What is the likely cause of syncope in a patient with a history of Abdominal Aortic Aneurysm (AAA) after spending an hour in a sauna?

Likely Cause of Syncope in AAA Patient After Sauna Exposure

The syncope was most likely caused by heat-induced vasodilation and orthostatic hypotension, not AAA rupture or acute aortic complications. 1

Primary Mechanism: Heat-Induced Vasodilation

• Prolonged sauna exposure (one hour) causes profound peripheral vasodilation and fluid shifts, leading to decreased venous return and subsequent hypotension 1
• This vasodilatory syncope is a common reflex-mediated mechanism in healthy individuals exposed to extreme heat, and the patient's history of AAA is likely incidental to the syncopal event 1
• The patient's survival and ability to present for evaluation strongly argues against AAA rupture, which carries 65-85% mortality and would typically manifest with severe abdominal or back pain, not isolated syncope 2

Why AAA Rupture is Unlikely

• Intact AAAs are typically asymptomatic, and rupture presents with severe abdominal or back pain, hypotension, and a pulsatile abdominal mass—not isolated syncope after heat exposure 2
• The mortality for ruptured AAA is 65-85%, with most patients not surviving to medical evaluation 2
• While syncope can occur with aortic dissection (in approximately 13% of cases), this is associated with cardiac tamponade, stroke, or severe aortic complications—not environmental heat exposure 1
• Aortic dissection typically presents with sudden, severe, tearing chest or abdominal pain that is abrupt in onset, which is not described in this scenario 1, 3

Critical Distinction: AAA vs. Acute Aortic Syndrome

• AAAs are chronic degenerative processes that develop over years and remain asymptomatic until rupture or reaching repair thresholds 3, 4
• Acute aortic syndrome (dissection, intramural hematoma, penetrating ulcer) presents with sudden severe tearing pain, not isolated syncope after sauna use 1, 3
• The European Heart Journal notes that syncope in aortic dissection is associated with life-threatening complications like cardiac tamponade (8-10% of cases) and has 34% mortality versus 23% in those without syncope 1

Clinical Evaluation Required

• Assess for AAA rupture red flags: severe abdominal/back pain, pulsatile abdominal mass, hypotension, and signs of hemorrhagic shock 5
• Check vital signs carefully: blood pressure in both arms, heart rate, and orthostatic measurements to confirm vasovagal/orthostatic mechanism 1
• Palpate abdomen: a strong, pulsatile mass would suggest AAA presence, but tenderness or rapid expansion would indicate rupture risk 5
• If the patient is hemodynamically stable, pain-free, and the syncope occurred immediately after or during sauna exposure with rapid recovery, this strongly supports benign vasovagal syncope 1

Important Caveats

• While heat-induced syncope is the most likely diagnosis, any patient with known AAA presenting with syncope requires urgent evaluation to exclude rupture or expansion 6
• The ACC/AHA guidelines note that syncope can be the presenting symptom of aortic dissection in rare cases, though this typically involves additional concerning features 1
• If the AAA diameter is ≥5.5 cm (men) or ≥5.0 cm (women), the patient requires closer surveillance regardless of the syncope etiology 3
• Consider imaging (ultrasound or CT) if there is any clinical suspicion for AAA complications, rapid growth, or if the patient has not had recent surveillance imaging 1, 3