American Heart Association


The stress of it all: Examining the hemodynamics of AVMs before and after treatment

Mark L. McAllister, MD

Alaraj A, Shakur SF, Amin-Hanjani S, Mostafa H, Khan S, Aletich VA, et al. Changes in Wall Shear Stress of Cerebral Arteriovenous Malformation Feeder Arteries After Embolization and Surgery. Stroke. 2015

Cerebral AVMs are a concern to the stroke neurologist because of their propensity to present as an intracerebral hemorrhage. The connections of arteries directly to veins without the intervention of a high resistance capillary network alter normal cerebral hemodynamics. How the long term changes in vessel characteristics including vascular remodeling respond to the abnormal physics caused by AVMS is not fully understood.

Using quantitative magnetic resonance angiography (QMRA), Alaraj et al. estimated the wall shear stress (WSS), the force of blood against the cerebrovascular endothelium, in the patients with AVMs before and after treatment. In a cohort of 21 patients undergoing embolization of their AVM, the investigators demonstrated that the WSS was increased in the feeder arteries of the AVM compared to the normal contralateral vessel prior to the procedure. After embolization, the WSS fell to levels comparable to the contralateral vessels.

Additionally, in a subset of 17 patients who underwent resection of the AVM after embolization further reduction of the WSS was demonstrated. The mean WSS forces after surgical receptions demonstrated a trend to be lower than the mean on the contralateral normal vessel, but this did not achieve statistical significance.
Given that WSS has been implicated as a stimulus for vessel remodeling and vessel diameter, noninvasive measurement of WSS using QMRA may represent an intriguing method to monitor the efficacy of treatment for cerebral AVMs. Further, this study is important in that it is contrast to the only other study of WSS in AVMs which found identical WSS in the AVM feeders and normal contralateral vessels. The authors contend that their use of QMRA is more accurate than the TCD used in the 1995 study.

Interleukin 23 levels are increased in carotid atherosclerosis – A possible role for the IL-23/IL-17 axis?

Michelle Christina Johansen, MD

Abbas A, Gregersen I, Holm S, Daissormont I, Bjerkeli V, Krohg-Sørensen K, et al. Interleukin 23 Levels Are Increased in Carotid Atherosclerosis: Possible Role for the Interleukin 23/Interleukin 17 Axis. Stroke. 2015

The world of immunology and elucidation of cytokine pathways is not usually the focus of the vascular neurologist, but perhaps our attention should be redirected. It is well established that atherosclerosis is a state of inflammation and prior studies have shown an increased expression of IL-23 in carotid lesions, with particularly high levels in symptomatic patients. Targeting of IL-23, a member of the IL-12 family of cytokines with pro-inflammatory properties, is already underway in other autoimmune diseases including psoriasis, inflammatory bowel disease and rheumatoid arthritis. How is this interleukin, with its role in producing IL-17 related to cerebrovascular disease?

Abbas et. al in their study reinvestigated the association of IL-23 to atherosclerosis and sought to better establish any relationship between expression and cerebrovascular disease. 177 patients with internal carotid stenosis (≥50%) were recruited and classified according to symptoms: 69 patients had a stroke/TIA/amaurosis fugax ipsilateral to the stenosed carotid artery in the prior 2 months and 108 patients either had symptoms >2 months or had no symptoms. The patients were compared to 24 healthy controls from the same area of Norway. Plasma samples were obtained by venipuncture. Plaque samples were obtained for examination from 68 of the patients with carotid atherosclerosis and compared to non-atherosclerotic control vessels of organ donors.

Those with carotid atherosclerosis (177) were found to have markedly raised plasma IL-23 levels compared to controls (24). Notably, the level of IL-23 increased in a step wise fashion with the highest plasma levels in those with the most recent symptoms (<1month). Even those without symptoms still had higher levels of IL-23 than healthy controls. When the plaque samples were evaluated, IL-23 as well as IL-23 receptors (R) were 18 fold higher in those with atherosclerosis. However, there was no association between levels of IL-23 and presence or absence of symptoms.

