Asymptomatic versus symptomatic episodes in patients with paroxysmal atrial fibrillation via long-term monitoring with implantable loop recorders.

BACKGROUND: The presentation of atrial fibrillation (AF) varies remarkably, from totally asymptomatic to symptomatic patients, while the same individual may present symptomatic and asymptomatic episodes. We aimed to identify electrocardiographic differences between symptomatic and asymptomatic episodes and to find parameters related to the appearance of symptoms. METHODS: Thirty consecutive patients (age 66.9±10years) with paroxysmal AF received an implantable loop recorder. Three types of episodes were defined: asymptomatic (ASx), symptomatic (Sx), and mixed asymptomatic-symptomatic (AS-Sx). The heart rate (HR) and heart rate variability (HRV) were recorded during the first 2min of each ASx or Sx episode, and during the first 2min of both the symptomatic and asymptomatic periods in AS-Sx. RESULTS: Eighty-two episodes from twenty-five patients were evaluated. Mean HR was 142.48±25.84bpm for Sx and 95.71±19.29bpm for ASx (p<0.001). Mean HRV was 92.62±42.29ms for Sx and 150.06±49.68ms for ASx (p<0.001). In AS-Sx, mean HR was 102.91±24.54bpm for the asymptomatic and 141.88±23.43bpm for the symptomatic period (p<0.001). Mean HRV was 173.55±61.30ms for the asymptomatic and 87.33±30.65ms for the symptomatic period (p=0.003). There were no significant correlations between patients' characteristics and the clinical presentation of the arrhythmia. CONCLUSIONS: The ASx were characterized by a lower HR and higher HRV compared to Sx. In As-Sx, the asymptomatic period was characterized by a lower HR and higher HRV compared to the symptomatic. These findings suggest a possible contribution of variations in the autonomic nervous system activity to the perception of the arrhythmia.

Pre-operative versus post-operative gait variability in patients with acute anterior cruciate ligament deficiency.

Change in gait variability at least 6 months after surgical reconstruction of the anterior cruciate ligament (ACL) was assessed in 20 male patients with acute ACL deficiency and compared with pre-operative data and that from 20 healthy male controls. Gait was measured using a triaxial accelerometer and data were analysed by the Gait Evaluation Differential Entropy Method (GEDEM) to determine gait variability. Pain was assessed with a visual analogue scale and functional ability with the Oswestry Disability Index and the International Knee Documentation Committee score. Mean gait variability was significantly lower after than before surgery, with values for the anterior-posterior axis being in the normal range of controls after 6 months, whereas in the mediolateral axis mean gait variability remained significantly higher, indicating that some rotational instability remained in the time-frame of the study. Pain and functional ability scores improved after surgery compared with before surgery. The combination of accelerometry and GEDEM may be a useful orthopaedic tool for the post-operative evaluation of patients who have undergone ACL reconstruction.

Gait variability measurements in lumbar spinal stenosis patients: part A. Comparison with healthy subjects.

The objective of this study is to compare the gait variability of patients with lumbar spinal stenosis (experimental group) with healthy individuals (control group). The hypothesis is that the preoperative gait variability of the experimental group is higher than the control group. The experimental group consisted of 35 adults (18 males, 17 females). The subjects of the experimental group suffered exclusively from spinal stenosis. The patients were determined by MRI scans. A tri-axial accelerometer sensor was used for the gait measurement, and differential entropy algorithm was used to quantify the gait acceleration signal. The Oswestry Low Back Pain Questionnaire was used to determine the condition on the day of the measurement. Receiver operating characteristic (ROC) was utilized to assess the diagnostic value of the method and determine a cut-off value. There is a statistically significant difference between gait variability in the control group and the experimental group. ROC analysis determines a cut-off differential entropy value. The cut-off value has a 97.6% probability of separating patients with spinal stenosis from healthy subjects. The Oswestry Low Back Questionnaire is well correlated with the spectral differential entropy values.

Gait variability measurements in lumbar spinal stenosis patients: part B. Preoperative versus postoperative gait variability.

The objective of this study was to assess the gait variability of lumbar spinal stenosis (LSS) patients and to evaluate its postoperative progression. The hypothesis was that LSS patients' preoperative gait variability in the frequency domain was higher than the corresponding postoperative. A tri-axial accelerometer sensor was used for the gait measurement and a spectral differential entropy algorithm was used to measure the gait variability. Twelve subjects with LSS were measured before and after surgery. Preoperative measurements were performed 2 days before surgery. Postoperative measurements were performed 6 and 12 months after surgery. Preoperative gait variability was higher than the corresponding postoperative. Also, in most cases, gait variability appeared to decrease throughout the year.

