Feasibility of using self-reported ethnicity in pregnancy according to the gestation-related optimal weight classification: a cross-sectional study.

OBJECTIVE: To evaluate the feasibility of self-reported ethnicity using the gestation-related optimal growth (GROW) classification in a contemporary multicultural antenatal population. DESIGN: Cross-sectional study. SETTING: Tertiary obstetric hospital in Melbourne, Australia. POPULATION: Pregnant women attending the antenatal clinic. METHODS: We surveyed pregnant women during April-June 2016 regarding their understanding of the term 'ethnicity', and how they would classify the ethnicity of themselves, their partner, and family members according to the Australian GROW classification. RESULTS: Two hundred and thirty-five women completed the survey. When describing 'ethnicity', most women (103, 44%) chose multiple descriptors, most frequently country of birth (54%) and region of ancestry (47%). Interpretation of 'ethnicity' varied significantly between ethnic groups: those choosing 'country of birth' were more likely to identify as Indian (odds ratio, OR 3.5, P = 0.03), whereas those choosing 'physical appearance' were more likely to identify as Chinese (OR 3.0, P = 0.047). Thirty participants (13%) were unable to describe their ethnicity from the available GROW options. Sixty-one (26%) respondents' ethnicity was inconsistent with that of their parents' heritage. A further 35% had a partner of different ethnicity. The agreement between country of birth and self-reported ethnicity was only fair (kappa 0.73, 95% confidence interval, 95% CI 0.64-0.82). CONCLUSION: This study confirms the complexity of defining ethnicity in contemporary multicultural settings. Self-reported ethnicity is often inaccurate, concepts of ethnicity vary by ethnic group, and country of birth is a poor descriptive surrogate. Adjustment for maternal ethnicity should be undertaken with caution in the customised assessment of fetal growth. TWEETABLE ABSTRACT: Is self-reported maternal ethnicity reliable? We think not.

A mobile health intervention promoting healthy gestational weight gain for women entering pregnancy at a high body mass index: the txt4two pilot randomised controlled trial.

OBJECTIVE: To determine the feasibility and effectiveness of an mHealth intervention promoting healthy diet, physical activity and gestational weight gain in pregnant women. DESIGN: Randomised controlled trial (RCT). SETTING: Australian tertiary obstetric hospital. POPULATION: One hundred pregnant women who were overweight or obese prior to pregnancy. METHODS: Women recruited at the first antenatal clinic visit were randomised to either an intervention or a control group. The intervention consisted of a tailored suite of strategies delivered (from first antenatal visit until 36 weeks' gestation) via multiple modalities available on mobile devices. MAIN OUTCOME MEASURES: The primary outcome was intervention feasibility and secondary outcomes were objectively measured changes in gestational weight gain (GWG) and self-reported dietary intake and physical activity. RESULTS: Ninety-one women completed the study. Delivery to protocol provides evidence of program feasibility. Most women engaged regularly with the program, with the majority (97.6%) reporting that the intervention was helpful. Secondary outcomes demonstrated a significantly lower GWG in the intervention group (7.8 kg ± 4.7 versus 9.7 kg ± 3.9; P =0.041) compared with the control group at intervention completion. Intervention group women reported significantly smaller reductions in total, light- and moderate-intensity physical activity from baseline to completion of the intervention (P = 0.001) compared with the control group, but no differences in consumption frequencies of key food groups. CONCLUSION: An intervention that aimed to deliver healthy diet, physical activity and GWG guidance utilising innovative technology can be feasibly implemented and produce positive physical activity and GWG outcomes. TWEETABLE ABSTRACT: txt4two mHealth study improved gestational weight gain and physical activity in pregnant women with high BMIs.

Self-weighing and simple dietary advice for overweight and obese pregnant women to reduce obstetric complications without impact on quality of life: a randomised controlled trial.

