RESUMO
Upright posture requires rapid and effective circulatory and neurologic compensations to maintain blood pressure and consciousness. Although it has been recognized over the past 100 years or more that the act of standing may cause hypotension in patients with autonomic dysfunction, only recently several of the pathophysiologic mechanisms resulting in orthostatic intolerance have been discovered. In patients with orthostatic hypotension, failure of reflex vasoconstriction causes pooling of blood in the legs during standing. Not everyone with a postural blood pressure drop requires treatment, nor does everyone with posturally induced symptoms have orthostatic hypotension. This review will discuss current knowledge of a broad, heterogeneous group of disturbances in the autonomic nervous system, each of which is manifested by hypotension, orthostatic intolerance, and often syncope.
Assuntos
Hipotensão Ortostática/diagnóstico , Hipotensão Ortostática/etiologia , Humanos , Hipotensão Ortostática/terapia , Estados Unidos/epidemiologiaRESUMO
BACKGROUND: Our purpose was to determine the repeatability, after 2 weeks, of frequency domain measures of heart rate variability (HRV) during simple cardiovascular reflex tests. METHODS: Twenty healthy volunteers aged 29.3 +/- 2.5 years were assessed twice (at weeks 0 and 2). Continuous electrocardiogram and minute-to-minute blood pressure were recorded during spontaneous and metronome-paced breathing (0.2 Hz). Under paced breathing, two tests were performed: 1) active change of posture: 5 min supine position, 5 min seated upright, and 5 min standing up, and 2) cold pressor test: the right hand was immersed in cold water (5 degrees C) for 2 min. RESULTS: Paced breathing elicited a significant increase of the high-frequency (HF) component of HRV. This effect was repeatable on 95% of the subjects. Active change of posture induced a significant increase of the heart rate with an increase of the low-frequency/high-frequency ratio of HRV. Although repeatability was better for the response to being seated upright than for the response to being standing up, it was always higher than 90%. The cold pressor test induced a significant increase of the heart rate and blood pressure, but with variable changes on the HRV measurements (either a decrease or an increase). Repeatability of responses was evident for 95-100% of the subjects. Although repeatability of HRV measurements in the same subject during the tests was higher than 95%, coefficients of repeatability reflected large differences among the subjects. CONCLUSIONS: The results suggest that it is not advisable to use isolated HRV changes to interpret the response to simple cardiovascular reflex tests in groups of healthy subjects.
Assuntos
Fenômenos Fisiológicos Cardiovasculares , Frequência Cardíaca/fisiologia , Reflexo , Temperatura Baixa , Humanos , Postura , Valores de Referência , RespiraçãoRESUMO
OBJECTIVE: Reactive hypoglycemia is a common medical problem whose pathophysiology is not completely understood. The objective of this study was to investigate the prevalence of autonomic nervous system abnormalities in patients with reactive hypoglycemia compared with controls. METHODS: Six women, mean age 31 +/- 5 years, with reactive hypoglycemia, and 5 healthy controls women aged 24 +/- 4 years were studied. We investigated the heart rate variability and blood pressure changes after an upright tilt with and without an isoproterenol infusion. A positive result was defined as syncope or presyncope associated with bradycardia, hypotension or both. RESULTS: In response to the orthostatic stress alone or in conjunction with a 4 micrograms isoproterenol infusion, 5 of 6 patients had a positive test as did one of the five control subjects. Patients had a baseline hyperadrenergic tone, with a sympathetic to parasympathetic ratio of 2.3 +/- 0.8 under basal conditions and 10.1 +/- 4.1 during the isoproterenol infusion, compared to 0.7 +/- 0.3 (p = 0.06) and 0.5 +/- 0.1 (p < 0.01) respectively, in the control group. CONCLUSION: Patients with reactive hypoglycemia may be at the extreme end of a spectrum of normal biologic variability, they may have an hyperadrenergic tone and, after a provocative stimulus, sympathetic nerve firing and or synaptic release of NE may not be sufficient to maintain an adequate vascular tone. Alternatively, the vascular response to NE may be impaired. An excessive and paradoxic vasovagal or parasympathetic response was not observed.