The role of the post-cardioversion time course of hs-CRP levels in clarifying the relationship between inflammation and persistence of atrial fibrillation.

OBJECTIVES: Although recent studies suggest that inflammation is involved in the pathogenesis of atrial fibrillation (AF), it remains controversial whether it is a consequence or a cause of the arrhythmia. DESIGN: Prospective study. SETTING: Tertiary referral centre. PATIENTS AND INTERVENTIONS: In 52 patients with persistent AF lasting >3 months, high-sensitivity C-reactive protein (hs-CRP) was measured before and after electrical cardioversion. MEASUREMENTS AND RESULTS: All patients were successfully cardioverted to sinus rhythm (SR), but the recurrence rate was 23% at 1 month. Baseline hs-CRP was higher in patients with AF recurrence than in those who remained in SR (0.5 (SD 0.18) mg/dl vs 0.29 (SD 0.13) mg/dl, respectively, p<0.001). Similarly, arrhythmia recurrence was associated with greater left atrial diameters (45.4 (SD 3.3) mm vs 40.7 (SD 3.1) mm, respectively, p<0.001). However, logistic regression analysis showed that hs-CRP was the only independent predictor for AF recurrence (p<0.001). Additionally, patients who were in SR on final evaluation had significantly lower hs-CRP levels than at baseline (0.10 (SD 0.06) mg/dl vs 0.29 (SD 0.13) mg/dl, respectively, p<0.001), while those who experienced AF recurrence had similar values on final and on initial evaluation (0.56 (SD 0.24) mg/dl vs 0.50 (SD 0.18) mg/dl, respectively, p = 0.42). CONCLUSION: High levels of hs-CRP are associated with an increased risk of AF recurrence after cardioversion. The restoration and maintenance of SR result in a gradual decrease of hs-CRP while AF recurrence has a different effect, suggesting that inflammation is a consequence, rather than a cause, of AF.

Autonomic imbalance during the day in patients with inflammatory bowel disease in remission. Evidence from spectral analysis of heart rate variability over 24 hours.

BACKGROUND: Autonomic function in inflammatory bowel disease has not yet been studied by means of analysis of 24-hour heart rate variability. AIM: To measure heart rate variability in inflammatory bowel disease patients in remission. PATIENTS AND METHODS: Study population comprised 27 patients with inflammatory bowel disease in remission and 28 healthy, sex- and age-matched controls. Two frequency ranges were analysed: low frequency (0.06-0.15 Hz) and high frequency (0.15-0.40 Hz). RESULTS: Mean values of low frequency and low frequency/high frequency ratio were lower in patients than in controls (p < 0.001). High frequency in patients tended to be higher than in controls (p = 0.09). The only factor that had a marginal effect on heart rate variability indexes was age. In high frequency, there was a significant time effect (p = 0.001) for both groups. There was also a significant time effect in low frequency/high frequency ratio in both groups (p < 0.001). During daytime, the mean values in low frequency/high frequency ratio were lower in patients than in controls (p < 0.001). CONCLUSIONS: There is a shift in the autonomic balance in patients with inflammatory bowel disease in remission towards a condition of relative parasympathetic predominance, which, in the first place, reflects a sympathetic pullback. This imbalance has a circadian rhythm and it is more pronounced during the day.

Changes in atrial electrical properties following cardioversion of chronic atrial fibrillation: relation with recurrence.

