End-diastolic velocity increase predicts recanalization and neurological improvement in patients with ischemic stroke with proximal arterial occlusions receiving reperfusion therapies

Effect of Ultrasound on Thrombus debris during Sonothrombolysis in a Microfluidic device

Microbubble-mediated sonothrombolysis has been proven to be a non-invasive and efficient method for thrombolysis. Nevertheless, there is a potential risk that the thrombus debris generated during the dissolution of the original thrombus are too large and can lead to hazardous emboli. Using a sonothrombolysis microfluidic platform, we investigated the effects of ultrasound power, thrombolytic agent and microbubble concentration on the size of thrombus debris with the example of microbubble-mediated sonothrombolysis of arterial thrombus. Additionally, we studied the effects of ultrasound power on the size and shape of thrombus debris produced by acute and chronic arterial sonothrombolysis. In acute arterial sonothrombolysis, ultrasound power has significant effect on the size of thrombus debris and steadily increases with the increase of ultrasound power. Conversely, in chronic arterial sonothrombolysis, the size of thrombus debris is minimally affected by ultrasound power. Using the sonothrombolysis microfluidic platform, the relationship between ultrasound power and the safety of sonothrombolysis has been illustrated, and the sonothrombolysis microfluidic platform is demonstrated to be a promising tool for further studies on the process of sonothrombolysis.

Validation of the transcranial Doppler rescue criteria for mechanical thrombectomy

BACKGROUND AND PURPOSE

Transcranial Doppler (TCD) identifies acute stroke patients with arterial occlusion where treatment may not effectively open the blocked vessel. This study aimed to examine the clinical utility and prognostic value of TCD flow findings in patients enrolled in a multicenter prospective study (CLOTBUST-PRO).

METHODS

Patients enrolled with intracranial occlusion on computed tomography angiography (CTA) who underwent urgent TCD evaluation before intravenous thrombolysis was included in this analysis. TCD findings were assessed using the mean flow velocity (MFV) ratio, comparing the reciprocal ratios of the middle cerebral artery (MCA) depths bilaterally (affected MCA-to-contralateral MCA MFV [aMCA/cMCA MFV ratio]).

RESULTS

A total of 222 patients with intracranial occlusion on CTA were included in the study (mean age: 64 ± 14 years, 62% men). Eighty-eight patients had M1 MCA occlusions; baseline mean National Institutes of Health Stroke Scale (NIHSS) score was 16, and a 24-hour mean NIHSS score was 10 points. An aMCA/cMCA MFV ratio of <.6 had a sensitivity of 99%, specificity of 16%, positive predictive value (PV) of 60%, and negative PV of 94% for identifying large vessel occlusion (LVO) including M1 MCA, terminal internal carotid artery, or tandem ICA/MCA. Thrombolysis in Brain Ischemia scale, with (grade ≥1) compared to without flow (grade 0), showed a sensitivity of 17.1%, specificity of 86.9%, positive PV of 62%, and negative PV of 46% for identifying LVO.

CONCLUSIONS

TCD is a valuable modality for evaluating arterial circulation in acute ischemic stroke patients, demonstrating significant potential as a screening tool for intravenous/intra-arterial lysis protocols.

The Sky's the Limit: Expanding Nursing's Contribution to Acute Stroke Science

Stroke is the number one cause of preventable disability in adults in the United States. Significant advances have occurred in medications and technology supporting rapid stroke diagnosis and treatment during the past 30 years, along with blurring of the lines of what traditionally constituted nursing or medical research. Ischemic stroke is a disease of vascular insufficiency that mirrors myocardial infarction more than any other neurologic diagnosis. My primary program of research is focused on exploration of methods to improve intracranial blood flow in patients with hyperacute ischemic stroke who have viable, yet vulnerable, brain tissue to prevent worsening or enable improvement of stroke symptoms. I am also examining augmentation of recombinant tissue plasminogen activator treatment and stimulation of both arteriogenesis and angiogenesis with external counter-pulsation in patients with intracranial atherosclerosis. My secondary program of research focuses on methods to improve stroke systems of care, including improvement of advance practice providers' contributions to acute stroke care, use of innovative mobile stroke units, and improvement of quality core measure processes. Lessons learned along the way are highlighted, along with the value of interdisciplinary "team science" to build knowledge and enhance the care of highly vulnerable patients with acute stroke.

Possible effects of short rest after lunch on hemodynamics in the afternoon

PURPOSE

Drowsiness is often experienced in the afternoon after lunch. Decreases in blood flow to the brain secondary to increases in blood flow to the digestive organs after food intake could represent an underlying cause. As various beneficial effects of short rests on mental activities have been reported, the present study investigated hemodynamics using Doppler sonography of the common carotid artery (CCA) and superior mesenteric artery (SMA) after lunch, comparing resting and non-resting cases.

METHODS

Subjects comprised 24 healthy young adults (10 men, 14 women; mean age 22 ± 1 years). Sonography was performed to measure blood flow before and after lunch on each day, with and without a 15-min lying rest with eyes closed after lunch in each subject.

RESULTS

The timing of the peak velocity-time integral in the SMA in resting cases was delayed to 1.5 h after lunch compared to 0.5 h in non-resting cases. Although end-diastolic velocity in the CCA decreased after lunch, this decrease was suppressed in resting cases compared to non-resting cases even 4.5 h after lunch (median 96%, interquartile range [IQR] 83-102% vs. median 87%, IQR 77-92%; P = 0.037). Mean velocity (MV) in the CCA maintained unchanged after lunch in resting cases (P = 0.318), whereas non-resting cases showed decreased MV after lunch (P < 0.001).

