Your browser doesn't support javascript.
loading
Show: 20 | 50 | 100
Resultados 1 - 8 de 8
Filtrar
1.
N Engl J Med ; 382(1): 9, 2020 01 02.
Artículo en Inglés | MEDLINE | ID: mdl-31738483

RESUMEN

BACKGROUND: The use of intensive lipid-lowering therapy by means of statin medications is recommended after transient ischemic attack (TIA) and ischemic stroke of atherosclerotic origin. The target level for low-density lipoprotein (LDL) cholesterol to reduce cardiovascular events after stroke has not been well studied. METHODS: In this parallel-group trial conducted in France and South Korea, we randomly assigned patients with ischemic stroke in the previous 3 months or a TIA within the previous 15 days to a target LDL cholesterol level of less than 70 mg per deciliter (1.8 mmol per liter) (lower-target group) or to a target range of 90 mg to 110 mg per deciliter (2.3 to 2.8 mmol per liter) (higher-target group). All the patients had evidence of cerebrovascular or coronary-artery atherosclerosis and received a statin, ezetimibe, or both. The composite primary end point of major cardiovascular events included ischemic stroke, myocardial infarction, new symptoms leading to urgent coronary or carotid revascularization, or death from cardiovascular causes. RESULTS: A total of 2860 patients were enrolled and followed for a median of 3.5 years; 1430 were assigned to each LDL cholesterol target group. The mean LDL cholesterol level at baseline was 135 mg per deciliter (3.5 mmol per liter), and the mean achieved LDL cholesterol level was 65 mg per deciliter (1.7 mmol per liter) in the lower-target group and 96 mg per deciliter (2.5 mmol per liter) in the higher-target group. The trial was stopped for administrative reasons after 277 of an anticipated 385 end-point events had occurred. The composite primary end point occurred in 121 patients (8.5%) in the lower-target group and in 156 (10.9%) in the higher-target group (adjusted hazard ratio, 0.78; 95% confidence interval, 0.61 to 0.98; P = 0.04). The incidence of intracranial hemorrhage and newly diagnosed diabetes did not differ significantly between the two groups. CONCLUSIONS: After an ischemic stroke or TIA with evidence of atherosclerosis, patients who had a target LDL cholesterol level of less than 70 mg per deciliter had a lower risk of subsequent cardiovascular events than those who had a target range of 90 mg to 110 mg per deciliter. (Funded by the French Ministry of Health and others; Treat Stroke to Target ClinicalTrials.gov number, NCT01252875.).


Asunto(s)
Anticolesterolemiantes/uso terapéutico , Enfermedades Cardiovasculares/prevención & control , LDL-Colesterol/sangre , Ezetimiba/uso terapéutico , Inhibidores de Hidroximetilglutaril-CoA Reductasas/uso terapéutico , Ataque Isquémico Transitorio/tratamiento farmacológico , Accidente Cerebrovascular/tratamiento farmacológico , Adulto , Anciano , Anticolesterolemiantes/efectos adversos , Aterosclerosis/complicaciones , Aterosclerosis/tratamiento farmacológico , Isquemia Encefálica/tratamiento farmacológico , Enfermedades Cardiovasculares/mortalidad , Quimioterapia Combinada , Femenino , Humanos , Análisis de Intención de Tratar , Ataque Isquémico Transitorio/complicaciones , Estimación de Kaplan-Meier , Masculino , Persona de Mediana Edad , Accidente Cerebrovascular/sangre
2.
J Nucl Cardiol ; 29(3): 1329-1336, 2022 06.
Artículo en Inglés | MEDLINE | ID: mdl-33462787