OBJECTIVE: To determine the effect of serial weighing and dietary advice compared with standard antenatal care on obstetric outcomes. DESIGN: Randomised controlled clinical trial. SETTING: Australian tertiary obstetric hospital. POPULATION: Three hundred and eighty-two overweight or obese non-diabetic pregnant women at less than 20 weeks gestation with a singleton pregnancy. METHODS: Women were randomised to targeted, serial self-weighing and simple dietary advice, (intervention), or standard antenatal care (control). MAIN OUTCOMES MEASURES: The primary outcome was a reduction in a composite of obstetric complications: gestational hypertension, pre-eclampsia, diabetes, assisted or caesarean birth, shoulder dystocia, severe perineal trauma, postpartum haemorrhage and maternal high dependency care. Secondary outcomes were gestational weight gain at 36 weeks' gestation, quality of life (QOL) and maternal serum levels of 28-week leptin, adiponectin and C-reactive protein (CRP). RESULTS: There was no difference in the rate of the primary composite outcome of obstetric complications: 124/184 (67% control), 124/187 (66% intervention) [relative risk 0.98 (95% confidence interval (CI) 0.85-1.14)]. There was no difference in mean gestational weight gain [-0.9 kg (95% CI -2.0, 0.25)], QOL or leptin, adiponectin or CRP levels between intervention and control groups. CONCLUSIONS: This low-cost, pragmatic intervention failed to prevent obstetric complications or modify maternal biochemistry or gestational weight gain in overweight or obese pregnant women. Participation in the study did not impair participants' QOL. TWEETABLE ABSTRACT: Serial self-weighing and dietary advice failed to reduce obstetric complications in overweight pregnant women.

A sex comparison of the anatomy and function of the main olfactory bulb-medial amygdala projection in mice.

We previously reported that some main olfactory bulb (MOB) mitral/tufted (M/T) cells send a direct projection to the "vomeronasal" amygdala in female mice and selectively respond to volatile male mouse urinary odors. We asked whether MOB M/T cells that project to the vomeronasal amygdala exist in male mice and whether there is a sexually dimorphic response of these neurons to volatile male urinary pheromones. Gonadectomized male and female mice received bilateral injections of the retrograde tracer, Cholera toxin-B (CTb) into the medial amygdala (Me), which is part of the vomeronasal amygdala. All subjects were then treated with estradiol benzoate and progesterone before being exposed to volatile male urinary odors whereupon they were sacrificed 90 min later. Sections of the MOB were immunostained for Fos protein and/or CTb. Male mice, like females, displayed a small population of MOB M/T cells that project to the Me. While the general localization of these cells was similar in the two sexes, there were statistically significant sex differences in the percentage of MOB M/T cells in the anterior and posterior medial segments of the MOB that were retrogradely labeled by CTb. Male urinary volatiles stimulated equivalent, significant increases in Fos expression by MOB M/T neurons projecting to the Me in the two sexes. By contrast, in the same mice exposure to male urinary volatiles stimulated a significant increase in Fos expression by mitral cells in the accessory olfactory bulb (AOB) only in female subjects. Thus any sexually dimorphic behavioral or neuroendocrine responses to male urinary volatiles likely depend on the differential processing of these odor inputs in the AOB and/or other downstream forebrain structures after their detection by the main olfactory system.

Factors affecting success of thymus transplantation for complete DiGeorge anomaly.

Thymus transplantation shows promise for the treatment of athymia in complete DiGeorge anomaly. This report reviews the effects of dose of thymus tissue, ABO compatibility, HLA matching, culture conditions, age of donor and immunosuppression of recipient on immune outcomes at 1 year after transplantation. Forty-nine athymic subjects have been treated with cultured postnatal allogeneic thymus tissue; 36 (73%) survive with only one subject on immunosuppression at 1.5 years. Of 31 surviving subjects more than 1 year after transplantation, 30 (97%) developed naive T cells, T-cell proliferative responses to mitogens and a diverse T-cell receptor beta variable (TCRBV) repertoire. The dose of thymus tissue, HLA matching and use of immunosuppression had nonsignificant effects on these outcome variables. Removal of deoxyguanosine from culture medium and length of culture did not adversely affect outcomes. Use of thymus tissue from donors over 1 month of age, versus under 1 month, resulted in higher total T-cell numbers (p = 0.03). However, this finding must be confirmed in a prospective trial. Although subtle immune effects may yet be associated with some of the factors tested, it is remarkable that consistently good immune outcomes result despite variation in dose, HLA matching and use of immunosuppression.