CONCLUSION

These findings suggest that a short lying rest with eyes closed suppresses increases in blood flow to the digestive organ and maintains blood flow to the brain after lunch. These hemodynamic changes might help explain the benefits of afternoon rests.

Age-specific cerebral haemodynamic effects of early blood pressure lowering after transient ischaemic attack and non-disabling stroke

INTRODUCTION

There is limited knowledge of the effects of blood pressure (BP) lowering on cerebral haemodynamics after transient ischaemic attack (TIA) and non-disabling stroke, particularly at older ages. We aimed to evaluate changes in transcranial Doppler (TCD) haemodynamic indices in patients undergoing early blood pressure lowering after TIA/non-disabling stroke, irrespective of age.

PATIENTS AND METHODS

Among consecutive eligible patients attending a rapid-access clinic with suspected TIA/non-disabling stroke and no evidence of extra/intracranial stenosis, hypertensive ones underwent intensive BP-lowering guided by daily home telemetric blood pressure monitoring (HBPM). Clinic-based BP, HBPM, End-tidal CO2 and bilateral middle cerebral artery (MCA) velocity on TCD were compared in the acute setting versus one-month follow-up; changes were stratified by baseline hypertension (clinic-BP≥140/90) and by age (<65, 65-79 and ≥80).

RESULTS

In 697 patients with repeated TCD measures, mean/SD baseline systolic-BP (145.0/21.3 mmHg) was reduced by an average of 11.3/19.9 mmHg (p < 0.0001) at one-month (133.7/17.4 mmHg), driven by patients hypertensive at baseline (systolic-BP change = -19.0/19.2 mmHg, p < 0.001; vs -0.5/15.4, p = 0.62 in normotensives). Compared with baseline, a significant change was observed at one-month only in mean/SD MCA end diastolic velocity (EDV) (0.77/7.26 cm/s, p = 0.005) and in resistance index (RI) (-0.005/0.051, p = 0.016), driven by hypertensive patients (mean/SD EDV change: 1.145/6.96 cm/s p = 0.001, RI change -0.007/0.06, p = 0.014). Findings were similar at all ages (EDV change - ptrend=0.357; RI change - ptrend=0.225), including 117 patients aged ≥80. EDV and RI changes were largest in 100 patients with clinic systolic-BP decrease ≥30 mmHg (mean/SD EDV change = 2.49/7.47 cm/s, p = 0.001; RI change -0.024/0.063, p < 0.0001).

CONCLUSION

There was no evidence of worsening of TCD haemodynamic indices associated with BP-lowering soon after TIA/non-disabling stroke, irrespective of age and degree of BP reduction. In fact, EDV increase and RI decrease observed after treatment of hypertensive patients suggest a decrease in distal vascular resistance.

Transcranial Doppler to evaluate postreperfusion therapy following acute ischemic stroke: A literature review

Cerebral vessel recanalization therapy, either intravenous thrombolysis or mechanical thrombectomy, is the main treatment that can significantly improve clinical outcomes after acute ischemic stroke. The degree of recanalization and cerebral reperfusion of the ischemic penumbra are dependent on cerebral hemodynamics. Currently, the main imaging modalities to assess reperfusion are MRI and CT perfusion. However, these imaging techniques cannot predict reperfusion-associated complications and are not readily available in many centers. It is also not feasible to repeat them frequently for sequential assessments, which is important because of the changing nature of cerebral hemodynamics following stroke. Transcranial Doppler sonography (TCD) is a valid, safe, and inexpensive technique that can assess recanalized vessels and reperfused tissue in real-time at the bedside. Post thrombectomy reocclusion, hyperperfusion syndrome, distal embolization, and remote infarction result in poor outcomes after mechanical or intravenous reperfusion therapy. Managing blood pressure following these endovascular treatments can also be a dilemma. TCD has an important role, with major clinical implications, in evaluating cerebral hemodynamics and collateral vessel status, guiding clinicians in making individualized decisions based on cerebral blood flow during acute stroke care. This review summarizes the most relevant literature on the role of TCD in evaluating patients after reperfusion therapy. We also discuss the importance of performing TCD in the first few hours following thrombolytic therapy in identifying hyperperfusion syndrome and embolic signals, predicting recurrent stroke, and detecting reocclusions, all of which may help improve patient prognosis. We recommend TCD during the hyperacute phase of stroke in comprehensive stroke centers.

Transcranial Doppler Combined With Quantitative Electroencephalography Brain Function Monitoring for Estimating the Prognosis of Patients With Posterior Circulation Cerebral Infarction

Posterior circulation cerebral infarction (PCCI) can lead to deceased infratentorial cerebral blood flow (CBF) and metabolism. Neural activity is closely related to regional cerebral blood flow both spatially and temporally. Transcranial Doppler (TCD) combined with quantitative electroencephalography (QEEG) is a technique that evaluates neurovascular coupling and involves synergy between the metabolic and vascular systems. This study aimed to monitor brain function using TCD-QEEG and estimate the efficacy of TCD-QEEG for predicting the prognosis of patients with PCCI. We used a TCD-QEEG recording system to perform quantitative brain function monitoring; we recorded the related clinical variables simultaneously. The data were analyzed using a Cox proportional hazards regression model. Receiver-operating characteristic (ROC) curve analysis was used to evaluate the cut-off for the diastolic flow velocity (VD) and (delta + theta)/(alpha + beta) ratio (DTABR). The area under the ROC curve (AUROC) was calculated to assess the predictive validity of the study variables. Forty patients (aged 63.7 ± 9.9 years; 30 men) were assessed. Mortality at 90 days was 40%. The TCD indicators of VD [hazard ratio (HR) 0.168, confidence interval (CI) 0.047-0.597, p = 0.006] and QEEG indicators of DTABR (HR 12.527, CI 1.637-95.846, p = 0.015) were the independent predictors of the clinical outcomes. The AUROC after combination of VD and DTABR was 0.896 and showed better predictive accuracy than the Glasgow Coma Scale score (0.75), VD (0.76), and DTABR (0.781; all p < 0.05). TCD-QEEG provides a good understanding of the coupling mechanisms in the brain and can improve our ability to predict the prognosis of patients with PCCI.