In order to better elucidate the role of IL-23, plasma dendritic cells, peripheral blood mononuclear cells and monocytes from patients with carotid atherosclerosis were evaluated. The investigators found those with carotid atherosclerosis had increased levels of IL-23/IL-23R in dendritic cells as well as increase release of IL-17 from mononuclear cells when stimulated with IL-23 in comparison to healthy controls. IL-23 promoted release of tumor necrosis factor (TNF) only in those with carotid atherosclerosis.

Recent data indicate that IL-23 is a dominant cytokine controlling inflammation in peripheral tissues and joints, but what role does it have to play in stoke? This study suggests that IL-23 plays a unique role in the patient with atherosclerosis compared to healthy controls. The study has limitations such as a small control sample size, but is it possible that the release of IL-23, the interaction with its receptor or the stimulation of IL-17 represent three potential targets for new therapies? Could we control some of the sequela of stroke by a modulation of this cascade? While other trials targeting the inflammatory response in stroke are underway using Methotrexate and Tysabri, perhaps further research should be directed at the IL-23/IL-17 cascade in hopes that in vivo trials could provide even more exciting results.

Paragonimus Hemorrhagicus

Vikas Pandey, MD

Xia Y, Ju Y, Chen J, You C. Hemorrhagic stroke and cerebral paragonimiasis. Stroke. 2014

Paragonimiasis is a parasitic infection caused by the Paragonimus species (most commonly Paragonimus Westermani) of lung flukes and is particularly common in East Asia however the more than 30 species of the flukes are becoming more prevalent worldwide. Commonly causing a pulmonary syndrome consisting of lung parenchymal hemorrhage and hemoptysis, the species is becoming more and more notorious for causing intracerebral hemorrhage, as those with both acute and chronic cerebral paragonimiasis appear at risk of having cerebral hemorrhages. The group from West China Hospital at Sichuan University set out to characterize cerebral paragonimiasis and its impact on cerebrovascular disease.

The authors retrospectively analyzed the clinical and imaging characteristics, diagnosis and treatment outcomes of 10 patients with hemorrhagic cerebral paragonimiasis. The group had an average age of 15.7 years and ranged from 4 to 46 showing the younger cohort that the disease affects. The diagnosis of paragonimiasis was done by ELISA serologic testing for Paragonimus-specific IgG antibody and blood eosinophil quantification was conducted on blood samples. The manifestations of the paragonimiasis were vascular malformation, tumor apoplexy, subarachnoid hemorrhage, intraventricular hemorrhage, cavernous hemangioma, subdural hemorrhage and spontaneous intracerebral hemorrhage. Four out of the ten cases were confirmed by pathology. The hemorrhages seen were atypical of occult vascular malformations and the hemorrhages themselves had atypical appearances such as dot, strip, sheet or cord-shaped hematomas. Other imaging testing was done to rule out other cerebrovascular disease on an as needed basis. The misdiagnosis rate was approximately 100%.

The importance of early detection of paragonimiasis is exemplified by the fact that paragonimiasis can be cured by therapy upon early diagnosis but delayed treatment can cause death in as high as 5% of patients. The mechanism of hemorrhage is thought to be due to vessel wall changes caused by parasitic inflammation resulting in concentric thickening, lumen stenosis and occlusion, as well as erosion of the vessel wall causing subsequent rupture. The alarmingly high misdiagnosis rate and the known increase in prevalence of paragonimiasis makes this disease one that should not be overlooked, especially in areas where the parasite is endemic or in cases of atypical hemorrhagic stroke symptom presentation and appearance on imaging.


Effects of Extracranial Carotid Stenosis on Intracranial Blood Flow

Rajbeer Singh Sangha, MD

Shakur SF, Hrbac T, Alaraj A, Du X, Aletich VA, Charbel FT, and Amin-Hanjani S. Effects of Extracranial Carotid Stenosis on Intracranial Blood Flow. Stroke. 2014

A higher degree of extracranial carotid stenosis is associated with increased stroke risk and has become a key determinant in treatment decision-making. The dominant mechanism via which strokes occur is thought to be thrombo-embolic, however it has been postulated that hemodynamically-consequential narrowing of the vessel lumen can also result in cerebral hypoperfusion and may even potentiate the effects of distal embolization. Shakur et al. looked to characterize impact of degree of stenosis, stenosis length, and residual lumen on intracranial blood flow in patients with extracranial carotid stenosis.

