Review highlights overlooked PDA-PFO interplay in veterinary cardiology

A new narrative review in Veterinary Medicine and Science is drawing attention to a gap in veterinary cardiology: the underappreciated interplay between patent ductus arteriosus, or PDA, and patent foramen ovale, or PFO. The article by Amir Mohammad Barati examines how these two fetal shunts, both normal before birth and expected to close soon after delivery, may interact physiologically and pathophysiologically in ways that influence diagnosis and case interpretation, particularly in neonates.

That focus lands in a field where PDA is familiar territory, but PFO is often less emphasized unless it becomes hemodynamically important. Merck Veterinary Manual describes PDA as a common congenital defect in dogs, less common in cats, and one that typically causes continuous left-to-right shunting, pulmonary overcirculation, left-sided volume overload, and often congestive heart failure within the first 1 to 2 years if untreated. The same reference also notes that, during fetal life, blood bypasses the lungs through either the foramen ovale or the ductus arteriosus, making the review’s comparative framework clinically intuitive even if it has received limited attention in veterinary literature. (merckvetmanual.com)

The review’s premise is that these shunts shouldn’t always be considered in isolation. In routine PDA workups, echocardiography is already used to confirm ductal flow and to rule out concurrent congenital defects. But the literature suggests there may be situations where a persistent or functionally altered PFO changes the hemodynamic picture, including atrial decompression, modified shunt flow, or atypical oxygenation findings. Merck specifically notes that reverse PDA can emerge when pulmonary pressures exceed systemic pressures, producing right-to-left flow and differential cyanosis. In that kind of altered-pressure setting, the presence of an interatrial communication could further complicate presentation and interpretation. (merckvetmanual.com)

Additional veterinary literature supports the idea that PFO can be more dynamic than many clinicians assume. A case report from Ohio State described an 8-year-old cat with hypertrophic cardiomyopathy and congestive heart failure that developed acquired left-to-right shunting through a valve-incompetent PFO. The authors said severe left atrial dilation was suspected to create the interatrial shunt, and they noted that a similar mechanism has been reported in human infants with left-to-right shunting PDA, where valve-incompetent PFO was associated with a relatively larger ductal shunt. That doesn’t prove the same relationship is common in dogs and cats, but it does support the review’s broader argument that fetal remnants can become clinically meaningful when pressure relationships shift. (journals.sagepub.com)

There also appears to be an evidence gap the review is trying to address. ACVIM describes systematic reviews and consensus statements as tools to guide practice where evidence is limited or clinical variation exists. In congenital heart disease, that’s relevant: a 2021 review on congenital heart disease in dogs and cats highlighted expanding imaging and treatment options, while also pointing to the diversity and complexity of congenital lesions seen in practice. Meanwhile, recent PDA-focused research continues to center on device closure techniques and outcomes, reinforcing how much the field has advanced procedurally, even as nuanced questions about concurrent shunts and neonatal physiology remain less settled. (acvim.org)

Why it matters: For general practitioners, emergency clinicians, and cardiologists, this review is a reminder that congenital shunts don’t always behave as tidy single-lesion problems. In puppies and kittens with suspected PDA, especially those with atypical echocardiographic findings, cyanosis patterns, or pressure changes, the possibility of a concurrent or functionally significant PFO may deserve more deliberate consideration. That could affect diagnostic workups, interpretation of bubble studies or Doppler findings, referral timing, and discussions with pet parents about prognosis and treatment planning. The practical takeaway is not that every PDA patient has a meaningful PFO, but that concurrent fetal shunts may be underrecognized in the cases that don’t follow the usual script. (merckvetmanual.com)

Expert reaction specific to this paper was limited in publicly accessible sources at the time of reporting, but the broader specialty context supports its relevance. ACVIM continues to frame evidence synthesis as important where data are sparse, and current teaching materials in veterinary cardiology still emphasize careful candidate selection, structural assessment, and individualized planning for congenital heart interventions. Inference: this review is likely to be most useful as a framework-setting paper that encourages more targeted prospective research, rather than as a practice-changing publication on its own. (acvim.org)

What to watch: The next step to watch is whether future PDA case series, neonatal echocardiography studies, or interventional cardiology reports begin documenting concurrent PFO more systematically, which would help clarify how often this interaction changes management in real-world veterinary practice. (acvim.org)