What is the likely cause and treatment for sinus bradycardia in a 40-year-old female presenting with profuse vomiting and severe dehydration?

Sinus Bradycardia in a 40-Year-Old Woman with Profuse Vomiting and Severe Dehydration

Most Likely Cause

In this clinical scenario, the sinus bradycardia is most likely caused by increased vagal tone secondary to severe dehydration and hypovolemic shock, with gastrointestinal distress triggering a vagal reflex. 1, 2

Pathophysiology and Mechanism

The combination of profuse vomiting and severe dehydration creates a perfect storm for bradycardia through multiple mechanisms:

• Hypovolemic shock directly causes sinus bradycardia as a reversible cause that must be identified and treated before any other interventions 1, 3
• Vagal stimulation from abdominal pain and gastrointestinal distress triggers reflex bradycardia, which is a well-recognized phenomenon in acute abdominal conditions 2
• Electrolyte abnormalities (hyperkalemia, hypokalemia, hypoglycemia) from vomiting and dehydration can contribute to bradycardia 1, 4
• Metabolic acidosis from severe dehydration should be corrected as it represents a reversible cause 3

Additional Considerations in a Newly Married 40-Year-Old Woman

Early pregnancy must be ruled out immediately given her newly married status, as this could represent hyperemesis gravidarum with associated vagal-mediated bradycardia 5

Other reversible causes to evaluate in this specific patient:

• Hypothyroidism can cause bradycardia and should be assessed with thyroid function tests 1, 3, 4
• Medications including beta blockers, calcium channel blockers, digoxin, antiarrhythmic drugs, lithium, methyldopa should be reviewed in the history 1, 4
• Infections such as typhoid fever, which can present with vomiting and bradycardia 1

Immediate Treatment Approach

First Priority: Address the Underlying Cause

Aggressive fluid resuscitation is the primary treatment to correct hypovolemic shock and dehydration 1, 3, 2

• Pain control is crucial as it addresses the vagal reflex component of bradycardia 2
• Correct electrolyte abnormalities and metabolic acidosis 3
• Antiemetic therapy to stop vomiting

Acute Pharmacologic Management (If Hemodynamically Unstable)

Atropine 0.5-1 mg IV is reasonable for symptomatic bradycardia with hemodynamic compromise, repeated every 3-5 minutes to a maximum of 3 mg 1, 3, 2, 4, 5

• Atropine blocks vagal effects and is particularly effective for vagally-mediated bradycardia 2, 4
• Alternative agents if atropine is insufficient: dopamine 5-20 mcg/kg/min IV, isoproterenol 1-20 mcg/min IV, or epinephrine 2-10 mcg/min IV 1, 4

Critical Clinical Pitfall

Do not pursue permanent pacemaker implantation for this reversible cause of bradycardia 2. The bradycardia should resolve completely once the underlying dehydration, hypovolemia, and vagal triggers are addressed. Persistent bradycardia after resolution of the acute illness would warrant investigation for other causes such as intrinsic sinus node dysfunction, hypothyroidism, or medication effects 2, 4.

Monitoring and Follow-Up

• If bradycardia persists after adequate fluid resuscitation and symptom resolution, investigate for other underlying causes including hypothyroidism, medications, or primary sinus node dysfunction 2
• Asymptomatic sinus bradycardia after recovery does not require treatment 3, 4
• Document correlation between symptoms (lightheadedness, syncope, dyspnea) and heart rate if bradycardia persists, as this determines need for permanent pacing 1, 3, 4