OBJECTIVE: To study the reversibility of atrial electrical remodeling and its relation with recurrence in post-conversion chronic atrial fibrillation (CAF) patients. METHODS: In 28 drug-free CAF patients (mean AF duration 41+/-39 months) electrically converted to sinus rhythm effective refractory period (ERP) at 500 ms, monophasic action potential at 90% of repolarization (MAPd90) at five cycle lengths (CL, 350, 400, 450, 500, 600 ms), and P wave duration were measured three times: within the interval 5-20 min post-conversion, 24 h and 1 month later. Fifteen subjects with no history of AF and normal atrial structure served as a control group. Patients were followed up for recurrence for 1 month; 12 relapsed. RESULTS: ERP changed from 205+/-20 to 243+/-31 to 241+/-24 ms (P<0. 001), attaining a level comparable to that of the controls (238+/-21 ms) within 24 h. MAPd90 significantly (P<0.001) increased (from 175+/-11 to 190+/-19 to 191+/-10 ms at CL 350 ms and 201+/-12 to 234+/-20 and 233+/-23 ms at CL 600 ms) also reaching control levels within 24 h. MAPd90 exhibited an abnormal adaptation to rate only in the first evaluation. P wave duration was prolonged (137+/-33 ms) and exhibited a slower course of shortening (130+/-32 to 123+/-27 ms, P<0.001), reaching control levels within 1 month. Patients with higher values of MAPd90 at CL 350 in the immediate post-conversion period were more likely to relapse (P<0.005). CONCLUSIONS: ERP and repolarization shortening as a result of CAF are reversed within 24 h after conversion, while P wave duration reduces more slowly. Post-conversion MAPd90 values contain prognostic information for recurrence.

Amiodarone as a first-choice drug for restoring sinus rhythm in patients with atrial fibrillation: a randomized, controlled study.

STUDY OBJECTIVES: To investigate the efficacy and safety of amiodarone administered as the drug of first choice in the conversion of atrial fibrillation, regardless of its duration. DESIGN: : Prospective, randomized, controlled clinical study. SETTING: : Tertiary cardiac referral center. PATIENTS: Two-hundred eight consecutive patients (102 men; mean [+/- SD] age, 65 +/- 10 years) with atrial fibrillation. INTERVENTIONS: One-hundred eight patients received amiodarone, and 100 patients received placebo treatment. Patients randomized to amiodarone received 300 mg IV for 1 h, and then 20 mg/kg for 24 h. They were also given 600 mg/d orally, divided into three doses, for 1 week, and thereafter 400 mg/d for 3 weeks. Patients randomized to placebo treatment received an identical amount of saline solution IV over 24 h, and oral placebo treatment for 1 month. MEASUREMENTS AND RESULTS: Baseline clinical characteristics were similar in the two groups. Conversion to sinus rhythm was achieved in 87 of 108 patients (80.05%) who received amiodarone, and in 40 of 100 patients (40%) in the placebo group (p < 0.0001). Statistical analysis showed that the duration of the arrhythmia and the size of the left atrium affected both the likelihood of conversion to sinus rhythm and the time to conversion in both groups. No side effects requiring discontinuation of treatment were observed in either group. CONCLUSIONS: Amiodarone appears to be safe and effective in the termination of atrial fibrillation. However, extreme cases with a large left atrium and long-lasting arrhythmia need long-term therapy.

Assessment of left ventricular ejection dynamics in patients with coronary artery disease during dipyridamole-stress Doppler echocardiography.

OBJECTIVES: To investigate the contribution of Doppler-echocardiographically derived aortic indexes of left ventricular systolic function during dipyridamole-stress to the diagnosis of coronary artery disease (CAD). DESIGN: This was a clinical study. METHODS: Echocardiographic studies under baseline and peak dipyridamole stresses were performed on 15 normal subjects and 32 patients with angiographically confirmed CAD. Peak Doppler velocity, acceleration, and acceleration time of the ascending aorta, as well as segmental left ventricular wall motion, were analyzed. RESULTS: The sensitivity, specificity and overall accuracy of wall-motion abnormalities induced by dipyridamole for the detection of CAD were 62.5, 100, and 74.5%, respectively. When wall-motion abnormalities were combined with the percentage changes in peak aortic velocity and acceleration, the overall sensitivities were 84.38 and 78.15%, respectively, the specificities were 66.7 and 80.00%, respectively, and the accuracy was 78.72% for both models. When all three parameters were combined, the sensitivity, specificity and overall accuracy of the method were 87.5, 86.7, and 87.2%, respectively. CONCLUSIONS: Doppler-echocardiographically derived aortic indexes of left ventricular systolic function during dipyridamole stress could be a useful adjunct to two-dimensional echocardiography by improving its sensitivity in the diagnosis of CAD.

Amiodarone versus propafenone for conversion of chronic atrial fibrillation: results of a randomized, controlled study.

