation of the ascending aorta를 보이며, 때때로 LV failure로 인한 pulmonary edema가 관찰되기도 한다.

3.Diagnosis

1)     Doppler echocardiography : invaluable noninvasive tool!

Peak systolic gradient across the aortic valve, aortic regurgitation정도를 알 수 있다.

2)     2D echocardiography : valve thickening, calcification, immobility, EF 등을 알 수 있다.

3)     Cardiac catheterization : echocardiography와 다르게 coronary a. 의 anatomy도 확인할 수 있다. 적응증으로는 age>40, CAD의 risk가 있는 경우 또는 borderline degree of stenosis(impaired LV function인 경우) 가 있다.

4.Natural history

1)     Mild aortic stenosis 환자들은 대부분 무증상으로 수 십 년을 보낸다.

(∵compensatory lt. ventricular hypertrophy)

2)     Moderate, severe aortic stenosis 환자들은 angina, CHF, syncope 의 증상을 나타낸다.

-       Ross and Braunwald study에 따르면, 위의 증상을 나타낸 다음 average survival은 각각 angina 3-5년, syncope 3년, CHF 1.5-2년 정도가 된다고 한다.

3)     치료를 받지 않은 aortic stenosis 환자의 대부분은 CHF로 사망하지만, 상당수의 환자들은 ventricular arrhythmia의 발생으로 sudden death 하게 된다.

4)     Balloon valvuloplasty는 수술시기를 늦추거나, 수술을 해야 하는 사람들에게 preoperative rehabilitation 목적으로 시행된다. 이 방법을 시행하게 되면 증상의 50%정도가 호전되지만, 이 benefit은 6개월 동안만 유효하게 된다. (즉 balloon valvuloplasty를 시행하고 6개월이 지나게 되면 증상이 다시 생기게 된다) Balloon valvuloplasty 단독시행과 balloon valvuloplasty 시행 후 aortic valve replacement를 시행 받은 환자들의 survival을 비교해보면 후자가 훨씬 높다. 

5.Management

1)  증상이 있는 환자들에게 medical treatment는 매우 제한적인 역할을 한다. CHF의 증상이 있는 환자들에게는 diuretics, AF이 있는 환자들에게는 digoxin or antiarrhythmics가 사용될 수 있지만, 증상의 완화만 도울 뿐 질병 자체의 natural course를 바꿀 수 없다.

2)     Angina, CHF, syncope 의 증상이 나타나게 되면 aortic valve replacement의 적응증이 된다. 증상이 없더라도 valve area가 0.8cm² 또는 1.2cm²/m² 이 되면 수술의 적응증이 된다. 또한 impaired LV function이 의심되는 경우(decreased EF, LV dilatation, significantly elevated LV diastolic pressure)도 수술의 적응증이 된다.

3)     Aortic valve repair는 aortic valve replacement에 비해 long-term result가 좋지 않다.

<AR>

1.cause

aortic valve regurgitation은 aortic stenosis와 같이 생기기도 하고 원인도 많이 겹친다.

1)Degenerative calcific aortic valve disease

- leaflet fixation -> diastole때 full closure을 막음 -> aortic insufficiency

2)rheumatic heart disease

- aortic valve leaflets을 fibrosis -> secondary failure

3)Congenital bicuspid aortic valve disease

- leaflets에 fibrosis&calcification -> aortic valve regurgitation

4)annuloaortic ectasia

- aortic valve annulus의 aortic root의 abnormal dilatation

- Cystic medial necrosis of the aortic wall

- degeneration of elastic bands in the aortic wall

- abnormal organization of smooth muscle bundles, increased collagen

5)Other causes

- myxoid degeneration of the aortic valve leaflets

- Aortic dissection, Bacterial endocarditis (perforation or rupture)

- rheumatoid arthritis, ankylosing spondylitis, Reiter’s syndrome

- blunt or penetrating chest trauma

2.Pathophysiology

1)Aortic regurgitation -> volume overload of the left ventricle.

