Impact of Anomalous Vertebral Artery Anatomy on Management of Coronary Artery Disease

Feb 06, 2020   |  Fahad Younas, MD, MPH; Kristy Gama, MSN,APRN,NP; T. Brett Reece, MD, FACC; Robert Kevin Rogers, MD

Expert Analysis

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Abstract

A cornerstone of surgical coronary revascularization is the use of a left internal mammary artery (LIMA) as a bypass conduit to the left anterior descending artery (LAD). However, obstructive disease of the left subclavian artery can compromise flow through the LIMA and prevent adequate perfusion of the anterior left ventricle. Subclavian stenosis occurs in up to 4.6% of patients referred for a coronary artery bypass graft (CABG) surgery. Though there are multiple clinical modalities to detect left subclavian disease prior to CABG, a common scenario is to discover retrograde left vertebral artery flow on a routine, preoperative carotid duplex. However, 5%-6% of left vertebral arteries arise directly from the aorta, rather than the subclavian. In this setting, left subclavian disease could be missed if the clinician solely relies on a carotid duplex for detection. Herein, we share a case of a patient with an anomalous left vertebral artery who underwent LIMA-LAD grafting. Post operatively, the patient was found to have a subtotally occluded left subclavian artery and coronary steal physiology, the left subclavian was treated percutaneously. This report is the first case of orbital atherectomy in the left subclavian proximal to a LIMA-LAD graft in the setting of an anomalous left vertebral artery.

Introduction

Coronary artery bypass grafting is often recommended for patients with ≥50% diameter stenosis of the left main coronary artery or multivessel coronary artery disease, particularly in patients with diabetes, to improve survival.1 This benefit of CABG is driven by the use of the pedicle LIMA as a conduit to the LAD artery.2-4

Among patients with three-vessel or left main coronary disease, proximal left subclavian stenosis is not uncommon (0.5 - 6.8 %).4-8 Obstructive left subclavian artery disease may compromise flow to the LIMA, and result in a subclavian-coronary steal phenomenon (retrograde flow occurs in the LIMA away from the anterior left ventricular wall at rest or with left arm exertion).9 This physiology is analogous to subclavian steal syndrome involving the ipsilateral vertebral artery, which results in retrograde flow in the vertebral artery that can be readily recognized on the routine preoperative carotid duplex prior to CABG.10 However, about 5-6% of such patients will have an anomalous origin of the left vertebral artery arising from the aortic arch rather than from the subclavian artery. With this anatomy, duplex ultrasound of the vertebral artery will not identify retrograde flow, and left subclavian disease will be missed, unless other physical examination or imaging studies are used.11,12

We herein present a case and literature review relevant to the topic of subclavian artery management surrounding CABG in the setting of anomalous left vertebral artery anatomy. This case involved atherectomy, angioplasty and stenting of a heavily calcified subtotally occluded left subclavian artery in the setting of an anomalous left vertebral artery following CABG. To our knowledge, this case is the first of orbital atherectomy in the subclavian artery in the setting of an anomalous ipsilateral vertebral artery.13,14

Case Presentation

The patient is a 66-year-old female who originally presented with a non-ST segment myocardial infarction at a referring hospital. Coronary angiography showed critical disease of the left main and severe disease of the ostial left anterior descending and left circumflex coronary artery [Figure 1].

Figure 1

Figure 1
Figure 1: Coronary angiography showing critical disease of the left main, ostial left anterior descending and left circumflex coronary artery.

The patient was referred for CABG. A pre-operative carotid duplex was unremarkable with normal left vertebral artery doppler waveforms [Figure 2]. Coronary bypass was performed with a placement of a LIMA to the LAD artery and a saphenous vein graft (SVG) to the left circumflex coronary artery.

Figure 2

Figure 2
Figure 2: Preoperative carotid duplex showing normal antegrade flow in the left vertebral artery.

Post-operatively, it was noticed that the non-invasive left brachial blood pressure was 42 mm Hg lower than the right non-invasive brachial artery pressure. Hence, left subclavian artery disease was suspected. A computed tomography (CT) angiogram was performed revealing subtotal occlusion of the left subclavian artery and an anomalous takeoff of the left vertebral artery from the aortic arch.

The decision was made to attempt percutaneous revascularization. Due to the high degree of calcification, orbital atherectomy was planned and deemed safe as the anomalous left vertebral artery takeoff should preclude cerebral embolization [Figure 3]. Intravascular ultrasound (IVUS)-guided stenting was performed with distal embolic protection in the axillary artery. Final angiography showed a patent left subclavian with no evidence of embolization more distally in the left arm [Figure 4].

Figure 3

Figure 3
Figure 3: Angiography of the left subclavian artery with heavy calcification, and a 1.5mm solid crown orbital atherectomy catheter in the left subclavian artery (a) with a distal embolic protection in the axillary artery (b).

Figure 4

Figure 4
Figure 4: Final angiogram following IVUS guided stenting.

Discussion

This case demonstrates the importance of recognizing left subclavian artery disease prior to CABG using a LIMA conduit in the setting of an anomalous left vertebral takeoff. CABG is one modality of revascularization used to treat obstructive coronary artery disease, which is the leading cause of death in the United States, and the survival benefit of CABG is primarily driven by the use of a LIMA to LAD conduit. As such, it is important to recognize left subclavian disease preoperatively to optimize outcomes.15,16

Duplex of the carotid arteries and vertebral arteries is routinely performed prior to CABG in many institutions and can readily identify subclavian steal physiology, provided the left vertebral artery arises from the left subclavian artery. However, duplex typically cannot characterize the intrathoracic subclavian artery. For the significant minority of cases in which the left vertebral artery arises from the aorta, we would propose routinely performing bilateral upper extremity noninvasive blood pressure measurements in all patients prior to CABG. Blood pressure variation of 10-20 mmHg is suggestive of subclavian stenosis, albeit with a low sensitivity (50-65%) and low positive predictive value (13%), but high specificity (85-90%) and negative predictive value (99%).5,17,18 A gradient of 10-20 mm Hg might prompt additional testing. One could also advocate for routine catheter-based, selective left subclavian angiography during the pre-operative coronary angiogram; however, this approach does require additional catheter manipulation exposing patients to potential risk as well as incremental iodinated contrast and radiation exposure.

Conclusion

This case exemplifies the importance of diagnosing left subclavian artery disease in the setting of CABG surgery utilizing a LIMA-LAD conduit. In the case of an anomalous left vertebral artery, physical exam is essential for facile diagnosis. In addition, an anomalous left vertebral allows relatively safe use of an atherectomy device for left subclavian revascularization.

References

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Clinical Topics: Cardiac Surgery, Cardiovascular Care Team, Invasive Cardiovascular Angiography and Intervention, Noninvasive Imaging, Vascular Medicine, Atherosclerotic Disease (CAD/PAD), Aortic Surgery, Interventions and Coronary Artery Disease, Interventions and Imaging, Interventions and Vascular Medicine, Angiography, Computed Tomography, Echocardiography/Ultrasound, Nuclear Imaging

Keywords: Aneurysm, Subclavian Steal Syndrome, Coronary Angiography, Subclavian Artery, Vertebral Artery, Coronary Artery Disease, Axillary Artery, Aorta, Thoracic, Blood Pressure, Constriction, Pathologic, Saphenous Vein, Brachial Artery, Cause of Death, Physical Exertion, Coronary Artery Bypass, Angioplasty, Atherectomy, Myocardial Infarction, Carotid Arteries, Tomography, X-Ray Computed, Diabetes Mellitus, Ultrasonography, Interventional, Tomography


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