Medical School · Year 1 · Cardiovascular · includes a quiz and discussion video

Lecture 15: Peripheral Vascular Disease

Unit 1.7: Cardiovascular System

Learning Objectives

By the end of this lecture, students will be able to:

1. Describe the pathophysiology of peripheral arterial disease
2. Recognize the clinical presentation of acute and chronic limb ischemia
3. Explain the diagnosis and staging of peripheral arterial disease
4. Describe venous thromboembolism and its complications
5. Explain the pathophysiology and management of chronic venous insufficiency
6. Describe aortic aneurysms and their management

Lecture Content

Peripheral Arterial Disease: Epidemiology and Pathophysiology

Peripheral arterial disease represents atherosclerosis affecting non-coronary arteries, most commonly the lower extremities. The pathological process is identical to that occurring in coronary artery disease: lipid accumulation, inflammatory cell infiltration, plaque formation, progressive stenosis, and ultimately occlusion. Understanding that PAD is a manifestation of systemic atherosclerosis rather than an isolated local problem is critical because it carries profound implications for cardiovascular morbidity and mortality.

Smoking stands as the strongest risk factor for PAD, increasing risk two to fourfold. Diabetes similarly elevates risk two to fourfold while also promoting more distal disease patterns affecting tibial vessels. Hypertension contributes a 1.5 to twofold increased risk, hyperlipidemia approximately doubles the risk, and advancing age dramatically increases prevalence. Chronic kidney disease increases risk two to threefold, likely through accelerated vascular calcification and endothelial dysfunction. These risk factors are multiplicative, making aggressive modification essential for disease management.

The anatomical distribution of atherosclerotic lesions follows predictable patterns. Femoropopliteal disease predominates, accounting for eighty to ninety percent of cases and typically manifesting at the adductor canal where the superficial femoral artery transitions through Hunter's canal. Aortoiliac disease represents approximately thirty percent of cases and produces characteristic proximal symptoms. Tibial disease occurs frequently in diabetics due to their propensity for small vessel involvement. Upper extremity PAD remains rare and should prompt evaluation for unusual causes including arteritis or thoracic outlet syndrome.

<image>Panel A: Full-length anterior view of the lower extremity arterial tree from abdominal aorta to feet, with color-coded common stenosis locations at the aortoiliac bifurcation, femoropopliteal segment at Hunter's canal, and tibial vessels. Panel B: Cross-section of an atherosclerotic femoral artery showing eccentric plaque with lipid core, fibrous cap, and narrowed lumen. Panel C: Fontaine stages I and II showing asymptomatic disease and claudication with calf discomfort during walking. Panel D: Fontaine stages III and IV showing rest pain with foot elevated at night and tissue loss with ulceration on toes and heel.</image>

Intermittent Claudication

Claudication derives from the Latin word for "to limp" and perfectly describes the exercise-induced muscle pain that forces patients to stop walking. This symptom represents the hallmark of stable PAD, reflecting the fundamental mismatch between blood supply and metabolic demand during exercise. At rest, even significantly stenosed arteries can deliver adequate blood flow, but the increased metabolic demands of walking muscle outstrip the limited supply, causing ischemic pain.

The clinical characteristics of claudication are remarkably consistent and diagnostically useful. Pain occurs in muscle groups distal to the arterial lesion: calf claudication indicates femoropopliteal disease, thigh and buttock claudication suggests aortoiliac disease (Leriche syndrome when combined with erectile dysfunction), and foot claudication implies tibial disease. The character is typically cramping, aching, or a sensation of fatigue rather than sharp or shooting pain. Most distinctively, claudication occurs at a predictable walking distance unique to each patient and resolves within two to five minutes of rest without requiring any positional change.

Differentiating claudication from other causes of leg pain during exertion is clinically important. Neurogenic claudication from spinal stenosis produces similar exercise-induced leg discomfort but characteristically improves with forward flexion (the "shopping cart sign") and worsens with extension. Unlike vascular claudication, neurogenic symptoms often involve bilateral symptoms, paresthesias, and relief with sitting rather than simple standing. Venous claudication from chronic venous obstruction produces a bursting quality pain relieved by leg elevation. Hip or knee arthritis causes joint rather than muscle pain and varies with specific movements rather than distance.

