Introduction
Atherosclerotic upper extremity obstructive disease is predominantly secondary to subclavian or innominate artery stenosis (SAS or IAS). The diagnosis is usually suspected when a significant (often ≥15 mm Hg) systolic brachial blood pressure discrepancy (SBBP) is detected between the two arms. Applying this threshold, the prevalence of SAS in the general population is estimated at approximately 2% and increases with advancing age. In a high-risk population with known or suspected vascular disease, including individuals referred for coronary artery bypass surgery, the prevalence is estimated at about 7%. Involvement of the left subclavian artery (L-SCA) is three to four times more common than the right brachiocephalic and subclavian arteries. This may be explained by increased flow turbulence in the L-SCA due to its acute angle of origin. Moreover, one third of the stenotic lesions on the right side are found in the innominate trunk, proximal to the subclavian origin.
The presence of SAS correlates well with known atherosclerotic risk factors and is a strong indicator of the presence of PAD, defined as ABI ≤0.90. The incidence is much higher in patients with symptomatic PAD. In one study of 48 subjects with PAD who underwent aortic arch angiography, 19% had more than 50% stenosis of at least one brachiocephalic artery. Furthermore, SAS predicts total and cardiovascular mortality (independent of both risk factors and existent cardiac disease at baseline) and all-cause mortality. On the other hand, SAS is present in 11.5% of patients with known PAD. Therefore, we routinely recommend bilateral blood pressure measurements in high-risk patients.
Nonatherosclerotic conditions that can result in SBPD and SAS include Takayasu’s arteritis, giant cell arteritis, coarctation of the aorta, thoracic outlet syndrome causing compression from an overlying rib, radiation-induced vascular disease, and, rarely, fibromuscular dysplasia (FMD), arterial thrombosis ( Figure 19-1 ), and neurofibromatosis. Therefore, routine evaluation for these disorders is not warranted. FMD is more likely to affect small and medium size arteries, notably the brachial artery, and can occasionally lead to upper extremity ischemia and bilateral pulse discrepancy. Importantly, the presence of a BBPD with associated acute chest pain should alert the clinician for the possibility of aortic dissection.
Diagnosis and Clinical Syndromes
Isolated SAS rarely leads to symptoms, perhaps due to the lower muscular mass it supplies (compared to that supplied by the lower extremity inflow arteries) and the high degree of collaterals that develop. Symptoms related to vertebrobasilar insufficiency (also referred to as vertebral subclavian steal syndrome, or vSSS) remain uncommon with isolated SAS and most likely occur when multiple craniocervical arteries are stenotic or occluded. The clinical manifestations of SAS are listed in Table 19-1 .
| Arm ischemia | Arm claudication, muscle fatigue, hand or finger pain, paresthesias, coldness in the arm, Raynaud’s phenomenon, distal embolization, and its sequelae of tissue loss and necrosis. |
| Vertebral subclavian steal syndrome (vSSS) | Symptoms of vertebrobasilar insufficiency: paroxysmal vertigo, drop attacks, ataxia, diplopia, motor dysphagia, dysarthria, and facial motor deficits. Typically seen with concurrent vertebral and carotid disease. |
| Coronary subclavian steal syndrome (cSSS) | Angina pectoris, refractory unstable angina, myocardial infarction, heart failure in patients with LIMA (or, rarely, RIMA) graft. |
| CVA or paralysis after TEVAR with coverage of the L-SCA | Risk estimated at 4.7% vs. 2.7% in patients without LSA coverage. Preemptive revascularization offers no protection against CVA when coverage is applied. |
| Lower extremity claudication following AXF bypass | |
| Arm ischemia | Arm claudication, muscle fatigue, hand or finger pain, paresthesias, Raynaud’s phenomenon, distal embolization, tissue loss, and necrosis. |
| Vertebral subclavian steal syndrome (vSSS) | Symptoms of vertebrobasilar insufficiency: vertigo, syncope, ataxia, diplopia, motor dysphagia, dysarthria, and facial motor deficits. Typically seen with concurrent vertebral and carotid disease. |
| Carotid subclavian steal syndrome | Rare, except in proximal innominate artery stenosis. |
Lord et al. showed that the discontinuity of the circle of Willis due to the vertebral-vertebral shunt (from the patent vertebral artery [VA] to the occluded one, across the circle of Willis) is responsible for symptoms experienced during repetitive use of the affected upper extremity. Occasionally, the blood is routed from the anterior circulation through the descending cervical branches of the ipsilateral external carotid artery, providing collateral pathways to the occluded subclavian artery. In these case, symptoms of anterior circulation ischemia, such as transient hemiparesis paresis, speech disturbances, and sensory loss, may be reported. On the other hand, ischemic syndromes attributable to the anterior circulation are common in symptomatic patients presenting with occlusive lesions of the right innominate trunk. Fifty percent of such patients express anterior ischemia, while 40% present with posterior symptoms, and up to 10% manifest global (anterior and posterior) symptoms.