Accelerated sonothrombolysis with Definity in a xenographic porcine cerebral thromboembolism model

Adjuvant ultrasound at 2 MHz with or without an ultrasound contrast agent improves the rate of thrombus resolution by recombinant tissue plasminogen activator (rt-PA) in laboratory and clinical studies. A sub-megahertz approach can further expand this therapy to a subset of patients with an insufficient temporal bone window, improving efficacy in unselected patient populations. The aim of this study was to determine if a clinical ultrasound contrast agent (UCA), Definity, and 220 kHz pulsed ultrasound accelerated rt-PA thrombolysis in a preclinical animal model of vascular occlusion. The effect of Definity and ultrasound on thrombus clearance was first investigated in vitro and subsequently tested in a xenographic porcine cerebral thromboembolism model in vivo. Two different microcatheter designs (end-hole, multi-side-hole) were used to infuse rt-PA and Definity at the proximal edge or directly into clots, respectively. Sonothrombolysis with Definity increased clot mass loss relative to saline or rt-PA alone in vitro, only when rt-PA was administered directly into clots via a multi-side-hole microcatheter. Combined treatment with rt-PA, Definity, and ultrasound in vivo increased the rate of reperfusion up to 45 min faster than clots treated with rt-PA or saline. In this porcine cerebral thromboembolism model employing retracted human clots, 220 kHz ultrasound, in conjunction with Definity increased the probability of early successful reperfusion with rt-PA.

Effects of continuous-flow left ventricular assist devices on cerebral hemodynamics

Continuous-flow left ventricular assist devices (LVADs) reduce peak systolic flow, increase diastolic flow, and eliminate pulsatility of circulation. Altered blood flow may lead to a change in end-organ perfusion. Analysis of the flow dynamics of the arteries of end organs, such as the brain, may indicate whether an organ is perfused sufficiently. The aim of this study is to evaluate and identify the flow pattern changes of carotid (CA) and middle cerebral arteries (MCA) in LVAD patients and to compare with heart failure patients and healthy volunteers. Eighty-nine individuals were included in this cross-sectional study. Participants were divided into three groups: LVAD patients (n = 31), heart failure patients (n = 26), and healthy volunteers (n = 27). Carotid and transcranial Doppler ultrasonography were performed for all study groups for peak systolic velocity (PSV), end-diastolic velocity (EDV), pulsatility (PI), and resistive (RI) indices of CA and MCA. Flow dynamics were compared between the groups. Doppler ultrasonographic data were analyzed at a median 12 (3-47) months after LVAD implantation. CA-PSV was lower in LVAD group compared with the other two groups (P < .001), MCA-PSV of LVAD and heart failure groups were similar and lower than healthy volunteers (P < .05). The highest values for CA-EDV were found in the LVAD group (P < .05). MCA-EDV values were found to be lowest in heart failure group (P < .05). For PI and RI, in all CA and MCA, the LVAD group had lower indices compared with the other two groups (P < .001). In addition, MCA flow analysis in patients with LVADs was identified for the first time with this study.

The effect of 220 kHz insonation scheme on rt-PA thrombolytic efficacy in vitro

Ultrasound-enhanced recombinant tissue plasminogen activator (rt-PA) thrombolysis is under development as an adjuvant to ischemic stroke therapy. The goal of this study was to design a pulsed ultrasound (US) exposure scheme that reduced intracranial constructive interference and tissue heating, and maintained thrombolytic efficacy relative to continuous wave (CW) insonation. Three 220 kHz US schemes were evaluated, two pulsed insonation schemes (15 cycles, 68 µs pulse duration, 33% or 62.5% duty cycle) and an intermittent CW insonation scheme (50 s active, 30 s quiescent) over a 30-min treatment period. An in silico study using a finite-difference model of transcranial US propagation was performed to estimate the intracranial acoustic field and temperature rise in the skull for each insonation scheme. In vitro measurements with flow were performed to assess thrombolysis using time-lapse microscopy. Intracranial constructive interference was not reduced with pulsed US using a pulse length of 15 cycles compared to intermittent CW US. The 33.3% duty cycle pulsed US scheme reduced heating in the temporal bone as much as 60% relative to the intermittent CW scheme. All insonation schemes promoted sustained stable cavitation in vitro and augmented thrombolysis compared to rt-PA alone (p   <  0.05). Ultraharmonic (UH) and harmonic cumulative energy over a 30 min treatment period was significantly higher (p   <  0.05) for the intermittent CW US scheme compared to either pulsed US scheme. Despite the difference in cavitation emissions, no difference was observed in the clot lysis between the three US schemes. These findings demonstrate that a 33.3% duty cycle pulsed US scheme with a 15-cycle burst can reduce bone heating and achieve equivalent thrombolytic efficacy as an intermittent CW scheme.