The natural history of claudication is more benign than many patients fear. Over five years, seventy to eighty percent of patients remain stable or improve with conservative management. Only ten to twenty percent experience worsening claudication, and merely one to two percent progress to critical limb ischemia requiring amputation. However, this optimistic limb prognosis contrasts starkly with the systemic outlook: twenty to thirty percent of claudicants die from cardiovascular causes within five years, reflecting the systemic nature of their atherosclerosis.

<image>Panel A: Walking person with arterial stenosis in the superficial femoral artery and oxygen supply-demand curves showing exercise increasing demand beyond supply capacity, compared to a resting person with supply meeting resting demand. Panel B: Walking distance to claudication timeline showing pain onset at a consistent distance, peak pain intensity, and resolution within 2-5 minutes of rest. Panel C: Vascular claudication characteristics including cramping muscle pain relieved by standing still, occurring at predictable walking distance. Panel D: Comparison table distinguishing vascular claudication from neurogenic claudication relieved by flexion, venous claudication relieved by elevation, and arthritis varying with movement.</image>

Critical Limb Ischemia

Critical limb ischemia represents the most severe manifestation of PAD, defined by chronic ischemia causing rest pain, tissue loss, or both. Unlike claudication where symptoms occur only with exertion, CLI patients experience ischemia even at rest, indicating that blood supply cannot meet even basal metabolic demands. This condition constitutes a limb-threatening and life-threatening emergency requiring prompt evaluation and revascularization.

Rest pain typically affects the forefoot and toes, the most distal and therefore most vulnerable territory. Patients characteristically report worsening pain at night when the beneficial effects of gravity-assisted dependent flow are lost. They often sleep with the affected leg dangling over the bedside or sleep in a chair to maintain dependency. This positional relationship is so characteristic that its absence should prompt reconsideration of the diagnosis.

Physical examination reveals several characteristic findings. Dependent rubor, a dusky red color when the leg is dependent, reflects maximally dilated capillaries attempting to compensate for poor inflow. This contrasts with pallor on elevation, easily demonstrated by having the patient lie supine and elevating the legs to sixty degrees for one minute. Skin changes include thin, shiny atrophic skin, hair loss, and thickened nails. Arterial ulcers typically occur at pressure points such as toes, heel, and malleoli, appearing as punched-out lesions with pale bases and minimal granulation tissue. In advanced cases, gangrene develops, beginning as dry gangrene in toes and potentially progressing to wet gangrene with superimposed infection.

Diagnostic criteria for CLI require hemodynamic confirmation. Ankle systolic pressure below fifty to seventy millimeters of mercury, toe pressure below thirty to fifty millimeters of mercury, or transcutaneous oxygen tension below thirty millimeters of mercury confirms the severity of ischemia. These thresholds indicate that perfusion pressure is inadequate for tissue viability.

The prognosis of untreated CLI is grim. Within one year, approximately twenty-five percent require major amputation and twenty percent die. These statistics underscore the urgency of revascularization, which should be pursued in more than fifty percent of patients when anatomically feasible.

<image>Panel A: Patient sitting with affected leg dangling at night for rest pain relief, with anatomical inset showing severely occluded tibial arteries and reduced perfusion pressure. Panel B: Pallor-rubor test showing marked foot pallor with leg elevated to 60 degrees and dark red dependent rubor when the leg is lowered. Panel C: Arterial ulcer characteristics including punched-out appearance, pale base, location on toes and heel, and minimal granulation tissue, with early digital gangrene. Panel D: Hemodynamic diagnostic criteria showing ankle pressure below 50-70 mmHg, toe pressure below 30-50 mmHg, and transcutaneous oxygen tension below 30 mmHg confirming critical limb ischemia.</image>

Acute Limb Ischemia

Acute limb ischemia occurs when a sudden decrease in limb perfusion threatens viability, typically developing within two weeks of symptom onset. Unlike the gradual progression of chronic PAD, acute limb ischemia presents as an emergency requiring immediate assessment and often urgent intervention to prevent limb loss.