Observations on the transition from intermittent to permanent atrial fibrillation.

BACKGROUND: Quantitative data on the frequency with which transition from intermittent to permanent atrial fibrillation occurs are lacking. We conducted this study to determine the proportion of patients with intermittent atrial fibrillation who progress to permanent atrial fibrillation and to investigate baseline clinical characteristics that might predict such a progression. METHODS: This retrospective cohort study included 231 patients who were seen with intermittent atrial fibrillation at a university hospital-based clinic from January 1978 through December 1997. Patients' medical records and electrocardiograms were reviewed and data were collected for all clinic visits through May 1998. The proportion of patients who remained free of transition from intermittent to permanent atrial fibrillation was calculated by the Kaplan-Meier method. A Cox proportional hazards model was used to determine the effect of some baseline characteristics on this transition. RESULTS: The number of patients who remained free of transition from intermittent to permanent atrial fibrillation was 92% (95% confidence interval 88%-96%) at 1 year and 82% (95% confidence interval 75%-88%) at 4 years. Among 5 baseline characteristics (age, sex, structural heart disease, atrial fibrillation at presentation, and use of an antiarrhythmic medicine before presentation), the 2 significant predictors of progression from intermittent to permanent atrial fibrillation were age (P =.0003) and being in atrial fibrillation at presentation (P =.0006). The hazard ratio associated with 10 years of advancing age was 1.82 (95% confidence interval 1.31-2.51), and the hazard ratio associated with atrial fibrillation at presentation was 3.56 (95% confidence interval 1.73-7.34). CONCLUSIONS: Approximately 18% of patients who had intermittent atrial fibrillation were permanently in atrial fibrillation after 4 years of follow-up. Age and being in atrial fibrillation at presentation were the only 2 important clinical variables identified in predicting such a progression.

Heart rate during spontaneous and induced paroxysmal supraventricular tachycardia.

It is generally assumed that paroxysmal supraventricular tachycardia (PSVT) induced during invasive electrophysiological study reproduces the patient's spontaneous, clinical arrhythmia. Even in the absence of antiarrhythmic drugs, however, there may be significant differences in characteristics of the induced and spontaneous arrhythmias. We compared the heart rate of PSVT in 38 patients who had undergone electrophysiological study with induction of PSVT who also had a spontaneous episode of PSVT documented by transtelephonic ECG monitoring during a period when all antiarrhythmic drugs were withheld. The heart rate during spontaneous PSVT was faster than the heart rate of PSVT induced during electrophysiological study; the mean difference was 16 beats/min (P < 0.001). We conclude that heart rate of PSVT induced during electrophysiological study generally underestimates the heart rate of spontaneous PSVT in the antiarrhythmic drug-free state. This may be due to differences in the autonomic and hemodynamic states during spontaneous and induced arrhythmias.

Incidence of symptomatic atrial fibrillation in patients with paroxysmal supraventricular tachycardia.

