Bidirectional flow in the vertebral artery is not always indicative of the subclavian steal phenomenon

Association of Subclavian Steal Phenomenon with Prevalence of Contralateral Vertebral Artery Atherosclerotic Stenosis: A Hospital-Based Cohort Study

AIMS

It is uncertain if there is a connection between subclavian steal phenomenon (SSP) and atherosclerotic stenosis in the opposite vertebral artery (VA). We aimed to explore the association between SSP and the incidence of contralateral vertebral artery stenosis (VAS) in vivo.

METHODS

In this prospective registry study, we included patients diagnosed with ＞50% stenosis of proximal subclavian artery (SA) or innominate artery (INA) by digital subtraction angiography (DSA) from our comprehensive stroke center between 2011 and 2022. VAS and SSP was diagnosed by DSA in the resting state. Propensity score matching (PSM) was conducted among all participants and subgroups with a 1:1 ratio according to the presence of SSP. We further conducted sensitivity analysis by dividing all participants into subgroups according to the degree of stenosis and type of SSP. Binomial logistic regression analysis was applied to investigate the association of SSP with contralateral VAS.

RESULTS

A total of 774 patients were included in this study and 309 (39.9%) were found with SSP. After PSM, presence of SSP was associated with lower prevalence of contralateral VAS among all participants (OR 0.45; 95% CI 0.31-0.65; p＜0.001). In subgroup analysis, the association was respectively found within left subclavian (LSA) stenosis group (OR 0.43; 95% CI 0.29-0.65; P＜0.001) and right subclavian artery (RSA) / INA stenosis group (OR 0.36; 95% CI 0.19-0.69; P=0.002).

CONCLUSIONS

SSP is associated with lower prevalence of contralateral VAS.

Computed Tomography Angiography in the Diagnosis of Subclavian-Vertebral Artery Steal

Purpose

Computed tomography angiography (CTA) is commonly used in the diagnosis and evaluation of subclavian steal (SS). However, the abnormal manifestations of vertebral artery (VA) in SS on CTA are vastly under-recognized and prone to misdiagnosis. We reported for the first time the abnormal CTA manifestations of VA in SS, and evaluated the value and pitfalls of CTA in the diagnosis of SS, aiming to avoid misdiagnosis and facilitate correct diagnosis of SS using CTA.

Patients and Methods

This study retrospectively included 19 patients diagnosed with SS using carotid duplex sonography (CDS) and digital subtraction angiography (DSA) between 2018 and 2022 at a tertiary neurology clinic in Chongqing, China. Their CDS, DSA and CTA results were collected and analyzed. The diagnostic consistency between CTA and DSA in grading subclavian artery stenosis was evaluated, and the CTA manifestations of VA were summarized.

Results

All patients presented subclavian steno-occlusion on the affected side, without steno-occlusion of the contralateral subclavian artery or bilateral VA on DSA. A high concordance was observed between CTA and DSA in grading subclavian artery stenosis (Kappa = 0.825, P = 0.000). However, only 26.3% of patients presented normal VA on CTA, whereas 73.7% of patients presented shallow VA ipsilateral to subclavian steno-occlusion. A 28.6% of patients with shallow VA were misdiagnosed as having vertebral arteriopathy. The presence of shallow VA had no significant correlation with age, gender, severity of subclavian artery stenosis, diameter of VA or model of CT scanner (all P>0.05). Although not statistically significant, the incidence of shallow VA increased with higher SS grade.

Conclusion

Carotid CTA is highly accurate for diagnosing subclavian steno-occlusion, whereas shallow VA is the pitfall of CTA in diagnosing SS. It is important to improve the recognition of shallow VA to avoid misdiagnosis.

Color Doppler Ultrasonography for the Evaluation of Subclavian Artery Stenosis

BACKGROUND

It is of great significance to evaluate symptomatic subclavian artery (SA) stenosis by color Doppler ultrasonography. More than 50% SA stenosis may induce symptoms. Currently, there is a paucity of published literature and lack of practitioner consensus for how ultrasonic findings should be interpreted in patients with SA stenosis.

OBJECTIVE

The study aimed to prospectively evaluate SA stenosis using color Doppler ultrasonography, with digital subtraction angiography as a reference. Moreover, we aimed to determine the optimal thresholds to predict SA stenosis (≥50%).