The etiology divides into two major categories with distinct implications. Embolism from a cardiac source accounts for the majority of cases, with atrial fibrillation being the most common origin, followed by left ventricular thrombus after myocardial infarction and valvular vegetations. Embolic events characteristically produce sudden, severe symptoms in patients without prior claudication history, and the embolus typically lodges at arterial bifurcations where vessel caliber abruptly decreases. In contrast, thrombosis occurs in situ on preexisting atherosclerotic disease and often presents more gradually because collateral circulation has developed over time. Distinguishing embolism from thrombosis guides both immediate treatment and long-term management to prevent recurrence.

The classic presentation is described by the "Six P's," which should be assessed systematically. Pain is typically sudden and severe. Pallor produces a white, waxy, or mottled appearance. Pulselessness manifests as absent distal pulses. Poikilothermia results in a cold limb compared to the contralateral side. Paresthesias indicate sensory nerve ischemia and represent an early warning of threatened viability. Paralysis reflects motor nerve and muscle ischemia and represents an ominous late finding suggesting limited time for salvage.

The Rutherford classification guides management based on viability assessment. Class I (viable) limbs show no sensory or motor deficit and can tolerate elective revascularization. Class IIa (marginally threatened) limbs have minimal sensory loss limited to toes and require urgent revascularization within hours to days. Class IIb (immediately threatened) limbs demonstrate sensory loss beyond the toes and mild-to-moderate motor weakness, demanding emergency revascularization within hours. Class III (irreversible) limbs show profound sensory loss and paralysis, indicating that salvage is impossible and amputation is necessary to prevent life-threatening reperfusion syndrome.

Treatment begins with immediate anticoagulation using heparin to prevent thrombus propagation. Surgical embolectomy using balloon catheters is preferred for embolic occlusion in viable limbs. Catheter-directed thrombolysis offers an alternative for thrombotic occlusion when the limb remains viable or marginally threatened, allowing gradual clot dissolution and identification of underlying stenoses. Bypass surgery may be required when thrombosis occurs on complex atherosclerotic disease with inadequate outflow. For irreversibly ischemic limbs, primary amputation is necessary because revascularization would release toxic metabolites from necrotic muscle, causing potentially fatal reperfusion syndrome.

<image>Panel A: Embolus lodging at the common femoral artery bifurcation, with inset showing the cardiac source from atrial fibrillation with left atrial thrombus. Panel B: Six Ps examination checklist on a leg diagram: pain with sudden onset, pallor with white or mottled skin, pulselessness with absent dorsalis pedis and posterior tibial pulses, and poikilothermia with temperature gradient. Panel C: Remaining Ps showing paresthesias indicating sensory nerve ischemia as an early warning, and paralysis reflecting motor nerve and muscle ischemia as an ominous late finding. Panel D: Rutherford classification flowchart: Class I viable for elective revascularization, Class IIa marginally threatened for urgent revascularization, Class IIb immediately threatened for emergency revascularization, and Class III irreversible requiring amputation.</image>

Diagnosis of Peripheral Arterial Disease

The diagnostic evaluation of PAD begins with a thorough history and physical examination that can establish the diagnosis with high confidence before any testing. The history should focus on walking distance, symptom location, relieving factors, and risk factor profile. Physical examination must include systematic pulse assessment at femoral, popliteal, dorsalis pedis, and posterior tibial locations, comparison between limbs, auscultation for bruits over the femoral and iliac arteries, and inspection for trophic changes including hair loss, skin atrophy, cool temperature, and ulceration.

The ankle-brachial index serves as the cornerstone diagnostic test, providing both diagnostic confirmation and severity stratification. The ABI is calculated by dividing the highest ankle systolic pressure (from either dorsalis pedis or posterior tibial) by the highest brachial pressure. A normal ABI ranges from 0.91 to 1.30, indicating that ankle pressure equals or slightly exceeds arm pressure. An ABI of 0.71 to 0.90 indicates mild PAD, 0.41 to 0.70 indicates moderate PAD, and 0.40 or below indicates severe PAD. Importantly, an ABI above 1.30 suggests non-compressible vessels due to medial calcification, commonly seen in diabetes and chronic kidney disease, rendering the ABI unreliable.

When vessels are non-compressible, the toe-brachial index provides an alternative because digital arteries rarely calcify. A TBI above 0.7 is normal, with lower values indicating PAD. Exercise ABI testing can unmask disease when resting ABI is normal but clinical suspicion remains high; a drop in ABI of more than twenty percent after treadmill exercise confirms PAD.