OBJECTIVES: This study was performed to determine the incidence of symptomatic, sustained atrial fibrillation in a group of patients with paroxysmal supraventricular tachycardia. The effects of the mechanism of paroxysmal supraventricular tachycardia (atrioventricular [AV] node reentry vs. AV reentry through an accessory pathway) and heart rate during the tachycardia on the occurrence of atrial fibrillation were also assessed. BACKGROUND: There is a substantial incidence of atrial fibrillation in patients with paroxysmal supraventricular tachycardia, but the precise incidence and the factors that determine it are unknown. METHODS: One hundred sixty-nine patients with paroxysmal supraventricular tachycardia were followed up by regular clinic visits and transtelephonic electrocardiographic monitoring during symptomatic episodes of arrhythmia. The Kaplan-Meier product-limit method was used to estimate the proportion of patients remaining free of atrial fibrillation during the observation period. The Cox proportional hazards model was used to assess the effect of mechanism and heart rate during paroxysmal supraventricular tachycardia on the atrial fibrillation-free period. RESULTS: Thirty-two (19%) of the 169 patients had an episode of atrial fibrillation during a mean follow-up period of 31 months. The cumulative percent of patients experiencing an episode of atrial fibrillation was 6% within 1 month, 9% within 4 months and 12% within 1 year. The mechanism of paroxysmal supraventricular tachycardia was not associated with the time to occurrence of atrial fibrillation; the hazard ratio corresponding to classification in the AV node reentry group was 0.8 (p > 0.6). The heart rate during paroxysmal supraventricular tachycardia was not associated with the time to occurrence of atrial fibrillation; the hazard ratio associated with an increase in heart rate of 50 beats/min during the tachycardia was 1.15 (p > 0.5). CONCLUSIONS: This study suggests that atrial fibrillation will develop in approximately 12% of patients with paroxysmal supraventricular tachycardia during a 1-year follow-up period. The occurrence of atrial fibrillation is not related to the mechanism or heart rate of the paroxysmal supraventricular tachycardia.

Pharmacokinetic evaluation of aconiazide, a potentially less toxic isoniazid prodrug.

STUDY OBJECTIVE: To determine the bioavailability and renal elimination of isoniazid, acetylisoniazid, monoacetylhydrazine, diacetylhydrazine, aconiazide, and 2-formylphenoxyacetic acid. STUDY DESIGN: Randomized, double-blind, two-period, crossover phase I study. SETTING: Pharmacokinetics unit at a referral hospital that specializes in the treatment of mycobacterial infections. SUBJECTS: Twelve healthy volunteers selected from the hospital staff. INTERVENTIONS: Subjects received aconiazide tablets 650 mg (containing isoniazid 300 mg) and isoniazid tablets 300 mg. Blood and urine samples were collected over 24 hours after the dose. MEASUREMENTS AND MAIN RESULTS: Intact aconiazide and 2-formylphenoxyacetic acid were not detected in the serum. Compared with isoniazid tablets, aconiazide's relative bioavailability (based on the area under the serum concentration-time curve) was 50.7%; its relative maximum serum concentration was 13.4%. CONCLUSIONS: Isoniazid is less bioavailable after aconiazide tablets than after isoniazid tablets. The optimum dose of aconiazide remains to be determined.

Asymptomatic arrhythmias in patients with symptomatic paroxysmal atrial fibrillation and paroxysmal supraventricular tachycardia.

