| Part Ⅰ Severity Assessment of Intracranial Large Artery Stenosis by Pressure Gradient Measurements:A Feasibility StudyBackground and Objective:Intracranial artery atherosclerotic stenosis is one of the main causes of ischemic stroke, especially in Chinese Han population. Currently treatment for intracranial artery atherosclerotic stenosis include balloon angioplasty, stenting and aggressive medical intervention. The Stenting and Aggressive Medical Management for Prevention of Recurrent Stroke in Intracranial Stenosis (SAMMPRIS) trial compared aggressive medical management alone versus aggressive medical management plus percutaneous transluminal angioplasty and stenting (PTAS) among patients with symptomatic 70-99% stenosis and found a high rate of periprocedural complications after PTAS and a lower rate than expected on aggressive medical therapy. However, other researchers confirmed that Wingspan stenting for high-risk intracranial atherosclerotic stenosis patients compares favorably with that of antithrombotic therapy alone. Thus, It may be more important to select the high-risk patients than chasing the technologically perfect. Without hemodynamic data, management of chronic occlusions is always in confusion. In intracranial atherosclerotic disease, paradoxically, nearly half of all recurrent strokes occur in patients with 40-69% stenosis. Thus, in the evaluation of the significance of angiographic cerebral artery stenosis, physiologic assessment would be of great value. A specific kind of guide micro wire with a pressure sensor located at the junction between the 3-cm-long radiopaque tip and the remainder was developed and introduced to coronary hemodynamic assessment by N. Pijls and B. De Bruyne in the early 1990s. It has achieved great success and established the FFR-guided revascularization strategy which has become more popular and was classified as a Class IA recommendation in 2010 European Guidelines on myocardial revascularization.FFR-guided revascularization strategy has become more popular during coronary intervention. However, the feasibility of assessing stenotic severity in intracranial large arteries using pressure gradient measurements still remains unclear.Methods:Between March 2013 and May 2014,12 consecutive patients with intracranial large artery stenosis (including internal carotid siphon, middle cerebral M1 segment, vertebral V4 segment, and basilar artery) assessed by CTA or MRA were enrolled in this study. To be eligible for the study, each patient was required to suffered from a TIA or nondisabling stroke within 30 days before enrollment. Intracranial arterial stenosis were calculated according to WASID criteria:percent stenosis= [(1-(Dstenosis/Dnormal))]×100, where Dstenosis= the diameter of the artery at the site of the most severe degree of stenosis and Dnormal= the diameter of the proximal normal artery. The trans-stenotic pressure gradient was measured before and/or after percutaneous transluminal angioplasty and stenting (PTAS), and was then compared with percent diameter stenosis. And, a Pd/Pa cut-off of≤0.70 to guide stenting of hemodynamically significant stenoses. Follow-up assessment was done at the time of study entry,24h after the pressurewire assessment, at discharge,30 days, 90 days, and 180 days. The study assessed age, sex, NIHSS score, development of complications, and recurrent ischemic event (TIA or ischemic stoke). The complication defined as device-related and procedure-related serious adverse events, included vessel perforation, intramural arterial dissection, intracranial hemorrhage, embolisation, death within 24h, and other adverse events confirmed by neurologists.Results:The target vessel could be reached in all cases. All patients obtained excellent pressure signals at baseline and after stenting. No technical complications occurred due to the specific study protocol. Excellent pressure signals were obtained in all patients. For seven patients who performed PTAS, the mean pre-procedural pressure gradient decreased from 59.0±17.2 mmHg to 13.3±13.6 mmHg after the procedure (P<0.01). Complete 6-month follow-up data were obtained for all patients. Only one patient who refused stenting occurred a TIA in the ipsilateral MCA territory, no recurrent ischemic event occurred in other patients. No vessel perforation, intramural arterial dissection, intracranial hemorrhage, embolisation, or death occurred in all patients.Conclusion:Mean transstenotic pressure gradients can be safely and easily measured with a 0.014-in. fluid-filled guide wire in intracranial large arteries.Part Ⅱ Severity Assessment of Extracranial Carotid Artery Stenosis by Pressure Gradient Measurements on Beagles:A Feasibility StudyBackground and Objective:Cerebrovascular disease has become to the first cause of death in urban and rural residents. Ischemic cerebrovascular disease were mainly caused by intracranial and external larger artery stenosis according with the cumulative lesion distribution division. Epidemiological studies show that the ischemic events caused by carotid artery, the internal carotid artery cervical (C1 segment) stenosis and occlusive account about 25 percent of all strokes. The main purpose of reconstruction of the carotid artery stenosis is prevent the occurrence of stroke. From the pathophysiological level, if patients can benefit from carotid artery stenting, which may through improving hemodynamics and/or vulnerable plaque is covered by the stent. However, in the current clinical practice, asymptomatic patients with stenosis above 70% who need stent planting, is based more on fear of hemodynamics narrow. From the hemodynamic point of view, for more than 70% stenosis, whether stenosis patients whose local vascular wall without vulnerable plaques need stenting is not clear. In order to simulate different degrees of carotid stenosis, the study used balloon expansion to make stenosis of the carotid artery until occlusion. Thereby obtaining the distal pressure value of stenosis/occlusion, the proximal pressure value of narrow and Pd/Pa values of hemodynamic parameters. And whether the observed parameters obtained can be used to guide the screening of functional significance of carotid stenosis lesions; and observation willis artery rings are in compensatory redistribution of blood flow and its possible mechanism.Methods:Five adult beagle dogs, clean healthy, all male, weighing 13-18 kg. Use Sumianxin (dose of 0.1ml/kg) combined with atropine sulfate (dose 0.5mg) for induction of anesthesia. After anesthesia, the dog was fixed to the operating table homemade, intubation, with independent ventilation after intubation. Intraoperative use of propofol injection pump to maintain anesthesia (dose of 1mg/kg/h), given continuous oxygen, oxygen flow control at 2ml/min. According to experimental animals corneal reflex disappeared, and breathing rhythm is maintained at 12-16 times/min to control the depth of anesthesia. First select the side of the common carotid artery pressure guide hemodynamic assessment. CCA will 6F guiding catheter placed near the lower opening of the guide catheter tip and the CCA opening distance of less than 2cm. The balloon (size 4.0 X 20mm) placed in the common carotid artery proximal mark the middle of the balloon into the use of pressure guide wire for support. The baroreceptor pressure guidewire distal balloon is placed at about 3cm by adjusting the pressure of the balloon, get a different Pd/Pa value (From 1.0 gradually approaching 0.95,0.9,0.8,0.7 and occlusion tolerance range ±0.01). Each node After stabilizing for 3 minutes or more, corresponding to the use of TCD observe bilateral MCA flow velocity spectrum changes. By two skilled ultrasound diagnosis by physicians while beagles bilateral temporal window to complete TCD hemodynamic parameters collection. TCD by temporal window observation of bilateral MCA peak systolic velocity, the average flow rate, end-diastolic velocity, pulsatility index. Then observe the contralateral carotid artery, methods of operation and the same as before.Intraoperative hemodynamic parameters in different nodes at the same time, the use of hemodynamic parameters observed TCD cerebral artery blood flow velocity spectrum changes, record balloon dilatation of the ipsilateral and contralateral MCA.Results:During Pd/Pa value from 1.0 down to 0.95, TCD blood flow parameters, including peak systolic velocity, mean velocity and diastolic velocity were no significant changes. Comparison between the two groups were ipsilateral Vs, Vm and Vd values:40.6±9.7 vs 39.7±9.6, P=0.837; 28.4±7.2 vs 27.9 ± 7.3, P =0.879; 23.4 ± 7.6 vs 23.2 ± 7.7, P=0.954. Compare Vs, Vm and Vd values between the two groups were contralateral:46.1±6.6 vs 45.9 ± 6.3, P=0.946; 29.9±4.4 vs 30.2±4.3, P=0.879; 24.0±6.0 vs 23.9±6.3, P=0.971. Continue to Pd/Pa value dropped gradually from 0.95 0.9,0.8,0.7 until complete occlusion of the common carotid artery balloon. Respectively, for each node in the Pd/Pa value stable at more than three minutes, record hemodynamic parameters corresponding TCD, TCD parameters change significantly (P<0.05). When Pd/Pa from 1.0 down to 0.95, TCD ipsilateral or contralateral