RESUMEN

OBJECTIVES: Non-stenotic plaques are an underestimated cause of ischemic stroke. Imaging aspects of high-risk carotid plaques can be identified on CT angiography (CTA) and 18F-fluoro-deoxyglucose positron emission tomography (FDG-PET) imaging. We evaluated in patients with cryptogenic ischemic stroke the usefulness of FDG-PET-CTA. METHODS: 44 patients imaged with CTA and FDG-PET were identified retrospectively. Morphological features were identified on CTA. Intensity of FDG uptake in carotid arteries was quantified on PET. RESULTS: Patients were imaged 7 ± 8 days after stroke. 44 non-stenotic plaques with increased 18F-FDG uptake were identified in the carotid artery ipsilateral to stroke and 7 contralateral. Most-diseased-segment TBR on FDG-PET was higher in artery ipsilateral vs. contralateral to stroke (2.24 ± 0.80 vs. 1.84 ± 0.50; p < .05). In the carotid region with high FDG uptake, prevalence of hypodense plaques and extent of hypodensity on CTA were higher in artery ipsilateral vs. contralateral to stroke (41% vs. 11%; 0.72 ± 1.2 mm2 vs. 0.13 ± 0.43 mm2; p < .05). CONCLUSIONS: In patients with ischemic stroke of unknown origin and non-stenotic plaques, we found an increased prevalence of high-risk plaques features ipsilateral vs. contralateral to stroke on FDG-PET-CTA imaging suggesting a causal role for these plaques.


Asunto(s)
Accidente Cerebrovascular Isquémico , Placa Aterosclerótica , Accidente Cerebrovascular , Arterias Carótidas , Angiografía por Tomografía Computarizada , Fluorodesoxiglucosa F18 , Humanos , Placa Aterosclerótica/complicaciones , Placa Aterosclerótica/diagnóstico por imagen , Tomografía de Emisión de Positrones/métodos , Estudios Retrospectivos , Accidente Cerebrovascular/diagnóstico por imagen
3.
Circulation ; 142(8): 748-757, 2020 08 25.
Artículo en Inglés | MEDLINE | ID: mdl-32594766

RESUMEN

BACKGROUND: The TST trial (Treat Stroke to Target) showed the benefit of targeting a low-density lipoprotein cholesterol (LDL-C) concentration of <70 mg/dL in terms of reducing the risk of major cardiovascular events in 2860 patients with ischemic stroke with atherosclerotic stenosis of cerebral vasculature. The impact on carotid atherosclerosis evolution is not known. METHODS: TST-PLUS (Treat Stroke to Target-Plaque Ultrasound Study) included 201 patients assigned to an LDL-C concentration of <70 mg/dL and 212 patients assigned to a target of 100±10 mg/dL. To achieve these goals, investigators used the statin and dosage of their choice and added ezetimibe as needed. Ultrasonographers were certified and carotid ultrasound examinations were performed using M'Ath software at baseline and at 2, 3, and 5 years. All images were uploaded to the Intelligence in Medical Technologies database directly from the carotid ultrasound device. The central core laboratory performed all offline measurements of the intima-media thickness of both common carotid arteries blinded from the randomization arm. The main outcomes were newly diagnosed atherosclerotic plaque on carotid bifurcation or internal carotid artery using the Mannheim consensus definition and between-group comparison of common carotid arteries intima-media thickness change. RESULTS: After a median follow-up of 3.1 years, the achieved LDL-C concentrations were 64 mg/dL (1.64 mmol/L) in the lower-target group and 106 mg/dL (2.72 mmol/L) in the higher-target group. Compared with the higher-target group, patients in the lower-target group had a similar incidence of newly diagnosed carotid plaque: 46/201 (5-year rate, 26.1%) versus 45/212 (5-year rate, 29.7%). The change in common carotid arteries intima-media thickness was -2.69 µm (95% CI, -6.55 to 1.18) in the higher-target group and -10.53 µm (95% CI, -14.21 to -6.85) in the lower-target group, resulting in an absolute between-group difference of -7.84 µm (95% CI, -13.18 to -2.51; P=0.004). CONCLUSIONS: In patients with ischemic stroke and atherosclerosis, an LDL-C target of <70 mg/dL (1.8 mmol/L) did not reduce the incidence of new carotid plaques but produced significantly greater regression of carotid atherosclerosis than an LDL-C target of 90 to 110 mg/dL. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT01252875.


Asunto(s)
Enfermedades de las Arterias Carótidas , LDL-Colesterol/sangre , Ezetimiba/administración & dosificación , Accidente Cerebrovascular Isquémico , Anciano , Anciano de 80 o más Años , Enfermedades de las Arterias Carótidas/sangre , Enfermedades de las Arterias Carótidas/complicaciones , Enfermedades de las Arterias Carótidas/diagnóstico por imagen , Enfermedades de las Arterias Carótidas/tratamiento farmacológico , Ezetimiba/efectos adversos , Femenino , Estudios de Seguimiento , Humanos , Accidente Cerebrovascular Isquémico/sangre , Accidente Cerebrovascular Isquémico/diagnóstico por imagen , Accidente Cerebrovascular Isquémico/etiología , Accidente Cerebrovascular Isquémico/prevención & control , Masculino , Persona de Mediana Edad , Ultrasonografía
4.
Stroke ; 51(8): 2355-2363, 2020 08.
Artículo en Inglés | MEDLINE | ID: mdl-32640939

RESUMEN

BACKGROUND AND PURPOSE: As a result of contraindications (eg, frailty, cognitive impairment, comorbidities) or patient refusal, many patients with stroke and atrial fibrillation cannot be discharged on oral anticoagulant. Among them, the proportion of potential candidates for left atrial appendage closure (LAAC) and their 12-month outcome is not well known. METHODS: The prospective WATCH-AF registry (Warfarin Aspirin Ten-A Inhibitors and Cerebral Infarction and Hemorrhage and Atrial Fibrillation) enrolled consecutive patients admitted within 72 hours of an acute stroke associated with atrial fibrillation in 2 stroke centers. Scales to evaluate stroke severity, disability, functional independence, risk of fall, cognition, ischemic and hemorrhagic risk-stratification, and comorbidities were systematically collected at admission, discharge, 3, 12 months poststroke. The 2 main end points were death or dependency (modified Rankin Scale score >3) and recurrent stroke (brain infarction and brain hemorrhage). RESULTS: Among 400 enrolled patients (370 with brain infarction, 30 with brain hemorrhage), 31 died before discharge and 57 (14.3%) were possible European Heart Rhythm Association/European Society of Cardiology and American Heart Association/American College of Cardiology/Heart Rhythm Society candidates for LAAC. At 12 months, the rate of death or dependency was 17.9%, and the rate of stroke recurrence was 9.8% in the 274/400 (68.5%) patients discharged on a long-term oral anticoagulant strategy, as compared with 17.5% and 24.7%, respectively, in 57 patients candidate for LAAC. As compared with patients on a long-term oral anticoagulant strategy, there was a 2-fold increase in the risk of stroke recurrence in the group with an indication for LAAC (adjusted hazard ratio, 2.58 [95% CI, 1.40-4.76]; P=0.002). CONCLUSIONS: Fourteen percent of patients with stroke associated with atrial fibrillation were potential candidates for LAAC. The 12-month stroke risk of these candidates was 3-fold the risk of anticoagulated patients.


Asunto(s)
Anticoagulantes/administración & dosificación , Apéndice Atrial , Fibrilación Atrial/tratamiento farmacológico , Fibrilación Atrial/epidemiología , Sistema de Registros , Accidente Cerebrovascular/tratamiento farmacológico , Accidente Cerebrovascular/epidemiología , Anciano , Anciano de 80 o más Años , Aspirina/administración & dosificación , Apéndice Atrial/diagnóstico por imagen , Fibrilación Atrial/diagnóstico por imagen , Femenino , Estudios de Seguimiento , Humanos , Masculino , Prevalencia , Estudios Prospectivos , Accidente Cerebrovascular/diagnóstico por imagen , Resultado del Tratamiento , Warfarina/administración & dosificación
5.
Stroke ; 48(4): 1005-1010, 2017 04.
Artículo en Inglés | MEDLINE | ID: mdl-28289241

RESUMEN

BACKGROUND AND PURPOSE: After carotid endarterectomy (CEA) or carotid artery stenting (CAS) in patients with transient ischemic attack or minor ischemic stroke, recurrent stroke risk falls to a low rate on modern medical treatment. METHODS: We used data from 4583 patients with recent transient ischemic attack or minor stroke enrolled in the TIAregistry.org to perform a nested case-control analysis to evaluate pre- and post-CEA/CAS risk. Cases were defined as patients with a CEA/CAS during the 1-year follow-up period. For each case, 2 controls with a follow-up time greater than the time from qualifying event to CEA/CAS were randomly selected, matched by age and sex. Primary outcome was defined as major vascular events (MVE, including stroke, cardiovascular death, and myocardial infarction). RESULTS: The median delay from symptom onset of qualifying event to CEA/CAS was 11 days (interquartile range, 6-23). Overall, patients with CEA/CAS had a higher 1-year risk of MVE than other patients (14.8% versus 5.8%; adjusted hazard ratio, 2.40; 95% confidence interval, 1.61-3.60; P<0.001). During the matched preprocedural period, MVE occurred in 14 (7.5%) cases and in 13 (3.5%) controls, with an adjusted odds ratio =2.46 (95% confidence interval, 1.07-5.64; P=0.03). In the postprocedural period, the risk of MVE was also higher in cases than in controls (adjusted P<0.03). CONCLUSIONS: Patients with CEA/CAS had a higher 12-month risk of MVE, as well as during pre- and postprocedural periods. These results suggest that patients in whom CEA/CAS is anticipated are likely to be an informative population for inclusion in studies testing new antithrombotic strategies started soon after symptom onset.