In vitro characterization of sonothrombolysis and echocontrast agents to treat ischemic stroke

The development of adjuvant techniques to improve thrombolytic efficacy is important for advancing ischemic stroke therapy. We characterized octafluoropropane and recombinant tissue plasminogen activator (rt-PA)-loaded echogenic liposomes (OFP t-ELIP) using differential interference and fluorescence microscopy, attenuation spectroscopy, and electrozone sensing. The loading of rt-PA in OFP t-ELIP was assessed using spectrophotometry. Further, it was tested whether the agent shields rt-PA against degradation by plasminogen activator inhibitor-1 (PAI-1). An in vitro system was used to assess whether ultrasound (US) combined with either Definity or OFP t-ELIP enhances rt-PA thrombolysis. Human whole blood clots were mounted in a flow system and visualized using an inverted microscope. The perfusate consisted of either (1) plasma alone, (2) rt-PA, (3) OFP t-ELIP, (4) rt-PA and US, (5) OFP t-ELIP and US, (6) Definity and US, or (7) rt-PA, Definity, and US (n = 16 clots per group). An intermittent US insonation scheme was employed (220 kHz frequency, and 0.44 MPa peak-to-peak pressures) for 30 min. Microscopic imaging revealed that OFP t-ELIP included a variety of structures such as liposomes (with and without gas) and lipid-shelled microbubbles. OFP t-ELIP preserved up to 76% of rt-PA activity in the presence of PAI-1, whereas only 24% activity was preserved for unencapsulated rt-PA. The use of US with rt-PA and Definity enhanced lytic efficacy (p < 0.05) relative to rt-PA alone. US combined with OFP t-ELIP enhanced lysis over OFP t-ELIP alone (p < 0.01). These results demonstrate that ultrasound combined with Definity or OFP t-ELIP can enhance the lytic activity relative to rt-PA or OFP t-ELIP alone, respectively.

Characterization and Imaging of Lipid-Shelled Microbubbles for Ultrasound-Triggered Release of Xenon

Xenon (Xe) is a bioactive gas capable of reducing and stabilizing neurologic injury in stroke. The goal of this work was to develop lipid-shelled microbubbles for xenon loading and ultrasound-triggered release. Microbubbles loaded with either xenon (Xe-MB) or xenon and octafluoropropane (Xe-OFP-MB) (9:1 v/v) were synthesized by high-shear mixing. The size distribution and the frequency-dependent attenuation coefficient of Xe-MB and Xe-OFP-MB were measured using a Coulter counter and a broadband acoustic attenuation spectroscopy system, respectively. The Xe dose was evaluated using gas chromatography/mass spectrometry. The total Xe doses in Xe-MB and Xe-OFP-MB were 113.1 ± 13.5 and 145.6 ± 25.5 μl per mg of lipid, respectively. Co-encapsulation of OFP increased the total xenon dose, attenuation coefficient, microbubble stability (in an undersaturated solution), and shelf life of the agent. Triggered release of gas payload was demonstrated with 6-MHz duplex Doppler and 220-kHz pulsed ultrasound. These results constitute the first step toward the use of lipid-shelled microbubbles for applications such as neuroprotection in stroke.

The End-Diastolic Velocity of Thyroid Arteries Is Strongly Correlated with the Peak Systolic Velocity and Gland Volume in Patients with Autoimmune Thyroiditis

Background

The end-diastolic velocity (EDV) of thyroid arteries reflects peripheral blood flow resistance.

Objective

The aim was to evaluate EDV correlations with other Doppler sonography parameters and with clinical and biochemical variables in a sample of patients with hypothyroidism caused by chronic autoimmune thyroiditis (CAT).

Methods

A sample of 48 CAT hypothyroid patients receiving treatment with stable doses of levothyroxine was selected. The participants underwent clinical evaluation and measurement of serum thyrotropin (TSH), total triiodothyronine (T3), total thyroxine (T4), free T4, thyroid peroxidase antibodies (anti-TPO), and antithyroglobulin antibodies (anti-Tg) and Doppler sonography.

Results

The EDV of the inferior thyroid arteries (ITA-EDV) was strongly and positively correlated with the peak systolic velocity of the inferior thyroid arteries (ITA-PSV, r = 0.919), thyroid volume (r = 0.711), and thyroid visual vascularization pattern (TVP, r = 0.687). There was no correlation between ITA-EDV and the clinical variables, hormones, anti-TPO, or anti-Tg.

Conclusion

The strong correlation of ITA-EDV with ITA-PSV, TVP, and volume suggests that increased vascularization in CAT may be associated with a reduction in thyroid blood flow resistance, possibly due to an angiogenesis-induced increase in the total vascular cross-sectional area of the parenchyma.

Comparative lytic efficacy of rt-PA and ultrasound in porcine versus human clots

Introduction

Porcine thrombi are employed routinely in preclinical models of ischemic stroke. In this study, we examined the differential lytic susceptibility of porcine and human whole blood clots with and without the use of microbubbles and ultrasound (US) as an adjuvant.

Materials and methods

An in vitro system equipped with time-lapse microscopy was used to evaluate recombinant tissue-plasminogen activator (rt-PA) lysis of porcine and human clots in the same species or cross species plasma. Human and porcine whole blood clots were treated with rt-PA and an echo contrast agent, Definity^®, and exposed to intermittent 120 kHz US.

Results and conclusions

The rt-PA lytic efficacy observed for porcine clots in porcine plasma was 22 times lower than for human clots in human plasma reported previously. Further, porcine clots did not exhibit increased lysis with adjuvant Definity^® and US exposure. However, the rt-PA lytic susceptibility of the porcine clots in human plasma was similar to that of human clots in human plasma. Human clots perfused with porcine plasma did not respond to rt-PA, but adjuvant use of Definity^® and US enhanced lysis. These results reveal considerable differences in lytic susceptibility of porcine clots and human clots to rt-PA. The use of porcine clot models to test new human thrombolytic therapies may necessitate modulation of coagulation and thrombolytic factors to reflect human hemostasis accurately.

