Asymptomatic embolisation in non-valvular atrial fibrillation and its relationship to anticoagulation therapy

Atrial fibrillation: villain or bystander in vascular brain injury

Atrial fibrillation (AF) and stroke are inextricably connected, with classical Virchow pathophysiology explaining thromboembolism through blood stasis in the fibrillating left atrium. This conceptualization has been reinforced by the remarkable efficacy of oral anticoagulant (OAC) for stroke prevention in AF. A number of observations showing that the presence of AF is neither necessary nor sufficient for stroke, cast doubt on the causal role of AF as a villain in vascular brain injury (VBI). The requirement for additional risk factors before AF increases stroke risk; temporal disconnect of AF from a stroke in patients with no AF for months before stroke during continuous ECG monitoring but manifesting AF only after stroke; and increasing recognition of the role of atrial cardiomyopathy and atrial substrate in AF-related stroke, and also stroke without AF, have led to rethinking the pathogenetic model of cardioembolic stroke. This is quite separate from recognition that in AF, shared cardiovascular risk factors can lead both to non-embolic stroke, or emboli from the aorta and carotid arteries. Meanwhile, VBI is now expanded to include dementia and cognitive decline: research is required to see if reduced by OAC. A changed conceptual model with less focus on the arrhythmia, and more on atrial substrate/cardiomyopathy causing VBI both in the presence or absence of AF, is required to allow us to better prevent AF-related VBI. It could direct focus towards prevention of the atrial cardiomyopathy though much work is required to better define this entity before the balance between AF as villain or bystander can be determined.

Asymptomatic spontaneous cerebral emboli predict cognitive and functional decline in dementia

BACKGROUND

Spontaneous cerebral emboli (SCE) are frequent in Alzheimer's disease (AD) and vascular dementia (VaD). We investigated the effect of SCE on the rates of cognitive and functional decline in AD and VaD.

METHODS

One hundred thirty-two patients with dementia (74 AD, National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association [NINCDS/ADRDA] criteria; 58 VaD, National Institute of Neurological Disorders and Stroke-Association Internationale pour la Recherche et l'Enseignement en Neurosciences [NINDS/AIREN] criteria) underwent 1-hour transcranial Doppler for detection of SCE (mean [SD] age 75.5 (7.4) years; 46% female). Neuropsychological tests (Mini-Mental State Examination [MMSE], Alzheimer's Disease Assessment Scale-Cognitive subscale [ADAS-Cog], and Neuropsychiatric Inventory [NPI]) and assessment of activities of daily living (Interview for Deterioration in Daily Living Activities in Dementia [IDDD]) were performed initially and 6 months later. SCE positive (SCE+ve, n = 47) and SCE negative (SCE-ve, n = 85) patients were compared using repeated measures analyses of variance (ANOVAs) adjusted for age, gender, and cardiovascular risk factors.

RESULTS

SCE+ve patients with dementia, both AD and VaD, suffered a more rapid decline in cognitive functioning over 6 months (ADAS-cog, mean increase 7.1 for SCE+ve compared with 3.3 for SCE-ve, p = .006) and activities of daily living (IDDD, mean increase 24.4 for SCE+ve compared with 10.8 for SCE-ve, p = .014).

CONCLUSIONS

Asymptomatic SCE are associated with an accelerated cognitive and functional decline in dementia. SCE may be a potentially treatable cause of disease progression in dementia.

Asymptomatic spontaneous cerebral emboli and cognitive decline in a cohort of older people: a prospective study

BACKGROUND

Asymptomatic spontaneous cerebral emboli (SCE) are common in dementia and are associated with cognitive decline in dementia. The significance of their presence in older people is unknown.

METHOD

We included 96 participants (mean (SD) age 76.8 (6.7) years, 46% female) who were the control group in a case-control study to evaluate SCE in dementia. Cognitive functioning was assessed prospectively over 2.5 years, using the MMSE and CAMCOG.

RESULTS

The mean (SD) MMSE score was 28.7 (1.4) at baseline with an average (SD) drop of 0.79 (0.91) per year. The presence of SCE was not related to the annual drop in MMSE score, nor to the CAMCOG score at follow-up (p = 0.88 and p = 0.41, respectively). Linear regression analyses identified higher age in years (beta = 0.29, p = 0.003), history of stroke (beta = 0.31, p = 0.001) and carotid stenosis (beta = 0.28, p = 0.003) as independent predictors of cognitive decline.

