Prevalence of Subclavian Artery Stenosis in Patients With Coronary Artery Disease

Background : Atherosclerosis is the most common and serious vascular disease that affects both the brain and the heart . (1) Subclavian stenosis/occlusion is a marker for atherosclerotic disease (eg, carotid, coronary & lower extremity arteries) and future adverse cardiovascular events. (2) In this study, we identied the prevalence of subclavian artery stenosis in patients presented with coronary artery disease (CAD) through changes in the Doppler tracing of vertebral arteries that appear to represent a clue of subclavian artery stenosis. Methods: On the basis of extracranial Doppler ultrasound & supplementary intracranial Doppler ultrasound, we assessed the pattern of Doppler waveform in both carotid & vertebrobasilar systems among 100 consecutive patients who were hospitalized for CAD in the cardiovascular department. Results: Among 100 consecutive CAD patients studied, we identied stenosis and occlusion of subclavian artery in 5 patients (5%). In those patients, subclavian arterial disease was indirectly discovered by changes in Doppler waveforms of vertebral artery. Conclusions: Prevalence of subclavian artery stenosis in patients with CAD is 5%. Changes in the pulse contour of antegrade vertebral artery Doppler waveforms seem to represent a good screening method for subclavian steal phenomena. Clinical & laboratory evaluation of cardiovascular risk factors Echocardiographic assessment of left ventricular systolic function was done in Ultrasound Laboratory in the Cardiovascular Department, Cairo University using Phillips HDI 5000 ultrasound equipment, Using : 2–4 MHz phased-array transducer Color Doppler Ultrasonographic evaluation of extra and intra cranial vasculature : a high frequency (7-10MHz) linear array transducer was employed to scan the carotid from the most proximal common carotid artery to the internal carotid artery as far as the mandible permitted. The identied parameters and measures named: Intima Media Thickness , presence of carotid plaque, degree of carotid stenosis and occlusion. The measures and quantications of extra-cranial carotid atherosclerosis was performed according to the internationally published data. (6) a 2–4 MHz phased-array transducer through the following bone windows:


Introduction
Atherosclerosis is the most common and serious vascular disease that affects both the brain and the heart. (1) Subclavian stenosis/occlusion is a marker for atherosclerotic disease (eg, carotid, coronary & lower extremity arteries) and future adverse cardiovascular events. (2) Subclavian artery occlusion or a hemodynamically signi cant stenosis proximal to the origin of the vertebral artery results in lower pressure in the distal subclavian artery. As a result, blood ows from the contralateral vertebral artery to the basilar artery, and may ow in a retrograde direction down the ipsilateral vertebral artery, away from the brainstem with a subsequent deleterious neurologic effects & signi cant morbidity as it can lead to symptomatic ischemic issues affecting the upper extremities & brain. (3, 4&5) The incidence of subclavian stenosis in the general population ranges from 3% to 4% . (2) In this study, we identi ed the prevalance of subclavian stenosis in CAD patients by color Doppler evaluation of vertebral arteries that appear to represent a clue of subclavian artery stenosis .

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The present study was performed at Cairo University Hospital in Egypt. The protocol was approved by the local ethical committee of the Cairo University.
The study was performed for 100 consecutive patients who were hospitalized with CAD and underwent coronary angiography. All patients were subjected to: Clinical & laboratory evaluation of cardiovascular risk factors Echocardiographic assessment of left ventricular systolic function was done in Ultrasound Laboratory in the Cardiovascular Department, Cairo University using Phillips HDI 5000 ultrasound equipment, Using : 2-4 MHz phased-array transducer Color Doppler Ultrasonographic evaluation of extra and intra cranial vasculature : a high frequency Evaluation of CAD severity of studied patients : Results of coronary angiography of studied patients were reviewed and severity of the CAD was assessed as follows : The diseased coronary vessels divided into 4 groups according to number of diseased vessels involvement : no signi cant vessel involvement , 1 signi cant vessel involvement, 2 signi cant vessel involvement, > 3 signi cant (multi) vessel involvement), (8) Statistical Analysis Descriptive statistics reported the mean age, gender distribution, prevalence or means for the atherosclerotic risk factors (hypertension, diabetes mellitus ,dyslipidaemia, and smoking) & for subclavian artery stenosis . Data was expressed as percent for discrete variables and as mean value +SD for continuous variables. Correlations between normally distributed variables were done using Pearson correlation coe cient. P value ≤ 0.05 was considered signi cant for all tests.