In vitro thrombolytic efficacy of echogenic liposomes loaded with tissue plasminogen activator and octafluoropropane gas

Echogenic liposomes loaded with the thrombolytic recombinant tissue-type plasminogen activator (rt-PA) are under development for the treatment of ischemic stroke. These agents are designed to co-encapsulate cavitation nuclei to promote bubble activity in response to ultrasound exposure, and to enable localized delivery of thrombolytic. Stable cavitation improves the efficacy of the thrombolytic through enhanced fluid mixing. Echogenic liposomes that encapsulate air-filled microbubbles nucleate scant stable cavitation activity in response to 120 kHz intermittent ultrasound exposure, and have demonstrated thrombolytic efficacy equivalent to rt-PA alone. It was hypothesized that encapsulating octafluoropropane (OFP) gas within rt-PA-loaded liposomes instead of air will enhance ultrasound-mediated stable cavitation activity and increase thrombolytic efficacy compared to previous studies. The thrombolytic efficacy and cavitation activity nucleated from liposomes that encapsulate OFP microbubbles and rt-PA (OFP t-ELIP) was evaluated in vitro. Human whole blood clots were exposed to human fresh-frozen plasma alone, rt-PA (0, 0.32, 1.58, and 3.15 µg ml^-1), or OFP t-ELIP at equivalent enzymatic activity, with and without exposure to intermittent ultrasound. Further, numerical simulations were performed to gain insight into the mechanisms of cavitation nucleation. Sustained ultraharmonic activity was nucleated from OFP t-ELIP when exposed to ultrasound. Furthermore, the thrombolytic efficacy was enhanced compared to rt-PA alone at concentrations of 1.58 µg ml^-1 and 3.15 µg ml^-1 (p  <  0.05). These results indicate that OFP t-ELIP can nucleate sustained stable cavitation activity and enhance the efficacy of thrombolysis.

Blood Pressure, Carotid Flow Pulsatility, and the Risk of Stroke: A Community-Based Study

BACKGROUND AND PURPOSE

High blood pressure is a major cause of cardiovascular events, and carotid flow pulsatility may be associated with cardiovascular events. However, the combined effect of blood pressure and flow pulsatility on the development of stroke remains unclear. Therefore, we investigated the combined influence of central blood pressure and pulsatility index (PI) on the incidence of stroke.

METHODS

Baseline data from 2033 adults (≥30 years) without stroke history in the Cardiovascular Disease Risk Factor Two-Township Study were linked to incident stroke. Common carotid flow PI was calculated by peak systolic velocity, end-diastolic velocity, and mean vessel velocity, which were measured in the common carotid artery. Hazard ratios for the risk of total stroke resulting from high central systolic blood pressure (CSBP) and high PI were calculated with Cox proportional hazard models.

RESULTS

Over a median follow-up of 9.81 years, 132 people incurred stroke events. The incidence rates of stroke were 1.3, 6.4, and 13.2 per 1000 person-years for tertile groups of CSBP (P for trend<0.05) and 4.3, 7.0, and 9.4 per 1000 person-years for tertile groups of PI (P for trend<0.05). Compared with the first tertile of CSBP, hazard ratios were 4.88 (95% confidence interval, 2.29-10.43) for the second tertile and 10.42 (5.05-21.53) for the third tertile. Hazard ratios of PI were 2.18 (1.39-3.42; third tertile) and 1.64 (1.02-2.63; second tertile) compared with the first tertile. The individuals with a high CSBP and high PI had a 13-fold higher stroke risk compared with those with low CSBP and low PI (13.2; 1.75-99.71) after adjusting for age, sex, and traditional cardiovascular risk.

CONCLUSIONS

CSBP and common carotid PI jointly and independently predicted future stroke. Carotid flow pulsatility may play an important role in the development of stroke.

Hemodynamic correlates of transient cognitive impairment after transient ischemic attack and minor stroke: A transcranial Doppler study

Background and aims

Transient cognitive impairment (TCI) on the Mini Mental State Evaluation score is common after transient ischemic attack/minor stroke and might identify patients at increased risk of dementia. We aimed to replicate TCI using the Montreal Cognitive Assessment (MoCA), compare it with persistent Mild Cognitive Impairment (PMCI), and to determine whether global cerebral hemodynamic changes could explain transient impairment.

Methods

Consecutive patients with transient ischemic attack/minor stroke (NIHSS ≤ 3) were assessed with the MoCA and transcranial Doppler ultrasound acutely and at 1 month. We compared patients with TCI (baseline MoCA < 26 with ≥ 2 points increase at 1 month), PMCI (MoCA < 26 with < 2 points increase), and no cognitive impairment (NCI; MoCA ≥ 26).

Results

Of 326 patients, 46 (14.1%) had PMCI, 98 (30.1%) TCI, and 182 (55.8%) NCI. At baseline, TCI patients had higher systolic blood pressure (150.95 ± 21.52 vs 144.86 ± 22.44 mmHg, p = 0.02) and lower cerebral blood flow velocities, particularly end-diastolic velocity (30.16 ± 9.63 vs 35.02 ± 9.01 cm/s, p < 0.001) and mean flow velocity (48.95 ± 12.72 vs 54 ± 12.46 cm/s, p = 0.001) than those with NCI, but similar clinical and hemodynamic profiles to those with PMCI. Systolic BP fell between baseline and 1 month (mean reduction = 14.01 ± 21.26 mmHg) and end-diastolic velocity and mean flow velocity increased (mean increase = + 2.42 ± 6.41 and 1.89 ± 8.77 cm/s, respectively), but these changes did not differ between patients with TCI, PMCI, and NCI.