CONCLUSION

We found no association between the presence of SCE and subsequent cognitive decline in older people without dementia.

Stroke in atrial fibrillation: update on pathophysiology, new antithrombotic therapies, and evolution of procedures and devices

Atrial fibrillation (AF) is said to be an epidemic, affecting 1%-1.5% of the population in the developed world. The clinical significance of AF lies predominantly in a 5-fold increased risk of stroke. Strokes associated with AF are usually more severe and confer increased risk of morbidity, mortality, and poor functional outcome. Despite the advent of promising experimental therapies for selected patients with acute stroke, pharmacological primary prevention remains the best approach to reducing the burden of stroke. New antithrombotic drugs include both parenteral agents (e.g. a long-acting factor Xa inhibitor idraparinux) and oral anticoagulants, such as oral factor Xa inhibitors and direct oral thrombin inhibitors (ximelagatran, dabigatran). Ximelagatran had shown significant potential as a possible replacement to warfarin therapy, but has been withdrawn because of potential liver toxicity. Its congener dabigatran appears to have a better safety profile and has recently entered a phase III randomized clinical trial in AF. Oral factor Xa inhibitors (rivaroxaban, apixaban, YM150) inhibit factor Xa directly, without antithrombin III mediation, and may prove to be more potent and safe. Selective inhibitors of specific coagulation factors involved in the initiation and propagation of the coagulation cascade (factor IXa, factor VIIa, circulating tissue factor) are at an early stage of development. Additional new agents with hypothetical, although not yet proven, anticoagulation benefits include nematode anticoagulant peptide (NAPc2), protein C derivatives, and soluble thrombomodulin. A battery of novel mechanical approaches for the prevention of cardioembolic stroke has recently been evaluated, including various models of percutaneous left atrial appendage occluders which block the connection between the left atrium and the left atrial appendage, minimally invasive surgical isolation of the left atrial appendage, and implantation of the carotid filtering devices which divert large emboli from the internal to the external carotid artery, preventing the embolic material from reaching intracranial circulation. Despite recent advances and promising new approaches, prevention of recurrent AF may be one of the best protections against AF-related stroke and may reduce the prevalence of stroke by almost 25%. Improved pharmacological and nonpharmacological rhythm control strategies for AF as well as primary prevention of AF with 'upstream' therapy and risk factor modification are likely to produce a larger effect on the reduction of stroke rates in the general population than will specific interventions.

Stroke prophylaxis in atrial fibrillation: who gets it and who does not?

AIMS

Underuse of warfarin for stroke prophylaxis in atrial fibrillation (AF) is extensive and represents a major problem in clinical practice. To identify factors associated with warfarin treatment in eligible AF patients.

METHODS AND RESULTS

The study population consisted of all Swedish resident AF patients at the Stockholm South General Hospital during 2002 (n=2796). Medical records were examined and complemented by data from the Swedish National Hospital Discharge Register. Sixty-eight percent of the patients (1898/2796) had indications, and no apparent contraindications for warfarin treatment. Of these 54% (1029/1898) got warfarin. Factors favouring warfarin treatment after adjustment for other factors were history of ischaemic stroke, an implanted pacemaker, treatment in a cardiology rather than internal medicine ward and valvular defect. Factors associated with a reduced likelihood of warfarin treatment were paroxysmal type of AF and age >80 years. Important risk factors for stroke in AF like heart failure, hypertension, and diabetes did not increase the chances of warfarin treatment.

CONCLUSION

Risk stratification using known risk factors of stroke seems to affect warfarin treatment only to a minor degree in clinical practice. Undertreatment was particularly common in patients with paroxysmal AF and in patients aged >80 years and calls for improved clinical routines in accordance with international guidelines.

Transcranial Doppler Detection of Microembolic Signals During Pulmonary Vein Antrum Isolation: Implications for Titration of Radiofrequency Energy

BACKGROUND

Cerebrovascular events are an important complication during pulmonary vein antrum isolation (PVAI). Microembolic signals (MES) have been associated with stroke and neurological impairment. However, the incidence of MES during PVAI, and their relationship to microbubble formation and radiofrequency (RF) parameters are unknown.

OBJECTIVES

We sought to assess the relationship between MES, microbubble detection, and neurological outcome and the impact of RF titration strategy on these parameters.

