Interrupted Aortic Arch — #2 Pathophysiology

Date
November 8, 2025
URL
https://x.com/WithAScalpel/status/1987158890887205008?s=20
Categories
Interrupted Aortic Arch

Interrupted Aortic Arch — #2 Pathophysiology

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Definition and dependency.

Interrupted aortic arch (IAA) is a complete discontinuity between the ascending and descending aorta that renders systemic output to the distal body entirely ductal-dependent via the patent ductus arteriosus (PDA). The ascending aorta perfuses the coronaries and head–neck vessels, whereas the lower body depends on right-to-left flow from the main pulmonary artery across the PDA [1].

Anatomic context and associations.

IAA is classified by the Celoria–Patton scheme into Types A, B, and C according to the site of interruption; Type B (between the left common carotid and left subclavian arteries) is most frequent, accounting for ~80–85% of cases [1, 2]. Intracardiac anomalies are present in the vast majority, most commonly a ventricular septal defect (VSD), and lesions of the left heart–aorta complex are frequent, including subaortic narrowing or a hypoplastic aortic valve/annulus [3, 4].

Core physiology.

Because the distal aorta is supplied from the pulmonary artery through the PDA, IAA constitutes a ductal-dependent systemic circulation. In utero this arrangement is well tolerated; after birth, any reduction in ductal caliber compromises lower-body perfusion, leading to lactic acidosis, oliguria, weak/absent femoral pulses, and rapid shock, while preductal (coronary/cerebral) perfusion may remain relatively preserved as these vessels arise proximal to the interruption.

Oxygenation pattern (differential cyanosis).

Arterial oxygen saturation reflects intracardiac mixing and the interruption level:

  • Upper body (preductal) blood derives from the LV–ascending aorta and is typically better oxygenated.
  • Lower body (postductal) blood derives from the pulmonary artery via the PDA and is typically less oxygenated.

    • This produces preductal–postductal saturation differences (pink right hand, cyanotic lower extremities); the magnitude varies with Type A/B/C anatomy, ductal resistance, and pulmonary vascular resistance (PVR) [5].

LV outflow considerations.

Posterior malalignment of the infundibular (conal) septum and related subaortic narrowing can create LV outflow tract (LVOT) obstruction, further restricting antegrade flow into the ascending aorta and increasing reliance on ductal perfusion of the lower body. VSD morphology in IAA often reflects this conal malalignment and may contribute to outflow gradients [4].

Hemodynamic interplay.

  • Qp:Qs hinges on PVR and ductal resistance. As PVR falls after birth, pulmonary runoff may increase; however, if the PDA constricts, systemic output to the lower body collapses despite adequate pulmonary flow.
  • PDA shunt direction is usually right-to-left to supply the descending aorta when PVR ≥ systemic vascular resistance; it can become bidirectional with changing loading conditions, altering oxygen delivery to the lower body.

Clinical picture.

Tachypnea without frank pulmonary edema, differential cyanosis, cool lower extremities with poor pulses, metabolic acidosis, and low cardiac output are typical. A loud single S2 and a VSD murmur are common; a ductal murmur may be soft or absent.

Immediate management pearls.

  • Initiate prostaglandin E₁ (PGE₁) promptly to (re)establish ductal patency and restore postductal systemic flow [6, 7].
  • Optimize ventilation and perfusion while avoiding ductal constrictors (e.g., hyperoxia, alkalosis).
  • Correct acidosis and hypoglycemia; closely monitor renal and intestinal perfusion.

    • Definitive therapy is early arch repair (often single-stage with VSD closure and relief of LVOT obstruction when present), which has evolved with contemporary strategies to improve survival [8].

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References

[1] Celoria GC, Patton RB. Congenital absence of the aortic arch. Am Heart J. 1959;58:407-413.

[2] Schreiber C, Hörer J, Vogt M, et al. The interrupted aortic arch: an overview after 20 years of surgical treatment. Eur J Cardiothorac Surg. 1997;12(3):415-422.

[3] Reardon MJ, Hallman GL, Cooley DA. Interrupted aortic arch: Brief review and summary of an eighteen-year experience. Tex Heart Inst J. 1984;11(3):250-259.

[4] Freedom RM, Culham JAG, Rowe RD. Ventricular septal defect in interruption of aortic arch. Am J Cardiol. 1977;40(3):435-442.

[5] Galvis MMO, Sankaranarayanan S, Yarrarapu SNS. Cyanotic Heart Disease. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023.

[6] Akkinapally S, Natarajan G. Prostaglandin E1 for maintaining ductal patency in neonates with ductal-dependent cardiac lesions. Arch Dis Child Fetal Neonatal Ed. 2018;103(1):F67-F70.

[7] Radford DJ, Izukawa T, Rowe RD. Prostaglandin E1 for interrupted aortic arch in the neonate. Lancet. 1976;2(7976):95.

[8] Jonas RA, Mayer JE Jr, Cook NR, et al. Outcomes in patients with interrupted aortic arch and ventricular septal defect. J Thorac Cardiovasc Surg. 1994;107(3):676-691.