Results
Baseline characteristics of all studied patients are given in In patients having subclavian stenosis or total occlusion we observed a variety of Doppler waveforms in epsilateral vertebral artery that include: 1 -Retrograde ow: the whole Doppler wave form is below the baseline.

-Antegrade Doppler ow with a:
A -Transient sharp decline in blood ow velocity at mid systole, rounding of a subsequent second systolic peak, and restoration of forward ow in diastole.
B -Nadir of mid systolic cleft in blood ow velocity is at or below baseline, but with a rapid recovery of forward ow before diastole.
3-Retrograde & antegrade Doppler ow with a : nadir of mid systolic cleft falls well below baseline signifying greater reversal of ow during systole. Forward ow is restored in diastole.

Discussion
The current study describes the prevalence of subclavian steno-occlusive disease among patients with coronary artery disease ; 5 % which is higher than in general population (3-4%). The prevalence of subclavian artery stenosis in our duplex based study was nearly the same as that mentioned in trials that use a clinical criteria for subclavian artery stenosis. (9) The incidence was 6%. Diagnosis of subclvian artery stenosis in theses studies was diagnosed clinically as an interarm pressure difference of ≥ 15 mmHg.
We found a signi cant association between subclavian steno-occlusive disease and history of recent or old Stroke/ TIA , extra cranial moderate or severe carotid stenosis and multi-vessel or left main coronary disease. This association highlights the value for screening for subclavian stenosis or occlusion among ischemic heart disease patients at high risk or undergoing coronary artery bypass graft (CABG) operation.
Presence of subclavian artery stenosis may have an important impact in patients having CAD. The left internal mammary artery (LIMA) usually has an origin separate from the rst part of the subclavian artery.
Putting in mind that the LIMA is the rst choice in coronary artery bypass grafting because of reduced cardiac events and superior graft patency (10,11) & that left subclavian artery is four times more likely to had stenosis than the right subclavian or innominate arteries. (12,13,14) So, ischemic sequel of subclavian artery stenosis may extends to affect the heart in patients underwent or will do CABG operation.
This was observed in coronary-subclavian steal phenomenon in which the ow through the internal mammary artery may reverse and "steal" ow from the coronary circulation during upper extremity exercise. Identi cation of a signi cant subclavian artery stenosis prior to CABG can prevent this important problem. Those patients with a high-grade subclavian artery stenosis should be treated (percutaneously or surgically) prior to CABG operation. (15) Observation of vertebral artery Doppler waveform in our study revealed different blood ow patterns . These changes may re ect the different degree of severity of subclavian artery stenosis as mentioned with prior studies. (16)(17)(18)(19)(20) The earliest manifestation of the subclavian steal physiology is a transient sharp deceleration of blood ow after the rst systolic peak. The ow deceleration produces a notch in the pulse contour and gives rise to two systolic peaks: the rst sharp, the second blunt and rounded. As the subclavian pathology progresses more, the systolic notch becomes more pronounced and the second systolic peak diminishes and broadens. The nadir of the notch becomes progressively lower until it reaches and eventually crosses the baseline. The reversal of ow during systole is at rst minimal and transient but becomes increasingly more substantial until complete reversal of ow throughout the cardiac cycle is seen. (21) The physiologic explanation for these Doppler ndings may be twofold: a decrease in pressure in which blood ow velocity abruptly increases, and a loss of energy in which 78% disturbed or turbulent ow is present. (22) Our study had some limitations: 1 -It's not a population based study rather than hospital based study.

Conclusions
Prevalence of subclavian artery stenosis in patients with coronary artery disease is 5%. Screening of CAD patients for subclavian artery stenosis may be important specially for those who will undergo CABG operation.
Changes in the pulse contour of antegrade vertebral artery Doppler waveforms seem to represent a good screening method for subclavian steal phenomena.  Figure 1 Color & continuous wave Doppler Ultrasound of vertebral artery with an epsilateral subclavian artery total occlusion. It shows a totally retrograde Doppler waveform Color & continuous wave Doppler Ultrasound of vertebral artery with a signi cant stenosis of the epsilateral subclavian artery . It shows an antegrade ow with a : nadir of mid systolic cleft in blood ow velocity is at or below baseline, but with a rapid recovery of forward ow before diastole Figure 4 Color & continuous wave Doppler Ultrasound of vertebral artery with a signi cant stenosis of the epsilateral subclavian artery with a : nadir of mid systolic cleft falls well below baseline signifying greater