Anatomical imaging is reserved for patients being considered for revascularization. Duplex ultrasound localizes stenoses and quantifies severity through velocity measurements, with peak systolic velocity ratios above 2.5 indicating significant stenosis. Computed tomographic angiography provides detailed anatomical mapping of the entire arterial tree, valuable for procedural planning. Magnetic resonance angiography offers similar anatomical detail without radiation but is limited by availability and contraindications. Conventional angiography remains the gold standard and allows simultaneous intervention but carries procedural risks.

<image>Panel A: ABI measurement technique with patient supine, blood pressure cuffs on arms and ankles, Doppler probes over brachial, dorsalis pedis, and posterior tibial arteries, with formula ABI equals ankle SBP divided by brachial SBP. Panel B: ABI severity scale showing normal 0.91-1.30, mild PAD 0.71-0.90, moderate PAD 0.41-0.70, severe PAD 0.40 or below, and non-compressible above 1.30. Panel C: Duplex ultrasound of the superficial femoral artery with spectral Doppler showing elevated peak systolic velocity at stenosis with greater than 2.5x velocity ratio. Panel D: CTA 3D reconstruction of the lower extremity arterial tree with stenoses and occlusions highlighted, demonstrating typical femoropopliteal disease pattern.</image>

Management of Peripheral Arterial Disease

The management of PAD follows a structured approach that addresses both local limb symptoms and the systemic cardiovascular risk. Because PAD patients face greater mortality from myocardial infarction and stroke than from limb complications, aggressive risk factor modification forms the foundation of treatment regardless of symptom severity.

Smoking cessation is the single most important intervention, slowing disease progression more effectively than any other measure. Smoking status should be assessed and cessation support offered at every visit. Diabetes management aims to prevent progression of distal disease, with careful attention to foot care to prevent ulceration. Lipid management follows high-risk cardiovascular disease guidelines, typically targeting aggressive LDL reduction with high-intensity statin therapy. Blood pressure control targets less than 130/80 millimeters of mercury, and importantly, beta-blockers are not contraindicated in PAD despite historical concerns.

Pharmacological therapy for PAD includes antiplatelet agents, typically aspirin or clopidogrel, which reduce cardiovascular events rather than improving limb symptoms directly. Statins provide lipid lowering and plaque stabilization benefits. ACE inhibitors offer cardiovascular protection beyond blood pressure effects. Cilostazol, a phosphodiesterase-3 inhibitor, is the only medication proven to improve walking distance in claudication, typically increasing maximal walking distance by fifty to one hundred percent.

Supervised exercise therapy is remarkably effective for claudication, representing the first-line treatment before revascularization is considered. A structured program involving thirty to forty-five minutes of walking three times weekly for at least twelve weeks improves walking distance by fifty to two hundred percent. The mechanism involves both improved muscle metabolism and collateral vessel development. Supervised programs produce better outcomes than unsupervised home exercise.

Revascularization is reserved for lifestyle-limiting claudication that fails conservative management or for critical limb ischemia where it is mandatory to prevent amputation. Endovascular approaches including angioplasty with or without stenting have become first-line for most anatomical patterns, particularly aortoiliac disease where outcomes are excellent. Surgical bypass using autologous vein or prosthetic graft remains important for complex, long-segment disease or when endovascular approaches fail or are not technically feasible.

<image>Panel A: Treatment pyramid base showing risk factor modification including smoking cessation, diabetes management, lipid control with statins, and blood pressure target below 130/80. Panel B: Medical therapy layer showing antiplatelet agents, statins, ACE inhibitors, and cilostazol improving walking distance 50-200%, and supervised exercise therapy for 30-45 minutes three times weekly for at least 12 weeks. Panel C: Endovascular revascularization showing balloon angioplasty and stent deployment in the femoral artery for claudication failing conservative therapy. Panel D: Surgical revascularization showing vein bypass graft from femoral to popliteal artery, with indications for lifestyle-limiting claudication or critical limb ischemia.</image>

Venous Thromboembolism

Venous thromboembolism encompasses deep vein thrombosis and pulmonary embolism, representing a spectrum of a single disease process. Understanding the pathophysiology through Virchow's triad explains both the risk factors and the therapeutic approach.

