Noninvasive Vascular Testing for the Diagnosis of Lower Extremity, Carotid, Renal Artery, and Abdominal Aortic Diseases



Noninvasive Vascular Testing for the Diagnosis of Lower Extremity, Carotid, Renal Artery, and Abdominal Aortic Diseases


Michael R. Jaff



A thorough clinical evaluation and accurate noninvasive testing remain the cornerstones of successful patient stratification in vascular medicine. Given the myriad of therapeutic options in these complex patients, and the systemic nature of atherosclerosis, diagnostic methods must be accurate, safe, painless, and reproducible. Comprehensive methodical testing promotes improved outcomes through appropriate patient selection. Ultrasoundbased testing in the four major peripheral arterial beds are reviewed in this chapter: lower extremity, extracranial carotid, abdominal aortic, and renal. Magnetic resonance imaging and CT angiographic techniques for the diagnosis of arterial disease are discussed in later chapters (see Chapters 4 and 5, respectively).


BASICS OF VASCULAR ULTRASOUND

An understanding of the principles of ultrasonography is an essential prerequisite for successful vascular testing as this modality is used in the diagnostic evaluation of most vascular beds. Vascular ultrasound is based on the principle of Christian Doppler, who described a “frequency shift” of an emitted sound wave beam. This “shift” is the difference between the frequency of transmission and the frequency of reflection. The frequency of the sound waves used in diagnostic ultrasound, measured in megahertz (MHz), is above the frequency heard by the human ear. As the ultrasound beam is emitted into the body, it hits flowing blood, among other targets (bone, soft tissue structures, etc.) and is reflected back to the ultrasound transducer crystal. This information is then converted into a gray-scale image on a monitor. The addition of the Doppler waveform to the gray-scale B-mode (“brightness” mode) image is known as duplex ultrasonography (DUS). Modern, commercially available ultrasound machines add color to the gray-scale image. This provides more rapid identification of vascular structures and shortens the examination time significantly. Estimation of peak velocities requires the ultrasound beam to be parallel to the flow in the vessel. This can be adjusted on the machine (Fig. 2.1).







FIGURE 2-1. A: Incorrect Doppler angle. B: Correct Doppler angle where the angle of insonation is parallel to the direction of arterial flow.


DIAGNOSTIC EVALUATION OF LOWER EXTREMITY ARTERIAL DISEASE


Lower Extremity Arterial Testing

The evaluation of patients with peripheral artery disease (PAD) includes a historical review of patient symptoms and atherosclerotic risk factors, physical examination, and the use of noninvasive vascular tests. The equipment and training required to perform these examinations are minimal; therefore, these may be performed readily in the office in the initial diagnostic evaluation, immediately after or concomitant with physical examination.


Overall Approach to Lower Extremity Diagnostic Testing

Although many vascular practices, in conjunction with their vascular laboratories, use different algorithms for the diagnosis of PAD, there are some consistent patterns. Ankle-brachial indices (ABIs) are performed in every patient suspected of having PAD. If general information regarding the anatomic location of PAD is required, physiologic testing with segmental limb pressures (SLPs) and pulse volume recordings (PVRs) is sufficient. The addition of an exercise treadmill test to assess response of the ABI may be extremely helpful in confirming or excluding an arterial basis to lower extremity pain of a “claudication” nature. In addition, exercise testing provides an objective documentation of the true functional limitation of PAD and can be used to demonstrate physiologic improvement after intervention (Table 2.1). If specific information regarding the precise location of arterial stenoses or occlusion is required, DUS may be performed from the infrarenal abdominal aorta through the distal tibial arteries. In a number of vascular labs, ABIs, SLPs, and PVRs are obtained simultaneously as initial diagnostic tests in patients with suspected PAD, or limb discomfort without an obvious cause prior to or at the time of the initial visit.









TABLE 2.1 NONINVASIVE DIAGNOSTIC TESTING FOR PERIPHERAL ARTERIAL DISEASE



































Vascular Laboratory Examination

Information Obtained

Clinical Indication

Limitations


Segmental limb pressures

Localizes disease to specific segments of the lower extremity arteries; may aid in predicting wound healing potential

Moderate to severe claudication or limb ischemia with consideration to revascularization

Inaccurate in patients with noncompressible arteries; requires special cuffs; proximal thigh cuff occasionally uncomfortable for the patient


Pulse volume recordings

Localizes disease to specific segments of the lower extremity arteries; may aid in predicting wound healing potential

Moderate to severe claudication or limb ischemia with consideration to revascularization; useful in calcified arteries

Requires a skilled and meticulous technologist; mainly qualitative information


Segmental Doppler waveforms

Localizes disease to specific segments of the lower extremity arteries; easy to perform and interpret

Moderate to severe claudication or limb ischemia with consideration to revascularization

Not accurate in calcified arteries; less accurate in selected centers than PVRs


Exercise ABI

Confirms diagnosis of peripheral arterial disease when resting ABI is >0.90

Atypical symptoms of exertional limb discomfort Serial examinations to demonstrate clinical effects of intervention

Requires calibrated treadmill and close observation; many patients may not be able to complete exercise study; technologist must be competent to rapidly perform postexercise arterial pressures


Arterial duplex ultrasonography

Specific identification of sites of atherosclerotic disease: stenosis, occlusion; can accurately clarify options for invasive therapy

Advanced intermittent claudication, critical limb ischemia with need for revascularization; postcatheterization access site complication (i.e., pseudoaneurysm, hematoma, arteriovenous fistula)

Requires expensive equipment; requires skilled technologist; prolonged examination time; calcified arteries cause acoustic shadowing and inability to obtain Doppler velocities; provides only anatomic information and does not describe functional limitation


(Reprinted from Hiatt WR, Hirsch AT, Regensteiner J. Peripheral arterial disease handbook. Philadelphia: Lippincott, Williams & Wilkins, 2001:88-89, Table 5.1, with permission.)



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Jun 12, 2016 | Posted by in CARDIOLOGY | Comments Off on Noninvasive Vascular Testing for the Diagnosis of Lower Extremity, Carotid, Renal Artery, and Abdominal Aortic Diseases

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