What is the Jarisch reflex, also known as vasovagal reflex, in patients undergoing medical procedures?

What is the Bezold-Jarisch Reflex?

The Bezold-Jarisch reflex is a cardioinhibitory reflex that originates from sensory receptors (mechanoreceptors and chemoreceptors) in the inferoposterior wall of the left ventricle, transmitted via unmyelinated vagal C fibers, resulting in the paradoxical triad of hypotension, bradycardia, and sometimes apnea. 1

Physiologic Mechanism

The reflex is triggered when ventricular mechanoreceptors detect specific stimuli, particularly:

• Vigorous ventricular contraction in an underfilled ventricle (such as during hypovolemia, hemorrhage, or neuraxial anesthesia) 2, 3
• Serotonin stimulation of 5HT3 chemoreceptors and mechanoreceptors in the left ventricular wall 4
• The afferent pathway travels through unmyelinated type C vagal nerve fibers to the brainstem 1, 4
• The efferent response produces parasympathetic activation (bradycardia) and sympathetic inhibition (vasodilation and hypotension) 3

Clinical Presentation

The hallmark triad consists of: 2, 5

• Profound bradycardia (heart rate can drop to <20 bpm in severe cases)
• Severe hypotension (systolic blood pressure can fall to 30s mmHg)
• Bradypnea or apnea (respiratory rate may decrease to 6/min or cease)

A critical distinguishing feature is that hypotension typically precedes bradycardia, with an insidious decrease in blood pressure occurring first, followed by the heart rate drop 5, 3. This sequence differs from primary cardiac causes where bradycardia would precede hypotension.

Clinical Contexts Where It Occurs

High-risk situations include: 2, 5, 6, 3

• Neuraxial (spinal/epidural) anesthesia, particularly during cesarean sections
• Acute hemorrhage or hypovolemia, especially when combined with regional anesthesia
• Postoperative pediatric cardiac surgery (more prevalent than previously recognized in this population)
• Inferior vena cava compression in pregnancy
• Anaphylaxis (can cause bradycardia during anaphylactic reactions when tachycardia would otherwise be expected)

Relationship to Vasovagal Syncope

The Bezold-Jarisch reflex is mechanistically related to but distinct from vasovagal syncope: 1, 3

• Both involve parasympathetic activation and sympathetic withdrawal
• Vasovagal syncope is typically triggered by emotional stress, pain, or orthostatic stress 1, 7
• The Bezold-Jarisch reflex specifically originates from cardiac mechanoreceptors responding to ventricular wall stretch 1, 4
• The term "neurocardiogenic syncope" should be reserved for reflex syncope where the trigger originates in the heart itself 1

Critical Distinguishing Features from Vasovagal Reactions

When differentiating from simple vasodepressor (vasovagal) reactions: 1

• Vasovagal reactions typically present with bradycardia from the onset, cool pale skin, and normal or elevated blood pressure initially
• Bezold-Jarisch reflex shows hypotension preceding bradycardia, often in the context of reduced venous return
• Both lack the cutaneous manifestations (urticaria, flushing) seen in anaphylaxis
• However, bradycardia can occur during anaphylaxis due to the Bezold-Jarisch reflex, creating diagnostic complexity 1

Immediate Management

Treatment must be rapid and aggressive: 2, 5, 3

• Stop the precipitating factor (halt anesthetic administration if applicable)
• Atropine 0.01 mg/kg IV bolus is the first-line anticholinergic agent 5
• Continuous atropine infusion at 0.01 mg/kg/hour may be needed to prevent recurrence 5
• Epinephrine for severe cases with cardiovascular collapse (addresses both bradycardia and vasodilation) 2, 3
• Aggressive IV fluid resuscitation to restore venous return 2, 3
• Left lateral positioning in pregnant patients to relieve vena cava compression 2
• Prepare for emergency delivery if fetal bradycardia develops during obstetric procedures 2

Common Pitfalls to Avoid

• Do not assume bradycardia is the primary problem—the hypotension from vasodilation may be more severe than that caused by bradycardia alone, and treating only the heart rate without addressing volume status and vasodilation will fail 3
• Do not delay epinephrine in established cardiac arrest, especially after high regional anesthesia, as atropine alone may be insufficient 3
• Recognize that multiple risk factors are additive—regional anesthesia plus hemorrhage plus pregnancy creates exponentially higher risk 3
• In pediatric cardiac surgery patients, maintain high suspicion as the reflex is more prevalent than historically recognized in this population 5