Asunto(s)
Estenosis Carotídea/cirugía , Ataque Isquémico Transitorio/etiología , Infarto del Miocardio/etiología , Evaluación de Resultado en la Atención de Salud/estadística & datos numéricos , Sistema de Registros/estadística & datos numéricos , Stents , Accidente Cerebrovascular/etiología , Procedimientos Quirúrgicos Vasculares/métodos , Anciano , Anciano de 80 o más Años , Estudios de Casos y Controles , Endarterectomía Carotidea/efectos adversos , Endarterectomía Carotidea/métodos , Endarterectomía Carotidea/estadística & datos numéricos , Femenino , Estudios de Seguimiento , Humanos , Ataque Isquémico Transitorio/epidemiología , Masculino , Persona de Mediana Edad , Infarto del Miocardio/epidemiología , Accidente Cerebrovascular/epidemiología , Procedimientos Quirúrgicos Vasculares/efectos adversos , Procedimientos Quirúrgicos Vasculares/estadística & datos numéricos
6.
Lancet Neurol ; 21(10): 889-898, 2022 10.
Artículo en Inglés | MEDLINE | ID: mdl-36115361

RESUMEN

BACKGROUND: Patients who have had a transient ischaemic attack or minor stroke have an increased risk of cardiovascular events for the following 5 years. We aimed to assess 5-year functional outcomes in patients with transient ischaemic attack or minor ischaemic stroke and to determine the factors associated with long-term disability. METHODS: We analysed data from patients in TIAregistry.org, an international, prospective, observational registry of patients with transient ischaemic attack or minor ischaemic stroke from 61 specialised centres in 21 countries. Patients aged 18 years or older who had a transient ischaemic attack or minor stroke within the previous 7 days between May 30, 2009, and Dec 30, 2011, with a baseline modified Rankin scale (mRS) score of 0-1, and who had been followed up for 5 years, were eligible for inclusion in this study. We evaluated whether existing comorbidities and stroke recurrence, categorised as disabling (mRS score of >1, including death) or non-disabling (mRS score of 0-1), at 5 years after baseline, were associated with poor functional outcome (defined as an mRS score of >1). We used multivariable generalised equation models for factors associated with poor functional outcome at 5 years and multivariable cause-specific Cox hazard regression models in case of stroke recurrence. FINDINGS: Between May 30, 2009, and Dec 30, 2011, 3847 eligible patients were included in the study, 3105 (80·7%) of whom had an mRS evaluation at 5 years of follow-up. Median follow-up duration was 5·00 years (IQR 4·78-5·00). 710 (22·9%) of 3105 patients had an mRS score greater than 1 at 5 years. Factors associated with poor functional outcome at 5 years were older age (per 10-year increase, odds ratio [OR] 2·18, 95% CI 1·93-2·46; p<0·0001), diabetes of any type (1·45, 1·18-1·78; p=0·0001), history of stroke or transient ischaemic attack before the qualifying event (1·74, 1·37-2·22; p<0·0001), hypertension (1·38, 1·00-1·92; p=0·050), atrial fibrillation or flutter (1·52, 1·04-1·94; p=0·030), congestive heart failure (1·73, 1·22-2·46; p=0·0024), valvular disease (2·47, 1·70-3·58; p<0·0001), stroke as qualifying event (1·31, 1·09-1·57; p=0·0037), history of peripheral artery disease (1·98, 1·28-3·07; p=0·0023), history of coronary artery disease (1·32, 1·00-1·74; p=0·049), intracranial haemorrhage during follow up (4·94, 1·91-12·78; p=0·0013), and living alone (1·32, 1·10-1·59; p=0·0031). Regular physical activity before the index event was associated with reduced risk of poor functional outcome (OR 0·52, 95% CI 0·42-0·66; p<0·0001). 345 recurrent strokes had occurred at 5 years of follow-up, 141 (40·9%) of which were disabling or fatal. Stroke recurrence increased the risk of having a disability at 5 years (OR 3·52, 95% CI 2·37-5·22; p<0·0001). Recurrent disabling or fatal strokes were independently associated with older age (per 10-year increase, hazard ratio [HR] 1·61, 95% CI 1·35-1·92; p<0·0001), diabetes of any type (2·23, 1·56-3·17; p<0·0001), National Institutes of Health Stroke Scale score of greater than 5 at discharge (5·11, 2·15-12·13; p=0·0013), history of coronary artery disease (1·76, 1·17-2·65; p=0·0063), history of stroke or transient ischaemic attack before the qualifying event (1·54, 1·03-2·29; p=0·035), congestive heart failure (1·86, 1·01-3·47; p=0·044), stroke as qualifying event (1·73, 1·22-2·45; p=0·0024), mRS score of greater than 1 at discharge (2·48, 1·27-4·87; p=0·0083), and intracranial haemorrhage during follow-up (17·15, 9·95-27·43; p<0·0001). Regular physical activity before the index event was associated with reduced risk of recurrent disabling stroke at 5 years (HR 0·56, 95% CI 0·31-0·99; p=0·046), and 5-year disability without recurrent stroke (0·61, 0·47-0·79; p=0·0001). INTERPRETATION: We found a substantial burden of disability (mRS score of >1) at 5 years after transient ischaemic attack or minor ischemic stroke, and most predictors of this disability were modifiable risk factors. Patients who did regular physical exercise before the index event had a significantly reduced risk of disability at 5 years compared with patients who did no exercise. FUNDING: AstraZeneca, Sanofi, Bristol Myers Squibb, SOS Attaque Cérébrale Association.