Conclusions

TCI is detectable with the MoCA after transient ischemic attack and minor stroke and has similar clinical and hemodynamic profile to PMCI. However, TCI does not appear to be due to exaggerated acute reversible global hemodynamic changes.

In Vitro Evaluation of Focused Ultrasound-Enhanced TNK-Tissue Plasminogen Activator-Mediated Thrombolysis

INTRODUCTION

The low and incomplete recanalization performance of thrombolytic therapy in patients with acute ischemic stroke has created the need to use focused ultrasound (FUS) energy as a way to enhance thrombolysis efficiency (sonothrombolysis). Using an in vitro flow model, the role of various parameters involved in FUS-enhanced tenecteplase (TNK-tPA [tissue plasminogen activator])-mediated thrombolysis was evaluated.

MATERIALS AND METHODS

Fully retracted porcine blood clots were used for the proposed parametric studies. A spherically FUS transducer (4 cm diameter), focusing at 10 cm and operating at 1 MHz, was used. Pulsed ultrasound protocols were applied that maintained temperature elevation at the focus that never exceeded 1°C. Thrombolysis efficiency was measured as the relative reduction in the mass of the clot.

RESULTS

The role of various properties on thrombolysis efficacy was examined. These various properties are the acoustic power, the TNK-tPA concentration, the flow rate, the exposure time, the pulse length, the pulse repetition frequency, the duty factor, the formation of standing waves, the acoustic medium, and the administration of microbubbles. Study results have demonstrated that the parameters examined influenced thrombolysis efficacy and the degree of thrombolysis achieved by each parameter was measured.

CONCLUSIONS

Study findings helped us to optimize the treatment protocol for 1 MHz pulsed FUS that maximizes the thrombolytic efficacy of TNK-tPA, which potentially could be applied for therapeutic purposes. The outcome of the study showed poor thrombolysis efficacy, as with 30 minutes of FUS treatment only 370 mg of clot was removed.

Thrombolytic efficacy and enzymatic activity of rt-PA-loaded echogenic liposomes

Echogenic liposomes (ELIP), that can encapsulate both recombinant tissue-type plasminogen activator (rt-PA) and microbubbles, are under development to improve the treatment of thrombo-occlusive disease. However, the enzymatic activity, thrombolytic efficacy, and stable cavitation activity generated by this agent has yet to be evaluated and compared to another established ultrasound-enhanced thrombolytic scheme. A spectrophotometric method was used to compare the enzymatic activity of the rt-PA incorporated into ELIP (t-ELIP) to that of rt-PA. An in vitro flow model was employed to measure the thrombolytic efficacy and dose of ultraharmonic emissions from stable cavitation for 120-kHz ultrasound exposure of three treatment schemes: rt-PA, rt-PA and the perfluorocarbon-filled microbubble Definity^®, and t-ELIP. The enzymatic activity of rt-PA incorporated into t-ELIP was 28 % that of rt-PA. Thrombolytic efficacy of t-ELIP or rt-PA and Definity^® was equivalent when the dose of t-ELIP was adjusted to produce comparable enzymatic activity. Sustained bubble activity was nucleated from Definity but not from t-ELIP exposed to 120-kHz ultrasound. These results emphasize the advantages of encapsulating a thrombolytic and the importance of incorporating an insoluble gas required to promote sustained, stable cavitation activity.

Common carotid artery end-diastolic velocity is independently associated with future cardiovascular events

BACKGROUND

Carotid ultrasound is widely used to measure haemodynamic parameters, such as intima-media thickness and blood flow velocities (i.e. peak-systolic velocity [PSV], end-diastolic velocity [EDV], and resistive index [RI]). However, the association between blood flow velocities and cardiovascular events remains unclear.

DESIGN AND METHODS

Baseline data, including quantitative ultrasonography, were obtained from 3146 adults as part of the Cardiovascular Diseases Risk Factor Two-Township Study. Occurrence of ischaemic heart disease (IHD) and stroke was determined from insurance claims and death certificates. The hazard ratio (HR) of CVD (IHD and stroke combined) was calculated for EDV and PSV of the common carotid artery using Cox models. Net reclassification index and integrated discrimination index were used to evaluate the capacity of EDV to predict IHD, stroke, and CVD.

RESULTS

Median follow-up was 12.8 years. There were 220 cases of IHD and 247 cases of stroke. The HR (95% CI) for CVD from univariate analysis was 4.54 (3.51-5.85) for EDV <15 cm/s relative to EDV ≥ 20 cm/s (p < 0.0001), and 3.23 (2.51-4.15) for PSV < 65 cm/s relative to PSV ≥ 80 cm/s (p < 0.0001). The HR (95% CI) for CVD from multivariate analysis was 1.66 (1.22-2.26) for EDV < 15 cm/s relative to EDV ≥ 20 cm/s, and 1.39 (1.03-1.89) for PSV < 65 cm/s relative to PSV ≥ 80 cm/s. EDV slightly but significantly improved prediction of CVD (integrated discrimination index 0.56%, p = 0.016).

CONCLUSIONS

Low common carotid EDV and PSV were independently associated with future CVD, and EDV improved the prediction of future CVD. More prospective studies are required in different ethnic groups to understand the significance and implication of these findings.

