Peripheral Arterial Evaluation

Objectives

On completion of this chapter, you should be able to:

Describe the anatomy encountered during an arterial duplex examination
Understand arterial physiology as it relates to the development of peripheral arterial disease
Recognize the risk factors associated with peripheral arterial disease
Discuss the changes that occur to segmental pressures and pulse volume waveforms in the presence of occlusive arterial disease
Outline proper instrument control settings used during arterial duplex imaging
Describe the characteristics of arterial spectral Doppler signals obtained during arterial duplex imaging
Discuss the imaging characteristics associated with arterial narrowing

Key Terms

Ankle-brachial index (ABI)

Anterior tibial artery (ATA)

Axillary artery

Brachial artery

Claudication

Common femoral artery

Femoral artery

Dorsalis pedis artery (DPA)

Innominate artery

Ischemic rest pain

Peripheral arterial aneurysms

Peroneal artery

Popliteal artery

Posterior tibial artery (PTA)

Profunda femoris artery

Pseudoaneurysm

Radial artery

Raynaud phenomenon

Subclavian artery

Thoracic outlet syndrome

Tibial-peroneal trunk

Toe-brachial index (TBI)

Ulnar artery

In its advent, noninvasive testing was used to offer objectivity in the diagnosis of peripheral arterial disease (PAD). Today’s ultrasound and oscillometric technology allow clinicians to acquire both anatomic and physiologic information while evaluating patients with PAD. Capabilities have advanced from simple oscillometric measurements to segmental pressures, pulse volume recordings, stress testing, and direct evaluation of arteries by duplex imaging. This has allowed indications for its use to be expanded. Further, the current noninvasive evaluation is tailored to patients’ specific needs depending on clinical presentation and suspected pathology.

PAD affects an estimated 6.5 million people in the United States over the age of 40. In 2016, this resulted in 1.6 million office visits and 11,000 emergency visits. This results in an estimated $84 to $380 billion annual healthcare costs. PAD can present with a wide variety of symptoms, but may also remain asymptomatic even in patients with advanced stages. Therefore the physical examination alone has poor sensitivity and specificity. Only approximately 10% of individuals with PAD present with the classic symptom of intermittent claudication, while 50% present with non-specific leg symptoms other than claudication. Further, an estimated 40% of patients with PAD have no symptoms. Noninvasive arterial evaluations complement a patient history and physical examination. It has become a valuable tool for many patients and their physicians to confirm suspected diagnoses and detect arterial occlusive disease in the asymptomatic patient. Further, noninvasive testing stages disease severity and is used longitudinally to monitor disease progression and response to treatment ( Box 39.1 ).

Box 39.1

Purposes of Noninvasive Arterial Testing

Provide objective documentation of arterial disease severity
Aid in diagnosis of exercise-induced pain caused by occlusive arterial disease
Supplement clinical judgment regarding foot ulcer and amputation site healing
Evaluate pulsatile masses (aneurysms, pseudoaneurysms)
Evaluate suspected arterial trauma
Evaluate surrounding arterial anatomy
Evaluate angioplasty/stent placement (planning and follow-up)
Establish a baseline study before operative reconstruction
Provide postoperative monitoring, including bypass and dialysis graft surveillance

Noninvasive arterial testing consists of two different types of ultrasound technology: (1) indirect and (2) direct testing or duplex imaging. Although indirect tests and peripheral arterial duplex imaging are discussed separately in this chapter, a combination of tests from both categories is typically used in combination to obtain a more holistic depiction of disease.

Anatomy Associated with Peripheral Arterial Testing

The peripheral arterial system is made up of arteries, arterioles, and capillaries in the most distal portion. The main function of the arterial system is to transport oxygen-rich blood from the heart to perfuse organs and tissues throughout the body. After exiting the left ventricle of the heart, blood travels through the central arteries until it reaches the arteries of the periphery. The peripheral arteries located in the upper and lower extremities transport blood to the arterial system microcirculation. Blood enters the arterioles, then capillaries which make arterial microcirculation. After the capillaries, blood exits the arterial system and enters the venous system for its return to the heart.

The wall of an artery consists of three layers: (1) tunica intima (innermost), (2) tunica media (middle), and (3) tunica adventitia (outermost). The tunica media layer primarily consists of smooth muscle and connective tissue and provides the vessel with structure and support.

Lower Extremity

The descending aorta is the continuation of the aorta beyond the aortic arch. The descending aorta is divided into the thoracic and abdominal sections. The thoracic portion terminates at the aortic opening in the diaphragm, where the abdominal aorta begins at the approximate level of the twelfth thoracic vertebra as it passes through the aortic hiatus of the diaphragm. At the approximate level of the fourth lumbar vertebra, the abdominal aorta bifurcates to become the right and left common iliac arteries ( Fig. 39.1 ). Each common iliac artery bifurcates into an internal and external iliac artery. The internal iliac artery (hypogastric) perfuses the pelvis, while the external iliac artery continues distally to supply blood to the lower extremity. The external iliac artery terminates at the level of the inguinal ligament where it becomes the common femoral artery.

