14.2 Lecture Heart Sounds and Rheumatic Fever

• S1 heart sound results from the vibration of the AV valves and adjacent heart walls immediately after closure.
• S1 occurs at the beginning of ventricular systole.
• S2 heart sound is caused by the sudden closure of the semilunar valves.
• S2 occurs when the semilunar valves bulge, recoil, and cause blood to flow back into the arteries.
• S3 heart sound is caused by blood filling the ventricles from the atria.
• S4 heart sound is caused by the inrush of blood from the atria into the ventricles during atrial contraction.
• S4 cannot usually be heard with a stethoscope.

Rheumatic Fever

• Rheumatic fever is an autoimmune disease targeting areas, including heart valves.
• Rheumatic fever causes large lesions on the inflamed edges of the valves.
• The mitral valve is most seriously affected due to the trauma it undergoes.
• Lesions can cause adjacent valve leaflets to stick together.
• Scar tissue can form, permanently fusing the valve.
• Valves can become so destroyed that they cannot close properly, causing regurgitation.

Aortic Stenosis

• Aortic stenosis involves a narrowing of the aortic valve orifice.
• Aortic stenosis leads to outflow obstruction of the left ventricle.
• Aortic stenosis causes increased workload and concentric hypertrophy.
• Under resting conditions, the ejection fraction may be normal, but heart failure symptoms appear with moderate exercise.
• Ventricular pressure can rise to 300 mm of mercury, while aortic pressure remains normal.
• Aortic stenosis can cause a nozzle effect and severe turbulence in the aorta.
• Aortic stenosis results in an intense, harsh sound during systole.
• The sound of aortic stenosis can sometimes be heard several feet away from the patient.
• Regurgitation causes diastolic blowing murmurs as blood jets backward into the left ventricle.

Mitral Regurgitation

• Mitral regurgitation involves backwards blood flow through the mitral valve into the left atrium during systole.
• Mitral stenosis refers to the narrowing of the mitral valve between the left atrium and ventricle.
• With mitral stenosis, that the left atrium pressure does not rise and the usual heart sound is weak and has a low frequency.

Aortic Stenosis vs. Aortic Regurgitation

• In aortic stenosis, the left ventricle fails to empty adequately.
• In aortic regurgitation, blood flows backward into the ventricle after contraction.
• Stroke volume is reduced in both aortic stenosis and aortic regurgitation due to the increased workload.
• Muscular hypertrophy occurs in both aortic stenosis and aortic regurgitation.
• The increased volume of blood caused by the aortic regurgitation causes eccentric enlargement of the left ventricle.
• Hypertrophy needed to develop high pressures of the stenosis creates a thickened wall and a smaller chamber.
• Concentric hypertrophy occurs due to stenosis.
• Stenosis and regurgitation increase the need for coronary oxygen delivery.
• Blood flow to the coronary musculature can be decreased due to increased wall tension.

Left Ventricular Failure

• With regurgitation, the left ventricle dilates and cardiac output falls, causing a backup of blood into the left atrium.
• Left atrium pressure rises progressively to above a pressure of about 25, which is when edema can begin to appear in the lungs.
• High left atrial pressure causes enlargement of the atrium.
• Enlargement of the atrium increases the distance of the cardiac action potential pathway.
• Lengthening of the track from atrial enlargement can cause the development of movement circuits, leading to atrial fibrillation.

Congenital Heart Defects

• Congenital heart defects include stenosis somewhere in the heart.
• Congenital heart defects include left-to-right shunt, which allows blood to flow backwards from the left side of the heart to the right side of the heart
• Congenital heart defects include a right-to-left shunt, which allows deoxygenated blood to flow directly from the right side of the heart to the left side of the heart, and therefore to the body without passing the lungs.

Patent Ductus Arteriosus

• A special artery in the fetus connects the pulmonary artery with the aorta.
• High pulmonary pressures and low aortic pressures in utero causes blood to flow through this artery, bypassing the lungs.
• As the fetus takes a breath, the lungs inflate and decrease the resistance to blood flow causing aortic pressure to rise due to the loss of placental circulation.
• The new high oxygen concentration in the ductus and the backward flow causes constriction and occlusion of the ductus.
• High arterial oxygen concentration washing out inflammatory enzymes closes the ductus.
• Patent ductus arteriosus does not cause dysfunction in early life, but as the child ages, one-half to two-thirds of the blood flows backwards through the ductus into the pulmonary artery.
• Blood flows back through the lungs multiple times, causing enlarged pulmonary circulation.
• The left ventricle pumps two to three times the normal cardiac output, causing cardiac reserve to be severely limited.
• High pressures in the pulmonary vessels from patent ductus arteriosus can lead to congestion and edema.
• Most patients with uncorrected patent ductus die from heart disease between the ages of 20 and 40.

Tetralogy of Fallot

• Tetralogy of Fallot is caused by four different defects that work together.
• Tetralogy of Fallot causes deoxygenated blood to be circulated from the heart.
• The four defects causing Tetralogy of Fallot:
  • An aorta originates from the right ventricle instead of the left.
  • Pulmonary artery stenosis causes little blood to travel to the lungs.
  • Ventricular septal defect causing blood to flow from the left to the right ventricle.
  • Right ventricular hypertrophy caused by the increased workload of the heart.
• As much as 75% of venous blood passes through the arterial circulation without becoming oxygenated in patients with Tetralogy of Fallot.
• Tetralogy of Fallot leads to blue baby syndrome.
• Average life expectancy is only three to four years without surgery, but can be as high as 50 years after surgery

Causes of Congenital Heart Defects

• Congenital heart disease occurs at a rate of eight in every 1,000 live births.
• Congenital defects have been found in monozygotic twins.
• Children of patients treated for congenital heart disease have a ten times greater chance of having heart disease themselves.