Influence of poststenotic collateral pressure on blood flow velocities within high-grade carotid artery stenosis: differences between morphologic and functional measurements

Cerebrovascular Reserve Capacity as a Predictor of Postoperative Delirium: A Pilot Study

Introduction: Postoperative delirium is a common complication after cardiac surgery with cardiopulmonary bypass (CPB). Compromised regulation of the cerebral circulation may be a predisposing factor for delirium. However, the potential relationship between cerebrovascular reserve capacity and delirium is unknown. The aim of this study was to investigate if impaired cerebrovascular reserve capacity was associated with postoperative delirium. Methods: Forty-two patients scheduled for cardiac surgery with CPB were recruited consecutively. All patients underwent preoperative transcranial Doppler (TCD) ultrasound with calculation of breath-hold index (BHI). BHI < 0.69 indicated impaired cerebrovascular reserve capacity. In addition, patients were examined with preoperative neuropsychological tests such as MMSE (Mini Mental State Examination) and AQT (A Quick Test of cognitive speed). Postoperative delirium was assessed using Nursing Delirium Screening Scale (Nu-DESC) in which a score of ≥2 was considered as delirium. Results: Six patients (14%) scored high for postoperative delirium and all demonstrated impaired preoperative cerebrovascular reserve capacity. Median (25th-75th percentile) BHI in patients with postoperative delirium was significantly lower compared to the non-delirium group [0.26 (-0.08-0.44) vs. 0.83 (0.57-1.08), p = 0.002]. Preoperative MMSE score was lower in patients who developed postoperative delirium (median, 25th-75th percentile; 26.5, 24-28 vs. 28.5, 27-29, p = 0.024). Similarly, patients with postoperative delirium also displayed a slower performance during the preoperative cognitive speed test AQT color and form (mean ± SD; 85.8 s ± 19.3 vs. 69.6 s ± 15.8, p = 0.043). Conclusion: The present findings suggest that an extended preoperative ultrasound protocol with TCD evaluation of cerebrovascular reserve capacity and neuropsychological tests may be valuable in identifying patients with increased risk of developing delirium after cardiac surgery.

Superficial Temporal Artery-Middle Cerebral Artery Bypass Surgery for Refractory Symptomatic Intracranial Atherosclerotic Stenosis

OBJECTIVE

To evaluate blood flow changes after bypass surgery for refractory symptomatic intracranial atherosclerotic stenosis (ICAS).

METHODS

We examined a cohort of consecutive patients with symptomatic ICAS. Superficial temporal artery-middle cerebral artery (MCA) bypass was performed in refractory patients with poor perfusion. Angiograms were graded systematically for antegrade, collateral, and bypass flow, and clinical variables were collected preoperatively, at 7 days postoperatively, and 3, 6, and 12 months postoperatively.

RESULTS

Among 185 consecutive cases with ICAS, 15 patients who were unsuitable for or did not respond to the best medical therapy or stenting underwent bypass surgery. No patients had new ischemic deficits within 7 days postoperatively. The mean follow-up period was 30.2 ± 12.3 months. Within this period, all anastomoses were patent by methods of ultrasound or computed tomography angiography. In 2 patients, stenotic lesions exhibited early postoperative occlusion conversion at 7 days on digital subtraction angiography. In 2 patients, stenotic lesions showed progression of occlusion at 6 and 8 months. The 2 lesions with early occlusion were both located in the MCA. The extent of retrograde blood flow via bypass anastomosis was correlated with early occlusion conversion.

CONCLUSIONS

For refractory ICAS in patients with compromised hemodynamics, direct bypass might induce early occlusion of a stenotic area. MCA lesions may have a greater tendency toward early occlusion conversion.

Functional assessment of high-grade ICA stenosis with duplex ultrasound and transcranial Doppler

BACKGROUND

Duplex ultrasound (DUS) has shown a >90% accuracy compared to angiography, concerning the degree of internal carotid artery (ICA) stenosis. However, uncertainty may occur in a severe stenosis, in which peak systolic velocity (PSV) may decrease owing to high flow resistance or high backward pressure. We investigated intracranial collateral flows using transcranial Doppler (TCD) to further evaluate the hemodynamic significance of high-grade ICA stenosis.

METHODS

In this retrospective study, 320 consecutive symptomatic patients were examined. The degree of ICA stenosis and collateral capacity in the circle of Willis was investigated by DUS and TCD. In addition, magnetic resonance angiography (MRA) was added in a subgroup of 204 patients. The criterion for hemodynamic significant ICA stenosis was established collateral flow.

