Chapter 8. Cardiology

See Chapter 32.

Cardiac Diseases Are Better Understood by Comparing Individual Patients' Physiologies with Basic Pathophysiologic Schemas. Sometimes the Physiology Is More Complex, Bridging Multiple Categories.

1. Myocardial dysfunction

   • Examples: Myocarditis, cardiomyopathies
   • Systolic (contraction) and diastolic (relaxation) dysfunction may be present in combination or separately. Cardiac output is limited because of ventricular dysfunction.
   • Signs and symptoms: Tachypnea, orthopnea, respiratory distress, poor perfusion, hepatomegaly, vomiting, anorexia.
   • Treatment (systolic dysfunction): Afterload reduction (ACE inhibitors), β-blockers, or both. Diuretic therapy helpful for volume overload. IV inotropic support may be necessary for severe, acute symptoms or end-organ dysfunction.

2. Volume overload

   • Examples: ASD, VSD, CAVC, PDA, unobstructed TAPVC, truncus arteriosus, single ventricle with ↑ pulmonary blood flow.
   • L → R shunting causes excess pulmonary blood flow (pulmonary overcirculation).
   • Symptoms depend on the degree of increase of pulmonary blood flow and in extreme cases may lead to decreased systemic blood flow (end organ hypoxia → lactic acidosis and multisystem organ failure). These derangements are reflected in the Qp:Qs ratio (the ratio of pulmonary blood flow to systemic blood flow.) The Qp:Qs ratio is influenced by the size of the defect, the difference between SVR and PVR, and the relative location of the dominant shunt (before or after the tricuspid valve).
   • Signs and symptoms: Tachypnea, retractions, feeding difficulties, failure to thrive, diaphoresis, poor perfusion. Left-sided obstructive lesions (eg, coarctation of the aorta) must be excluded, particularly in patients who present with symptoms in the first few days of life.
   • Treatment: Definitive treatment is through surgical or transcatheter correction. Temporizing measures include diuretics, avoidance of oxygen therapy (a potent pulmonary vasodilator), optimization of hemoglobin to improve systemic O2 delivery, permissive hypercapnia to induce pulmonary vasoconstriction (if intubated), infusions to increase cardiac output (IV inotropic agents and vasodilators).

3. Obstruction to systemic blood flow

   • Examples: Aortic valve stenosis, coarctation of the aorta, interrupted aortic arch, HLHS.
   • Obstruction causes increased afterload (ventricular pressure overload). In the most extreme cases, this reduces cardiac output (critical obstruction).
   • Systemic blood flow may be ductal dependent.
   • Signs and symptoms: Poor perfusion, weak pulses, metabolic acidosis, shock, respiratory failure; may be confused with neonatal sepsis.
   • Management: Early diagnosis, rapid intervention to restore systemic blood flow (PGE1, surgery, catheter-based intervention), mechanical ventilation, inotropic agents.

4. Obstruction to pulmonary blood flow

   • Examples: Pulmonary valve stenosis, pulmonary atresia, TOF.
   • Decreased pulmonary blood flow may also be seen with pulmonary venous obstruction.
   • Obstructed or diminished pulmonary blood flow may result in R → L shunting and systemic desaturation.
   • Pulmonary circulation may be ductal dependent.
   • Signs and symptoms: Cyanosis, hyperpnea, seizures, or shock if severely cyanotic (rare).
   • Treatment: PGE1, minimize RV outflow tract obstruction in TOF (sedation, increase preload, ± β-blocker, avoid inotropes), surgical or catheter-based intervention. In extreme cases when a definitive approach to increase pulmonary blood flow is not possible, maneuvers to increase SVR (eg, phenylephrine), minimize PVR (supplemental O2, sedation ± paralytic, lung recruitment, alkalinization with IV bicarbonate) should be used.

5. Transposition or parallel circulation

   • Example: d-TGA
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