MCA did not find significant hemodynamic changes. When less Pd/Pa continues to drop to 0.9 and, with the gradual decline Pd/Pa ratio can be observed ipsilateral MCA hemodynamic parameters were decreased and eventually reaches a minimum, Contralateral MCA hemodynamic parameters of the rise, and ultimately achieving the maximum.Conclusion:This study confirmed the intercept point Pd/Pa value in a narrow assessment of extracranial carotid artery segment is used to distinguish functional extracranial carotid artery stenosis may be between 0.95-0.9. When reduced to between 0.95-0.9 in Pd/Pa value, willis artery rings compensatory function begins to activate, and play an important role in the redistribution of blood flow in compensatory. Future in a narrow assessment of extracranial carotid artery using a pressure guidewire technology obtained Pd/Pa value may be an important hemodynamic parameters.Part Ⅲ Review:Hemodynamic Assessment of Cerebral Vascular StenosisTraditional assessment of cerebrovascular stenosis prefer morphological determination to functional significance, particularly lack of understanding of hemodynamics. The mechanism of stroke includes embolic and hemodynamic disorders, and mixed mechanisms of interaction between the two. Different cerebral vascular occlusion site, located at the distal or proximal end, a series of small lesions or vascular lesions, clinical manifestations are numerous, all mixed with factors of impaired hemodynamics. In recent years, assessment of cerebral hemodynamics has been greatly developed. However, our current clinical guidelines for cerebrovascular stenosis decisions based more on morphologic assessment, whether it is non-invasive color Doppler ultrasound, transcranial Doppler ultrasound, CT arterial imaging, MR imaging artery, or invasive DSA, cerebral angiography, often used to measure the rate of stenosis severity of stenosis. This is more on the assessment of the structure, and less assessment for the functional significance of the narrow, and therefore whether it will cause long-term adverse judgment endpoint events seem insufficient basis for a particular stenosis. This may cause some require interventional treatment of stenotic lesions are missing, or some unwanted intervention therapy stenosis was laid stent/ balloon angioplasty. Functional assessment, conventional cerebral blood flow reserve assessment methods such as CT perfusion imaging, MRI perfusion imaging, PET perfusion imaging, SPECT perfusion imaging and other noninvasive tests usually indicate the presence of ischemia in patients with multi-vessel disease, but it can not determine whether a particular the ischemic area caused by stenosis and ischemic lesions in the region, the spatial resolution of vascular lesions is poor, not well guided interventional treatment decisions. Recently, in theory FFR in coronary stenosis assessment rise, with many unique features. So that the index is particularly suitable for the guidance of functional assessment of coronary artery stenosis, intervention and help physicians make appropriate treatment decisions in the catheterization laboratory. Its main advantages include:1. with a clear reference, FFR values equal to 1.0 on normal vessels; 2. Threshold of ischemic lesion assessment is quite clear, is less than 0.75 is recommended stents, greater than 0.80 is recommended to postpone the stent, the gray area between 0.75 and 0.80 is narrow; 3. The evaluation process is not affected by changes in systemic hemodynamics; 4.This parameter takes into account the contribution of collateral circulation; 5.FFR value could establish a special link between the severity of the stenosis to be perfused tissue region; 6.FFR has excellent spatial resolution, real-time dynamic help clinical assessment. Provided with a pressure guidewire with vascular hemodynamic assessment of coronary intervention has been a mature application. It has a very high value to guide the assessment of coronary artery stenosis, more and more attention of clinicians. And has been extended for interventional treatment strategies within the guidance of severe renal artery stenosis of blood vessels, but the current application in cerebral blood flow reserve assessment is still empty. Whether we are able to be widely applied in the future to assess cardiovascular FFR theory to narrow assessment of cerebral blood vessels. Currently, researchers have begun preliminary exploration. The hemodynamic assessment of cerebral vascular stenosis were summarized and prospect on this section. |
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