(left ventricular hemodynamics are relatively normal during systole)

2)left ventricular diastolic filling from both the left atrium and the ascending aorta

3)certain fraction of the forward cardiac output during systole returns to the left ventricle during diastole -> cardiac output is increased by autonomic reflexes to maintain a normal net forward cardiac output.

4)increased left ventricular diastolic filling and the increased stroke volume -> increases left ventricular diastolic filling pressure -> raises left ventricular diastolic volume and diastolic wall stress -> eccentric hypertrophy -> progressive left ventricular dilatation, massive enlargement of the left ventricle -> cor bovinum.

3.Clinical Findings

1)congestive heart failure

-dyspnea, orthopnea, and paroxysmal nocturnal dyspnea.

2)Angina(1/2이하)

3)syncope(relatively unusual)

4)Physical examination

-lateral displacement of the left ventricular apical impulse

-aortic pulse pressure : increased to over 50 mm Hg with aortic regurgitation

-peripheral pulses : dramatically pulsatile (water hammer)

-Cardiac auscultation : early diastolic decrescendo murmur radiating toward the left ventricular apex

-severe aortic regurgitation : middiastolic Austin Flint murmur at the left ventricular apex

-third heart sound : association with left ventricular dilatation

4.Diagnosis

1)chest radiograph

-normal or left ventricular enlargement

-enlargement of the ascending aorta

-pulmonary edema, or pulmonary venous engorgement. Left ventricular hypertrophy with strain may be present on electrocardiogram.

2)Doppler echocardiography

-diastolic regurgitation of blood flow across the aortic valve(1+ to 4+ scale) -Two-dimensional echocardiography : leaflet thickening, calcification, stenosis, left ventricular dilatation, hypertrophy, impaired ejection fraction

3)Cineradiography

-diastolic regurgitation of dye across the aortic valve (1+ to 4+scale)

-Left ventriculography and aortography : left ventricular dilatation, impaired left ventricular ejection fraction, dilatation of the ascending aorta.

-Coronary arteriography : age of 40 years or with risk factors for coronary artery disease.

5.Natural History

1)clinical symptoms

-appear even 3–10 years after onset of severe aortic regurgitation

-The onset of symptoms correlates with elevation of left ventricular end-diastolic pressure, left ventricular dilatation, depressed left ventricular contractility, and generally follows within 3–6 months of detectable left ventricular dilatation in patients with asymptomatic aortic regurgitation.

2)Survival

-81% at 5 years in medically treated patients with aortic regurgitation, no symptoms, normal left ventricular function.

3)Once symptoms develop

-left ventricular performance : fall rapidly

-mean survival : 5 years after onset of angina and 2 years after onset of heart failure with medical therapy

4)Acute onset of severe aortic regurgitation

-aortic valve endocarditis : accelerate clinical deterioration with decompensated heart failure or even death within days or weeks.

6.Management

1)asymptomatic aortic regurgitation (normal left ventricular function)

-medically : Diuretics or afterload reduction, or both

-improve early symptoms until surgical correction can be performed

-intraaortic balloon pump :

useful means of afterload reduction in other critically ill patients

relatively contraindicated in patients with aortic regurgitation

2)aortic valve repair or replacement

-the presence of symptoms

-any impairment of left ventricular function, left ventricular dilatation, significant elevation of left ventricular end-diastolic pressure.

7.Imaging

1)Cardiac Catheterization

-traditional tool for the diagnosis of valvular heart disease

-necessary for operative candidates

-disadvantages to catheterization include the intravenous dye load, discomfort with arterial access, and the limited amount of information available

2)Echocardiography

-revolutionized the diagnosis and management of valvular heart disease

-real-time monitoring of ventricular performance and valvular performance in a noninvasive manner

-Valvular function and size can be carefully measured and eval‎uated

-Intraoperative transesophageal echocardiography : routine for valvular heart surgery, immediate eval‎uation of the repaired or replaced valve

3)Magnetic Resonance Imaging

-diagnosis of valvular heart disease and heart disease

-very specific information : myocardial function, valvular function, quantitation of regurgitant flow, degree of obstruction in stenosis.