METHODS

A total of 423 SAs from 234 patients with normal or stenotic lumen were enrolled. The peak systolic velocity (PSV) and acceleration time at the stenotic and distal segments of the SA, peak reversed velocity of the vertebral artery, and waveforms of the stenotic SA, distal SA, and vertebral artery were recorded. The ratios of stenotic PSV to distal PSV (PSVr) and distal AT to stenotic AT were also calculated. The optimal cutoff values were determined using receiver operating characteristic analysis.

RESULTS

All ultrasonic parameters were significantly correlated with the degree of SA stenosis, whereas PSV (r = 0.624, P < 0.001), PSVr (r = 0.654, P < 0.001) and VA waveform change (r = 0.631, P < 0.001) had the strongest correlation with SA stenosis. The optimal cutoff values were as follows: PSV ≥ 230 cm/s and PSVr ≥ 2.2 to predict ≥ 50% stenosis, and PSV ≥ 340 cm/s and PSVr ≥ 3.0 to predict ≥ 70% stenosis.

CONCLUSIONS

Symptomatic patients with the ultrasonic parameters of PSV ≥ 230 cm/s and PSVr ≥ 2.2 need to be considered for further verification by computed tomographic angiography or magnetic resonance angiography, or by digital subtraction angiography with a view to percutaneous transluminal angioplasty/stent implantation in the same session. The recommended graded cutoff values can help in long-term management of patients with SA stenosis.

Isolated reversal of flow in the vertebral artery - A missed entity

Isolated reversal of flow in the vertebral artery is a rare phenomenon occurring in the general population and is due to intrinsic anatomical defects. The most common cause is subclavian stenosis; however, reversal of flow in the vertebral artery can occur regardless of any detection of anatomic deterioration. In this series, we report three asymptomatic cases where the extracranial Doppler scan preceding off-pump coronary arterial bypass grafting showed isolated reversal of flow in the vertebral artery. No signs of subclavian stenosis or steal syndrome were elicited. However, all patients subsequently suffered from a posterior circulation stroke following off-pump coronary arterial bypass grafting but recovered fully with medical management. We conclude that a detailed pre-operative neurological investigation can mitigate this risk and improve neurological outcomes following off-pump coronary arterial bypass grafting.

Lack of flow on time-of-flight MR angiography does not always indicate occlusion

A patient presented acutely with symptoms of cerebellar ischaemia. While non-contrast CT imaging was normal, MRI demonstrated an apparent occlusion of the left vertebral artery on time-of-flight angiography. However, concurrent contrast-enhanced MR angiography (and subsequent CT angiography) demonstrated normal contrast filling of the left vertebral artery. This article discusses the benefits and limitations of time-of-flight angiography for the investigation of possible stroke and highlights a particular technical limitation which could be misinterpreted as an arterial occlusion.

Waveform patterns and peak reversed velocity in vertebral arteries predict severe subclavian artery stenosis and occlusion

This study investigated the value of analyzing spectral Doppler waveform patterns and measuring the peak reversed velocity (PRV) of the vertebral artery (VA) in predicting proximal severe subclavian artery (SA) stenosis and occlusion. Fifty-one patients with proximal SA stenosis were studied retrospectively. Based on the depth of the mid-systolic notch, the Doppler waveforms of the ipsilateral VA were divided into five subtypes (type I, n = 8; type II, n = 8; type III, n = 6; type IV, n = 13; and type V, n = 16). PRV was also measured. PRV receiver operating characteristic curves were constructed to obtain the best cutoff value for predicting severe SA stenosis or complete SA occlusion. The results indicated that both VA Doppler waveform and PRV were associated with the degree of SA stenosis (p < 0.05). PRV and the Doppler waveform in the VA had similar accuracy in predicting SA occlusion (84.3%, 43/51). PRV was more accurate than VA waveforms in predicting severe SA stenosis (98%, 50/51 vs. 94.1%, 48/51). However, no significant differences between the two methods in predicting severe SA stenosis were observed (p = 0.84). Thus, with severe obstruction of the SA, typical Doppler waveform patterns of the VA could be observed. PRV is a helpful criterion in predicting severe stenosis and occlusion of the SA.