Med Quizzes

Left-to-Right Shunts

Left-to-Right Shunts Cheatsheet

Key Concept: L-to-R shunts cause pulmonary overcirculation and worsen as PVR drops at 4–8 weeks. VSD = holosystolic murmur. PDA = continuous murmur + bounding pulses. Eisenmenger = irreversible PVR elevation → shunt reversal → cyanosis. Fetal circulation = high PVR, R→L shunts.

Category	Key Features
VSD Pathophysiology	L→R shunt through interventricular septum Holosystolic murmur at left lower sternal border Palpable thrill if large shunt volume Symptoms worsen at 4–8 weeks as PVR falls and shunt volume increases Pulmonary edema → rales + respiratory distress Hepatomegaly from right heart backup Diuretics + caloric supplementation until surgical repair
PVR & Shunt Timing	Fetal PVR is HIGH → little L-to-R shunting immediately after birth PVR falls over weeks → shunt volume increases → symptoms appear at 4–8 weeks Persistently high PVR (Eisenmenger) → shunt reversal R→L → cyanosis Eisenmenger physiology is irreversible — early repair prevents it Diaphoresis with feeds — high sympathetic tone from heart failure
PDA Pathophysiology	L→R shunt through ductus arteriosus Continuous (machinery) murmur best heard at left infraclavicular area Bounding peripheral pulses + widened pulse pressure Disproportionately affects premature infants (ductus fails to close) Indomethacin (COX inhibitor) promotes closure in premature infants Surgical or catheter ligation if medical therapy fails
Normal Fetal Circulation	Fetal circulation: high PVR + low SVR → R→L shunts via PDA + foramen ovale Oxygenated blood from placenta via umbilical vein → ductus venosus → IVC Fetal lungs deflated — minimal pulmonary blood flow At birth: lungs inflate → PVR falls dramatically Ductus arteriosus closes functionally (oxygen ↑ + PGE2 ↓) Foramen ovale closes functionally at birth; anatomic closure by 3–6 months

Press / or Esc to close

Left-to-Right Shunts

A VSD Pathophysiology

B PVR & Shunt Timing

C PDA Pathophysiology

D Normal Fetal Circulation