OBJECTIVES: The purpose of this study was to investigate the efficacy and safety of amiodarone and propafenone in the conversion of chronic atrial fibrillation in a prospective, randomized, placebo-controlled study. BACKGROUND: The effectiveness of amiodarone and propafenone in the treatment of patients with chronic atrial fibrillation has not been adequately studied. METHODS: One hundred one patients (48 men, mean age 64 +/- 9 years) with atrial fibrillation lasting >3 weeks participated in the study. Thirty-four patients received amiodarone (300 mg intravenously over 1 h, followed by 20 mg/kg over the next 24 h plus 600 mg orally, in three doses, for 1 week, then 400 mg/day orally, for three weeks), 32 received propafenone (2 mg/kg intravenously over 15 min, followed by 10 mg/kg over 24 h and then 450 mg/day orally, for one month) and the remaining 35 served as control subjects. All patients received digoxin and anticoagulant treatment as indicated (International Normalized Ratio 2 to 3). RESULTS: Conversion to sinus rhythm was achieved in 16 (47.05%) patients who received amiodarone, in 13 (40.62%) who received propafenone and in none of the control subjects (p < 0.001 for both groups vs. control subjects). Those who converted had smaller atria than those who did not and atrial fibrillation of shorter duration in both the amiodarone and propafenone groups. Treatment was discontinued in one patient of the propafenone group because of significant QRS widening. CONCLUSIONS: Amiodarone and propafenone appear to be safe and equally effective in the termination of chronic atrial fibrillation. Left atrial diameter and arrhythmia duration are independent predictors of conversion.

Efficacy of amiodarone for the termination of persistent atrial fibrillation.

The efficacy and safety of amiodarone in the conversion of persistent atrial fibrillation (AF) were investigated in a prospective, randomized, controlled study. Of 67 consecutive patients (32 men, mean age 64+/-9 years) with AF lasting >48 hours, 33 received amiodarone and 34 received placebo. Baseline clinical characteristics were similar in the 2 groups. Patients randomized to amiodarone received 300 mg intravenously for 1 hour and then 20 mg/kg for 24 hours. They were also given 600 mg/day orally, divided into 3 doses, for 1 week and thereafter 400 mg/day for 3 weeks. Patients randomized to placebo received an identical amount of saline IV over 24 hours and then oral placebo for 1 month. Conversion to sinus rhythm was achieved in 16 of the 33 patients (48.5%) who received amiodarone and in none of the 34 patients in the placebo group (p <0.001). None of the patients converted to sinus rhythm within the first 3 days. Those who converted had smaller atria than those who did not (diameter 41.9+/-7.2 vs 50.4+/-5.7 mm, p <0.001). Sex, age, baseline heart rate, left ventricular ejection fraction, and the duration of AF did not differ significantly between patients who converted and those who did not. No side effects requiring discontinuation of treatment were observed in either group. Amiodarone, administered both intravenously and orally, appears to be safe and effective in the termination of persistent AF. Left atrial diameter is the sole independent predictor of conversion.

Effects of long-term digoxin therapy on heart rate variability, baroreceptor sensitivity, and exercise capacity in patients with heart failure.

We evaluated the effects of long-term digoxin therapy on exercise capacity and on physiological parameters reflecting autonomic tone in 23 patients with mild to moderate heart failure. Before and after maintenance digoxin treatment, all patients underwent cardiopulmonary exercise testing and indexes of heart rate variability (HRV) and baroreceptor sensitivity (BRS) were measured. Long-term digoxin therapy significantly (P < 0.05) increased time domain indexes (rMSSD, pNN50) which reflect parasympathetic activity (from 30 +/- 16 to 37 +/- 14 and from 8 +/- 9 to 12 +/- 7, respectively). High-frequency (HF) and low-frequency (LF) power spectral components also showed a significant increase (from 4.5 +/- 1 to 5.1 +/- 1 and from 5.4 +/- 1 to 5.8 +/- 1, respectively), but the ratio LF/HF decreased, indicating a predominance of vagal activity. The magnitude of these changes exhibited a strong negative Pearson correlation coefficient when compared with initial values before treatment. BRS increased from 2.95 +/- 1.2 to 5.32 +/- 3 ms/mmHg (P < 0.05). Oxygen consumption at peak exercise and at the anerobic threshold increased significantly (from 17 +/- 3 to 19 +/- 3 mL/kg/min and from 14.7 +/- 3 to 16.5 +/- 3 mL/kg/min, respectively). A persistent negative correlation was found between initial values of HRV and the magnitude of changes in exercise capacity. These findings show that long-term digoxin therapy increases vagal activity and improves exercise capacity in patients with mild to moderate heart failure and seems to exert a more marked therapeutic effect on patients with poorer initial autonomic function.

