Cath Lab Digest

Introduction

Seven million of the 25 million Americans with venous insufficiency exhibit serious symptoms such as edema, skin changes and venous ulcers.¹ One million of these patients seek medical advice annually. Overall, 80% of patients with venous insufficiency are managed conservatively, e.g., leg elevation and support stockings, and 20% are treated with vein stripping or endovenous ablation.

Etiology

The underlying cause of chronic venous insufficiency (CVI) is venous hypertension, where primary valve incompetence is the causative factor in 70–80% of cases.2 The other 20–25% of cases are caused by secondary valve incompetence as a result of deep vein thrombosis (DVT) or trauma. Congenital anomalies are responsible for < 3%.² Generally, a combination of reflux and obstruction is more common than either abnormality.

Diagnostic Testing for CVI

The ideal test for CVI should provide anatomic and hemodynamic data. Over the past few decades, the standard tests used for the diagnosis of CVI have included descending/ascending phlebography and ambulatory venous pressures, however, both tests are invasive and have some limitations. Competent proximal valves may prevent assessment of distal reflux, whereas a hypertonic contrast medium may stream past normal valves in elevated legs. Evaluation of the great and small saphenous veins is also limited when using these techniques.³ Measurement of the ambulatory venous pressure reflects the global hemodynamics within the extremity and has a linear relationship with the presence of ulceration.⁴ Ambulatory venous pressure, however, cannot localize hemodynamic abnormalities, and is influenced by reflux and obstruction. Because of these limitations, the modern diagnosis of CVI relies on the use of noninvasive testing.

Noninvasive Testing for CVI

Indirect physiological methods include strain-gauge plethysmography (SPG) and impedance plethysmography (IPG), both of which are outdated; and photoplethysmography (PPG) and air plethysmography (APG), both of which have limited use in some vascular laboratories, therefore we will only discuss these tests briefly.

Photoplethysmography (PPG)

PPG is an indirect method of measuring volume change occurring in the cutaneous capillary network using a light (photo) source. PPG is mainly used to detect the presence of venous reflux (venous valvular incompetence). The test is performed by placing an infrared light source on the leg with an adjacent photoreceptor (sensor) to receive the backscattered light. This allows for the continuous recording on a strip chart of the signal intensity reflected from the cutaneous capillary network.

The patient is seated and legs are allowed to hang freely. (Figure 1). A baseline recording is obtained, then the patient performs five successive plantar flexion/extension maneuvers. The venous refill time with PPG measures the time it takes capillaries to empty and is dependent on the arterial inflow and efficiency of the venous outflow (Figure 2).^5,6 When reflux is identified by PPG, the placement of a tourniquet (or narrow occluding cuff inflated to 50 mmHg) alternately above and below the knee may help the investigator in localizing the site of reflux (Figure 3).⁶

There may be considerable variability in the measurements obtained from the same patient. Transducer position may also cause variations in measurements.

Color-flow scanning can identify the sites of reflux more precisely and is currently the preferred method to evaluate patients with valvular incompetence and CVI.7

Air Plethysmography (APG)

APG is more accurate than impedance plethysmography, strain-gauge plethysmography or photo plethysmography in measuring true volume and is easier to use. Essentially, it has three major components: a transducer, which is a form of closed air bladder used to surround the limb segment, a pressure sensor that measures the pressure in the air bladder as a function of time and an electrical circuit that controls the pressure sensor and displays measured results (Figure 4). Since the air bladder surrounds the limb, any change in volume will cause pressure within the bladder to change. If limb volume increases, bladder volume will decrease, causing bladder pressure to increase. The test will detect changes in venous limb volume, secondary to patient maneuvers.

Parameters/Maneuvers Used for the Diagnosis of CVI Using APG

The patient is placed in supine position. This will lower venous pressure in the lower extremities to a value only slightly above the right atrial pressure (~0 mmHg). A baseline volume in the segment of interest is then recorded. When the patient is placed in the erect position, lower-extremity venous pressure increases due to the hydrostatic column of blood extending from the right atrium to the segment of interest. This volume increase is displayed on a graph as seen in Figure 5. The Y-axis is volume and the X-axis is time, since all measurements are either times or ratios.