Asunto(s)
Isquemia Encefálica , Enfermedad de la Arteria Coronaria , Insuficiencia Cardíaca , Ataque Isquémico Transitorio , Accidente Cerebrovascular Isquémico , Accidente Cerebrovascular , Isquemia Encefálica/complicaciones , Enfermedad de la Arteria Coronaria/complicaciones , Insuficiencia Cardíaca/complicaciones , Humanos , Hemorragias Intracraneales/complicaciones , Ataque Isquémico Transitorio/complicaciones , Ataque Isquémico Transitorio/epidemiología , Estudios Prospectivos , Accidente Cerebrovascular/complicaciones , Estados Unidos
7.
Open Heart ; 6(2): e001187, 2019.
Artículo en Inglés | MEDLINE | ID: mdl-31908815

RESUMEN

Aims: Long-term oral anticoagulant (LTOAC) reduces ischaemic stroke recurrences. Because of bleeding history, frailty, cognitive impairment, comorbidities or patient refusal, many cannot be discharged from stroke unit on LTOAC. Proportion and outcome of these patients is not well known. Methods: The Warfarin Aspirin Ten-a inhibitor Cerebral infarction and Haemorrhage and atrial fibrillation (AF) prospective registry enrolled consecutive patients with an acute stroke associated with AF. Scales to evaluate stroke severity, disability, functional independence, cognition, risk of fall, ischaemic and haemorrhagic risk stratification were systematically collected at admission, discharge, 3 and 12 months poststroke. The two main 12-month endpoints were death or dependency (modified Rankin Scale >3) and recurrent stroke. Results: Among 400 patients (370 brain infarctions, 30 brain haemorrhages), 274 were discharged on LTOAC, 31 died before discharge and 95 (24%) were not discharge on anticoagulant (frailty, bedridden or demented, EHRA/ESC contraindication to anticoagulant). Death or dependency and recurrent stroke occurred in 19.8% and 9.9%, respectively, in patient on anticoagulant, and 33.5% and 27.2% in those not on anticoagulant (both p<0.001). Patient not anticoagulated at discharge had a 1.6-fold increase in the risk of death or dependency at 12 months (HR 1.65; 95% CI 1.05 to 2.61; p=0.032) and a 2.5-fold increase in the risk of stroke (HR 2.46; 95% CI 1.36 to 4.44; p=0.003). Conclusions: One-fourth of patients with stroke associated with AF are not discharged on anticoagulation and have a dramatic increase in the risk of death or dependency at 12 months as well as recurrent stroke. Alternative treatments should be trialled in these patients.

