What is the appropriate dose of heparin (unfractionated heparin) for a patient with tachycardia?

Heparin Dosing for Tachycardia

Heparin is not indicated for the treatment of tachycardia itself; however, if the tachycardia is atrial fibrillation requiring anticoagulation, administer an initial intravenous bolus of 60-70 U/kg (maximum 5000 U) followed by a continuous infusion of 12-15 U/kg/hour, adjusted to maintain an aPTT of 1.5 to 2 times the control value. 1, 2

Critical Context: Tachycardia Type Determines Heparin Use

• Heparin has no role in treating most tachycardias including ventricular tachycardia, supraventricular tachycardia, or sinus tachycardia—these require rate control agents (beta-blockers, calcium channel blockers, digoxin) or antiarrhythmics, not anticoagulation 1

• Heparin is indicated only when tachycardia is atrial fibrillation (AF) with specific anticoagulation requirements based on duration and cardioversion plans 1, 3, 4

Heparin Dosing Algorithm for Atrial Fibrillation

For AF >48 Hours or Unknown Duration (Hemodynamically Stable)

• Initial bolus: 60-70 U/kg IV (maximum 5000 U) 1, 2
• Continuous infusion: 12-15 U/kg/hour, adjusted to maintain aPTT 1.5-2.0 times control (typically 60-80 seconds if control is 30-40 seconds) 1, 4, 2
• Monitoring: Check aPTT every 4 hours initially, then at appropriate intervals 2
• Duration: Continue until therapeutic oral anticoagulation established (INR 2.0-3.0) for at least 3 weeks before and 4 weeks after any cardioversion 1, 3, 4

For AF <48 Hours Duration

• Anticoagulation needs may be based on thromboembolic risk (CHADS₂ or CHA₂DS₂-VASc score) rather than mandatory heparin 1, 3
• If heparin is used, employ the same dosing as above 4

For Hemodynamically Unstable AF Requiring Immediate Cardioversion

• Administer heparin concurrently without delay: Initial bolus followed by continuous infusion as above 1, 3, 4
• Do not wait for therapeutic anticoagulation before cardioversion in the setting of angina, myocardial infarction, shock, or pulmonary edema 1
• Continue anticoagulation for at least 4 weeks post-cardioversion 1, 4

Alternative Approach: TEE-Guided Strategy

• Perform transesophageal echocardiography to exclude left atrial thrombus 1, 3, 4
• If no thrombus identified: Administer heparin immediately (bolus + infusion), proceed with cardioversion, then transition to oral anticoagulation for 4 weeks 1, 4
• If thrombus present: Anticoagulate for at least 3 weeks before cardioversion 1

Low Molecular Weight Heparin as Alternative

• LMWH can substitute for unfractionated heparin in the peri-cardioversion period, though evidence is more limited 1, 4
• LMWH significantly shortens time to cardioversion compared to warfarin bridging (median 27 days vs 138 days) 5
• Standard LMWH dosing: Enoxaparin 1 mg/kg subcutaneously twice daily 1

Monitoring Parameters

• Target aPTT: 1.5-2.0 times control value (50-70 seconds for acute coronary syndromes, 60-80 seconds for AF) 1, 4, 2, 6
• Check baseline: aPTT, INR, platelet count, hematocrit 2
• Ongoing monitoring: aPTT every 4 hours initially, then periodically; platelet counts throughout therapy to detect heparin-induced thrombocytopenia 2
• Occult blood in stool should be monitored during entire course 2

Critical Pitfalls to Avoid

• Do not use heparin for ventricular tachycardia—this requires antiarrhythmics (amiodarone, lidocaine) or immediate cardioversion, not anticoagulation 1

• Do not confuse Heparin Sodium Injection with catheter lock flush products—fatal medication errors have occurred with concentrated 10,000 units/mL vials 2

• Avoid heparin in patients with pericardial effusion—risk of hemorrhagic pericarditis and cardiac tamponade, particularly in dialysis patients 7

• Do not withhold anticoagulation completely in high-risk AF patients even with bleeding concerns—balance thrombotic vs hemorrhagic risk 3

• Contraindications include: History of heparin-induced thrombocytopenia, uncontrolled active bleeding (except DIC), inability to monitor coagulation tests 2

Special Populations

Pregnant Patients with AF

• Unfractionated heparin preferred during first trimester and last month of pregnancy 1
• Dosing: 10,000-20,000 U subcutaneously every 12 hours, adjusted to prolong mid-interval aPTT to 1.5 times control 1

Patients Already on Warfarin

• Reduce heparin bolus to 60-70 U/kg if INR already therapeutic 8
• Monitor more frequently (every 4-6 hours initially) 8
• Target lower aPTT range (1.5 times control rather than 1.5-2.5 times) if INR therapeutic 8