Dual Antiplatelet Therapy (DAPT): Ticagrelor + Aspirin in Inferior STEMI

Rationale for DAPT

Ticagrelor: Mechanism & Pharmacology

Key Evidence: The PLATO Trial

• n = 18,624 patients with ACS; 38% had STEMI
• Ticagrelor 180 mg load → 90 mg BID vs. clopidogrel 300–600 mg load → 75 mg daily
• ~2/3 underwent PCI

• 16% relative reduction in composite of vascular death, MI, or stroke with ticagrelor (9.8% vs 11.7%)
• CV death alone reduced (4.0% vs 5.1%; HR 0.79)
• Major bleeding unrelated to CABG: slightly higher with ticagrelor (4.5% vs 3.8%; P = 0.03)
• Fatal intracranial bleeding: higher with ticagrelor
• Stroke in STEMI subgroup: slightly higher with ticagrelor (1.7% vs 1.0%; P = 0.02) — a signal requiring attention

Dosing Regimen

• Aspirin should be non-enteric-coated in the acute setting to ensure rapid absorption
• IV aspirin 150 mg is an alternative for those unable to swallow (European guidelines)
• DAPT duration: 12 months is the standard recommendation for all STEMI patients regardless of revascularization strategy, absent high bleeding risk

Ticagrelor vs. Alternatives in STEMI

Timing in Inferior STEMI with Primary PCI

• Ticagrelor 180 mg loading dose should be given as early as possible — ideally at first medical contact / in the ED, before the patient reaches the cath lab
• Note: Despite rapid absorption, >30% of STEMI patients receiving a ticagrelor loading dose may show high residual platelet reactivity for up to 2 hours post-ingestion — likely due to delayed gastric emptying in the acute setting. Some centers bridge with IV cangrelor in this window

DAPT De-escalation and Duration Adjustments

Shortening DAPT (6 months)

• The DAPT-STEMI trial (n = 870) showed 6-month DAPT was non-inferior to 12 months in selected low-risk patients — but results must be interpreted cautiously (observed event rates far lower than projected)
• A larger ACS trial showed 6-month DAPT → higher MI rates vs. longer duration (1.8% vs 0.8%; P = 0.02)
• Current guidance: do not discontinue P2Y12 inhibition before 6 months post-STEMI

Aspirin-free strategy ("ticagrelor monotherapy")

• GLOBAL LEADERS (n = 15,968): 1 month DAPT → ticagrelor monotherapy reduced major bleeding by 48% vs standard DAPT (no difference in death/Q-wave MI)
• TICO trial: 3 months DAPT → ticagrelor monotherapy showed reduced MACE + bleeding vs 12-month DAPT
• Individual patient data meta-analysis (Ann Intern Med 2025, PMID 39961108): De-escalation to ticagrelor monotherapy associated with reduced bleeding without increase in ischemic events

Extended DAPT (>12 months)

• In PEGASUS-TIMI 54 (~53% had prior STEMI): aspirin + ticagrelor 60 mg BID for up to 3 years after MI reduced MACE (absolute risk reduction ~1%) at the cost of more bleeding
• Suitable only for high-ischemic/low-bleeding-risk patients beyond 1 year

Contraindications & Special Situations

Summary

1. Aspirin 162–325 mg (chewed, non-enteric) + Ticagrelor 180 mg loading dose as early as possible
2. Continue aspirin 75–100 mg daily + ticagrelor 90 mg BID for 12 months
3. Ticagrelor is preferred over clopidogrel (higher efficacy, no CYP variability) and over prasugrel (lower bleeding risk, suitable for older/lighter patients)
4. Consider ticagrelor monotherapy after 1–3 months in high-bleeding-risk patients
5. Do not use ticagrelor if fibrinolysis was the reperfusion strategy — use clopidogrel instead

Dermatome Assessment: Upper & Lower Limbs

What Is a Dermatome?

"There is considerable overlap between adjacent dermatomes, so lesions of a single nerve root ordinarily cause a decrease but not a complete loss of sensation in a given dermatome. There may be less overlap for smaller fibers, so pinprick is a more sensitive test for dermatomal sensory loss than touch." — Neuroanatomy Through Clinical Cases, 3rd Ed.

Dermatome Maps

How to Assess Dermatomes — Method

Tools Used

Pinprick is the most sensitive modality for detecting dermatomal sensory loss due to less inter-root overlap of small fibres. Light touch is less reliable in isolation.

General Technique

1. Expose the limb fully. Compare left vs. right symmetrically at each level.
2. Establish baseline — test a clearly normal area first (face or chest) so the patient knows what normal feels like.
3. Apply the stimulus at standardised landmark points for each dermatome (see tables below).
4. Ask the patient: "Does this feel sharp/normal/less than the other side?"
5. Map any deficit by moving from the abnormal area toward normal, rather than normal → abnormal (patients are more sensitive to detection of return of sensation).
6. Document as: normal / reduced / absent / hyperaesthetic / allodynia.

Upper Limb Dermatomes (C5–T1)

• C5–C6 → Biceps jerk
• C6 → Brachioradialis (supinator) jerk
• C7 → Triceps jerk

Lower Limb Dermatomes (L1–S2)

• L3–L4 → Patellar (knee) jerk
• S1 → Achilles (ankle) jerk — note: absent in ~50% of those >80 years (bilaterally), so unilateral absence is more significant

Practical Mnemonics

"Sit Down, Miss Pinky, Thank you"

• C5 = Shoulder/deltoid
• C6 = Thumb & index (lateral)
• C7 = Middle finger
• C8 = Pinky & ring (medial hand)
• T1 = medial forearm

"I Go Kick, Let's Start"

• L1 = Inguinal
• L2 = Groin/upper thigh
• L3 = Knee area (medial)
• L4 = Lateral shin / Leg medial
• L5 = Lateral shin + dorsum of foot
• S1 = Sole + lateral foot

Common Clinical Pitfalls

Provocative Tests to Support Dermatomal Findings