Assuntos
Doenças do Sistema Nervoso Autônomo/etiologia , Hipoglicemia/complicações , Adulto , Doenças do Sistema Nervoso Autônomo/fisiopatologia , Feminino , Frequência Cardíaca , Humanos , Hipoglicemia/fisiopatologia , Teste da Mesa InclinadaRESUMO
OBJECTIVE: To compare the diagnostic value of pharmacological stimulation with sublingual isosorbide dinitrate and intravenous isoproterenol during tilt testing in patients with neurocardiogenic syncope and with a negative tilt test without pharmacological provocation. METHODS AND RESULTS: One hundred and twenty patients with a history of neurocardiogenic syncope (aged 15 to 77 years) and 50 healthy volunteers (aged 25 to 70 years) were prospectively submitted to head-up tilt (HUT). Those who did not develop syncope or presyncope during passive HUT for 30 minutes underwent repeated HUT with isoproterenol infusion at 4 microg/min (ISOP HUT), for 10 minutes, and, subsequently, were tilted after sublingual administration of 5 mg of isosorbide dinitrate (ISDN HUT) for another 12 minutes. ISDN HUT was always performed after ISOP HUT. Sensitivity and specificity of passive HUT were 41% (95% C.I. 32.9% to 51.0%) and 100%, respectively. Sensitivity of ISOP HUT was 51.4% (95% C.I. 39.2% to 63.6%) and specificity 70% (95% C.I. 55.4% to 82.1%) and for ISDN HUT were 70% (95% C.I. 57.9% to 80.4%) and 88% (95% C.I. 75.7% to 95.5%), respectively. The accuracy of ISDN HUT was significantly higher than the accuracy of ISOP HUT 77.5% (95% C.I. 68.9% to 84.6%). There were fewer side effects during ISDN HUT. CONCLUSION: Sublingual isosorbide dinitrate is at least as sensitive as isoproterenol to assess patients with suspected neurocardiogenic syncope and with a negative tilt test without provocation. The low rate of side effects and the higher accuracy of ISDN HUT, along with the simplicity of this challenge compared to ISOP HUT, suggest that sublingual isosorbide dinitrate should be preferred as a provocative agent to evaluate neurocardiogenic syncope after a negative passive tilt test.
Assuntos
Agonistas Adrenérgicos beta , Isoproterenol , Dinitrato de Isossorbida , Síncope Vasovagal/diagnóstico , Teste da Mesa Inclinada/métodos , Vasodilatadores , Administração Sublingual , Adolescente , Agonistas Adrenérgicos beta/administração & dosagem , Adulto , Idoso , Intervalos de Confiança , Eletrocardiografia Ambulatorial/efeitos dos fármacos , Eletroencefalografia , Feminino , Frequência Cardíaca/efeitos dos fármacos , Humanos , Injeções Intravenosas , Isoproterenol/administração & dosagem , Dinitrato de Isossorbida/administração & dosagem , Masculino , Pessoa de Meia-Idade , Estudos Prospectivos , Sensibilidade e Especificidade , Índice de Gravidade de Doença , Síncope Vasovagal/fisiopatologia , Vasodilatadores/administração & dosagemRESUMO
BACKGROUND: Patients with syncope show different responses to head-up tilt (HUT) test, which may be due to different pathophysiological mechanisms. METHODS: HUT (70 degrees) was performed in 24 patients who experienced recurrent syncope. Nine patients had a cardioinhibitory (CI) response, 7 patients had a vasodepressor (VD) response, and 8 patients had a mixed (MX) response. Heart rate variability was analyzed at 60-sec periods during HUT. RESULTS: Total spectrum (TS) was greater at rest and 1 min after syncope in the CI and MX groups as compared to the VD group. Low frequency spectrum (LF) was significantly greater during rest and the first minute after syncope in the CI groups as compared with the VD group. After the rest period, the CI and MX groups showed more elevated high frequency spectrum (HF) values than the VD group (p < 0.01). One minute after syncope, the HF increased in the CI and MX groups but not in the VD group (p < 0.01). The VD group showed higher LF/HF ratio from the beginning of rest (3.9 +/- 4.1) as compared to the CI and MX groups (p < 0.01). This difference was most significant 2 min before syncope occurred. The CI and MX groups showed greater pNN50 and rMSSD as compared to the VD group. CONCLUSIONS: Our results suggest that vagal tone is higher in subjects showing cardioinhibitory and mixed responses to HUT. In contrast, patients with a vasodepressor response showed predominantly sympathetic activity. These findings suggest that there are different pathophysiological mechanisms underlying syncope.
Assuntos
Sistema Nervoso Autônomo/fisiopatologia , Frequência Cardíaca/fisiologia , Coração/inervação , Síncope/etiologia , Teste da Mesa Inclinada , Vasodilatação/fisiologia , Adolescente , Adulto , Criança , Feminino , Humanos , Hipotensão/fisiopatologia , Masculino , Pessoa de Meia-IdadeRESUMO
AIMS: Syncope in patients with the long QT syndrome is commonly attributed to a ventricular arrhythmia (torsades de pointes). The susceptibility of patients with the long QT syndrome (LQTS) to neurally mediated syncope is currently unknown. METHODS AND RESULTS: Head-up tilt table testing (70 degrees) was performed in six patients with the long QT syndrome and a history of syncope. All patients had syncope with a mixed response. The RR interval was significantly decreased 2 min before the onset of syncope (980 +/- 125 ms vs 630 +/- 91 ms, P=0.003), and significantly increased during syncope (983.17 +/- 224.71; P=0.006). Non-significant changes in QT intervals were observed. Baseline QT was 513 +/- 86 ms and decreased to 450 +/- 59 ms 2 min before the onset of syncope (P=0.11). Although not statistically significant, QT intervals during syncope were longer than at 2 min before syncope (485 +/- 85 ms vs 450 +/- 59 ms; P=0.29). CONCLUSION: Our results suggest that patients with the LQTS are susceptible to neurally mediated syncope. Whether this susceptibility differs from control populations remains unresolved. From a clinical standpoint, neurocardiogenic syncope should be considered a diagnostic alternative in patients with LQTS.