Shaken and stirred: mechanisms of ultrasound-enhanced thrombolysis

The use of ultrasound and microbubbles as an effective adjuvant to thrombolytics has been reported in vitro, ex vivo and in vivo. However, the specific mechanisms underlying ultrasound-enhanced thrombolysis have yet to be elucidated. We present visual observations illustrating two mechanisms of ultrasound-enhanced thrombolysis: acoustic cavitation and radiation force. An in vitro flow model was developed to observe human whole blood clots exposed to human fresh-frozen plasma, recombinant tissue-type plasminogen activator (0, 0.32, 1.58 or 3.15 μg/mL) and the ultrasound contrast agent Definity (2 μL/mL). Intermittent, continuous-wave ultrasound (120 kHz, 0.44 MPa peak-to-peak pressure) was used to insonify the perfusate. Ultraharmonic emissions indicative of stable cavitation were monitored with a passive cavitation detector. The clot was observed with an inverted microscope, and images were recorded with a charge-coupled device camera. The images were post-processed to determine the time-dependent clot diameter and root-mean-square velocity of the clot position. Clot lysis occurred preferentially surrounding large, resonant-sized bubbles undergoing stable oscillations. Ultraharmonic emissions from stable cavitation were found to correlate with the lytic rate. Clots were observed to translate synchronously with the initiation and cessation of the ultrasound exposure. The root-mean-square velocity of the clot correlated with the lytic rate. These data provide visual documentation of stable cavitation activity and radiation force during sub-megahertz sonothrombolysis. The observations of this study suggest that the process of clot lysis is complex, and both stable cavitation and radiation force are mechanistically responsible for this beneficial bio-effect in this in vitro model.

Relationship between pulsatility index and clinical course of acute ischemic stroke after thrombolytic treatment

Background. The relationship between the arterial recanalization after intravenous recombinant tissue plasminogen activator (rtPA) and outcomes is still uncertain. The aim of our study was to evaluate whether there is an association between the pulsatility indexes (PI) of the middle cerebral artery (MCA) measured by transcranial Doppler (TCD) after iv rtPA treatment and short- and long-term outcomes in ischemic stroke patients. Methods. Forty-eight patients with acute ischemia in the MCA territory who achieved complete recanalization after the administration of intravenous thrombolytic treatment were included in the study. The TCD was applied to patients after the iv rtPA treatment. Clinical and functional outcomes were assessed by National Institutes of Health Stroke Scale (NIHSS) scores and modified Rankin Scores (mRS), respectively. Results. Significant positive correlations were found between the PI value and NIHSS score at 24 hours, NIHSS score at 3 months, and mRS at 3 months (P < 0.005 for all). The cut-off value for PI in predicting a favorable prognosis and a good prognosis might be less than or equal to 1.1 and less than or equal to 1.4, respectively. Conclusions. PI may play a role in predicting the functional and clinical outcome after thrombolytic therapy in acute ischemic stroke patients.

Exploratory analysis of estimated acoustic peak rarefaction pressure, recanalization, and outcome in the transcranial ultrasound in clinical sonothrombolysis trial

PURPOSE

Acoustic peak rarefaction pressure (APRP) is the main factor that influences ultrasound-enhanced thrombolysis. We sought to determine whether recanalization rate and functional outcomes in the Transcranial Ultrasound in Clinical SONothrombolysis (TUCSON) trial could be predicted by estimated in vivo APRP.

METHODS

We developed an acoustic attenuation model to estimate the in vivo APRP at the arterial occlusion site in each subject of the TUCSON trial with CT scans eligible for measurements. Variables included temporal bone thickness, depth of arterial occlusion site, and average attenuation of skin and brain tissues. Recanalization was defined as partial or complete using the Thrombolysis in Brain Infarction flow grades. Functional independence was assessed at 3 months using the modified Rankin Scale score (mRS, 0-1).

RESULTS

APRP was calculated in 20 acute ischemic stroke patients treated with sonothrombolysis (mean age, 64 ± 15 years, 65% men; median NIHSS score, 13; IQR, 6-17). The mean APRP was 30.2 ± 15.5 kPa (range, 8-68 kPa). Patients with persisting occlusion had nonsignificantly lower APRP than patients with partial or complete recanalization (25.2 ± 8.0 versus 32.3 ± 17.7 kPa; p = 0.228). Patients who were functionally independent at 3 months had nonsignificantly higher APRP than patients with worse outcome (35.1 ± 19.5 versus 25.9 ± 11.2 kPa; p = 0.217).

CONCLUSIONS

Our exploratory analysis suggests a potentially important role of successful energy delivery to augment thrombolysis with 2-MHz ultrasound in acute ischemic stroke patients.

Clot retraction affects the extent of ultrasound-enhanced thrombolysis in an ex vivo porcine thrombosis model

We investigated ultrasound-enhanced thrombolysis in two whole-blood clot models using a Food and Drug Administration-approved contrast agent (Definity, Lantheus Medical Imaging; Billerica, MA USA) and thrombolytic drug (recombinant tissue-type plasminogen activator [rt-PA]) (Genentech; South San Francisco, CA USA). Porcine venous blood was collected from donor hogs and coagulated in vials made of two different materials. This method produced clots with differing compositional properties, as determined by routine scanning electron microscopy and histology. Clots were deployed in an ex vivo porcine thrombosis model, and exposed to an intermittent ultrasound scheme previously developed to maximize stable cavitation while acoustic emissions were detected. Exposure to 3.15 μg/mL rt-PA promoted lysis in both clot models, compared with exposure to plasma alone. However, only unretracted clots experienced significant enhancement of thrombolysis in the presence of rt-PA, Definity, and ultrasound, compared with treatment with rt-PA. In these clots, microscopy revealed loose erythrocyte aggregates, a significantly less extensive fibrin network and a higher porosity, which may facilitate increased penetration of thrombolytics by cavitation.