The common femoral artery (CFA) originates beneath the inguinal ligament and travels distally in proximity to the common femoral vein. In the distal portion of the groin, the CFA bifurcates into the femoral and profunda femoris (deep femoral) arteries. The profunda femoris artery is located posterior and lateral to the femoral artery. It begins at the CFA bifurcation and terminates in the lower third of the thigh. The profunda femoris artery travels deep within the leg in close association with the profunda femoris vein to perfuse the muscles of the thigh and hip. The femoral artery (FA) originates from the CFA bifurcation and travels through the adductor (Hunter) canal and continues along the length of the medial thigh in close proximity to the femoral vein. The proximal FA begins superficial to the profunda femoris artery but dives deep in the distal portion of the thigh. The FA terminates at the opening of the adductor magnus muscle, at which point it becomes the popliteal artery. The popliteal artery travels behind the knee in the popliteal fossa with the popliteal vein. Major branches of the popliteal artery are the sural and genicular arteries that perfuse the popliteal fossa and calf muscles. The popliteal artery terminates distally into the anterior tibial artery and the tibioperoneal trunk.

The anterior tibial artery (ATA) arises from the popliteal artery in the proximal calf and travels distally along the lateral calf into the anterior compartment of the ankle. At this level, it courses superficial and becomes the dorsalis pedis artery. The dorsalis pedis artery (DPA) is located on the dorsal foot. At its distal portion, the DPA joins with branches of the posterior tibial artery to form the plantar arch. Arising off the plantar arch are the metatarsal arteries that divide into the digital branch arteries.

The tibial-peroneal trunk (tibial-fibular trunk) begins in the proximal calf from the bifurcation of the popliteal artery. The tibial-peroneal trunk briefly travels distally until its bifurcation into the posterior tibial artery and the peroneal artery. The posterior tibial artery (PTA) travels down the medial calf in the posterior compartment, parallel to the posterior tibial veins. The PTA terminates between the ankle and the heel into the medial and lateral plantar arteries. The peroneal artery is located deep within the calf and travels with the peroneal veins near the medial aspect of the fibula, parallel and deep to the PTA. The peroneal artery terminates in the distal third portion of the calf. Its branches communicate with branches of the PTA and ATA.

Upper Extremity

The ascending aorta originates from the left ventricle. The transverse aortic arch is located in the superior mediastinum and is formed as the aorta ascends and curves posteroinferiorly from right to left. This occurs superior to the left mainstem bronchus. Three main branches arise from the superior convexity of the arch in its normal configuration. The first is the innominate artery (brachiocephalic), which divides into the right subclavian and the right common carotid artery. Next, the left common carotid artery arises, followed by the left subclavian artery ( Fig. 39.2 ).

The subclavian artery originates at the inner border of the scalenus anterior muscle in close proximity to the subclavian vein and travels beneath the clavicle to the outer border of the first rib. Here it becomes the axillary artery. Major branches of the subclavian artery are the vertebral artery, thyrocervical trunk, costocervical trunk, internal mammary artery, and dorsal scapular artery. The axillary artery is a continuation of the subclavian artery, which begins at the outer border of the first rib and travels through the axilla in close association with the axillary vein. The axillary artery terminates at the lower border of the tendon of the teres major muscle where it becomes the brachial artery. The brachial artery travels near and parallel to the paired brachial veins along the medial portion of the upper arm. The brachial artery typically terminates just below the antecubital fossa into the radial and ulnar arteries, but anatomic variations in this area are common.

The radial artery begins at the brachial artery bifurcation and travels distally along the lateral forearm. At the level of the palm, the radial artery terminates to form the deep palmar arch. The ulnar artery originates at the brachial artery bifurcation and travels distally along the medial forearm. At the level of the palm, the ulnar artery terminates to form the superficial palmar arch. Both palmar arches supply blood to the digital arteries.

Arterial Physiology

The arterial portion of the circulatory system transports oxygenated, nutrient-rich blood from the heart to the various organs and tissues of the body. On cardiac contraction, the left ventricle ejects a stroke volume of arterial blood into the arterial system. Contraction of the left ventricle applies significant pressure to the ejected blood, creating a large amount of kinetic energy for the blood within the arterial system. The arterial system is characterized as a closed, high-pressure system. Being a closed system preserves the amount of kinetic energy within it. High levels of kinetic energy allow arterial blood to travel far distances within the arterial system quickly and efficiently.