Assuntos
Síndrome do QT Longo/fisiopatologia , Síncope Vasovagal/fisiopatologia , Teste da Mesa Inclinada , Adolescente , Criança , Feminino , Hemodinâmica , Humanos , Síndrome do QT Longo/complicações , Síndrome do QT Longo/diagnóstico , Masculino , Pessoa de Meia-Idade , Síncope Vasovagal/complicaçõesRESUMO
OBJECTIVE: To determine the accumulated 24-hour cardiovascular autonomic modulation and its circadian variations in patients with fibromyalgia, by means of heart rate variability analysis. METHODS: Thirty patients with fibromyalgia and 30 age- and sex-matched controls were studied prospectively. Assessments included a 24-hour ambulatory recording of heart rate variability, time-domain analysis of the accumulated 24-hour R-R interval variations, and power spectral analysis to determine the sympatho/ vagal balance at different hours (calculated as the power spectral density of the low-frequency [0.04-0.15-Hz] sympathetic band divided by the power of the high-frequency [0.15-0.50-Hz] parasympathetic band). RESULTS: Fibromyalgia patients had diminished accumulated 24-hour heart rate variability, manifested by a decreased standard deviation of all R-R intervals (mean +/- SD 126 +/- 35 ms, versus 150 +/- 33 ms in controls; P = 0.008) and a decreased ratio of pairs of adjacent R-R intervals differing by >50 ms (mean +/- SD 12.0 +/- 9.0% versus 20.1 +/- 18.0%; P = 0.031). Patients lost the circadian variations of sympatho/vagal balance, with nocturnal values significantly higher than those of controls at time 0 (mean +/- SD 3.5 +/- 3.2 versus 1.2 +/- 1.0; P = 0.027) and at 3 hours (3.3 +/- 3.0 versus 1.6 +/- 1.4; P = 0.01). CONCLUSION: Individuals with fibromyalgia have diminished 24-hour heart rate variability due to an increased nocturnal predominance of the low-frequency band oscillations consistent with an exaggerated sympathetic modulation of the sinus node. This abnormal chronobiology could explain the sleep disturbances and fatigue that occur in this syndrome. Spectral analysis of heart rate variability may be a useful test to identify fibromyalgia patients who have dysautonomia.
Assuntos
Ritmo Circadiano/fisiologia , Fibromialgia/fisiopatologia , Equilíbrio Postural/fisiologia , Sistema Nervoso Simpático/fisiopatologia , Adulto , Eletrocardiografia Ambulatorial , Feminino , Frequência Cardíaca/fisiologia , Humanos , Masculino , Estudos ProspectivosRESUMO
BACKGROUND: There is increasing evidence that an open infarct-related artery results in increased electrical stability of the heart and that this effect is at least in part responsible for the favorable outcome of these patients. In the thrombolytic era the optimal strategy for risk stratification remains controversial. This study examined the predictors of serious arrhythmic events during the first year after myocardial infarction. METHODS: A total of 222 patients with acute myocardial infarction, 41.4% of whom were treated with thrombolysis, were studied. At hospital discharge, signal-averaged electrocardiography was performed on 196 subjects and Holter monitoring on 200. One hundred and ninety-seven patients underwent coronary angiography. Left ventricular ejection fraction was determined in 201 subjects. RESULTS: An open infarct-related artery was documented in 106 patients. The incidence of late potentials was 34% (66 patients). Twenty-four patients (10.8%) had an arrhythmic event during follow-up (sudden death in seven, sustained ventricular tachyarrhythmias in 15, unexplained syncope in two). Signal-averaged electrocardiography had a sensitivity of 94% and a specificity of 72% for prediction of arrhythmic events. An occluded infarct-related artery was 78% sensitive and 58% specific, a left ventricular ejection fraction below 40% had a sensitivity of 71% and specificity of 80%, and Holter monitoring was only 38% sensitive and 92% specific. A combination of late potentials plus an occluded infarct-related artery was 68% sensitive and 84% specific. Positive predictive value was low for all variables examined, but could be improved by the combination of several risk factors. The highest positive predictive value was provided by the combination of an abnormal signal-averaged ECG and complex ventricular arrhythmias on ambulatory ECG. On multivariate analysis, in rank order, presence of late potentials, ejection fraction below 40%, high-grade ventricular ectopic activity and an occluded infarct-related artery were predictive of arrhythmic events. CONCLUSION: Among patients surviving an acute myocardial infarction, the occurrence of malignant arrhythmic events can be reliably predicted by the combination of an abnormal signal-averaged ECG, left ventricular dysfunction, complex ventricular arrhythmias on Holter monitoring and an occluded infarct-related artery at the time of hospital discharge.