8.
JAMA Neurol ; 75(2): 203-211, 2018 02 01.
Artículo en Inglés | MEDLINE | ID: mdl-29279888

RESUMEN

Importance: Patients who have experienced stroke with intracranial atherosclerotic disease (ICAD) may also have concomitant atherosclerosis in different arterial beds and other possible causes for ischemic stroke. However, little is known about the frequency and prognostic effect of such overlapping diseases. Objectives: To describe the prevalence of systemic atherosclerotic burdens and overlapping stroke etiologies and their contributions to long-term prognoses among patients who have experienced stroke with ICAD. Design, Setting, and Participants: The Asymptomatic Myocardial Ischemia in Stroke and Atherosclerotic Disease study is a single-center prospective study in which 405 patients with acute ischemic stroke within 10 days of onset were consecutively enrolled between June 2005 and December 2008 and followed up for 4 years. After excluding 2 patients because of incomplete investigations, 403 were included in this analysis. Main Outcomes and Measures: Significant ICAD was defined as having 50% or greater stenosis/occlusion by contrast-enhanced/time-of-flight magnetic resonance angiography, computed tomography angiography, and/or transcranial Doppler ultrasonography. Systemic vascular investigations on atherosclerotic disease were performed with ultrasonography in carotid arteries, aorta and femoral arteries, and by angiography in coronary arteries. Coexistent stroke etiologies were assessed using the atherosclerosis, small-vessel disease, cardiac pathology, other cause, and dissection (ASCOD) grading system. We estimated the 4-year risk of major adverse cardiovascular events (MACE), including vascular death, nonfatal cardiac events, nonfatal stroke, and major peripheral arterial events. Results: Of 403 participants, 298 (74%) were men and the mean (SD) age was 62.6 (13.1) years. Significant ICAD was found in 146 (36.2%). Patients with significant ICAD more often had aortic arch (70 [60.9%] vs 99 [49.0%]; P = .04) and coronary artery (103 [76.9%] vs 153 [63.2%]; P = .007) atherosclerosis than those without. Among patients with ICAD, concurrent stenosis in the extracranial carotid artery (24 [23.4%] vs 3 [9.0%]; P = .08; adjusted hazard ratio[aHR] = 2.12) and the coronary artery (19 [29.9%] vs 8 [12.8%]; P = .01; aHR = 1.90) increased the MACE risk. Furthermore, patients with ICAD who also had any cardiac pathology (ASCOD grade C1-3) were at a higher MACE risk than others (grade C0) (20 [28.2%] vs 7 [11.4%]; P = .01; aHR = 2.24). By contrast, patients with ICAD with any form of small vessel disease (grade S1-3) had a lower MACE risk than those without (grade S0) (20 [17.3%] vs 6 [34.6%]; P = .05; aHR = 0.23). Conclusions and Relevance: Patients with ICAD often have coexisting systemic atherosclerosis and multiple potential stroke mechanisms that affect their prognosis, suggesting that extensive evaluations of overlapping diseases may allow better risk stratification.


Asunto(s)
Arteriosclerosis Intracraneal , Isquemia Miocárdica/fisiopatología , Accidente Cerebrovascular , Anciano , Angiografía por Tomografía Computarizada , Manejo de la Enfermedad , Femenino , Fibrinolíticos/uso terapéutico , Humanos , Arteriosclerosis Intracraneal/complicaciones , Arteriosclerosis Intracraneal/epidemiología , Arteriosclerosis Intracraneal/etiología , Angiografía por Resonancia Magnética , Masculino , Persona de Mediana Edad , Isquemia Miocárdica/tratamiento farmacológico , Prevalencia , Pronóstico , Estudios Prospectivos , Estudios Retrospectivos , Factores de Riesgo , Accidente Cerebrovascular/complicaciones , Accidente Cerebrovascular/epidemiología , Accidente Cerebrovascular/etiología , Factores de Tiempo
SELECCIÓN DE REFERENCIAS
Detalles de la búsqueda