In a patient who recently underwent coronary artery bypass graft surgery after myocardial infarction and now presents with painful, red, swollen legs, what is the most urgent next step in management?

Urgent Evaluation for Deep Vein Thrombosis

In a post-CABG patient presenting with painful, red, swollen legs, the most urgent next step is immediate duplex ultrasound to rule out deep vein thrombosis (DVT), as this represents a life-threatening complication that requires emergent anticoagulation to prevent pulmonary embolism and death.

Immediate Diagnostic Workup

Primary Concern: Deep Vein Thrombosis

• Post-CABG patients are at markedly elevated risk for DVT due to prolonged immobilization, hypercoagulability from surgical stress, and cardiopulmonary bypass-induced coagulation disturbances 1
• Bilateral leg involvement suggests either bilateral DVT or systemic inflammatory response, both requiring urgent intervention 2
• DVT presents with the exact triad described: swelling, pain, and erythema 3, 4

Urgent Diagnostic Steps

• Order immediate bilateral lower extremity duplex ultrasound as the first-line diagnostic test 4, 5
• If ultrasound is unavailable, clinical probability scoring can stratify risk: high-probability patients (bilateral symptoms post-surgery) warrant empiric anticoagulation while awaiting imaging 4
• Measure D-dimer if ultrasound will be delayed, though post-surgical patients typically have elevated levels regardless 4

Critical Differential Diagnoses to Exclude

Saphenous Vein Harvest Site Complications

• Bilateral saphenous vein graft (SVG) harvest creates surgical wounds in both legs that can develop cellulitis, hematoma, or lymphedema 6
• Cellulitis typically presents unilaterally with higher fever and more pronounced erythema spreading from the incision 3
• If cellulitis is suspected, measure edema fluid protein concentration: >19 g/L suggests cellulitis vs. <6 g/L for DVT 3

Cardiac-Related Causes

• Rule out acute graft failure or recurrent MI causing bilateral lower extremity edema from acute heart failure 7, 1
• Check troponin, BNP, and obtain ECG immediately 7
• Early post-CABG ischemia (<30 days) typically reflects graft thrombosis and requires urgent coronary angiography 7, 6

Risk Stratification

High-Risk Features Requiring Immediate Intervention

• Bilateral involvement (suggests systemic process or bilateral DVT) 2
• Timing within first 30 days post-CABG (peak period for graft thrombosis and DVT) 7, 1
• Recent immobilization or ICU stay (major DVT risk factor) 1
• Systemic inflammatory markers elevated (WBC and CRP significantly increased in DVT) 2

Management Algorithm

If DVT Confirmed on Ultrasound

1. Initiate therapeutic anticoagulation immediately with weight-adjusted subcutaneous low-molecular-weight heparin or intravenous unfractionated heparin 4
2. Do NOT delay anticoagulation for confirmatory testing if clinical suspicion is high and ultrasound is positive 4
3. Transition to oral anticoagulation (warfarin or DOAC) for minimum 3-6 months 5
4. Consider IVC filter only if anticoagulation is absolutely contraindicated due to active bleeding 5

If DVT Excluded

• Evaluate for cellulitis at SVG harvest sites: start empiric antibiotics covering Staphylococcus and Streptococcus species 1
• Assess for heart failure: obtain echocardiogram and optimize diuretic therapy 1
• Consider lymphedema from surgical disruption: initiate compression therapy and elevation 7

Critical Pitfalls to Avoid

• Never dismiss bilateral leg symptoms as "normal post-surgical edema" without objective testing—DVT carries 20-30% risk of fatal pulmonary embolism if untreated 2, 4
• Never delay ultrasound beyond 24 hours in symptomatic post-CABG patients; if unavailable, transfer to facility with imaging capability 4
• Never use clinical examination alone to exclude DVT—even experienced physicians have only 49% accuracy for high-probability cases 4
• Never forget that post-CABG patients may have multiple simultaneous complications: DVT can coexist with graft failure, infection, or heart failure 1, 6
• Never start anticoagulation without considering recent surgical bleeding risk, but recognize that untreated DVT mortality exceeds bleeding risk in most cases 1, 4

Monitoring Requirements

• Continuous cardiac monitoring for at least 48 hours to detect arrhythmias or ischemic changes 1
• Serial troponin measurements if any concern for graft failure 7, 1
• Daily assessment of leg circumference and symptoms if DVT is excluded 7, 8
• Follow-up ultrasound in 5-7 days if initial study is negative but clinical suspicion remains high 4