BACKGROUND: Paroxysmal atrial fibrillation and paroxysmal supraventricular tachycardia are recognized clinically when patients seek treatment for symptoms due to recurrent arrhythmias; atrial fibrillation also increases the risk of stroke. The frequency with which asymptomatic arrhythmias occur in patients with these arrhythmias is unknown. METHODS AND RESULTS: Twenty-two patients with paroxysmal atrial fibrillation (n = 8) or paroxysmal supraventricular tachycardia (n = 14) were studied for 29 days with two different ambulatory ECG-monitoring techniques to measure the relative frequency of asymptomatic and symptomatic arrhythmias. All class I antiarrhythmic drugs, calcium channel blockers, beta-blockers, and digitalis were withheld. Sustained asymptomatic arrhythmia events (defined as lasting at least 30 seconds) were documented using continuous ambulatory ECG monitoring once weekly for a total of 5 of the 29 study days; symptomatic arrhythmia events were documented using transtelephonic ECG monitoring for all 29 days of the study. In the group of patients with paroxysmal atrial fibrillation, asymptomatic arrhythmia events occurred significantly more frequently than symptomatic arrhythmia events; the mean rates, expressed as events/100 d/patient (95% confidence interval), were 62.5 (40.4, 87.3) and 5.2 (2.7, 9.0) (P < .01); the ratio of the mean rates was 12.1 (5.8, 26.4). In contrast, in the group of patients with paroxysmal supraventricular tachycardia, asymptomatic arrhythmia events were significantly less frequent than symptomatic arrhythmia events; the mean rates were 0.0 (0.0, 5.3) and 7.4 (5.0, 10.6) (P = .02). The ratio of the mean rates was 0.0 (0.0, 0.8). CONCLUSIONS: In a group of patients with paroxysmal atrial fibrillation, sustained asymptomatic atrial fibrillation occurs far more frequently than symptomatic atrial fibrillation. However, it is not known whether asymptomatic atrial fibrillation is a potential risk factor for stroke even when patients are not having symptomatic arrhythmias.

Spontaneous occurrence of symptomatic paroxysmal atrial fibrillation and paroxysmal supraventricular tachycardia in untreated patients.

BACKGROUND: Ambulatory outpatients (n = 150) with a history of paroxysmal supraventricular arrhythmia were studied to establish the characteristics of the first recurrence of symptomatic tachycardia (time to first recurrence, heart rate during tachycardia, and observed rhythm that was regular versus irregular) when no antiarrhythmic drug was being taken. Baseline variables were examined to assess their impact on time to first recurrence: index arrhythmia (paroxysmal atrial fibrillation [n = 37] versus paroxysmal supraventricular tachycardia [n = 113]), age (mean +/- SD, 43.3 +/- 16.1 years), female sex (n = 71), or presence of other heart or lung disease (n = 53). METHODS AND RESULTS: Transtelephonic monitoring of the ECG was used to document the rhythm during recurrences of symptomatic tachycardia. Time to first recurrence of symptomatic tachycardia and heart rate during tachycardia were measured, the observed rhythm was classified as irregular (consistent with paroxysmal atrial fibrillation) or regular (consistent with paroxysmal supraventricular tachycardia), and the hour of recurrence was recorded. Advancing age was significantly associated with a decreasing time to first recurrence (p < 0.001); the estimated increase in the hazard function was 25% with each 10 years of advancing age. After the effect of age was adjusted for, neither the classification of arrhythmia (p > 0.2), presence of other heart or lung disease (p > 0.8), nor sex (p > 0.9) was significantly associated with time to first recurrence. Among patients with paroxysmal supraventricular tachycardia, 6.5% had atrial fibrillation recorded at the next symptomatic arrhythmia; among patients with paroxysmal atrial fibrillation, 11.8% had a regular tachycardia recorded at the next symptomatic arrhythmia. There was a circadian pattern to the hour of occurrence of paroxysmal supraventricular tachycardia but not paroxysmal atrial fibrillation. CONCLUSIONS: Age is more important than other clinical variables, including the ECG classification of a paroxysmal supraventricular arrhythmia in predicting the occurrence of symptomatic arrhythmias. Arrhythmias documented by ECG during symptoms are often different from the arrhythmia documented at the time of referral, which may confound interpretation of antiarrhythmic drug effects.

Treatment of paroxysmal supraventricular tachycardia with oral diltiazem.

Symptomatic paroxysmal supraventricular tachycardia is a troubling arrhythmia for many patients. To test the efficacy of oral diltiazem to reduce symptomatic recurrences of paroxysmal supraventricular tachycardia, we enrolled 17 patients in a double-blind, placebo-controlled crossover study. Sixteen of 17 patients completed a dose-ranging phase and were entered into the randomized phase. Although the time to first recurrence of tachycardia was slightly longer when patients took diltiazem, the difference was not significant (p = 0.15). The hazard ratio of the time to first recurrence on placebo compared with oral diltiazem was 2.7 (95% confidence interval, 0.8 to 9.1). Of the patients who had a recurrence of tachycardia in both treatment periods, the median reduction in heart rate in patients receiving diltiazem was 20 beats/min. (p less than 0.01; 95% confidence interval, 6 to 42).