Assuntos
Arritmias Cardíacas/etiologia , Eletrocardiografia , Infarto do Miocárdio/complicações , Processamento de Sinais Assistido por Computador , Potenciais de Ação , Idoso , Angiografia Coronária , Eletrocardiografia Ambulatorial , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Análise Multivariada , Infarto do Miocárdio/fisiopatologia , Valor Preditivo dos Testes , Prognóstico , Estudos Prospectivos , Medição de Risco , Sensibilidade e Especificidade , Volume Sistólico , Grau de Desobstrução Vascular , Disfunção Ventricular Esquerda/complicaçõesRESUMO
BACKGROUND: Recent evidence suggests that late reperfusion of an occluded infarct-related artery after an acute myocardial infarction may reduce the frequency of subsequent arrhythmic events. Late mechanical reperfusion by percutaneous transluminal coronary angioplasty (PTCA) under these circumstances has a high success rate. The present study was performed to test the hypothesis that the late mechanical restoration of anterograde flow in an occluded infarct artery after an acute myocardial infarction causes a resolution of late potentials. METHODS: Twenty subjects (10 men, one woman; aged 32-77 years) suffering a first acute myocardial infarction, with signal-averaged electrocardiographic (ECG) recordings and a severely occluded infarct-related artery, were prospectively identified. RESULTS: Eighteen patients underwent successful PTCA of the occluded artery 6-32 days after a first acute myocardial infarction. Late potentials were observed in 14 patients 5-22 days after the infarction. A follow-up signal-averaged ECG was performed 1-8 days later. In the subgroup of 12 patients with successful reperfusion and an abnormal signal-averaged ECG before PTCA, seven (58.3%) showed resolution of the late potentials at follow-up; in these patients the filtered QRS duration showed a significant reduction (112.1 +/- 14.2 to 96.7 +/- 12.7 ms, P = 0.02), the root-mean-square voltage increased (9.8 +/- 6.5 to 33.1 +/- 15.5 microV, P = 0.017), and the duration of low-amplitude signals < 40 microV decreased after angioplasty (46.3 +/- 11.0 to 28.5 +/- 6.5 ms, P < 0.022). In contrast, two patients with late potentials before PTCA and unsuccessful reperfusion had no significant changes in signal-averaged ECG. CONCLUSIONS: In some patients with an acute myocardial infarction, late mechanical reperfusion of the culprit vessel may reduce the incidence of abnormalities on the signal-averaged ECG. Whether this will improve long-term survival has yet to be confirmed in a large trial.
Assuntos
Angioplastia Coronária com Balão , Eletrocardiografia , Infarto do Miocárdio/fisiopatologia , Infarto do Miocárdio/terapia , Adulto , Idoso , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Reperfusão MiocárdicaRESUMO
Neither the presence nor the absence of pathological Q waves are related to the transmural or subendocardial localization of an acute myocardial infarction. The prognosis of an acute myocardial infarction without pathological Q waves is controversial. We studied 23 hospitalized patients with prolonged, typical chest pain, enzymatic elevation, an EKG without pathological Q waves but with changes in ventricular repolarization and a positive scintigraphy with radioactive pyrophosphates. The patients were classified in two groups according to the pattern of pyrophosphate uptake; group A had grade 2+ focal uptake (N = 13) and group B with grade 2+ diffuse uptake (N = 10). The level of serum glutamic transaminase was significantly greater in group A as compared to group B (p less than 0.05). However, levels of creatine kinase and lactic dehydrogenase were no different. The clinical hospital course was similar in both groups. Eleven patients were followed by 31.7 months: 30.4% had chronic angina, one underwent coronary bypass surgery, another suffered a recurrent myocardial infarction and there were no deaths. The diagnosis of acute myocardial infarction should be suspected in patients with prolonged angor pectoris, electrocardiographic changes in ventricular repolarization, increased enzymatic levels and a positive scintigraphy with a grade 2+ diffuse myocardial uptake of Tc 99m pyrophosphates. The diagnosis is certain if the uptake has a focal distribution.