Javid test is a highly reliable clinical maneuver in demonstrating flow reversal via the circle of Willis. In this test, the examiner compresses the ipsilateral carotid artery, thereby decreasing intracranial pressure and flow and abolishing retrograde flow into the arm. This leads to an abrupt change in the quality of the ipsilateral radial pulse.
Acute symptoms of arm or cerebral ischemia usually result from acute injury to the subclavian artery, as seen with sharp and blunt trauma, inadvertent misplacement of a large venous catheter into an SCA, and coverage by a stent graft during TEVAR.
Most cases of SAS are asymptomatic and diagnosed either incidentally on imaging studies or during routine physical exam. In addition to BBPD ≥15 mm Hg, careful physical examination can yield absent or markedly diminished distal pulses and a systolic supraclavicular bruit. The bruit is best auscultated by lightly applying the stethoscope bell in each supraclavicular fossa while the patient sits looking forward with the shoulders relaxed and hands resting on the lap. Once detected, firm compression of the patient’s ipsilateral radial artery decreases the SCA outflow and should shorten or obliterate the bruit. Arm exercises that can be carefully performed in the office (with the patient in a supine position to avoid provoking syncope) will induce peripheral vasodilation, thus augmenting the SCA outflow, which increases the turbulence across the stenotic lesion, rendering the bruit louder and longer.
Duplex ultrasound (DUS) with color flow is the diagnostic first test of choice. This modality provides excellent information of the lesion, identifies disease in the rest of the aortic arch vessels, and adequately assesses flow direction in the vertebral artery. Once the diagnosis is made and the symptoms are considered significant enough to warrant intervention, we routinely obtain a CTA or MRA to confirm the diagnosis, exclude proximal VA stenosis or occlusion (difficult to visualize by DUS and when present can manifest as retrograde vertebral flow, mimicking vSSS), and clearly define the anatomic relationships between the SCA lesion, the aortic arch (since ostial lesions represent an extension of atherosclerosis arising in the aortic arch), and the origins of the ipsilateral vertebral and internal mammary arteries. This information can be very useful in planning the treatment modality. Angiography is reserved for patients who were determined to undergo endovascular therapy.
We advise all patients referred to CABG with BBPD ≥15 mm Hg or history of a nonatherosclerotic condition that is known to be associated with SAS (see above) and those with known vascular disease to undergo screening for SAS prior to their open heart surgery. This can be done in the outpatient setting by DUS or angiography during the index cardiac catheterization procedure.
Treatment
Asymptomatic SAS is treated medically by applying global cardiovascular risk reduction strategies, including smoking cessation, antiplatelet therapy, and achieving target blood pressure, glucose, and cholesterol. The goal of therapy in asymptomatic patients is to stabilize the systemic atherosclerotic process and prevent progressive disease. Currently the evidence for revascularization of asymptomatic patients with hemodynamically significant SAS is lacking. The exception to this rule is patients who are undergoing CABG with plans to utilize the LIMA, those who need an arteriovenous fistula for hemodialysis purposes and, rarely, when an axillo-femoral graft is considered.
Currently, more than 90% of patients undergoing subclavian artery revascularization are symptomatic. Indications for revascularization procedures include the presence of one or more of the clinical syndromes outlined in Table 19-1 .
Surgical Revascularization
Although surgical revascularization procedures were employed since the 1950s, endovascular therapy is now considered the modality of choice in contemporary practice.