Virchow's triad identifies three predisposing factors: venous stasis, endothelial injury, and hypercoagulability. Stasis occurs with immobility, prolonged travel, paralysis, or venous obstruction, allowing activated clotting factors to accumulate rather than being cleared. Endothelial injury from surgery, trauma, central venous catheters, or prior thrombosis exposes subendothelial collagen and tissue factor. Hypercoagulable states include both acquired conditions (malignancy, pregnancy, estrogen therapy, antiphospholipid syndrome) and inherited thrombophilias (Factor V Leiden, prothrombin gene mutation, protein C/S deficiency, antithrombin deficiency).

Deep vein thrombosis typically affects the lower extremity veins, classified as proximal (popliteal, femoral, iliac) or distal (calf veins). Proximal DVT carries significantly higher risk of embolization and is always treated, while isolated distal DVT management is more nuanced. Clinical presentation includes unilateral leg swelling, pain, warmth, and erythema. However, clinical diagnosis is unreliable, with many suspected cases proving negative on testing and many true DVTs presenting atypically or asymptomatically.

The diagnostic approach combines clinical probability assessment with testing. The Wells score stratifies pretest probability based on clinical features and risk factors. D-dimer, a fibrin degradation product, has high sensitivity but low specificity: a negative D-dimer in low-probability patients effectively excludes DVT, but positive results require imaging. Compression ultrasonography is the first-line imaging test, with lack of vein compressibility being the diagnostic criterion for acute thrombosis.

Treatment involves anticoagulation to prevent thrombus propagation and embolization while the body's fibrinolytic system gradually resolves the clot. Options include parenteral agents (low-molecular-weight heparin, fondaparinux, unfractionated heparin) or direct oral anticoagulants (rivaroxaban, apixaban, edoxaban, dabigatran). Warfarin remains an option but requires bridging with parenteral therapy. Duration depends on whether the DVT was provoked (three months) or unprovoked (extended duration considered). Inferior vena cava filters are reserved for patients with absolute contraindications to anticoagulation.

<image>Panel A: Virchow's triad as a triangular diagram with stasis illustrated by a seated airplane passenger, endothelial injury from surgery or catheter, and hypercoagulability with malignancy and pregnancy. Panel B: Cross-section and longitudinal view of a femoral vein with acute thrombus formation, red blood cells trapped in fibrin mesh, and partial lumen occlusion. Panel C: Compression ultrasound showing a normal vein that collapses completely with probe pressure versus a thrombosed vein that remains non-compressible. Panel D: Anticoagulation treatment timeline with initial phase of 0-10 days using LMWH or DOAC, long-term phase of 3-6 months, and extended phase consideration for unprovoked DVT.</image>

Pulmonary Embolism

Pulmonary embolism occurs when venous thrombus dislodges and travels through the right heart to lodge in the pulmonary arterial tree. The clinical consequences depend on the size of the embolus and the patient's underlying cardiopulmonary reserve. Most emboli originate from proximal lower extremity DVT, though upper extremity DVT (often catheter-associated) and pelvic vein thrombi also embolize.

The pathophysiology involves both mechanical obstruction and vasoactive mediator release. Mechanical obstruction increases pulmonary vascular resistance, raising right ventricular afterload. Released mediators including serotonin and thromboxane cause additional vasoconstriction. The right ventricle, a thin-walled structure designed for a low-pressure system, may fail acutely when afterload increases dramatically. Hypoxemia results from ventilation-perfusion mismatch in areas where ventilation continues without perfusion, and from shunting if a patent foramen ovale opens due to elevated right atrial pressure.

Clinical presentation varies widely based on clot burden and reserve. Dyspnea is the most common symptom, occurring in most patients. Pleuritic chest pain suggests peripheral emboli causing pleural irritation. Cough, hemoptysis, and syncope occur variably. Syncope and hypotension indicate massive PE with hemodynamic compromise, representing the most severe presentation.

Diagnostic evaluation follows a similar probabilistic approach to DVT. Clinical decision rules (Wells criteria, Geneva score) stratify pretest probability. D-dimer effectively excludes PE in low-probability patients but cannot confirm the diagnosis. CT pulmonary angiography has become the diagnostic gold standard, directly visualizing filling defects within pulmonary arteries. Ventilation-perfusion scanning remains an alternative when CT is contraindicated. Echocardiography cannot diagnose PE but identifies right ventricular dysfunction, which has prognostic significance.