Conversion of atrial fibrillation to sinus rhythm using acute intravenous procainamide infusion.

The efficacy and safety of intravenous procainamide in the conversion of atrial fibrillation was investigated. A total of 114 patients without severe heart failure were randomized to receive either intravenous procainamide (1 g over 30 minutes, followed by an infusion of 2 mg/min over 1 hour) or placebo in a double-blind trial. Digoxin (0.5 mg intravenously) was administered to all patients who had not previously been receiving digoxin. Treatment was considered successful if sinus rhythm was restored within 1 hour after starting the infusion. Conversion to sinus rhythm was achieved in 29 (50.9%) of the 57 patients treated with procainamide and in 16 (28.1%) of the 57 who received placebo (P approximately 0.012). When the duration of the atrial fibrillation was < or = 48 hours, conversion to sinus rhythm was achieved in 29 (69%) of the 42 patients receiving procainamide and in 16 (38.1%) of those receiving placebo (P approximately 0.004). None of the patients with atrial fibrillation lasting > or = 48 hours converted to sinus rhythm in either group. Another factor that played a role in the restoration of sinus rhythm was the size of the left atrium: the smaller the left atrium, the larger the success rate. The results of the study suggest that intravenous procainamide is an effective and safe means for the rapid termination of atrial fibrillation of recent onset and that its success rate is inversely related to the size of the left atrium. However, the drug is ineffective in the conversion of atrial fibrillation lasting more than 48 hours.

Reproducibility of tilt table testing in patients with vasovagal syncope and its relation to variations in autonomic nervous system activity.

To assess the variability of head-up tilt table testing, 35 patients with vasovagal syncope, shown by a positive tilt table test, underwent a second test 1 week later. Also, on the day before each test, spectral and time-domain indexes of heart rate variability were derived from Holter recordings to examine the stability of autonomous nervous system activity in these patients. Fifteen healthy volunteers served as a control group and also underwent two tilt table tests with prior Holter monitoring. Twenty-one (60%) of the 35 patients had a second positive test. None of the patients in the control group experienced syncope during either of the tests. The heart rate variability measures in the control group varied slightly from 1 day to the other, in contrast to the syncopal patients, where only low frequency spectral power and the mean of all 5-minute standard deviations of RR intervals showed comparable behavior. The indexes which reflect parasympathetic activity exhibited significant fluctuations in the syncopal patients. These fluctuations were due entirely to the patients who did not reproduce the outcome of the tilt table test, where high parasympathetic tone was associated with the positive test and normal parasympathetic tone with the negative test. In contrast, the patients with two positive tests had high parasympathetic tone during both test periods, with low individual variability. In conclusion, patients with vasovagal syncope show variations in vagal autonomic tone and appear to be more prone to syncope when their parasympathetic tone is elevated.

Assessment of autonomic function at rest and during tilt testing in patients with vasovagal syncope.

This study evaluated autonomic nervous system function in 30 patients with syncope and a positive tilt test result, 20 with a negative test result, and 20 healthy controls. Indexes of heart rate variability were measured during the intervals immediately before and after tilt, while all subjects were asymptomatic, and over a 24-hour period. There were no significant differences among the groups in any of the indexes of heart rate variability over the 24-hour period. In patients with a positive tilt result, tilting caused a decrease in low-frequency (LF) and high-frequency (HF) bands, although the LF/HF ratio did not significantly change. In patients with a negative tilt result there was a decrease in the HF band but no other significant changes. In the controls there was an increase in the LF band and LF/HF ratio and a decrease in the HF band. Our findings showed that patients with vasovagal syncope have no chronic differences from normal subjects in autonomic nervous system activity, but that these patients respond differently to the orthostatic stimulus.

Left ventricular diastolic filling changes during dipyridamole-induced ischaemia. An echo-Doppler study.

