Wilderness Journal Club: PFO and HAPE
/Welcome to the new recurring article on TamingtheSRU - Wilderness Journal Club with Drs Conal Roche, Brandon Berger and other guest writers
The Article
Allemann Y, Hutter D, Lipp E, Sartori C, Duplain H, Egli M, Cook S, Scherrer U, Seiler C. Patent foramen ovale and high-altitude pulmonary edema. JAMA. 2006 Dec 27;296(24):2954-8. doi:10.1001/jama.296.24.2954.
Take Home
Patent foramen ovale (PFO) is associated with greater degrees of hypoxia at altitude and higher rates of high-altitude pulmonary edema (HAPE).
Supplies (PerhaPs A box full of ultrasound Gel?) arriving to the RIFugio Capanna regina Marherita by Helicopter. Luca Fenzi, CC BY-SA 4.0, via Wikimedia Commons
Study Description
16 climbers with previous HAPE diagnosis were paired with 19 climbers who had multiple previous ascents without HAPE (termed “HAPE-resistant”). TTE (transthoracic echo) and TEE (transesophageal echo) with bubble contrast for PFO diagnosis and quantification were performed at the high-altitude research laboratory at Capanna Regina Margherita, Italy (4559 m). Not surprisingly, 9 refused a repeat TEE at low altitude, but still impressive that they found over 30 people willing to have a large ultrasound probe shoved down their gullet after climbing to 15,000ft. At altitude, a PFO was found in 11 of 16 previous HAPE patients and 8 of them developed HAPE symptoms during the study. Only 3 of the 19 “HAPE-resistant” participants had a PFO at altitude and none developed HAPE symptoms, leading to the commonly quoted statistic that HAPE patients are 4x more likely to have a PFO than baseline occurence.
Why Does This Matter?
Climbers with a known PFO, especially a large one, should be monitored closely for signs of HAPE even at low-moderate altitudes. Climbers who develop HAPE at less than moderate altitudes (<3500m) might consider screening for PFO. It is not unreasonable to imagine a climber seeking prophylactic closure of a PFO in order to decrease their risk for HAPE (and stroke), although there are no clear recommendations that I am aware of. The most recent guideline I could find from WMS in 2015 commented: “Patent foramen ovale is associated with HAPE, but its importance is unclear.” [1]
Deep Thoughts
The foramen ovale is a hole between the atria that allows blood in the developing fetus to bypass the pulmonary circulation and usually closes soon after birth. This fails to close completely in 25% of adults and is the most common anatomic abnormality that might lead to increased pulmonary blood flow (others include ASD, VSD, or congenital absence of PA). When exposing your body to hypobaric (hypoxic) conditions, pulmonary vascular resistance increases leading to increased right-sided pressures and increased mixing of blood across a Patent Foramen Ovale (PFO), thereby potentially worsening hypoxemia. Granted, this study provides a very small sample, but PFO has also been noted at higher than baseline rates in other conditions leading to higher right-sided pressures, such as COPD and sleep apnea. [2,3] This leads to a “cause-or-effect” discussion around presence of PFO and right sided pressures. Perhaps baseline higher right sided pressures are the true explanation for greater rates of HAPE in these individuals and PFO is simply a parallel association…
Post by Conal Roche, MD
Dr. Roche is an attending physician in Emergency Medicine at the University of Cincinnati, Fellowship trained in Wilderness Medicine
Editing by Brandon Berger, MD
Dr. Berger is a PGY-3 in Emergency Medicine at the University of Cincinnati.
References
Campbell AD, McIntosh SE, Nyberg A, Powell AP, Schoene RB, Hackett P. Risk Stratification for Athletes and Adventurers in High-Altitude Environments: Recommendations for Preparticipation Evaluation. Wilderness Environ Med. 2015 Dec;26(4 Suppl):S30-9. doi:10.1016/j.wem.2015.09.016.
Shanoudy H, Soliman A, Raggi P, Liu JW, Russell DC, Jarmukli NF. Prevalence of patent foramen ovale and its contribution to hypoxemia in patients with obstructive sleep apnea. Chest. 1998;113:91-96. doi:10.1378/chest.113.1.91.
Soliman A, Shanoudy H, Liu J, Russell DC, Jarmukli NF. Increased prevalence of patent foramen ovale in patients with severe chronic obstructive pulmonary disease. J Am Soc Echocardiogr. 1999;12:99-105. doi:10.1016/s0894-7317(99)70121-5.
