Does an above‑knee amputation reduce cardiac output?

Does Above-Knee Amputation Reduce Cardiac Output?

Above-knee amputation does not directly reduce cardiac output in the immediate perioperative period, but it fundamentally alters cardiovascular hemodynamics by reducing peripheral vascular resistance and redistributing blood flow, which can unmask underlying cardiac dysfunction and increase long-term cardiovascular risk. 1

Immediate Perioperative Cardiovascular Effects

Acute Hemodynamic Changes

• Above-knee amputation reduces total peripheral vascular resistance by removing a significant portion of the vascular bed, which paradoxically can increase cardiac workload rather than decrease it 2
• The loss of lower extremity vasculature leads to redistribution of blood perfusion volume to remaining vascular territories, potentially increasing blood pressure and cardiac afterload 2
• Patients with bilateral above-knee amputations lose the normal systolic output rise response during exercise testing, with cardiac output increases occurring solely through heart rate elevation rather than stroke volume augmentation 3

Perioperative Cardiac Risk

• Above-knee amputation carries a 30-day mortality risk of 4% to 30% and a 20% to 37% risk of major cardiovascular complications including myocardial infarction and stroke 4
• After propensity matching in a large retrospective analysis, no difference was observed in 30-day mortality or cardiac complications between regional and general anesthesia for above-knee amputation, suggesting the procedure itself—not the anesthetic technique—drives the cardiac risk 1

Long-Term Cardiovascular Consequences

Chronic Hemodynamic Alterations

• Higher severity of amputation produces higher peripheral vascular impedance and more pronounced blood flow redistribution, leading to altered wall shear stress patterns in the infrarenal abdominal aorta and iliac arteries 2
• These hemodynamic changes result in lower wall shear stress, higher oscillatory shear index, and higher relative residence time in major vessels, all of which are associated with increased atherosclerosis and cardiovascular disease risk 2

Myocardial Contractile Dysfunction

• The contractile capacity of myocardium is decreased in patients with above-knee or bilateral lower extremity amputations, independent of pre-existing cardiac disease 3
• Cardiac indicator values during submaximal exercise are lower in above-knee amputees compared to controls, reflecting reduced cardiac reserve 3
• The maximal oxygen intake is significantly reduced in bilateral lower extremity amputees, indicating compromised cardiovascular functional capacity 3

Major Adverse Cardiovascular Events

• Overall MACE rates are significantly higher in above-knee amputation patients compared to below-knee amputation (HR: 1.67,95% CI: 1.36-2.06) and limb-preserved patients (HR: 1.81,95% CI: 1.50-2.18) over mean follow-up of 2.45 years 5
• Overall mortality increases with larger area of amputation, with above-knee amputation showing the highest mortality (HR: 1.65,95% CI: 1.34-2.04 compared to below-knee) 5
• Atrial fibrillation prevalence is significantly higher in above-knee amputees (17%) compared to below-knee amputees (7%), contributing to thromboembolic risk 5

Clinical Implications and Risk Factors

Metabolic Consequences

• Obesity by hydrostatic weighing is significantly more common in bilateral above-knee amputees (p < 0.001), strongly associated with hypertension, decreased glucose tolerance, and marked hyperinsulinemia 6
• Long-term cardiovascular risks are related to metabolic and hemodynamic sequelae of excessive weight gain in immobilized patients after lower limb loss 6

Functional Cardiac Adaptation

• Movement capabilities depend not on amputation level alone but critically on the dynamic capabilities of cardiac and respiratory muscular systems to adjust to limb loss 3
• Breaking of correlation interrelationships between working capacity indicators occurs in bilateral lower limb amputees, suggesting disrupted cardiovascular-metabolic coupling 3

Key Clinical Pitfalls

• Do not assume cardiac output is simply reduced because tissue mass is removed; the hemodynamic reality is far more complex with increased afterload and altered flow distribution 2
• Recognize that patients with above-knee amputation require prolonged hospitalization (median 12.5 days) after cardiac surgery but can achieve good mid-term outcomes with appropriate rehabilitation 7
• Independent risk factors for death after above-knee amputation include advanced age, heart failure, dialysis requirement, and male gender 5
• Multispecialty evaluation is essential before proceeding with above-knee versus below-knee amputation, as preserving the knee joint has the greatest impact on quality of life and cardiovascular functional capacity 8, 4