OBJECTIVE: To evaluate the usefulness of the Doppler assessment of left ventricular diastolic functioning during dipyridamole-induced ischaemia in patients with coronary artery disease (CAD). METHODS: We studied 28 patients with angiographically proven CAD [18 men, aged 62 +/- 7 years (mean +/- SD)] and 18 normal subjects (12 men, aged 59 +/- 7.5 years). Two-dimensional and transmitral flow Doppler echocardiography studies were performed at baseline and after intravenous administration of a high dose of dipyridamole (0.84 mg/kg during 10 min). Left ventricular wall motion was evaluated by two-dimensional Doppler echocardiography, with the left ventricle divided into a 16-segment model, whereas peak velocities of early and late diastolic flow, the early:late diastolic flow ratio and the deceleration rate of early diastolic flow were determined from transmitral flow Doppler echocardiography. RESULTS: Sixteen patients developed new wall-motion abnormalities (WMA), whereas the remaining 12 patients and the controls did not. Multivariate logistic regression analysis was performed to identify which of the parameters had independent diagnostic value for revealing CAD. WMA was entered at the first step and yielded a 57% sensitivity and 100% specificity; the changes in deceleration rate were entered as the second step, which improved the sensitivity to 85.5%, and reduced the specificity to 83% and raised the overall accuracy to 85% from 70% for WMA alone. More specifically, the sensitivity improved from 37.5, 63.5 and 65.5% to 62.5, 91 and 100%, respectively, for patients with one-, two- and three-vessel disease. The cut-off value of the change in deceleration rate was 7%. CONCLUSIONS: Patients could be classified as having CAD either if they developed new WMA or if the deceleration rate of early diastolic flow during dipyridamole-stress echocardiography increased by more than 7% compared with the rest value.

Reproducibility of time-domain indexes of heart rate variability in patients with vasovagal syncope.

The aim of this study was to examine whether the indexes of heart rate variability (HRV) are stable from day-to-day in patients with vasovagal syncope and whether the stability of the HRV indexes is linked with that of the clinical results of the tilt test. Nineteen patients with a history of syncopal episodes and a positive tilt test underwent a second test 1 week later. Of these, 11 (group P-P) also had a positive second test, whereas 8 (group P-N) had a negative second test. Fifteen healthy volunteers served as a control group. Five time domain indexes were derived: the mean of all coupling intervals between normal beats (mean NN), the SD about the mean of all coupling intervals between normal beats (SDNN), the mean of all 5-minute standard deviations of NNs (SD), the proportion of adjacent normal RR intervals differing by >50 ms (pNN50), the root-mean-square of the difference between successive RRs (rMSSD) and the standard deviations of 5-minute mean NN intervals (SDANN). The control group showed good reproducibility of all HRV indexes (slope 0.86 to 0.97). The syncopal patients taken as a whole had significantly less reproducibility than the controls in the pNN50 parameter. This difference was due entirely to the patients in the P-N group, who had a remarkable lack of reproducibility in both the pNN50 and rMSSD measures (slope pNN50, 0.52; rMSSD, 0.78), whereas the P-P group had a reproducibility of all HRV indexes, which was no different from that in controls (slope 0.83 to 1.04). In patients with vasovagal syncope, certain HRV measures that express parasympathetic tone did not show the high reproducibility found in normal subjects. Syncopal patients who lack reproducibility in these HRV parameters also show a lack of reproducibility in the clinical result of tilt testing.

Spectral analysis of heart rate variability before and during episodes of nocturnal ischaemia in patients with extensive coronary artery disease.

Spectral analysis of heart rate variability was used to assess autonomic nervous system activity associated with episodes of nocturnal myocardial ischaemia in 32 patients (20 men, age 58 +/- 9 years) with extensive coronary artery disease. Twenty-four hour Holter tape recordings were analysed and spectral indexes of heart rate variability were computed by fast Fourier analysis on 2 min segments covering the period from 10 min before to 10 min after each nocturnal ischaemic episode, defined as ST segment depression > or = 1 mm lasting at least 4 min. Spectral power was measured at low frequencies (LF: 0.06-0.10 Hz) and high frequencies (HF: 0.15-0.40 Hz) and the ratio LF/HF was calculated. RESULTS. A total of 30 episodes of nocturnal ischaemia were analysed. High frequency spectral power showed a clear decrease during the 10 min before the onset of ischaemia, remained steady until the end of the episode, and returned to normal by 6 min after. Low frequency spectral power fluctuated throughout the ischaemic episodes with no clear pattern of variation. The low/high frequency ratio reflected mainly the changes in high frequency. CONCLUSIONS. Sympathetic predominance due to para-sympathetic withdrawal is the principal change in autonomic nervous system activity associated with episodes of nocturnal ischaemia.