A HANDBOOK OF AORTIC VALVE DISEASE

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Contents

Introduction......................................3Etiology..........................................5Pathophysiology...................................7Hemodynamics......................................9Clinical features.................................11Investigations....................................21Natural History...................................31Management........................................35Introduction......................................49Etiology..........................................51Pathophysiology...................................53Hemodynamics......................................55Chronic AR: Clinical Features.....................57Investigations....................................67Natural History...................................77AR: Management....................................81Suggested Reading.................................89Abbreviations.....................................91

Chapter One

Causes of left ventricular outflow tract obstruction (LVOTO)

Valvular Aortic stenosis

Acquired

Post inflammatory (usually rheumatic) The most distinctive aortic valve change secondary to valvulitis is commissural fusion, the single most important finding in determining that the cause is rheumatic (or post-inflammatory). Severe AS may be seen after brucellar or rickettsial infection.

Degenerative

Bi or tricuspid AV It is unusual for a bicuspid or tricuspid valve to be stenotic in absence of significant calcification. Non calcific AS with fibrosis is therefore more likely to be rheumatic in origin.

Congenital

Unicuspid valve Tricuspid with fusion of commissures Hypoplastic annulus

Rare causes

SLE (especially after steroid therapy)

Fabry's disease and Ochronosis (metabolic products accumulates in cusps)

Type II hyperlipoprotenemia

IE

Secondary to Radiotherapy

Nonvalvular aortic stenosis

Rare; as all acquired pathology and more than 70 % of congenital lesions are valvular stenosis

Subvalvular obstruction Discrete fibromembranous Diffuse fibromuscular (tunnel) Muscular (Hypertrophic subaortic stenosis)

Supravalvular obstruction Hourglass Hypoplastic Membranous

Age of presentation of LVOTO

Infancy to first decade: Congenital valvular, subvalvular or supravalvular pathology

Early childhood to late adulthood Rheumatic AS Hypertrophic subaortic stenosis

Early to late adulthood Degenerative AV disease Degenerative Tricuspid AV disease usually present after 65 yrs of age

Pathophysiology

Valvular aortic stenosis results in chronic left ventricular pressure overloading. The AVA has to be reduced by about 50% of normal before a measurable gradient can be demonstrated in humans. Pure aortic valve stenosis results in compensatory ventricular hypertrophy proportional to the degree of obstruction. Mild degrees of obstruction are usually well tolerated, with minimal hypertrophy and normal left ventricular function. As stenosis progresses, hypertrophy increases and reduces wall stress. In most patients with AS, cardiac output is in the normal range and initially increases normally with exercise. Eventually, however, left ventricular hypertrophy results in either 1) diastolic dysfunction with the onset of congestive symptoms, or 2) myocardial oxygen needs in excess of supply with the onset of angina. Some patients may also experience exertional syncope, because as the severity of AS increases progressively, the cardiac output remains within the normal range at rest, but, on exercise, it no longer increases in proportion to the amount of exercise undertaken or does not increase at all (fixed cardiac output). With the development of heart failure, there is a reduction in the resting cardiac output and tachycardia. As a result, stroke volume may be so lowered that it results in a small gradient across the left ventricular outflow tract in spite of severe AS.

At any stage of life, however, the natural history of aortic stenosis largely reflects the functional integrity of the mitral valve. As long as adequate mitral valve function is maintained, the pulmonary bed is protected from the systolic pressure overloading imposed by aortic stenosis. In contrast to mitral valve disease where the pulmonary circuit is directly involved, compensatory concentric left ventricular hypertrophy allows the pressure overloaded ventricle to maintain stroke volume with modest increases in diastolic pressure, and patients can remain asymptomatic for many years.

Hemodynamics

Reduction in valve size more than 50 % results in increased gradient across AV.

For hemodynamically significant AS, valve area should be reduced by more than 60 %. At this stage compensatory mechanism in form of LV hypertrophy starts.

The hemodynamic characteristics of significant AS are:

Raised LVEDP

High 'a' wave in LA pressure trace

No increase in mean LAP, PAWP or RVSP in asymptomatic patients with normal LV function.

Unlike MS, the AV gradient does not increase with exercise because tachycardia mainly occurs at the expense of diastolic time.

Clinical features

Symptoms

Classical Triad

Angina Syncope Congestive Heart Failure

1. ANGINA (angina pectoris)

Presenting feature in 70 % cases;

Usually indicates severe AS; in only less than 10 % patients AS may not be severe.

Usually the initial symptom

More frequent with AS than any other valve lesions

Life expectancy less than 5 years after onset of angina

Typically exertional angina

Mechanisms: Demand – supply mismatch Subendocardial ischemia Hypertrophied muscles more prone to ischemia Additional CAD

Responds to nitrate but avoid as nitrate induced hypotension can be dangerous

Angina at rest indicates associated coronary artery disease

2. SYNCOPE

Presenting feature in 33 % cases;

Indicates severe AS; only in less than 10% cases, AS may not be severe

Occurs during exercise as a consequence of

Reduction of the systematic vascular resistance (Vasodilation in skeletal muscle)

Failure of forearm vasoconstriction during leg exercise (Ventricular Bazold – Jarisch reflex)

Failure of cardiac output to rise due to severe fixed obstruction

Arrhythmias (Tachy or bradyarrhythmias): Can lead to syncope at rest also.

Syncope in 'mild AS': Causes

Coronary artery disease Hypertrophic cardiomyopathy Unrelated non cardiac cause

3. CONGESTIVE HEART FAILURE (CHF)

Seen in 15 % cases Symptoms include. Dyspnea. Orthopnea. Paroxysmal Noctural Dyspnea. Pulmonary Edema. Pulmonary Hypertension. End Stage: Right Ventricular Failure Dyspnea in AS Causes: Diastolic dysfunction of LV Congestive heart failure

Dyspnea in a case of 'Mild AS'

Associated Mitral valve disease; if in a case of RHD and AS, if the duration of dyspnea is longer than 5 yrs, then associated MV disease should be strongly suspected.

Hypertrophic cardiomyopathy

Coronary artery disease

Unrelated pathology (eg., Pulmonary cause)

Diastolic Dysfunction as cause of dyspnea:

It is a common cause of dyspnea on exertion in AS (seen in 45 % cases).

Mechanism:

AS leads to LV hypertrophy as a compensatory mechanism

Increase LV wall thickness reduces ventricular compliance: Leads to raised LVEDP

The Atrium needs higher pressure to fill the ventricle: Leads to raised LAP

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