What is patent ductus arteriosus (PDA), the significance of a displaced point of maximal impulse (PMI), and the anatomy of the heart including atria, ventricles, and valves?

Patent Ductus Arteriosus, Point of Maximal Impulse, and Heart Anatomy

Patent Ductus Arteriosus (PDA)

Patent ductus arteriosus is a congenital cardiovascular finding in which the ductus arteriosus, a vascular connection between the aorta and pulmonary artery present in fetal life, remains open beyond the normal age of spontaneous closure. 1

Epidemiology and Pathophysiology

• PDA is found in approximately 0.3% to 0.8% of term infants and is twice as common in females as males 1
• The clinical manifestations depend on the size of the vessel and the relative systemic and pulmonary vascular resistances 1
• PDAs range from small hemodynamically insignificant lesions to large ones causing congestive heart failure and pulmonary hypertension 1

Classification by Severity

• Trivial/silent PDA: Hemodynamically insignificant; no murmur on auscultation 1
• Small/audible PDA: Likely hemodynamically insignificant; murmur heard on auscultation 1
• Moderate to large PDA: Likely hemodynamically significant 1

Clinical Presentation

• Small PDA: Often asymptomatic with normal left ventricle and pulmonary artery pressure 1
• Moderate PDA with predominant LV volume overload: Large LV with normal or reduced function; may present with left heart failure 1
• Moderate PDA with predominant pulmonary arterial hypertension: Pressure-overloaded right ventricle; may present with right heart failure 1
• Large PDA: May develop Eisenmenger physiology with differential hypoxemia and differential cyanosis (lower extremities cyanotic, sometimes left arm too) 1

Diagnostic Evaluation

• Oxygen saturation measurement should be performed in feet and both hands to assess for right-to-left shunting 1
• Echocardiography is the key diagnostic technique to confirm diagnosis, assess LV volume overload, pulmonary artery pressure, and right heart changes 1
• Cardiac catheterization is useful in patients with suspected pulmonary hypertension 1
• CMR/CT may be indicated for additional quantification of LV volumes or evaluation of pulmonary artery anatomy 1

Management

• PDA closure is recommended if left atrial or LV enlargement is present and attributable to PDA with net left-to-right shunt, PA systolic pressure <50% systemic and pulmonary vascular resistance <1/3 systemic 1
• PDA closure may be considered with net left-to-right shunt if PA systolic pressure is ≥50% systemic, and/or pulmonary vascular resistance >1/3 systemic 1
• PDA closure should not be performed in adults with net right-to-left shunt and PA systolic pressure >2/3 systemic or pulmonary vascular resistance >2/3 systemic 1
• Device closure is the method of choice when technically suitable 1

Point of Maximal Impulse (PMI)

The point of maximal impulse is the most lateral and inferior point on the precordium where the cardiac apex beat is palpable, representing the apex of the left ventricle striking the chest wall during systole.

Normal Location

• The PMI is typically located in the 5th intercostal space at or medial to the midclavicular line
• In adults, it is normally 1-2 cm in diameter

Significance of Displaced PMI

• Lateral displacement: Indicates left ventricular enlargement (dilation or hypertrophy) due to conditions such as:
  • Aortic regurgitation
  • Mitral regurgitation
  • Dilated cardiomyopathy
  • Volume overload states
• Medial displacement: May indicate:
  • Right ventricular enlargement pushing the left ventricle laterally
  • Dextrocardia
• Inferior displacement: May indicate:
  • Left ventricular dilation
  • Aortic regurgitation
• Superior displacement: May indicate:
  • Left atrial enlargement
  • Elevation of the diaphragm

Clinical Assessment

• Palpate with patient in left lateral decubitus position for optimal assessment
• Assess for size, location, amplitude, and duration of the impulse
• An enlarged, sustained, or forceful PMI suggests left ventricular hypertrophy
• A diffuse PMI suggests left ventricular dilation

Heart Anatomy and Blood Flow

Chambers of the Heart

• Right Atrium (RA): Receives deoxygenated blood from the superior vena cava, inferior vena cava, and coronary sinus
• Right Ventricle (RV): Receives blood from the right atrium and pumps it to the pulmonary artery
• Left Atrium (LA): Receives oxygenated blood from the pulmonary veins
• Left Ventricle (LV): Receives blood from the left atrium and pumps it to the aorta

Heart Valves

• Tricuspid valve: Between the right atrium and right ventricle
• Pulmonary valve: Between the right ventricle and pulmonary artery
• Mitral valve: Between the left atrium and left ventricle
• Aortic valve: Between the left ventricle and aorta

Direction of Blood Flow

1. Deoxygenated blood enters the right atrium from the body via the superior and inferior vena cavae
2. Blood flows through the tricuspid valve into the right ventricle
3. The right ventricle contracts, pushing blood through the pulmonary valve into the pulmonary artery
4. Blood travels to the lungs where it becomes oxygenated
5. Oxygenated blood returns to the left atrium via the pulmonary veins
6. Blood flows through the mitral valve into the left ventricle
7. The left ventricle contracts, pushing blood through the aortic valve into the aorta
8. Oxygenated blood is distributed to the body through the systemic circulation

[Note: A diagram would be included here showing the heart with labeled chambers, valves, and arrows indicating blood flow direction]