Regular ventricular rhythms in patients with symptomatic paroxysmal atrial fibrillation.

Paroxysmal atrial fibrillation is a grossly irregular tachycardia. Forty-nine patients with paroxysmal atrial fibrillation who were taking a variety of antiarrhythmic medications including the class IC agents propafenone and flecainide were followed up for a median of 371 days with use of transtelephonic electrocardiogram (ECG) monitoring to document symptomatic rhythms. Eighteen patients had 96 episodes of regular tachycardia; the cumulative incidence rate was 25% at 6 months, 33% at 1 year and 41% at 18 months. Eighty of the 96 episodes occurred with a heart rate less than or equal to 180 beats/min and could have been explained by atrial flutter with 2:1 block. However, nine patients had a total of 16 episodes with a rate greater than 180 beats/min that were probably not due to atrial flutter with block; the cumulative incidence rate of these fast regular tachycardias was 14% at 6 months, 17% at 1 year and 25% at 18 months. QRS duration during the first episode of regular tachycardia was significantly longer in patients taking a class IC drug (median 105 vs 90 ms, p less than 0.001 Wilcoxon rank sum test). In contrast to drug therapy with amiodarone or the combination of digoxin and verapamil, the QRS duration of regular tachycardias during class IC therapy was directly related to the tachycardia heart rate (Spearman's rank, p less than 0.01). All episodes of fast, regular tachycardias with a QRS duration greater than 120 ms occurred in patients taking a class IC drug. Clinicians treating patients with paroxysmal atrial fibrillation should expect a substantial incidence of regular tachycardia in addition to atrial fibrillation.

Propafenone treatment of symptomatic paroxysmal supraventricular arrhythmias. A randomized, placebo-controlled, crossover trial in patients tolerating oral therapy.

OBJECTIVE: To test the hypothesis that propafenone, administered orally, prevents symptomatic paroxysmal supraventricular arrhythmias. DESIGN: a 6-month, open-label, dose-finding phase followed by a randomized, double-blind, placebo-controlled, crossover phase, with each treatment period lasting up to 60 days. SETTING: An outpatient clinic. PATIENTS: Thirty-three patients with either paroxysmal supraventricular tachycardia (n = 16) or paroxysmal atrial fibrillation (n = 17) were enrolled. Their arrhythmias were documented by electrocardiogram before enrollment. Twenty-three patients (14 with paroxysmal supraventricular tachycardia and 9 with paroxysmal atrial fibrillation) were randomized and the data obtained from these patients were used in the efficacy analysis. INTERVENTION: Propafenone (300 mg three times daily in 19 patients, 300 mg twice daily in 3 patients, and 150 mg twice daily in 1 patient) and matching placebo tablets were administered in a randomized sequence. MEASUREMENTS: Symptomatic arrhythmia was documented by telephone transmission of the electrocardiogram. MAIN RESULTS: The time to first recurrence was prolonged for the overall group of 23 patients while they received propafenone (P = 0.004). The recurrence rate of arrhythmia during treatment with propafenone was estimated to be approximately one fifth of the recurrence rate during treatment with placebo. CONCLUSIONS: Propafenone is effective in reducing symptomatic paroxysmal supraventricular arrhythmias.

Occurrence of atrial fibrillation in patients with paroxysmal supraventricular tachycardia due to atrioventricular nodal reentry.

