Gregory L. Moneta

Duplex ultrasound scanning in the diagnosis of renal artery stenosis: A prospective evaluation

Since ultrasonic energy can be used to interrogate vessels at great depth, it is only natural that it should be applied to deeply placed arteries in the abdomen. Early studies suggested that high-grade stenoses of the renal artery could be detected by this approach as long as the peak systolic velocity in the renal artery was normalized by that measured in the abdominal aorta. A retrospective study comparing the peak velocity in the renal artery to that from the adjacent abdominal aorta (the renal aortic ratio) showed that if this value exceeded 3.5, it is likely to be associated with a greater than 60% diameter-reducing stenosis. To test this hypothesis, we used duplex scanning to prospectively evaluate 58 renal arteries in 29 patients in whom arteriograms were available. There were 39 renal arteries with 0% to 59% stenosis, 14 with 60% to 99% stenosis, and five occlusions by angiography. Renal duplex scanning accurately diagnosed 38 of 39, 11 of 14, and four of five of these, respectively, giving a sensitivity of 84%, a specificity of 97%, and a positive predictive value of 94% for the detection of a greater than 60% diameter-reducing stenosis. The overall agreement with angiography was 93%. These data show that renal duplex scanning can be used to diagnose renal artery stenosis in patients with hypertension or renal dysfunction, thus providing a rational basis for the selection of patients for angiography.

Duplex Ultrasound Measurement of Postprandial Intestinal Blood Flow: Effect of Meal Composition

Duplex ultrasound was used to evaluate the effects of 350-cal, 300-ml protein, fat, carbohydrate, and mixed (Ensure-Plus) liquid meals on celiac, superior mesenteric, and femoral artery blood flow in 7 healthy volunteers. Ingestion of separate water and mannitol solutions served as controls for volume and osmolarity. Duplex parameters of peak systolic velocity, end-diastolic velocity, mean velocity, and volume flow were determined before, and serially for 90 min after, ingestion of each test meal. Maximal changes were compared with baseline values. There were no significant changes in any of the blood flow parameters derived from the celiac or femoral arteries after any test meal ingested. In contrast, maximal changes in all superior mesenteric artery parameters were increased significantly over baseline (p less than 0.05) after each of the test meals except water, with end-diastolic velocity showing proportionally the greatest increase. The study demonstrates that duplex ultrasound can provide a noninvasive means of studying the reactivity of the splanchnic arterial circulation to different stimuli and documents differing blood flow responses to variation of nutrients.

Operative versus nonoperative management of asymptomatic high-grade internal carotid artery stenosis: Improved results with endarterectomy

In a 4-year period, 129 asymptomatic high-grade (80-99%) internal carotid artery stenoses were identified in 115 patients. Because we previously demonstrated a strong relation between degree of carotid stenosis and subsequent development of ipsilateral related events (stroke, transient ischemic attack, and carotid occlusion), we changed our previous policy and began to offer carotid endarterectomy to good surgical risk patients referred to us with asymptomatic high-grade carotid stenosis. A total of 56 carotid endarterectomies were performed while 73 lesions were followed nonoperatively. Operated and nonoperated groups were similar with regard to age, prevalence of hypertension, cardiac disease, diabetes, and aspirin use. Life table analysis to 24 months revealed a higher rate of stroke (19 vs. 4%, p = 0.08), transient focal neurologic deficits (28 vs. 5%, p = 0.008), and carotid occlusion (29 vs. 0%, p = 0.003) in the nonoperated group. Eight of the 9 strokes in the nonoperated group occurred within 9 months of diagnosis of the high-grade lesion; none were preceded by a transient ischemic attack. There was 1 perioperative stroke (1.8%) but no in-hospital operative deaths and no difference in the late death rates of the two groups. This suggests that the preservation of neurologic status in patients with asymptomatic high-grade internal carotid artery stenosis can be improved by carotid endarterectomy.

Hypoperfusion as a possible factor in the development of gastrointestinal complications after cardiac surgery

This study has presented the spectrum of postoperative gastrointestinal system complications after open heart surgery at the University of Washington from 1980 through 1983. The frequent necessity for operative intervention and a mortality rate of 17 percent in our study of gastrointestinal complications in patients who have undergone open heart surgery indicates the need for early diagnosis and treatment. The data suggest that bypass times approaching 100 minutes and the presence of postoperative cardiogenic shock are important risk factors in the development of such complications in elective cardiac surgery patients. An incidence of gastrointestinal complications of 8.6 percent in those undergoing repair of acute aortic dissections makes gastrointestinal complaints particularly suspicious in this subgroup.

Follow-up of renal artery stenosis by duplex ultrasound

We have previously shown that duplex ultrasound is an accurate method of diagnosing renal artery stenosis (93% accuracy compared with angiography in the diagnosis of less than 60% stenosis, 60% to 99% stenosis, or occlusion). With this method we have now serially observed 35 renal arteries with 60% to 99% renal artery stenosis in 27 patients. Nineteen stenotic renal arteries in 15 patients were observed without intervention. There was a significant decrease in kidney size (mean difference - 1.0 cm; p less than 0.01; mean follow-up 13 months) but all 19 renal arteries remained patent. Percutaneous transluminal angioplasty (PTA) was performed in five patients (six renal arteries) for renovascular hypertension. Renal duplex scanning documented relief of renal artery stenosis in two patients whose hypertension improved after PTA and confirmed residual 60% to 99% renal artery stenosis in three patients whose hypertension did not improve after PTA (mean follow-up 6.5 months). Aortorenal bypass was performed for 10 stenotic renal arteries in seven patients. At a mean follow-up of 9 months duplex ultrasound documented eight patent and two occluded aortorenal bypass grafts. Duplex ultrasound is useful both for defining the natural history of untreated renal artery stenosis and assessing the results of renal artery angioplasty or bypass.