The study was a retrospective analysis of 105 patients that were identified having ≥ 50% carotid stenosis who underwent revascularization. Patients in this study had undergone quantitative flow measurements of the extracranial and intracranial arteries using quantitative magnetic resonance angiography (QMRA). On multivariate analysis, MCA flow ratio was not significantly associated with percentage stenosis, stenosis length, or residual lumen. However, mean MCA flow ratio was significantly lower in symptomatic compared to asymptomatic patients (0.92 vs. 1.22, P=0.001). In contrast, mean ICA flow ratio was similar among these two groups (0.55 vs. 0.55, P=0.99).
The study findings suggest that in symptomatic extracranial carotid disease, the reduction in MCA flow may play an important role, thus implicating intracranial hemodynamics in the pathophysiology of this disease. It would be interesting to be able to classify the level of collaterals in these patients as this may be a determinant in whether patients remain asymptomatic. Furthermore, more studies should be conducted to better quantify the characteristics present in patients who suffer from symptomatic extracranial carotid disease vs asymptomatic extracranial carotid disease. Elucidating the pathophysiological mechanisms will better allow us to stratify ischemic stroke risk in the asymptomatic population.  

Lefties are Never Right: Is Atherosclerotic plaque in the Left carotid artery more vulnerable than on the Right?

Michelle Christina Johansen, MD

Selwaness M, van den Bouwhuijsen Q, van Onkelen RS, Hofman A, Franco OH, van der Lugt A, et al. Atherosclerotic Plaque in the Left Carotid Artery Is More Vulnerable Than in the Right. Stroke. 2014

Left hemispheric strokes can be devastating, impacting the patient’s language center and leading to hemiparesis and hemiplegia. Large vessel atherosclerosis is an established stroke subtype and plaque located at the carotid bifurcation has been implicated in as high as 18% of all strokes. Selwaness et al open their paper by noting that a significantly higher proportion of ischemic events are diagnosed in the left hemisphere compared to the right.  The team hypothesize that the higher incidence of events occurring in the lefthemisphere is related to either a higher prevalence, severity or vulnerability of atherosclerotic disease in the left carotid artery. 

Carotid MRI’s were performed on 1414 stroke free participants to assess not only the location but also degree of stenosis and components of the carotid plaque. The authors invited participants from The Rotterdam Study, a prospective population based cohort study who were routinely undergoing carotid ultrasound to also undergo MRI imaging of the bilateral carotids. The mean age of the final cohort was 72 and 53% were male.  Image quality was considered sufficient in 95% of scans. Luminal stenosis was calculated using the NASCET criteria.  The investigators classified the composition of plaques as either lipid-rich, containing intraplaque hemorrhage or calcification based on imaging characteristics. 

Overall, 1196 subjects or 85% had plaque in both carotid arteries meaning only 218 subjects had unilateral plaques. Within these patients, the investigators found that left sided plaques were twice as prevalent as right sided with no sex predominance but those with unilateral left sided plaques tended to be younger (68 vs 71). The degree of luminal stenosis did not differ between right and left and clinically relevant stenosis defined by NASCET also did not differ. When the components were analyzed individually, lipid-rich plaques was slightly more prevalent on the left (27.6% vs 23.4% p 0.006) and intraplaque hemorrhage (IPH) was also more frequent in left carotid artery plaques (23.1% vs 19.7% p 0.01).  Calcification was equal on both sides. When a single or predominant component was assigned, IPH and lipid were most prevalent in left-sided plaques but this time right sided plaques were predominantly composed of calcification.

The conclusion of the investigators is that carotid atherosclerotic plaque size and composition are not symmetrically distributed and that plaques on the left are more vulnerable than on the right due to the presence of IPH versus calcification. 

This inference should give the practicing vascular neurologist pause. In treatment of asymptomatic carotid stenosis, the mantra has been best medical management. Many are familiar with the CREST data which showed that among asymptomatic patients, the primary outcome (periprocedural stroke, death and myocardial infarction rates) did not differ significantly between stenting and surgery (4.9% vs. 5.6%) but the study was not powered to obtain significance (p=0.07). There are ongoing trails (CREST-2) to evaluate if optimal medical management is in fact sufficient in these patients. If in fact left sided plaques are more vulnerable to rupture, while we wait for the outcome of clinical trials should a practicing Neurologist change practice? For example, would one lower the blood pressure of a patient with left sided stenosis more aggressively than their right sided counterpart? Is dual antiplatelet therapy warranted even in the absence of intracranial stenosis? The authors appropriately discuss many limitations in evaluation of their data to include the fact that significance was only obtained when the plaques were assigned a predominant component, a small n and potential observer bias. This limits the broad application of their study results but the questions raised demand further research and consideration. 

