Biology & Anatomy: How PA-IVS Affects the Heart

To understand Pulmonary Atresia with Intact Ventricular Septum (PA-IVS), it helps to first look at how a typical heart functions. In a normal heart, the right side is responsible for receiving oxygen-poor blood and pumping it through the pulmonary valve to the lungs ^[1]. In a baby with PA-IVS, anatomical differences change this entire process.

[Insert diagram of a normal heart vs. a PA-IVS heart here]

First, the pulmonary valve is “atretic,” meaning it is completely blocked or never formed, preventing blood from leaving the heart to get oxygen ^[2]. Second, the wall between the two lower chambers (the ventricular septum) is “intact,” meaning there is no hole (VSD) to let blood escape the right side of the heart ^[3]. These two factors create a high-pressure environment in the right ventricle that fundamentally changes how the heart develops.

The Right Ventricle and Tricuspid Valve

Because blood cannot exit through the pulmonary valve, the right ventricle (the lower right chamber) often becomes hypoplastic, or underdeveloped ^[4]. Since the heart is a muscle that grows based on the amount of work it does, the lack of blood flow through the right side often leads to a chamber that is much smaller and thicker than normal ^[1].

Doctors use the Tricuspid Valve (the “inlet” valve to the right ventricle) as a primary guide to measure this development. They calculate a Z-score, which compares your baby’s valve size to the average size for their weight ^[5].

• Z-score closer to normal (e.g., -2 or -1): Generally suggests the right ventricle is large enough that it might eventually be able to function normally (a biventricular repair) ^[6][7].
• Lower Z-scores (e.g., -4 or -5): May indicate the right ventricle is too small to handle the full job of pumping blood to the lungs, requiring a different surgical path ^[7].

The First Backdoor: The Atrial Septum

Because blood cannot exit the right ventricle, all oxygen-poor blood returning to the right side of the heart must cross over to the left side through a hole between the upper chambers (the atrial septum). This hole is typically a Patent Foramen Ovale (PFO) or an Atrial Septal Defect (ASD) ^[7]. This is a crucial “escape hatch.” If this hole is too small, the blood gets backed up, leading to severe lack of oxygen (cyanosis).

Sinusoids and VCACs: The Coronary “Backdoor”

When the right ventricle is blocked and under high pressure, it often looks for additional “relief valves.” During development, the heart may create abnormal channels called sinusoids or ventriculocoronary arterial communications (VCACs) ^[8].

These are essentially “backdoor” connections between the high-pressure right ventricle and the coronary arteries (the vessels that provide blood to the heart muscle itself) ^[9]. These connections are the heart’s attempt to deal with the trapped blood, but they significantly complicate how the heart functions.

Right Ventricle-Dependent Coronary Circulation (RVDCC)

In some cases, these abnormal connections become so dominant that the baby develops Right Ventricle-Dependent Coronary Circulation (RVDCC). This is a critical diagnosis where the heart muscle stops receiving its main blood supply from the aorta and instead depends on blood flowing backward from the high-pressure right ventricle through those sinusoids ^[10][11].

RVDCC is described as both a lifeline and a complication:

• The Lifeline: It is the only way the heart muscle is currently getting the blood it needs to stay alive while the baby is in the womb ^[11].
• The Complication: It prevents surgeons from simply “opening” the blocked pulmonary valve. If they were to release the pressure in the right ventricle, the “push” that sends blood into the coronary arteries would disappear, which could cause a heart attack (ischemia) because the heart muscle would lose its only blood supply ^[12][13].

Because of this, if RVDCC is present, the surgical team must often choose a single-ventricle pathway (like the Fontan procedure) to protect the heart muscle, rather than trying to make the right ventricle function normally ^[14][15]. Identifying whether these connections exist is one of the most important steps in your baby’s initial evaluation ^[5].