Can atropine (Antimuscarinic) IV diluted in 100 ml Normal Saline (NS) cause an increase in blood pressure (Hypertension) along with heart rate (Tachycardia)?

Atropine IV and Its Effects on Blood Pressure and Heart Rate

Yes, atropine IV diluted in 100 ml NS can cause an increase in both blood pressure and heart rate through its antimuscarinic effects. 1

Mechanism of Action

Atropine is an antimuscarinic agent that works by:

• Competitively antagonizing the actions of acetylcholine at muscarinic receptors
• Inhibiting parasympathetic activity, which normally slows heart rate and decreases blood pressure
• Removing vagal tone, which leads to increased sinus node discharge and enhanced atrioventricular (AV) conduction 2, 1

Cardiovascular Effects

Heart Rate Effects

• Atropine typically increases heart rate by blocking vagal influence on the sinoatrial node
• Standard dosage (0.5-1 mg IV) produces tachycardia within 3 minutes of administration 2
• Peak action occurs within 3 minutes of intravenous administration 2

Blood Pressure Effects

• Atropine can increase systolic blood pressure while slightly lowering diastolic pressure 1
• In patients with bradycardia-hypotension syndrome, atropine significantly increases both heart rate and systolic blood pressure 3
• In one study, atropine increased systolic blood pressure from 70±15 to 105±13 mm Hg in patients with bradycardia-hypotension syndrome 3

Clinical Applications

Atropine is indicated for:

1. Symptomatic sinus bradycardia with evidence of low cardiac output and peripheral hypoperfusion 2
2. Acute inferior infarction with symptomatic type I second-degree AV block 2
3. Bradycardia and hypotension after nitroglycerin administration 2
4. Asystole 2

Dosing Considerations

• Recommended dosage: 0.5-1 mg IV, repeated every 3-5 minutes if needed 2
• Maximum total dose: 3 mg 2
• Caution: Doses <0.5 mg may cause paradoxical bradycardia 2
• Dilution in 100 ml NS is an acceptable administration method and does not alter the cardiovascular effects

Potential Adverse Effects

• Excessive tachycardia may increase myocardial oxygen demand, potentially worsening ischemia 2, 4
• Significant reduction in diastolic time (from 55.6% to 32.4% of cardiac cycle) may reduce coronary perfusion 4
• Rarely, ventricular tachycardia and fibrillation may occur 2
• Postural hypotension can develop in some patients 1
• At very high doses (exceeding clinical recommendations), atropine may paradoxically cause bradycardia and hypotension 5

Special Considerations

1. Coronary Artery Disease: Use with caution as increased heart rate may worsen myocardial ischemia by reducing diastolic filling time 4

2. Heart Transplant Patients: Atropine should not be used in heart transplant patients without evidence of autonomic reinnervation 2

3. Monitoring: Careful observation is necessary after administration as the resulting tachycardia may increase ischemia in susceptible patients 2

4. Dose-Related Effects: Serious adverse effects correlate with either higher initial doses (≥1.0 mg) or cumulative doses exceeding 2.5 mg over 2.5 hours 6

Conclusion

Atropine IV diluted in 100 ml NS effectively increases both heart rate and blood pressure in most patients with bradycardia, particularly when bradycardia is associated with hypotension. This effect is due to its antimuscarinic properties that block vagal influence on the heart, resulting in increased chronotropy and improved hemodynamics.