Types of Systolic Murmurs:

1. Ejection Murmurs (Midsystolic)

   • These murmurs occur between S1 and S2, caused by blood flow through narrowed or stenotic valves.
   • Aortic Stenosis: A harsh, crescendo-decrescendo murmur best heard at the right upper sternal border, radiating to the neck.
   • Pulmonic Stenosis: Similar to aortic stenosis, but heard best at the left upper sternal border.

2. Regurgitant Murmurs (Holosystolic/Pansystolic)

   • These are heard throughout systole and are caused by blood flowing back through incompetent valves.
   • Mitral Regurgitation: A blowing, high-pitched murmur best heard at the apex, radiating to the axilla.
   • Tricuspid Regurgitation: Best heard at the left lower sternal border, often increases with inspiration.

3. Late Systolic Murmurs

   • These start after the mid-point of systole and continue until S2.
   • Mitral Valve Prolapse (MVP): Characterized by a mid-systolic click followed by a late systolic murmur, best heard at the apex.

Causes of Systolic Murmurs

1. Ejection Systolic Murmurs (Midsystolic)

These murmurs are caused by turbulence due to blood flow through narrowed valves or increased flow across normal valves.

• Aortic Stenosis: Narrowing of the aortic valve, leading to obstruction of blood flow from the left ventricle to the aorta. Causes include:
  • Degenerative calcification (common in older adults)
  • Congenital bicuspid aortic valve
  • Rheumatic heart disease
• Pulmonic Stenosis: Narrowing of the pulmonary valve, causing obstruction of blood flow from the right ventricle to the pulmonary artery. Causes include:
  • Congenital heart defects (e.g., tetralogy of Fallot)
  • Rheumatic heart disease (rare)
• Hypertrophic Obstructive Cardiomyopathy (HOCM): Thickening of the heart muscle (particularly the septum), leading to obstruction of blood flow during systole.

2. Regurgitant Systolic Murmurs (Holosystolic/Pansystolic)

These murmurs occur due to the backward flow of blood through an incompetent valve.

• Mitral Regurgitation: Caused by the failure of the mitral valve to close properly, leading to blood flow back into the left atrium during systole. Causes include:
  • Mitral valve prolapse
  • Rheumatic heart disease
  • Ischemic heart disease (post-myocardial infarction)
  • Infective endocarditis
• Tricuspid Regurgitation: Blood flows backward into the right atrium during systole due to tricuspid valve incompetence. Causes include:
  • Right ventricular dilation (from conditions like pulmonary hypertension)
  • Rheumatic heart disease
  • Congenital defects (e.g., Ebstein anomaly)
  • Infective endocarditis
• Ventricular Septal Defect (VSD): An abnormal opening in the ventricular septum allows blood to flow from the left ventricle to the right ventricle during systole. Causes include:
  • Congenital heart defects (often diagnosed in childhood)

3. Late Systolic Murmurs

These murmurs start after the mid-point of systole and are typically associated with mitral valve prolapse.

• Mitral Valve Prolapse (MVP): A condition in which the mitral valve leaflets bulge (prolapse) into the left atrium during systole. This can lead to mitral regurgitation. Causes include:
  • Myxomatous degeneration of the mitral valve
  • Connective tissue disorders (e.g., Marfan syndrome, Ehlers-Danlos syndrome)

4. Other Causes

• Increased Flow States: High-output states can cause systolic murmurs due to increased blood flow across normal valves. These include:
  • Pregnancy
  • Anemia
  • Hyperthyroidism
  • Fever
  • Sepsis

Pathophysiology of Systolic Murmurs

1. Aortic Stenosis

• Pathophysiology: Aortic stenosis is characterized by a narrowing of the aortic valve opening, which causes increased resistance to blood flow from the left ventricle into the aorta during systole. As the left ventricle contracts, it must generate higher pressures to overcome this obstruction. Over time, this increased workload leads to left ventricular hypertrophy (LVH).
  • The turbulent blood flow through the narrowed valve produces a crescendo-decrescendo (ejection) murmur.
  • The reduced blood flow into the systemic circulation leads to decreased cardiac output, potentially causing symptoms like angina, syncope, and heart failure.

2. Mitral Regurgitation

• Pathophysiology: Mitral regurgitation occurs when the mitral valve fails to close completely during systole, causing blood to flow backward from the left ventricle into the left atrium. This backflow increases left atrial pressure and volume.
  • The left ventricle must pump not only the normal systemic output but also the regurgitated volume, leading to left ventricular dilation over time.
  • The regurgitant flow produces a holosystolic murmur that is high-pitched and heard best at the apex.
  • Chronic mitral regurgitation leads to left atrial dilation, pulmonary hypertension, and eventually right-sided heart failure.

3. Ventricular Septal Defect (VSD)

• Pathophysiology: A VSD is an abnormal opening in the interventricular septum that allows blood to flow from the left ventricle (higher pressure) to the right ventricle (lower pressure) during systole. This shunt increases the volume load on the right side of the heart and the pulmonary circulation.
  • The murmur is holosystolic, best heard at the left lower sternal border, and is due to the turbulent flow across the septal defect.
  • If large, the left-to-right shunt can lead to pulmonary hypertension, right ventricular hypertrophy, and eventual Eisenmenger syndrome, where the shunt reverses, causing cyanosis.

4. Hypertrophic Obstructive Cardiomyopathy (HOCM)

• Pathophysiology: HOCM is characterized by abnormal thickening of the ventricular septum, which can obstruct blood flow during systole. The left ventricle must work harder to pump blood through the narrowed outflow tract, leading to increased ventricular pressure.
  • The obstruction creates a crescendo-decrescendo systolic murmur similar to aortic stenosis, but it is often louder with reduced preload (e.g., standing) and softer with increased preload (e.g., squatting).
  • This condition can lead to diastolic dysfunction and an increased risk of arrhythmias and sudden cardiac death.

5. Mitral Valve Prolapse (MVP)

• Pathophysiology: In MVP, one or both mitral valve leaflets bulge into the left atrium during systole, sometimes allowing blood to flow back into the left atrium (mitral regurgitation). The prolapsing leaflet creates the characteristic mid-systolic click, followed by a late systolic murmur if regurgitation is present.
  • MVP is often benign but can lead to progressive mitral regurgitation and associated complications like atrial fibrillation or infective endocarditis.

6. Pulmonic Stenosis

• Pathophysiology: Pulmonic stenosis involves narrowing of the pulmonic valve, leading to increased resistance to right ventricular outflow. The right ventricle must generate higher pressure to overcome the obstruction, which can lead to right ventricular hypertrophy over time.
  • The turbulent flow across the stenotic pulmonic valve produces an ejection systolic murmur, best heard at the left upper sternal border.

7. Increased Flow States

• Pathophysiology: In conditions like anemia, hyperthyroidism, and pregnancy, increased blood flow across normal valves can produce systolic murmurs. These are typically functional or physiological murmurs, meaning there is no underlying structural heart disease.
• The murmur is usually soft and systolic, caused by the increased volume and velocity of blood flow through the heart.