Leadless pacemaker implantation and azygos continuation in the inferior vena cava: a case description

Azygos continuation (AC) of the inferior vena cava (IVC), also known as the absence of the hepatic segment of the IVC with AC, is a rare anatomic variant in the general population with an incidence of 0.6% (1). AC of the IVC is congenital and independent from other anatomical variants. It is primarily caused by the absence or hypoplasia of the IVC’s hepatic segment. The IVC below the hepatic segments flows upward through the azygos into the superior vena cava (SVC) and eventually drains into the right atrium. The renal portion of the IVC receives blood flow from the kidneys and lower extremities and drains into the SVC through the azygos vein. The azygos vein, azygos arch, and SVC dilate to accommodate the increase in blood flow (2). Usually, AC in the IVC is asymptomatic and does not affect the functionality of the cardiovascular system. However, it significantly impacts leadless pacemaker (LP) implantation via the femoral vein. The LP is a feasible alternative to the single-ventricle pacemaker; that is, a pacemaker that simply paces the ventricle but not the atrium. LP is a novel technique that differs from traditional pacemakers in terms of the electronic components, implantation procedure, possible complications, and postoperative management. Unlike the conventional pacemaker implantation, where the lead is delivered to the heart by puncturing the subclavian veins to approach the SVC, the LP implantation involves puncturing the femoral vein and delivering the LP to the heart via the IVC (3). If a patient has AC of the IVC, an LP cannot be implanted through the IVC pathway or could be delivered to the wrong location, such as the SVC. Furthermore, routine preoperative examinations (e.g., cardiac ultrasound and chest X-ray) are ineffective in detecting AC. Herein, we report a case of AC of the IVC observed during LP implantation, which resulted in the abandonment of this procedure. Electrocardiogram (ECG)- gated computed tomography (CT) venography was used to identify the anatomic variant of the IVC as an AC. This patient eventually underwent conventional pacemaker implantation via the SVC.