METHODS

We studied 202 patients in two groups undergoing PVAI using an intracardiac echocardiography (ICE)-guided technique. MES were detected by transcranial Doppler (TCD) using insonation of the middle cerebral arteries. The number of microbubbles on ICE were qualitatively labeled as FEW, MODERATE, and SHOWER. In group I (n = 107), RF output was titrated to avoid microbubble formation and in group II (n = 95), standard power-limited RF output was used.

RESULTS

TCD detected MES in all 202 patients during PVAI with an average of 1,793 +/- 547 per patient; 90% were detected during left atrial ablation. Over 85% of MES occurred after microbubbles. Group I patients had significantly lower numbers of MES (1,015 +/- 438 per patient) compared to group II patients (2,250 +/- 864 per patient) (P < 0.05). Group II also had a 3.1% incidence of acute neurological complications versus 0.9% in group I (P = 0.10). Patients with clinical events had significantly higher numbers of MES. There were no significant correlations between RF power, temperature, or impedence and MES number.

CONCLUSIONS

MES directly correlate to the amount of microbubble formation on ICE, and may result in cerebroembolic complications. Titration of RF according to microbubble formation by ICE during PVAI may be important for minimizing the occurrence of MES and possibly acute neurological complications.

Time Period Required for Transcranial Doppler Monitoring of Embolic Signals to Predict Recurrent Risk of Embolic Transient Ischemic Attack and Stroke From Arterial Stenosis

BACKGROUND AND PURPOSE

We aimed to investigate whether the time period of transcranial Doppler monitoring for embolic signals can be reduced without loss of clinical yield compared with routinely performed 1-hour monitoring.

METHODS

Investigations on the basis of a post hoc analysis of a previously published cohort of 86 patients (55 men, 31 women; mean age 60.6 years) with a nondisabling arterioembolic ischemic event in the anterior circulation within the last 30 days (mean 7.3) and an ipsilateral medium-grade or high-grade stenosis of the carotid or middle cerebral artery. Patients underwent 1-hour monitoring for embolic signals and were followed up prospectively for 6 weeks to evaluate the relationship between embolic signals and risk of an early ischemic recurrence. Risk was also calculated after fictitious reduction of the monitoring period from 60 minutes to 50, 40, 30, 20, and 10 minutes, respectively, and compared with the results obtained from the 1-hour period.

RESULTS

The number of patients positive for embolic signals decreased with the decreasing monitoring period. By this, the odds ratio of embolic signals for an early ischemic recurrence "decreased" from 40 (derived from the 1-hour monitoring) to 10 when the monitoring lasted < or =30 minutes. The relationship between the rate of embolic signals per hour and risk of a recurrent stroke is described by an S-shaped curve. As a consequence, risk estimated from reduced monitoring periods can differ considerably from that derived from the 1-hour monitoring if the signal frequency lies within a medium range (eg, between 3 and 15 signals in 30 minutes).

CONCLUSIONS

The time period of monitoring for embolic signals may be reduced without loss of clinical relevant information when signal frequency is low or already high during the reduced monitoring period, but it should be prolonged to maximally an hour at signal numbers within a medium range. However, our results need to be externally validated on an independent cohort of patients or confirmed by a prospective study before this modification can be recommended in general.

New neurophysiology and central nervous system dysfunction

PURPOSE OF REVIEW

The goal of this article is to summarize very recent technologic advances in neurophysiologic monitoring and to illustrate their potential benefit to critical care medicine.

RECENT FINDINGS

Simplified, computer-processed electroencephalography devices now permit cost-effective, long-term critical care monitoring. They may be used alone to objectively assess sedation or coma level. In addition, these monitors serve as screening tools for more detailed electrophysiologic characterization of cortical dysfunction resulting from seizures, ischemia, or hypoxia. Somatosensory potentials broaden these capabilities to the entire neuraxis, whereas long-latency auditory evoked potentials facilitate measurement of changes in vigilance and cognition. Motor evoked potentials offer a sensitive and reliable method to determine the function of descending motor pathways in uncooperative or unresponsive patients. They may also yield a new measure of cortical excitability. New developments with transcranial Doppler ultrasonography promise noninvasive measures of cerebral perfusion pressure and particulate embolization. Near-infrared spectroscopy appears to enable noninvasive measurement of regional tissue oxygenation in both the brain and spinal cord.

SUMMARY

When used together, these continuous measures of synaptic function, cerebral perfusion, and oxygenation give the clinician a vast amount of otherwise unobtainable information regarding the functional status of the central nervous system.