Objective-To evaluate the stability of short recordings of heart rate variability (HRV) with time, and the association of HRV with age and sex. Design-Five minute Holter recordings were made twice over a two month interval (tracking study). In addition, HRV was measured in a cross sectional study. Setting-Residents of 11 Israeli kibbutzim were examined in their settlements. Subjects-32 men and 38 women (aged 31-67) participated in the tracking study and 294 (aged 35-65) were involved in the cross sectional study. Main outcome measures-Time and frequency domain analyses on Holter recordings were undertaken in two breathing conditions: spontaneous and controlled breathing (15 respirations per minute). Regression was used to assess the relations of sex, age, heart rate, and logarithmically transformed HRV indices. Results-HRV measures were highly consistent with time with correlations of 0.76-0.80 for high frequency and total power. Geometric mean total power declined with age by 45% in men and 32% in women, and was lower by 24% among women than among men (all p < 0.005). Men had a 34% higher very low and low frequency power and a higher ratio of low to high frequency power (p < 0.001). Conversely, high frequency power in women represents a greater proportion of total power than in men. Conclusion-Short recordings of HRV in a non-laboratory setting are stable over months and therefore characteristic of an individual. Strong age and sex eVects were evident. HRV derived from short recordings can be informative in population based studies. (Heart 1998;80:156-162) Keywords: heart rate variability; parasympathetic activity; reliability; sex diVerences Heart rate variability (HRV) measures can provide non-invasive information on the autonomic nervous system, including its vagal and sympathetic components. [1][2][3][4] Interest in these measures has increased recently in light of predictive associations between reduced HRV and increased mortality after an acute myocardial infarction (MI), 5-8 and between HRV and the incidence of coronary heart disease and mortality in a community based population. 9 10 These associations were independent of the eVect of conventional risk factors. 9 10 Most studies of HRV have used 24 hour Holter recorded electrocardiograms (ECGs). Such measurement is often not feasible for widescale epidemiological studies, and may be unnecessary. In men after an acute MI, HRV measures calculated from 2-15 minute segments were remarkably similar to those calculated over 24 hours, and provided predictive information similar in strength to the entire record. 8 A recently published report of a European and North American task force on measurement of HRV for clinical use indicated sparse availability of information on the reliability of short segment recordings. 11 We undertook two studies in an unselected free living population sample to determine the feasibility and potential usefulness of five minute recordings in men and women aged 35-65 years. Recordings were made under conditions of free and ...

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These data suggest that haemodynamic instability is strongly associated with a decreased HRV and an impaired sympathovagal balance, suggesting disturbed autonomic control in uraemic patients with cardiac damage. Patients with ischaemic heart disease, reduced left ventricular systolic function and decreased HRV may be at the highest risk to be haemodynamically unstable during haemodialysis. The role of early detection and treatment of ischaemic heart disease in preventing symptomatic hypotensive episodes in these patients remains to be determined.

Adequate sympathetic nervous system activation is essential for the compensatory mechanisms of blood pressure maintenance during the hemodialysis (HD) procedure. Chronic sympathetic nervous system overactivity, however, may lead to the development of hypertension and cardiovascular disease in HD patients. The present review focuses on recent findings on the sympathetic nervous system activity in these patients. Sympathetic overactivity has been demonstrated directly by muscle sympathetic nerve activity recordings (MSNA) in chronic renal disease, but only rarely in HD patients. In the latter, sympathetic activity has mostly been assessed using indirect methodology. Decreased heart rate variability, increased blood pressure variability (BPV), and suppressed baroreflex function are believed to represent chronic sympathetic overactivity in HD patients. The HD procedure and ultrafiltration are associated with enhanced sympathetic activity and baroreflex activation. During most episodes of intradialytic hypotension, the baroreflex is adequately activated; sympathetic withdrawal with bradycardia, however, has been reported during excessive hypovolemia. Sympathetic overactivity is also believed to be a mechanism associated with intradialytic hypertensive episodes and refractory hypertension. While successful renal transplantation is associated with improvement of heart rate variability (HRV), improvement and restoration of baroreflex function, persistent sympathetic overactivity has been documented in transplanted patients using MSNA recordings. Decreased HRV and baroreflex function have been reported to be associated with increased mortality and morbidity in HD patients. The predictive value of sympathetic outflow assessed by MSNA has yet to be determined. Optimization of HD treatment, pharmacological interventions, and renal sympathetic denervation are several approaches targeting sympathetic overactivity to improve cardiovascular morbidity and mortality.

We evaluated the effectiveness of early intravenous administration of 750,000 units of streptokinase in 53 patients with acute myocardial ischemia treated by a mobile-care unit at home (9 patients) or in the hospital (44 patients). Treatment was begun an average (+/- S.D.) of 1.7 +/- 0.8 hours from the onset of pain. Non-Q-wave infarctions developed subsequently in eight patients, whereas all the others had typical Q-wave infarct patterns. In 81 per cent of the patients the infarct-related artery was patent at angiography performed four to nine days after admission. Vessel patency was independent of the time of treatment, but residual left ventricular function was time dependent. Patients treated less than 1.5 hours after the onset of pain had a significantly higher ejection fraction (56 +/- 15 vs. 47 +/- 14 per cent; P less than 0.05) and infarct-related regional ejection fraction (51 +/- 19 vs. 34 +/- 20 per cent; P less than 0.01) and a lower QRS score (5.6 +/- 4.9 vs. 8.6 +/- 5.5; P less than 0.01) than patients receiving treatment between 1.5 and 4 hours after the onset of pain. Patients treated earlier by the mobile-care unit also had better-preserved left ventricular function than patients treated in the hospital. We conclude that thrombolytic therapy with streptokinase is most effective if given within the first 1.5 hours after the onset of symptoms of acute myocardial infarction.