Sonothrombolysis in ischemic stroke

OPINION STATEMENT

Acute ischemic stroke remains one of the most devastating diseases when it comes to morbidity and mortality, not to mention the personal and economic burden that occurs in long-term. Intravenous thrombolysis with tissue plasminogen activator (tPA) is the only effective acute stroke therapy that improves outcome if given up to 4.5 hours from symptom onset. However, recanalization rates are meager and the majority of treated patients still have residual disability after stroke, emphasizing the need for further treatment options that may facilitate or even rival the only approved therapy. Sonothrombolysis, the adjuvant continuous ultrasound sonication of an intra-arterial occlusive thrombus during thrombolysis, enhances the clot-dissolving capabilities of intravenous tPA presumably by delivering acoustic pressure to the target brain vessel. Higher recanalization rates produce a trend towards better functional outcomes that could be safely achieved with the combination of high-frequency ultrasound and intravenous tPA. However, data on ultrasound targeting of intracranial proximal occlusive lesions other than those in the middle cerebral arteries are sparse. Moreover, recent sonothrombolysis trials were exclusively conducted with operator-dependent hand-held technology hindering its further testing in clinical sonothrombolysis trials. An operator-independent 2-MHz transcranial Doppler device has been developed allowing health care professionals not formally trained in ultrasound apparatus to provide therapeutic ultrasound as needed. Currently, this operator-independent device covering 12 proximal intracranial segments that most commonly contain thrombo-embolic occlusions enters testing in a pivotal multicenter sonothrombolysis efficacy trial. If this trial demonstrates safety and efficacy, adjuvants, such as gaseous microbubbles that further potentiate the thrombolytic effect of intravenous tPA, could be tested along with this device.

Taboos and opportunities in sonothrombolysis for stroke

Systemic thrombolysis with tissue plasminogen activator (tPA) is the only approved treatment for acute ischaemic stroke that improves functional outcome if given up to 4.5 h from symptom onset. At least half of treated patients have unfavourable outcomes long-term though, emphasising the need to amplify the only approved acute stroke therapy. Ultrasound targeting of an intra-arterial occlusive clot and delivering mechanical pressure to its surrounding fluids (referred to as sonothrombolysis) accelerates the thrombolytic effect of tPA. Higher recanalisation rates produce a trend towards better functional outcomes that could be safely achieved with the combination of 2 MHz frequency ultrasound and systemic tPA. To further accelerate the clot-dissolving effect of ultrasound, a variety of frequencies and intensities as well as other adjuvant treatment elements are being studied. However, literature reports argue efficacy and safety of these novel approaches doubting promptly translation into the clinical practice. This review will summarise our current knowledge about potentially harmful (taboos) directions and what we think are promising avenues for these future stroke therapies. We also give a prospect for novel technologies such as operator-independent devices that aim to further spread the use of sonothrombolysis for stroke.

Common carotid flow velocity is associated with cognition in older adults

AIMS

To assess the relationship between carotid flow velocity and cognitive impairment in patients with mild-moderate (<50%) carotid artery disease.

METHODS

We studied 407 participants with available carotid ultrasound and cognitive measures. We related peak systolic velocity (PSV) and end diastolic velocity (EDV) of internal carotid artery (ICA) and common carotid artery (CCA) and intimal medial thickness (IMT) to Mini Mental State Examination (MMSE), Clock Draw Test (CDT), Activities of Daily Living Scale (ADL)and Montreal Cognitive Assessment (MoCA).

RESULTS

EDV of CCA was significantly different in higher and lower MoCA (MMSE) groups. Multiple regression analysis demonstrated that lower EDV was significantly associated with lower MoCA (+0.459 per standard deviation (SD), p<0. 01 for the left; +0.539 per SD, p<0. 01 for the right) and CDT (odds ratio (OR) 0.093, p< 0.05 for the left; OR) 0.120, p<0. 01 for the right) scores. PSV of left CCA (-0.205 per SD, p<0.05) and IMT (+42.536 per SD, p< 0.001) were associated with ADL. PSV of right CCA was associated with MMSE (+0.081 per SD, p<0.001). No significant relationship between ICA flow velocity and cognitive performance was observed.

CONCLUSIONS

Our preliminary data show that common carotid artery flow velocity was associated with cognitive performance.

Adjunctive and alternative approaches to current reperfusion therapy

BACKGROUND AND PURPOSE

Current ischemic stroke reperfusion therapy consists of intravenous thrombolysis given in eligible patients after review of a noncontrast CT scan and a time-based window of opportunity. Rapid clot lysis has a strong association with clinical improvement but remains incomplete in many patients. This review appraises novel adjunctive or alternative approaches to current reperfusion strategies being tested in all trial phases. Summary of Review- Alternative approaches to current reperfusion therapy can be separated into 4 main categories: (1) combinatory approaches with other drugs or devices; (2) novel systemic thrombolytic agents; (3) endovascular medical or mechanical reperfusion treatments; and (4) noninvasive or minimally invasive methods to augment cerebral blood flow and alleviate intracranial blood flow steal.

CONCLUSIONS

Reperfusion treatments must be provided as fast as possible in patients most likely to benefit. Patients who fail to rapidly reperfuse may benefit from other strategies that maintain collateral flow or protect tissue at risk.