What is the activated clotting time (ACT) protocol for anticoagulation during percutaneous coronary interventions, including heparin dosing, target ACT range, monitoring, and alternative agents?

ACT Protocol for Percutaneous Coronary Intervention

For PCI procedures, administer unfractionated heparin (UFH) at 70-100 U/kg IV bolus targeting an ACT of 250-300 seconds (HemoTec/I-Stat devices) or 300-350 seconds (Hemochron devices), with ACT measured 2-5 minutes post-administration and additional boluses given as needed to maintain target range. 1, 2

Heparin Dosing Strategy

Initial Bolus Dosing

• Standard dose: 70-100 U/kg IV bolus for patients not receiving glycoprotein IIb/IIIa inhibitors 1, 2
• With GP IIb/IIIa inhibitors: Reduce to 50-70 U/kg targeting ACT 200-250 seconds 1, 3
• No prior anticoagulation: Use full weight-based dose 2
• Prior anticoagulation: Give additional UFH as needed (typically 2,000-5,000 units) to achieve target ACT 1

Device-Specific ACT Targets

The ACT target varies by measurement platform—this is critical and often overlooked 1:

• HemoTec or I-Stat devices: 250-300 seconds
• Hemochron devices: 300-350 seconds (50 seconds higher than HemoTec)
• These differences reflect inherent platform variability, not clinical judgment 4

Monitoring Protocol

Timing of ACT Measurements

1. Baseline ACT: Measure before heparin administration 5
2. Post-bolus ACT: Check 2-5 minutes after initial heparin bolus 1, 2
3. Supplemental dosing: If ACT below target, give additional heparin and recheck
4. During procedure: No consensus on routine intra-procedural monitoring for standard PCI 6

Blood Sampling Location

Draw ACT samples from the arterial access sheath, not the guiding catheter 7. Catheter samples yield falsely elevated ACT values (mean difference 43 seconds higher), potentially leading to under-anticoagulation. In 30% of cases, catheter ACT appears therapeutic while sheath ACT is subtherapeutic 7.

Supplemental Heparin Dosing

When initial ACT is below target 8:

• Calculate deficit: Each 10 U/kg raises ACT approximately 10 seconds 9
• Give additional bolus based on ACT deficit
• Recheck ACT 2-5 minutes after supplemental dose
• Important: Only 17% of patients achieve target ACT with guideline-recommended initial dosing 8

Special Populations

Obesity

Obese patients require lower weight-adjusted heparin doses 10. Body mass index is the only significant covariate affecting heparin dose-response after weight-based dosing. Consider starting at lower end of dosing range (70 U/kg) in severely obese patients 10.

Acute Coronary Syndromes

For STEMI/NSTE-ACS patients 2:

• Same weight-based dosing (70-100 U/kg)
• Same ACT targets (250-300 seconds)
• Continue anticoagulation until revascularization completed

Alternative Anticoagulants

Bivalirudin

For patients with heparin-induced thrombocytopenia, use bivalirudin or argatroban 1, 2:

• Bivalirudin dosing: 0.75 mg/kg IV bolus, then 1.75 mg/kg/hr infusion during PCI 1, 2
• ACT target with bivalirudin: 200-225 seconds (lower than UFH) 11
• Monitoring value: ACT is reproducible with bivalirudin but does not correlate with clinical events 12
• Bivalirudin reduces bleeding versus UFH but may increase acute stent thrombosis 2, 13

Enoxaparin

Enoxaparin is a reasonable alternative 1, 2:

• If no prior enoxaparin: 0.5-0.75 mg/kg IV bolus 1, 2
• If last subcutaneous dose 8-12 hours prior: Give 0.3 mg/kg IV 1, 2
• If last dose within 8 hours: No additional enoxaparin needed 1, 2
• Do not use UFH if last enoxaparin dose was within 12 hours—increases bleeding risk 1

Common Pitfalls

Heparin Resistance

Suspect when ACT remains <300 seconds despite >600 U/kg heparin 14:

• Causes: Antithrombin III deficiency, prior heparin therapy, thrombocytosis, sepsis
• Management: Administer fresh frozen plasma or antithrombin III concentrate 14

Post-PCI Anticoagulation

Discontinue heparin immediately after uncomplicated PCI 15. Continued heparin increases bleeding without reducing ischemic events. The exception is ongoing ACS with high-risk features (dissection, thrombus, ongoing ischemia) where brief continuation may be considered 16.

Platform Confusion

Know which ACT device your lab uses 4, 6. Real-world practice shows substantial variation in heparin dosing and ACT targets based on platform, with many operators unaware of device-specific differences. When switching platforms, adjust targets accordingly 4.

Weight-Based Dosing Variability

Despite guideline recommendations, significant variability exists in achieving therapeutic ACT 8, 6. Measure ACT routinely rather than assuming weight-based dosing is adequate—only 49% achieve target with initial recommended dose 8.