Heart Murmurs - Stenosis & Regurgitation
Heart Murmurs
Overview:
Review Heart Anatomy
In present times, echocardiography is used to visualize the valvular disease but auscultation of a murmur is a quick, important way to identify whether pathology is present.
Heart murmurs are abnormal sounds created by turbulent blood flow across defective cardiac valves.
Key causes of valvular damage:
Endocarditis, an infection of the endocardium (inner heart lining) commonly affects the valvular leaflets and causes murmur.
Calcification deposits on the valve leaflets create an audible murmur.
Rheumatic fever, which is an autoimmune disease (typically associated with Group A streptococcal infection) affects the leaflets and causes murmur.
Congenital defects of the valves can also be heard on heart auscultation.
Pressure Graphs:
Pressure graphs illustrate changes in aortic, left ventricular, and left atrial pressures during a cardiac cycle; if you are unfamiliar with these graphs, you may want to review our tutorial on the Wigger's diagram.
Normal blood flow and pressures in the left side of the heart:
– The left atrium is characterized by low blood pressure, approximately 10 mmHg; this allows passive blood flow to the ventricle.
– Blood pressure in the left ventricle is 120 mmHg during systole, 10 during diastole.
– Aortic pressure is 120/80. Notice that aortic and ventricular pressures during systole are the same.
Valvular insufficiency, aka, regurgitation
Mitral valve regurgitation
Phonocardiogram:
Characterized by a high-pitched holosystolic murmur that lasts from S1 to S2.
Aortic valve regurgitation
Anatomical and physiological effects:
Faulty aortic valve allows "backflow" of blood to the left ventricle.
Because only a portion of blood remains in the aorta, its diastolic pressure falls.
The blood that "backflows" into the ventricle combines with blood from the atria, increasing ventricular preload.
Thus, stroke volume and systolic aortic pressures increase.
Furthermore, increased ventricular filling and pressure causes blood to "back up" and raise pressure in the left atrium and pulmonary veins.
As in mitral valve insufficiency, chronic overload leads to atrial and ventricular dilation to increase compliance and mitigate pressure changes.
In graphical form:
Atrial and ventricular pressures increase.
Systolic aortic pressure is increased, but diastolic pressure is reduced (and, therefore, aortic pulse pressure is increased).
Phonocardiogram:
Characterized by high-pitched murmur is heard after S2.
Clinical Correlation:
Aortic valve insufficiency can lead to heart failure, and is characterized clinically by "head bobbing," aka, Corrigan's Sign, aka, dancing carotids, in which carotid pulsation is easily visible in the neck.
Valvular Stenosis
Mitral Valve Stenosis
Anatomical and physiological effects:
Stiffened mitral valve raises the pressure gradient between the atrium and ventricle and creates blood flow turbulence.
To effectively move blood into the ventricle across the valve, the atrial muscle must generate additional force; it hypertrophies to meet this demand, and pressure is increased.
The opposite occurs in the ventricle, where filling and pressure are reduced.
Consequently, stroke volume, aortic pressure, and, in the absence of compensatory mechanisms, cardiac output, are reduced.
In graphical form:
Ventricular and aortic pressure are reduced.
Left atrial pressure is increased
We shade the area between the atrial and ventricular pressure curves to highlight the unusually high pressure gradient between them.
Phonocardiogram:
The weak diastolic murmur occurs after the opening snap; notice that this delay after S2 distinguishes the diastolic murmur of mitral valve stenosis from that of aortic valve regurgitation.
Aortic Valve Stenosis
In graphical form:
Pressure in both chambers is elevated.
Aortic pressure is drastically reduced during systole, which increases the pressure gradient between the aorta and the left ventricle.
Phonocardiogram:
Very loud systolic murmur with a crescendo-decrescendo pattern. Notice that this differentiates it from the murmur heard in mitral valve regurgitation, which is steadier.
Systolic vs. Diastolic murmurs
Clinical Correlation: Atrial Hypertrophy
Complications of valvular lesions
Heart failure and pulmonary edema; enlargement of the atria can cause atrial fibrillation when cardiac electrical signals have to travel increased distances through the atrial wall.