RESULTS

In 91% of all symptomatic vessels (291 vessels), an ICA stenosis of ≥70% was found. Established collateral flow always indicated precerebral carotid artery disease of ≥70%. Furthermore, in 11% of the whole study material, collateral reserve capacity was found despite high-grade (≥70%) ICA stenosis. PSV in ICA <2·5 m s(-1) was combined with established collateral flow and MRA stenosis of ≥70% in 9% (19 arterial systems). In 4%, doubt existed concerning the degree of stenosis after DUS.

CONCLUSION

Transcranial Doppler helps to determine whether an ICA stenosis is of hemodynamic significance and to assess collateral patterns. Established collateral blood flow will help to identify patients with ≥70% (ECST) carotid artery disease. TCD might be of value when flow velocity criteria combined with plaque assessment by DUS are inclusive. Other diagnostic methods may also be considered.

Spect measurements of regional cerebral perfusion and carbondioxide reactivity: correlation with cerebral collaterals in internal carotid artery occlusive disease

BACKGROUND

The aim of the present study was to assess the regional variation in cerebral perfusion, vasomotor reactivity (VMR) and the role of cerebral collaterals in patients with symptomatic internal carotid artery (ICA).

METHODS

Seventeen functionally independent patients (60+/-9 years, mean+/-SD) with a unilateral symptomatic internal carotid artery occlusion and a <30% contralateral ICA stenosis were investigated. (99 m) Tc-hexamethyl propyleneamine oxime (HMPAO) single photon emission computed tomography (SPECT) was performed to study cerebral blood flow in rest and during a CO(2) challenge in the cerebellum, temporal lobe, occipital lobe, basal ganglia, frontal lobe and parietal lobe. Time of flight and phase contrast MRA were used to study collateral flow via circle of Willis.

RESULTS

In rest, cerebral perfusion on the side ipsilateral to the ICA occlusion was decreased compared with the contralateral side in the basal ganglia (p<0.05), frontal lobe (p<0.01) and parietal lobe (p<0.01). During a CO(2) challenge only the ipsilateral frontal lobe demonstrated a perfusion decrease compared with the contralateral frontal lobe (p<0.05). Furthermore, in patients without collateral flow via the anterior circle of Willis the perfusion of the ipsilateral frontal lobe was significantly decreased (p<0.01) during the CO(2) challenge and crossed cerebellar diaschisis with a decreased perfusion on the contralateral cerebellar hemisphere was detected (p<0.05). No cerebral blood flow (CBF) differences were found for present/absent collateral flow via the posterior communicating artery.

CONCLUSION

Regional assessment of cerebral perfusion and VMR with SPECT demonstrated the heterogeneity of cerebral hemodynamics and the importance of collateral flow via the anterior circle of Willis.

Effect of carotid endarterectomy on primary collateral blood flow in patients with severe carotid artery lesions

BACKGROUND AND PURPOSE

In patients with severe obstruction of the internal carotid artery (ICA), it is recognized that the preoperative failure to visualize collaterals of the circle of Willis increases the risk of hemispheric ischemia before, during, and after carotid endarterectomy (CEA). The purpose of the present study was to assess the effect of CEA on the anatomy and function of the circle of Willis.

METHODS

Time-of-flight and phase-contrast MR angiography were used to study changes in vessel diameter and collateral flow of the circle of Willis in 48 patients with 70% to 99% ICA stenosis before and after CEA.

RESULTS

In patients with unilateral ICA stenosis, all preoperative vessel diameters on both sides of the circle of Willis were larger than in control subjects. All demonstrated a significant diameter decrease to reach normal values after CEA. Furthermore, preoperative collateral flow patterns normalized after CEA (P=0.03). In patients with stenosis and contralateral ICA occlusion, CEA resulted in a significant increase in the prevalence of collateral flow via the anterior communicating artery (33% to 83%, P<0.01) and a significant increase in diameter of both A1 segments (P<0.05) in patients in whom collateral flow developed after CEA.

CONCLUSIONS

CEA reduces the caliber of compensatory collateral channels to normal levels by MR angiography measurements in the presence of severe unilateral stenosis; when the opposite side is occluded and the stenosis is removed ipsilaterally, a greater amount of compensatory collateral circulation can be measured on both the occluded side and the fully opened side.