Risk stratification guides management intensity. Massive (high-risk) PE presents with sustained hypotension or shock and requires aggressive intervention including thrombolysis or embolectomy. Submassive (intermediate-risk) PE shows right ventricular dysfunction or elevated cardiac biomarkers but maintains hemodynamic stability, requiring close monitoring and consideration of advanced therapies if deterioration occurs. Low-risk PE shows no evidence of right ventricular strain and can often be managed as an outpatient with anticoagulation alone.

<image>Panel A: Pathophysiology showing a thrombus from the femoral vein traveling through the IVC and right heart to lodge in the pulmonary artery, with hemodynamic consequences of increased pulmonary vascular resistance and right ventricular strain. Panel B: Right ventricular dilation with interventricular septum bowing into the left ventricle creating a D-shaped LV and decreased cardiac output. Panel C: CT pulmonary angiography showing filling defects within contrast-enhanced pulmonary arteries in main and lobar vessels. Panel D: Risk stratification scale: massive with hypotension requiring thrombolysis, submassive with RV dysfunction requiring close monitoring, and low-risk suitable for outpatient anticoagulation.</image>

Chronic Venous Insufficiency

Chronic venous insufficiency results from sustained venous hypertension, typically due to valvular incompetence or chronic venous obstruction following DVT (post-thrombotic syndrome). Normal venous return depends on the calf muscle pump and competent valves preventing reflux. When this system fails, ambulatory venous pressure remains elevated rather than decreasing with walking, leading to progressive tissue damage.

The pathophysiology involves extravasation of fluid and macromolecules into the interstitial space due to elevated capillary pressure. Red blood cells leak and break down, depositing hemosiderin that causes characteristic brown discoloration. White blood cells become trapped and activated, releasing inflammatory mediators. Over time, fibrosis develops in the subcutaneous tissue (lipodermatosclerosis), and eventually ulceration occurs.

The CEAP classification stages CVI clinically. Class C0 shows no visible signs. Class C1 demonstrates telangiectasias or spider veins. Class C2 shows varicose veins. Class C3 manifests edema. Class C4 indicates skin changes including pigmentation (C4a) or lipodermatosclerosis (C4b). Class C5 indicates healed ulceration. Class C6 represents active ulceration.

Venous ulcers characteristically occur at the medial malleolus in the "gaiter area" where venous pressure is highest. Unlike arterial ulcers, they have irregular borders, shallow depth, and a moist base with granulation tissue. Surrounding skin shows the stigmata of CVI: edema, hemosiderin staining, and the "inverted champagne bottle" appearance of lipodermatosclerosis.

Treatment centers on reducing venous hypertension. Compression therapy with graduated compression stockings (typically 30-40 mmHg) is the cornerstone, reducing ambulatory venous pressure and promoting ulcer healing. Leg elevation above heart level several times daily assists venous return. Wound care for ulcers involves appropriate dressings and debridement as needed. For patients with superficial venous reflux, ablation procedures (endovenous laser, radiofrequency, or surgical stripping) can eliminate the source of reflux. Sclerotherapy treats superficial varicosities for symptomatic or cosmetic benefit.

<image>Panel A: Normal venous physiology with competent valve showing unidirectional upward flow aided by calf muscle contraction, versus CVI with incompetent valve allowing bidirectional flow and reflux with elevated capillary pressure. Panel B: CEAP classification progression: C1 telangiectasias, C2 varicose veins, C3 pitting edema, C4 hemosiderin staining and lipodermatosclerosis with inverted champagne bottle appearance. Panel C: Advanced CEAP stages: C5 healed ulcer scar at medial malleolus and C6 active venous ulcer with irregular borders, shallow depth, and moist granulation tissue, contrasted with arterial ulcers at toe and heel with pale base. Panel D: Treatment options including graduated compression stockings at 30-40 mmHg, leg elevation above heart level, wound care with dressings, and endovenous ablation procedures for superficial reflux.</image>

Abdominal Aortic Aneurysm

Abdominal aortic aneurysm represents localized dilation of the aorta beyond fifty percent of its normal diameter, with infrarenal location being most common. The normal infrarenal aortic diameter is approximately two centimeters, making three centimeters the threshold for aneurysm definition.