“Let not the right side of your brain know what the left side doeth.”
~ George Bernard Shaw

Cryptogenic stroke in elderly: Is heart where the answer lies?

Chirantan Banerjee, MD

Seo JY, Lee KB, Lee JG, Kim JS, Roh H, Ahn MY, et al. Implication of Left Ventricular Diastolic Dysfunction in Cryptogenic Ischemic Stroke. Stroke. 2014

Despite technological progress, about 1 in 3 ischemic strokes remains cryptogenic. More than 30% of these patients will have a recurrent stroke in the next 5 years. Several studies in the last few years have brought into focus atrial fibrillation (AF) as the underlying etiology in a sizeable proportion of these patients, especially those above 60 years. The longer we look for atrial fibrillation, the more likely we are to find it. In the recently published CRYSTAL – AF trial, 12.4% patients had atrial fibrillation detected when monitored for 1 year. This is especially important, as the therapeutic implications are major.

Clinical, electrocardiographic and echocardiographic markers of atrial fibrillation may be especially important to assess in cryptogenic stroke patients, as they may point out which patients are more likely to have occult atrial fibrillation, and thus may need to be monitored longer. Left ventricular diastolic dysfunction (LVDD) is thought to be a marker of paroxysmal non-valvular AF.

In the current study, Seo et al. compared the prevalence of left ventricular diastolic dysfunction (LVDD) in cryptogenic stroke (CS) v/s  stroke with AF and stroke without AF (lacunar strokes, and strokes with >50% referable large artery stenosis). Also, they compared the proportion of severe LVDD between CS  patients with cardioembolism (CE)-mimic DWI pattern and non CE-mimic DWI pattern, with the aim to delineate if LVDD can be used as a marker to predict occult AF in CS patients with CE-mimic pattern on MRI. The study cohort consists of 1901 patients with acute stroke enrolled into a prospective registry at the Soonchunhyang University Hospital in Seoul, Korea between January 2004 to March 2013, with a mean age of 58 years. After excluding patients with missing workup, and patients with known sources for cardioembolism which may affect LVDD such as mechanical valve, mitral stenosis, atrial myxoma etc, 55 CS patients, 310 strokes with AF and 969 strokes without AF were included in analysis. LVDD was ascertained by 2 cardiologists and assigned grades I-III based on accepted parameters.  When dichotomized at grade III, severe LVDD was much more prevalent in CS than stroke without AF, and almost comparable to stroke with AF.  Moreover, among the CS patients, the presence of LVDD was much higher in CE-mimic patients than non-mimics. On the contrary, although left atrial enlargement (LAE) was predominantly detected in stroke with AF, its frequency was not different between CS and stroke without AF. In a multivariable model, LVDD was associated with stroke with AF, despite controlling for hypertension, LAE and PFO.

These findings are significant, as they validate LVDD being a marker for AF in a stroke population, despite controlling for hypertension. The fact that most of our current AF detection techniques including ambulatory cardiac telemetry or implantable devices are contingent on timing, more permanent markers are needed that precede or predict AF to save time and money. Also, in this study, LVDD proved to be a good, if not a more sensitive marker than LAE for AF.  The higher prevalence of LVDD in CS with CE-mimic lesion distribution suggests that these patients likely have underlying AF as a cause for the CS. However, being a retrospective single center study, the findings cannot be generalizable to our stroke patients. Also, there may be an inherent selection bias because a significant proportion of patients, who did not have a full workup were excluded. Despite these limitations, it makes a strong argument for patients that suffer CS with CE mimic lesion patterns and have LVDD to undergo longer cardiac monitoring, as their risk of having AF is very high. In our aging population, where the prevalence of AF is predicted to double by 2050 to 5.5 million, tools to increase pre-test probability of detecting AF will help us tailor stroke care to individual stroke patients, while saving resources by avoiding unnecessary testing on others.