Duplex ultrasound assessment of venous diameters, peak velocities, and flow patterns

Duplex ultrasound was used to study the diameters, flow patterns, and peak blood flow velocities of the common femoral vein (CFV) in 12 normal subjects (mean age 35 years). Each subject was supine and non-weight-bearing on a tilt table and rotated in 10-degree increments from -10 degrees (head down) to +30 degrees (head up). Cross-sectional B-mode image was used to monitor continuously CFV diameter for 5 minutes in each position. Doppler flow patterns were recorded in longitudinal axis; heart rate and respiratory movements were also noted. CFV flow was affected by respiratory and cardiac events. At -10 degrees flow was primarily related to cardiac events, with flow increasing during diastole. At +30 degrees flow varied minimally with the cardiac cycle and was primarily respiration dependent, stopping at peak inspiration. Proceeding from -10 to +30 degrees the mean maximal CFV diameter corrected for body surface area increased 92% (0.47 +/- 0.11 cm/m2 to 0.90 +/- 0.16 cm/m2, p less than 0.001), whereas peak flow velocity decreased from 41 +/- 10 cm/sec to 13 +/- 5 cm/sec, p less than 0.001. There was a linear, inverse relationship between mean peak velocity and mean corrected diameter, r = -0.99. The study confirms the multiple influences on venous flow patterns and establishes a quantitative relationship between venous diameters and flow velocities.

Asymptomatic high-grade internal carotid artery stenosis: Is stratification according to risk factors or duplex spectral analysis possible?

High-grade (80% to 99% diameter reduction) asymptomatic internal carotid artery stenoses are associated with an increased neurologic event rate (transient ischemic attack, stroke, asymptomatic internal carotid artery occlusion) compared to less severe asymptomatic lesions. However, many do remain free of associated events. To determine which are most dangerous, we compared risk factors and duplex scan results in two groups with asymptomatic high-grade internal carotid artery stenoses. Group A included 31 patients with 33 unoperated high-grade lesions that remained asymptomatic for at least 12 months (mean 30 months). Group B included 25 patients with 26 initially asymptomatic lesions that subsequently were associated with a neurologic event (mean time to event 7.4 months). The groups did not differ significantly in average age, sex, aspirin use, smoking, or prevalence of hypertension, diabetes, or cardiac disease. With respect to the index high-grade lesion, there was no difference in the frequency of a greater than 50% contralateral internal carotid artery stenosis or greater than 50% ipsilateral external carotid stenosis. However, on duplex scanning, high-grade stenoses with greater than 6.5 kHz end-diastolic frequencies were more frequently associated with an event than high-grade lesions with lower end-diastolic frequency (p = 0.0004). Similarly, seven of 23 lesions (30%) with end-diastolic frequency greater than 6.0 kHz were associated with subsequent internal carotid artery occlusion compared to only one of 29 (3.5%) with end-diastolic frequency less than or equal to 6.0 kHz (p = 0.025). Analysis of internal carotid artery end-diastolic frequency may help select a subgroup of patients with asymptomatic high-grade lesions who are at greatest risk for subsequent neurologic symptoms or ICA occlusion or both.

Treatment of acute renal artery occlusion after percutaneous transluminal angioplasty

Four patients with occlusive complications after percutaneous transluminal renal artery angioplasty (PTA) have been treated from July 1, 1984, to March 14, 1988. During this interval such renal artery angioplasties were performed in 44 patients. Two resulted in complete main renal artery occlusion, one angioplasty resulted in occlusion of a stenotic renal artery bypass graft, and one renal PTA resulted in segmental branch renal artery narrowing, which was thought to represent a dissection. The latter segmental renal artery narrowing was treated expectantly with good long-term results. One of the main renal artery occlusions was treated by radiologic means by reentry and repeat transluminal dilation. The other two acute complete occlusions, one of an autogenous artery and the other of an aortorenal bypass graft, were treated by aortorenal or ileorenal bypass grafting, respectively. The overall incidence of main renal artery occlusion (including the bypass graft occlusion) after PTA requiring operative intervention was 4.5% (2/44). Revascularization was accomplished after 6 and 8 hours of renal ischemia time for the two surgical procedures. Despite this, the bypass grafts done emergently remain patent, and the involved kidneys appear to be functional. The incidence of main renal artery occlusion after PTA is not as low as would be apparent from a review of the literature. It is proposed that main renal artery occlusion after PTA can be treated successfully by surgical and interventional radiologic techniques because of the presence of protective renal collateral circulation whose formation was stimulated by the renal artery lesion that prompted PTA.

Duplex scanning in arterial and venous disease

A duplex ultrasonic system involves combining B-mode imaging and a pulsed Doppler in a single instrument. Since development of the first clinically useful system in the mid 1970’s [1], duplex scanning has rapidly become the most useful and widely applied method for the evalution of arterial and venous disease. It is now the most frequently used noninvasive diagnostic modality in the assessment of extracranial cerebral vascular disease [2].