Surgical techniques

Valve selection

1)     Bioprosthetic

(1)   easy to implant, easy to replace

(2)   require no anticoagulation

(3)   silent

(4)   limited durability

2)     Mechanical

(1)   easy to implant, easy to replace

(2)   durable structural function

(3)   soft ticking sound

(4)   need for life-long anticoagulation, typically with warfarin

3)     Stentless

(1)   more difficult to implant than stented valves

(2)   require no anticoagulation

(3)   silent

(4)   no durability benefit over traditional bioprosthetic valve

4)     Allograft

(1)   more resistant to endocarditis than prosthetic valve

(2)   more difficult to implant than stented valve

(3)   no durability benefit over traditional bioprosthetic valve

5)     Ross procedure

(1)   aortic valve replacement with a pulmonary autograft

(2)   allowing growth and development of the pulmonary valve in the aortic position

Aortic valve repair

Aortic valve repair는 aortic insufficiency가 있는 환자에게서 유용한 방법이다.

1)     bicuspid valve (한 leaflet이 길어져 있어서 prolapse가 발생함)

2)     leaflet perforation (endocarditis or healed endocarditis)

3)     traumatic rupture of the aortic valve

<RESULTS OF SURGICAL THERAPY>

1.Operative Mortality

1)in-hospital or 30-day

-isolated aortic valve replacement in large recent series : 2–5%

-increased to 6–15% by a prior median sternotomy

-increased to 6% by the addition of concurrent coronary bypass grafting

-increased to 10% by the addition of mitral valve replacement

-over the age of 80 years with aortic stenosis : 9%

2)Other significant predictors of increased mortality

-increased age, decreased left ventricular function, poor preoperative functional status, renal insufficiency, atrial fibrillation

3)most common causes of operative mortality

-cardiac failure or infarction in 58%

-hemorrhage in 11%, infection in 7%, arrhythmia in 5%, stroke in 4%

2.In-Hospital Complications

1)most common serious complications after aortic valve operation

-stroke in 1–2% of patients

-mediastinal bleeding requiring reoperation in 5–11%

-wound infection in 1–2%

-heart block requiring a permanent pacemaker in less than 1%

-renal failure requiring dialysis in 0.7%

-prolonged ventilation in 3%

-perioperative myocardial infarction in 2%

3.Late Complications

1)most frequent late complications from aortic replacement

-thromboembolism and anticoagulant-related hemorrhage

-related to the valve prosthesis implanted, patient age, atrial fibrillation,

2)most bioprosthetic valves

-thromboembolism 0.2–1.3% per patient year

-anticoagulant-related hemorrhage : 0.3% per patient year

3)mechanical aortic valves

-thromboembolism : 1.5–2.0% per patient year

-anticoagulant-related hemorrhage : 2–3% per patient year

4)Endocarditis

-0.5–1.0% per patient year after the first 6 months

4.Long-Term Survival

1)Long-term survival after aortic valve replacement

-decreased by many factors : older patient age, impaired left ventricular function, coronary artery disease, renal insufficiency

2)Typical survival 10 years after aortic valve replacement

-60–70%, with primary causes of death : cardiac failure or sudden death (42–83%), hemorrhage (4%), infection (5%), thromboembolism (6%)

5.Symptomatic Relief

1)Most patients with aortic valve replacement

-immediate improvement in preoperative symptoms

-persists in the long term, with 96% of patients belonging to (NYHA) functional class I or II 6 years after operation

-normal preoperative left ventricular function or with mildly depressed ejection fraction (aortic stenosis) : relatively normal postoperative exercise capacity