The pathophysiology involves degradation of the structural matrix proteins that provide aortic wall strength. Matrix metalloproteinases degrade elastin and collagen, inflammatory cells infiltrate the media, and smooth muscle cells undergo apoptosis. The resulting wall weakening leads to progressive dilation. The law of LaPlace explains the self-perpetuating nature: as the radius increases, wall tension increases for any given pressure, promoting further expansion.

Risk factors include smoking (the strongest modifiable risk), age over sixty-five, male sex (four to six times more common in men), family history (twofold increased risk in first-degree relatives), and atherosclerosis (though aneurysmal and occlusive disease are distinct processes). Connective tissue disorders including Marfan syndrome and Ehlers-Danlos syndrome predispose to aneurysms at younger ages and in thoracic locations.

Most AAAs remain asymptomatic and are discovered incidentally on imaging or physical examination as a pulsatile abdominal mass. Symptomatic aneurysms may cause vague abdominal or back discomfort from expansion. Rupture produces sudden severe abdominal or back pain, often with radiation to the flank, accompanied by hypotension and shock. Ruptured AAA carries fifty percent mortality even with emergency surgery and near-universal mortality without intervention.

Screening recommendations focus on the highest-risk population: men aged sixty-five to seventy-five who have ever smoked should receive a one-time ultrasound screening. Surveillance protocols for detected aneurysms depend on size: AAA less than four centimeters warrants annual ultrasound, four to 5.4 centimeters requires ultrasound every six to twelve months.

Repair is indicated for symptomatic aneurysms at any size, ruptured aneurysms emergently, or asymptomatic aneurysms reaching threshold size (5.5 centimeters in men, 5.0 centimeters in women) or expanding rapidly (more than 0.5 centimeters over six months). Endovascular aneurysm repair (EVAR) has become the dominant approach for suitable anatomy, deploying a stent-graft through femoral access to exclude the aneurysm from circulation. Open surgical repair involves replacing the aneurysmal segment with a prosthetic graft and remains necessary when anatomy precludes endovascular repair or for ruptured aneurysms in many settings. Medical management focuses on smoking cessation, blood pressure control (beta-blockers may slow expansion), and statin therapy.

<image>Panel A: Molecular pathophysiology showing aneurysmal aortic wall cross-section with MMP-mediated elastin degradation, inflammatory cell infiltration, and smooth muscle cell loss, with the Law of LaPlace equation showing wall tension equals pressure times radius. Panel B: Screening ultrasound measuring infrarenal AAA at 4.5 cm transverse diameter, with surveillance intervals of annual for less than 4 cm and every 6-12 months for 4-5.4 cm. Panel C: Rupture presentation with acute abdominal and back pain radiating to the flank, retroperitoneal hemorrhage on CT, and hemodynamic instability. Panel D: Repair options comparing EVAR with femoral access and stent-graft deployment versus open surgical repair with prosthetic graft interposition, with repair thresholds of 5.5 cm for men and 5.0 cm for women.</image>

Summary

Peripheral arterial disease represents atherosclerosis of non-coronary arteries, with smoking as the strongest risk factor and the femoropopliteal segment as the most common location. Intermittent claudication causes reproducible exercise-induced muscle pain relieved by rest within minutes. Critical limb ischemia manifests as rest pain or tissue loss and constitutes a limb-threatening emergency requiring revascularization. Acute limb ischemia presents with the six P's (pain, pallor, pulselessness, poikilothermia, paresthesias, paralysis) and requires urgent assessment using the Rutherford classification to guide treatment. The ankle-brachial index serves as the diagnostic cornerstone, with values below 0.9 confirming PAD and values above 1.3 indicating non-compressible vessels. Venous thromboembolism encompasses DVT and PE, with Virchow's triad (stasis, endothelial injury, hypercoagulability) explaining pathophysiology. Chronic venous insufficiency results from venous hypertension causing characteristic skin changes and ulceration managed primarily with compression therapy. Abdominal aortic aneurysm affects primarily older male smokers, with screening recommended for this population and repair indicated when size reaches 5.5 centimeters or symptoms develop.

Key Terms

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