In general, artery diameter decreases distally in the periphery. Vessel diameter has the greatest effect on flow volume and consequently directly influences arterial hemodynamics. Artery diameter and blood flow resistance are inversely related, meaning as the diameter of an artery decreases, arterial resistance increases. To this end, when a constant blood flow volume exists, a decrease in artery diameter will result in an increase in arterial blood flow velocity, as conveyed by Bernoulli’s principle (velocity = flow/area). Blood flow velocity is represented as peak systolic velocity (PSV) and end-diastolic velocity (EDV), typically measured in centimeters per second (cm/sec). Arterial PSV increases can be used as a marker for arterial pathology. Arterial occlusive disorders, such as PAD, cause a reduction in arterial lumen causing PSV elevation in the area of diminished diameter. Detection of PSV increase is used to diagnose, stage, and categorize arterial diseases. This is the main principle on which noninvasive testing relies. Measuring true lumen diameter compared to residual lumen diameter can also be used to detect arterial disease. This is known as a diameter reduction measurement.

Arterial Pathophysiology

PAD and other occlusive disorders are characterized by a reduction in arterial lumen diameter. Arterial lumen reduction causes an increase in arterial resistance and prevents optimal blood volume to flow through the afflicted segment(s) of the vessel. The result is an inadequate supply of arterial blood to the muscles and/or tissues of the body. When in use, muscle tissue requires more arterial perfusion to meet increased oxygen demand. Therefore, using muscles that are perfused by an artery affected by PAD will cause symptoms arising from muscle tissue oxygen deficiency. This is common in the lower extremities, as muscles require increased perfusion during ambulation. The inability to receive extra arterial blood required for muscle use is known as intermittent claudication. Intermittent claudication is characterized by muscle pain (cramp, ache, numbness, and/or fatigue) during use, which subside on rest. The classic presentation of intermittent claudication is in the calf muscles presenting during ambulation. In severe circumstances, arterial perfusion is diminished to the point at which it can no longer meet the oxygen demands of tissues, even while at rest. This results in tissue ischemia and death, which may present as tissue ulceration or gangrene.

Atherosclerosis is the primary disease process leading to PAD. Atherosclerosis is characterized as the buildup of atherosclerotic plaque on the arterial endothelium as a result of excess lipids present in the blood. Over time, the plaque hardens, while continual buildup reduces the lumen area. Atherosclerosis can also cause an arterial embolism, which can occur when plaque dislodges from the arterial wall and propagates distally in the arterial system. Emboli can travel to the brain resulting in stroke or can lodge in the extremities and occlude small vessels, causing ischemia.

Peripheral Arterial Disease

Treatments

Treatment methods for PAD aim to decrease patient symptoms and improve prognosis by preventing the risk of further cardiovascular events. Treatments can be categorized into three types: (1) medical management/conservative, (2) endovascular, and (3) surgical.

The first goal of conservative treatments is to reduce controllable risk factors for PAD such as tobacco use and poor diet through lifestyle modification. Exercise is also recommended, as evidence has demonstrated this leads to increased walking ability both in range and degree of pain, as compared with non-exercising PAD sufferers. Medical management can also be implemented using pharmacologic agents, but this generally results in only mild to moderate improvement of symptoms. Common types of agents prescribed are anticoagulants, antiplatelets, antihypertensives, and lipid-lowering agents.

Endovascular treatments aim to revascularize limbs afflicted with PAD. Endovascular procedures are becoming a popular treatment strategy, as they are much less invasive than other surgical options. Here, a catheter is introduced into the arterial system, typically in the FA at the groin, and is advanced to the site of the atherosclerotic lesion, where a variety of revascularization methods can be performed. Common types of endovascular revascularization interventions are percutaneous transluminal angioplasty (increases artery diameter in cases of focal lesions), endograft placements (for aneurysm repair), atherectomy (removes plaque), and thrombin injections (for pseudoaneurysm treatment). Although the long-term effects of endovascular revascularizations are debated, it is often the default interventional approach, followed by surgical intervention in case of failure.

Surgical interventions, like endovascular interventions, mainly focus on revascularizing the afflicted limb but are typically more invasive. The most common vascular surgical intervention is bypass graft surgery. Bypass graft surgery creates a new arterial conduit to provide blood flow with an alternative route. This conduit is anastomosed with the affected artery proximal and distal to the atherosclerotic lesion. A variety of bypass graft types can be used ranging from native vessels to synthetic materials. Other common revascularization surgical interventions are thrombectomy (removal of a thrombus or embolus) and endarterectomy (surgical removal of plaque and the intima and media layers of an artery). In severe cases of PAD, the goal of vascular surgical intervention is to prevent further disease progression. The most common form is limb amputation.

It is important for sonographers practicing arterial imaging to understand the different PAD treatment strategies. Familiarization with types of medical management is beneficial while obtaining patient histories. Furthermore, many of the aforementioned endovascular surgical interventions, such as percutaneous angioplasty, thrombin injections, and some bypass graft placements, are performed under ultrasound guidance. Occasionally, sonographers will be asked to assist in these surgeries to perform the ultrasound guidance imaging. If this occurs, an understanding of the surgery and why it is being performed will allow the sonographer to more effectively assist the vascular surgeon by providing accurate and relevant information.

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here