Author + information
- Robert Sabiniewicz, MD and
- Lidia Wozniak-Mielczarek, MD∗ ()
- ↵∗Department of Pediatric Cardiology and Congenital Heart Diseases, Medical University Gdansk, Poland, 7 Debinki Street, Gdansk 80-211, Poland
We read with interest an article by Kijima et al. (1), which highlights the fact that not only a patent foramen ovale (PFO) can be responsible for a cryptogenic stroke. Right-to-left shunting (RLS) through an PFO is undeniably the major cause of paradoxical embolism. However, rarely, it can also be caused by RLS at pulmonary level due to pulmonary arteriovenous malformation (PAVM). A PAVM is a direct communication between the branches of the pulmonary artery and pulmonary veins. Large or multiple PAVMs can cause cyanosis and exertional dyspnea, but usually patients are asymptomatic. Regardless of their size, PAVMs can affect the central nervous system causing migraines, transient ischemic attacks, strokes, or abscess. The reported incidence of strokes in patients with PAVM is 18% to 32% and up to 60% in cases of multiple PAVMs (2). It has also been shown that recurrent strokes occur more often in patients with PAVMs than with PFO (probably because of continuous RLS). Classical diagnostic tools used to confirm PAVM are contrast-enhanced computed tomography or magnetic resonance imaging and pulmonary angiography. Chest radiography suggests PAVM only in about 45% of patients.
It should be underscored that PAVMs can be also diagnosed using contrast transesophageal echocardiography (c-TEE) and contrast transcranial Doppler (c-TCD), which are considered the “gold standard” for revealing an PFO. In the case of an extracardiac shunt, c-TEE with a Valsalva maneuver shows bubbles entering the left atrium 3 to 8 cardiac cycles after they were seen in the right atrium. In contrast, in cardiac RLS, the “3-beat rule” is used, which means that bubbles should appear in the left atrium between first and third cardiac cycles (3). In addition, RLS can be identified by the use of c-TCD. The technique is based on the detection of an intravenously injected contrast within intracranial arteries. In case of an RLS, the contrast enters the arterial circulation and produces microembolic signals. Microembolic signals passing pulmonary shunts appear later in the cerebral circulation than those passing cardiac shunts. The time window characteristic for PAVMs is about 15 s (11 s for intracardiac shunts), but it depends on the heart rate (duration of about 6 heart beats) (3).
In conclusion, it is of great importance to distinguish the level of RLS in c-TEE and c-TCD. It seems that PAVM can be responsible for some “false-positive” results of c-TEE or c-TCD. Finally, it is reasonable to consider c-TCD or c-TEE after every PFO closure to identify potential persistent RLS. For complete prevention of recurrent strokes caused by paradoxical embolism, it is necessary to not only close a PFO, but all existing shunts.
Please note: The authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- American College of Cardiology Foundation