The occurrence of atrial fibrillation in patients with paroxysmal supraventricular tachycardia (PSVT) has been well documented when PSVT is secondary to atrioventricular reentry, but not when PSVT is secondary to atrioventricular nodal reentry (AVNRT). Seventeen patients with AVNRT were followed using transtelephonic electrocardiogram monitoring to document symptomatic tachycardias. The median length of telephone monitor surveillance was 357 days. Fifteen of 17 patients transmitted electrocardiograms that showed PSVT. Three of 17 patients (18%) transmitted electrocardiograms that showed atrial fibrillation. A transition from PSVT into atrial fibrillation was not recorded, but all three did have PSVT recorded on other days of follow-up. We report the occurrence of atrial fibrillation in patients with AVNRT and that its incidence is higher than expected for the general population.

Random and nonrandom behavior of symptomatic paroxysmal atrial fibrillation.

Little is known about the behavior of symptomatic paroxysmal atrial fibrillation (AF). The nature of the process formed by the successive occurrences of this arrhythmia was studied in 8 patients with a history of symptomatic paroxysmal AF. Trans-telephonic monitoring of the electrocardiogram was used to document the cardiac rhythm during symptoms. Patients were followed while successive attacks of paroxysmal AF were documented. A minimum of 12 and a maximum of 26 consecutive episodes of symptomatic paroxysmal AF were recorded from the 8 patients during 66 to 332 days. Methods developed in industrial reliability theory were used to show that, for the overall group of 8 patients, the interevent times between successive occurrences of symptomatic AF were not independent. However, for a subgroup including 6 of the patients, the interevent times were independent and governed by an exponential probability distribution. Differences in observed behavior of symptomatic AF may relate to differences in underlying mechanism within patients.

Clinical behavior of paroxysmal atrial tachycardia.

Paroxysmal atrial tachycardia is a familiar arrhythmia that has been studied extensively for the past decade using intracardiac recording and programmed electrical stimulation. These studies have thoroughly documented the mechanisms of this arrhythmia and its associated atrioventricular conduction abnormalities, but little is known about the spontaneous clinical behavior of this arrhythmia. A group of 34 patients with paroxysmal atrial tachycardia were studied using telephone transmission of the electrocardiogram to document recurrent tachycardia. When antiarrhythmic therapy was withdrawn, median time to the first recurrence of tachycardia was 19 days, mean heart rate during spontaneous tachycardia was 203.5 +/- 34.9 beats/min, and the median duration of an attack was 20 minutes. In a group of patients who were followed while many consecutive attacks were documented, the time intervals between attacks were found to be uncorrelated and to fit an exponential probability distribution (i.e., the occurrence of paroxysmal atrial tachycardia behaved like a Poisson process). Paroxysmal atrial tachycardia does not occur in a chaotic and unpredictable fashion; it is an event that occurs according to common probability models.

Circadian occurrence of symptomatic paroxysmal supraventricular tachycardia in untreated patients.

Fifty-two patients with paroxysmal supraventricular tachycardia were studied to determine whether there was a circadian pattern to the occurrence of this arrhythmia. Antiarrhythmic therapy was discontinued, and patients were followed until they had one recurrence of tachycardia documented by telephone transmission of the electrocardiogram. By least-squares analysis, the times of day that the 52 attacks (one from each patient) occurred were fit to a sinusoidal density function with a period of 24 hr. The highest relative incidence of tachycardia was at 4 P.M.; tachycardia was five times more likely to occur at 4 P.M. than at 4 A.M., the time of the lowest relative incidence. A second attack of tachycardia was recorded from 35 of the 52 patients. The times of the two attacks in individual patients were found to be independent; thus the times of day at which the second attacks occurred were used as a test set for the distribution estimated from the first. The empirical distribution for the times from the 35 second attacks was compared with the distribution function estimated from the 52 first attacks, and there was no significant departure; this finding confirmed the circadian pattern. Since the relative incidence of attacks of paroxysmal supraventricular tachycardia is higher in the afternoon, it may be helpful to target antiarrhythmic therapy to that time of day.