Early surgical procedures employed a direct revascularization via transthoracic approach and were associated with significant morbidity and mortality. Anatomic revascularization procedures include endarterectomy and bypass grafts. These are technically demanding and associated with relatively high peri-procedural complications. The evolution of extraanatomic cervical repair techniques improved surgical outcomes significantly. Therefore, extraanatomic revascularization procedures have been employed and include carotid-subclavian transposition, carotid-subclavian bypass, axillo-axillary bypass, subclavian-subclavian bypass, and carotid-contralateral subclavian bypass ( Figure 19-2 ). Hybrid procedures are generally reserved for aneurysmal disease when the stent graft (TEVAR) is extended to cover the subclavian artery. An open extraanatomical bypass is performed prior to deploying the graft. Of note, while this strategy may reduce the risk of spinal cord ischemia, it offers no protection against it, as demonstrated by Cooper et al.
A recent report by Aziz and Comerota elegantly reviewed the English literature and reported the outcomes of the different endovascular and open surgical treatment modalities of the brachiocephalic arteries ( Table 19-2 ). Their findings verified the remarkable improvement in surgical outcomes compared to the 22% mortality rate described in early experiences 50 years ago. Subclavian-to-carotid artery transposition appears to have the greatest long-term patency for proximal subclavian artery occlusive disease (100% at 10 years), whereas axillo-axillary artery bypass surgery has the lowest patency rates, ranging from 88% to 89%.
| Procedure | No. of studies | No. of patients | Mean FU | Surgical mortality (%) | CVA (%) | 10-year Survival (%) | Patency Rate (%) | Technical success |
|---|---|---|---|---|---|---|---|---|
| Anatomic revascularization of the brachiocephalic arteries | 22 | 1650 | 58 months | 7.8 | 3.8% | NA | ||
| Carotid-subclavian transposition | 8 | 381 | 0.4 | 1 | 83% (one study) | 100% (one study) | ||
| Carotid-subclavian bypass | 18 | 1041 | 53.8 months | 1.5 | 1.3 | 89% (four studies) | 91% (five studies) | |
| Axillo-axillary bypass | 16 | 426 | 51 months | 0.5 | 1.1 | 90% (one study) | 87% at 10 years (one study) | |
| Hybrid | 9 | 173 | 7.9 | 6.9 | 100% at 1 year | |||
| Endovascular | 26 | 1305 (1379 lesions) | 31 months | 94% (stenosis) 64% (occlusion) |
Endovascular Therapy
The combination of recent advancements in endovascular techniques, along with the technical challenges of surgical procedures and their associated serious complications (such as phrenic, vagus, and recurrent laryngeal nerve palsies, thoracic duct injuries, Horner’s syndrome, and cerebral ischemia imposed by the need for proximal and distal cross clamping), made surgical revascularization progressively less popular. Since its introduction in 1980 by Bachman and Kim, percutaneous transluminal angioplasty became the treatment of choice for SAS and IAS. Endovascular therapy of completely occluded subclavian and innominate arteries was first reported in 1993 by Mathias et al.
Interventional Technique
Once the decision to proceed with endovascular revascularization is made, a careful review of noninvasive studies (CTA or MRA) is critical for procedure planning. The anatomical relationships among the diseased segment, aortic arch, and other craniocervical arteries (carotid, VA, and IMA in the case of IAS and the VA and IMA when the L-SCA is being treated), as well as flow hemodynamics and collateral patterns, are reviewed. Special attention is given to the lesion characteristics, such as length, involvement of the ostium, presence of thrombus, atheromatous material or heavy calcification, proximal artery angulation, as well as the aortic arch type, orientation, and calcifications. Since peripheral vascular disease is common in these patients, access options are also evaluated. The innominate artery is short (2-5 cm) and large in diameter. It gives rise to the right carotid and vertebral subdivisions. It is also usually highly calcified and can be tortuous with a difficult takeoff depending on the aortic arch pattern. Therefore it is more challenging to treat endovascularly compared to the L-SCA.
Patients are started on ASA 325 mg daily and clopidogrel 75 mg daily 5 days prior to the procedure. We carefully perform a complete preprocedure and postprocedure neurologic and ipsilateral upper extremity examination to assess for possible periprocedure complications. The procedure is performed generally under conscious sedation and we apply the same protocols employed in cardiac catheterization procedures.
