Guyton and Hall Physiology Chapter 23 - Heart Valves and Heart Sounds

Tetralogy of Fallot

• Four heart abnormalities occur simultaneously:

  • Aorta originates from the right ventricle instead of the left ventricle
  • Pulmonary artery stenosis causes decreased blood flow from the right ventricle to the lungs
  • Blood flows from the left ventricle through a ventricular septal hole into the right ventricle and then into the aorta
  • Enlarged right ventricle due to pumping against high pressure in the aorta

• Tetralogy of Fallot often leads to cyanosis (blue coloration) in babies

• Most of the venous blood bypasses the lungs and is shunted directly into the aorta, leading to unoxygenated blood.

Surgical Treatment

• Surgical procedure involves:
  • Opening the pulmonary stenosis
  • Closing the septal defect
  • Reconstructing the flow pathway into the aorta
• Surgical treatment is effective in increasing life expectancy from 3-4 years to 50+ years.

Causes of Congenital Anomalies

• Congenital heart disease occurs in about 8 out of every 1000 live births
• Common causes include maternal viral infections, particularly German measles during the first trimester
• Certain medications like ACE inhibitors and isotretinoin, alcohol or drug abuse during pregnancy can increase risk
• Some defects are hereditary.

Extracorporeal Circulation During Cardiac Surgery

• Extracorporeal circulation (heart-lung machines) is used during cardiac surgery to take over the function of the heart and lungs
• This system consists of a pump and an oxygenating device
• This is necessary because it’s almost impossible to repair intracardiac defects while the heart is beating.

Abnormal Circulatory Dynamics in Congenital Heart Defects

• Stenosis: Narrowing of a blood flow channel in the heart or major blood vessels
• Left-to-right shunt: Abnormal blood flow from the left side of the heart or aorta to the right side of the heart or pulmonary artery, bypassing systemic circulation
• Right-to-left shunt: Abnormal blood flow from the right side of the heart directly into the left side of the heart, bypassing the lungs

Heart Muscle Hypertrophy

• Enlargement of the heart muscle due to pressure overload, often associated with valvular and congenital heart disease.
• Can lead to:
  • Ischemia due to disproportionate muscle growth compared to coronary blood flow
  • Angina
  • Arrhythmias
  • Increased risk of sudden death from fibrillation

Coarctation of the Aorta

• Narrowing of the aorta, often above the diaphragm
• Causes higher blood pressure in the upper body compared to the lower body
• Blood flow to the lower body is affected, requiring circulation through smaller collateral arteries

Patent Ductus Arteriosus (PDA)

• Open ductus arteriosus (a blood vessel connecting the aorta and pulmonary artery in the fetus) remaining open after birth
• Often closes within a few hours or days after birth
• Can lead to a "machinery murmur" in the pulmonary artery area
• Surgical treatment involves ligation (tying off) or division of the PDA.
  • Catheter-based devices are often used for larger infants and children.

Heart Sounds

• The first heart sound ("lub") is associated with the closure of the atrioventricular (A-V) valves at the beginning of systole.
• The second heart sound ("dub") is associated with the closure of the semilunar (aortic and pulmonary) valves at the end of systole.
• The third heart sound can be normal in children and young adults but usually indicates systolic heart failure in older adults.
• The fourth heart sound is rarely heard with a stethoscope but can be recorded with a phonocardiogram.
• The fourth heart sound occurs when atria contract, caused by the inrush of blood into the ventricles.

Valvular Lesions

• Rheumatic fever, an autoimmune disease, can damage or destroy heart valves.
• Rheumatic fever is often triggered by a streptococcal infection.
• Senile calcific aortic valve stenosis is characterized by valve calcium deposition and ossification, leading to narrowing of the aortic valve orifice.

Congenital Heart Defects

• Congenital heart defects occur in approximately 8 out of every 1000 live births.
• A viral infection in the mother during the first trimester of pregnancy is a common cause of congenital heart defects.
• German measles (rubella) contracted by the mother during the first trimester of pregnancy significantly increases the risk for heart defects in the developing fetus.
• Other risk factors for congenital heart defects include certain medications, alcohol or drug abuse during pregnancy.

Tetralogy of Fallot

• Tetralogy of Fallot is a complex congenital heart defect involving four simultaneous abnormalities:
  • The aorta originates from the right ventricle rather than the left and overrides a hole in the septum.
  • The pulmonary artery is stenosed, limiting blood flow from the right ventricle to the lungs.
  • Blood from the left ventricle flows through a ventricular septal hole into the right ventricle.
  • The right ventricle is enlarged due to pumping blood against high pressure.
• Tetralogy of Fallot can be successfully treated with surgery.

Patent Ductus Arteriosus

• The ductus arteriosus is a blood vessel connecting the aorta to the pulmonary artery in the fetal circulation.
• The ductus arteriosus usually closes shortly after birth due to the increased oxygen concentration in the aorta, constricting the muscle in the ductus wall.
• Patent ductus arteriosus occurs when the ductus does not close, causing backflow of blood from the aorta into the pulmonary artery.
• A patent ductus arteriosus can usually be successfully treated with surgery.

Heart Sounds

• The first heart sound, "lub", is about 0.14 seconds long and caused by the closure of the A-V valves (tricuspid and mitral valves) at the onset of ventricular systole
• The second heart sound, "dub", is about 0.11 seconds long and caused by the closure of the semilunar valves (aortic and pulmonary valves)
• The duration of the second heart sound is shorter due to the semilunar valves being tauter than the A-V valves
• The frequency of the heart sounds ranges from 40 to 500 cycles/sec, but a larger portion of sound is below the audible range and can be recorded electronically by phonocardiography

Aortic Stenosis

• Aortic valve stenosis refers to a narrowing of the aortic valve, restricting blood flow from the left ventricle to the aorta
• It can lead to an increase in intraventricular diastolic pressure, potentially compressing inner layers of the heart muscle and reducing coronary blood flow
• Severe aortic stenosis can cause ischemia of the heart muscle due to reduced blood flow to the heart tissue

Aortic Regurgitation

• Aortic regurgitation is a backflow of blood from the aorta into the left ventricle during diastole
• It also causes an increase in intraventricular diastolic pressure, potentially compressing inner layers of the heart muscle and reducing coronary blood flow
• Aortic diastolic pressure decreases in aortic regurgitation, further contributing to the reduced coronary blood flow and potential ischemia

Left Ventricular Failure and Pulmonary Edema

• In the early stages of aortic valve stenosis or regurgitation, the left ventricle can adapt to increased loads, preventing significant circulatory dysfunction during rest
• However, these conditions can eventually lead to left ventricular failure, causing a decline in cardiac output and the development of pulmonary edema
• Pulmonary edema develops due to the failure of the left ventricle to effectively pump blood, leading to fluid buildup in the lungs

Mitral Valvular Disease

• Mitral valvular disease refers to conditions affecting the mitral valve, including mitral stenosis, narrowing of the mitral valve, and mitral regurgitation, backflow of blood from the left ventricle to the left atrium
• In the early stages, the heart compensates for the mitral valvular disease by increasing blood volume, potentially reducing renal excretion of water and salt
• This increased blood volume improves venous return to the heart, mitigating the effects of cardiac debility
• However, in late stages, atrial fibrillation can occur, further reducing cardiac pumping effectiveness and exacerbating cardiac debility

Congenital Heart Defects

• Congenital anomalies of the heart refer to malformations that occur during fetal development
• Three major types include: stenosis, narrowing of blood flow channels, left-­to-­right shunt, blood flow from the left side of the heart to the right side, and right-­to-­left shunt, blood flow from the right side of the heart to the left side
• Some congenital defects, like aortic valve stenosis, mimic the effects of acquired conditions
• Some congenital heart defects are hereditary and can be found in twins and succeeding generations

Cardiac Hypertrophy

• Cardiac hypertrophy is an enlargement of the heart muscle, often occurring in response to increased workload
• It can be caused by valvular and congenital heart diseases, resulting in increased pressure against which the heart muscle must contract
• Cardiac hypertrophy can lead to detrimental effects, including relative ischemia, increased susceptibility to arrhythmias, and sudden death due to fibrillation

Extracorporeal Circulation

• Extracorporeal circulation is used during cardiac surgery to replace the function of the heart and lungs
• It consists of a pump and an oxygenating device that circulate blood outside the body, allowing for open-heart surgery

References

• J Am Coll Cardiol 71:2058, 2018
• Circ Res 113:223, 2013
• JAMA 310:1490, 2013
• N Engl J Med 379:655, 2018
• J Am Coll Cardiol 73:1978, 2019
• Circulation 135:e1159, 2017
• Curr Cardiol Rev 14:264, 2018
• Lancet 387:1335, 2016

This quiz covers the key aspects of Tetralogy of Fallot, including its four heart abnormalities and the associated surgical treatments. Understand how these congenital heart defects lead to symptoms like cyanosis and learn about the effectiveness of surgical intervention in improving life expectancy.