The common femoral artery (CFA) is the preferred primary route in most cases, when possible. A long (24 cm) 6 Fr sheath is placed for better catheter stability, particularly when iliac tortuousity is noted. Once access is obtained, unfractionated heparin boluses are given to maintain ACT ≥250 seconds. A complete aortic arch angiogram is then performed (utilizing DSA technique) to confirm the exact location, length, and severity of the stenotic lesion and collateral pathways. Late phase angiography allows for documentation of retrograde flow in the VA (or via branches of the carotid system).
Given the considerable movement of the ascending portion of the left SCA during respiration, which can occasionally cause kinking of the proximal segment during expiration, we perform angiography during breath hold immediately after expiration. The quality of the image depends on the patient’s ability to comply.
Identifying fluoroscopic landmarks can facilitate engagement of the destination vessel. The left SCA extends from the aorta (along the left side of the mediastinum) to the outer edge of the first rib while the right brachiocephalic trunk arises on a level with the upper border of the second right costal cartilage and ascends obliquely upward, over the trachea. It divides at the level of the upper border of the right sternoclavicular articulation.
We approach the lesion with a 6 Fr guiding catheter and an exchange-length hydrophilic 0.035 inch wire is utilized to traverse the stenosis in antegrade fashion. The wire tip is positioned in the axillary artery, within the fluoroscopic field of view, to provide stability to the system. Balloon angioplasty is then carried out with a properly sized balloon (for the reconstituted SCA). Tight calcific lesions and an unstable guiding catheter system may not allow passage of the intended balloon. Therefore, preliminary dilatation with a smaller (2 or 4 mm) balloon may facilitate delivery of the larger balloon. We typically dilate the balloon slowly to complete expansion. We then deploy a balloon expandable stent (BES), as these allow for precise placement, particularly when the SCA ostium is involved. We routinely allow the proximal edge of the BES to protrude into the aortic arch by about 1 mm to ensure coverage of the plaque extension into the aortic arch wall. We usually oversize the stent by 1 mm while the postdilatation balloon matches the vessel size and tolerate a mild waist, avoiding aggressive postdilatation, which can trigger the release of atheromatous debris.
Self-expanding stents (SES) have greater radial strength compared to BES. Therefore we utilized them in lesions distal to the VA, as these sites are subject to movement that may incur significant stress on the stent and cause fractures. SES are utilized for lesions distal to the vertebral artery and those involving the axillary and brachial arteries, as well as for lesions longer than 40 millimeters. Covered stents are reserved to repair direct injuries to the SCA, axillary, or brachial arteries.
We always avoid jailing the VA, when possible, to prevent VA closure (by plaque shift) or embolization. In cases of associated VA origin stenosis, however, we employ the “kissing balloon” technique and routinely advocate the use of distal embolus protection (DEP) devices when accessing the VA. Once the DEP device is deployed in the midcervical VA, we advance a coronary balloon over a 0.014 inch wire into the VA lesion and inflate both balloons simultaneously. The VA is accessed via the ipsilateral radial or brachial artery, after placement of a 6 Fr sheath. If the VA PTA result is unsatisfactory, it can be stented with a coronary drug-eluting stent. The “double balloon” technique can also be used. Here, the balloon is kept inflated while the SCA is accessed via the transfemoral route and treated with angioplasty and stenting.
When engagement of the SCA ostium with the guiding catheter is unsuccessful, we use a longer 4 Fr diagnostic catheter (curved or straight) through the 6 Fr guide or shuttle sheath. We then try to engage the ostium of the SCA with the 4 Fr catheter to support wire passage. When wire crossing is unsuccessful despite several careful attempts, which is usually the case in complete occlusion or when severe tortuousity is present, we combine the transfemoral antegrade with a transbrachial (or transradial) retrograde approach. We occasionally resort to this approach when the transfemoral catheter and guiding wire assembly stability remain unsatisfactory or in cases where severe ostial SCA stenosis (string sign, Figure 19-3 ) is noted. In a large series of 170 patients treated between 1993 and 2006, revascularization was attempted on 177 subclavian or innominate arteries (98% and 6%, respectively). The retrograde approach, mainly via the brachial artery, was used in 13 out of 21 (62%) total occlusion cases.
