The spectrum of cardiac rate and rhythm in normal newborns

Younger postnatal age is associated with a lower heart rate on Holter monitoring during the first week of life

To evaluate heart rate (HR), the presence of extrasystoles and other Holter findings among healthy newborns, and to collect data for new normal limits for Holter parameters in newborns. For this cross-sectional study, 70 healthy term newborns were recruited to undergo 24-h Holter monitoring. Linear regression analysis was used in HR analyses. The age-specific limits for HRs were calculated using linear regression analysis coefficients and residuals. The mean (SD) age of the infants was 6.4 (1.7) days during the recording. Each consecutive day of age raised the minimum and mean HR by 3.8 beats per minute (bpm) (95% CI: 2.4, 5.2; P < .001) and 4.0 bpm (95% CI: 2.8, 5.2; P < .001), respectively. Age did not correlate with maximum HR. The lowest calculated limit for minimum HR ranged from 56 bpm (aged 3 days) to 78 bpm (aged 9 days). A small number of atrial extrasystoles and ventricular extrasystoles were observed in 54 (77%) and 28 (40%) recordings, respectively. Short supraventricular or ventricular tachycardias were found in 6 newborns (9%).

CONCLUSION

 The present study shows an increase of 20 bpm in both the minimum and mean HRs of healthy term newborns between the 3rd and 9th days of life. Daily reference values for HR could be adopted in the interpretation of HR monitoring results in newborns. A small number of extrasystoles are common in healthy newborns, and isolated short tachycardias may be normal in this age group.

WHAT IS KNOWN

• The current definition of bradycardia in newborns is 80 beats per minute. • This definition does not fit into the modern clinical setting of continuously monitored newborns, where benign bradycardias are commonly observed.

WHAT IS NEW

• A linear and clinically significant increase in heart rate was observed in infants between the ages of 3 and 9 days. • It appears as though lower normal limits for heart rate could be applied to the youngest newborns.

Blood pressure and flow in pediatric anesthesia: An educational review

During recent years, a lot of interest has been focused on blood pressure in the context of pediatric anesthesia, trying to define what is normal in relation to age and what numeric values that should be regarded as hypotension, needing active intervention. However, blood pressure is mainly measured as a proxy for flow, that is, cardiac output. Thus, just focusing on specific blood pressure numbers may not necessarily be very useful or appropriate. The aim of this educational review is to put the issue of intraoperative blood pressure in the context of pediatric anesthesia in further perspective.

Automatic segmentation for neonatal phonocardiogram

This work addresses the automatic segmentation of neonatal phonocardiogram (PCG) to be used in the artificial intelligence-assisted diagnosis of abnormal heart sounds. The proposed novel algorithm has a single free parameter - the maximum heart rate. The algorithm is compared with the baseline algorithm, which was developed for adult PCG segmentation. When evaluated on a large clinical dataset of neonatal PCG with a total duration of over 7h, an F1 score of 0.94 is achieved. The main features relevant for the segmentation of neonatal PCG are identified and discussed. The algorithm is able to increase the number of cardiac cycles by a factor of 5 compared to manual segmentation, potentially allowing to improve the performance of heart abnormality detection algorithms.

Heart rate during the first 24 hours in term-born infants

OBJECTIVE

Heart rate (HR) is an important clinical parameter in newborn infants, but normal ranges are poorly defined. Our aim was to establish normal reference ranges and individual variations in HR as obtained by auscultation in healthy term-born infants during the first 24 hours of life.

DESIGN

Observational study.

SETTING

Single hospital in Norway.

METHODS

HR was assessed by auscultation for 30 s at 2, 4, 8, 16 and 24 hours of age. Auscultation was validated against ECG recordings.

SUBJECTS

Healthy term-born infants who were asleep or awake in a quiet resting state.

MAIN OUTCOME MEASURES

Construction of percentile curves for resting HR.

RESULTS

The study included 953 infants. The 50th percentile was 126 beats per minute (bpm) at age 2 hours and thereafter 120-122 bpm. The respective 2nd and 98th percentiles were 102 (thereafter 96-100) bpm and 162 (thereafter 150-156) bpm. The mean HR was 5.6 bpm higher when awake than asleep, 4.9 bpm higher when on the mother's chest than in the cot, 1.6 bpm higher in girls than in boys, and increased by 0.5 bpm per 0.1°C increase in rectal temperature. Mode of delivery, meconium staining, birth weight and maternal smoking during pregnancy were of no significance. For each infant, HR varied considerably during the first 24 hours (intraclass correlation 0.21 (95% CI 0.18 to 0.24), coefficient of variation 9.2%).

CONCLUSIONS

The HR percentiles allow for a scientifically based use of HR when assessing newborn infants born at term.

Structured inpatient evaluation of neonatal cardiac ectopy

OBJECTIVE(S)

In well-appearing newborns with suspected cardiac ectopy, we sought to evaluate our practice and test whether initial electrocardiogram (ECG) findings were associated with neonatal arrhythmias (NA).

STUDY DESIGN

We identified well-appearing, non-anomalous infants >34 weeks' gestation with suspected ectopy over 3.5 years. NA was defined as ≥10% premature atrial contractions (PAC), ≥5 beats of atrial tachycardia, ≥2% premature ventricular contractions (PVCs), or ≥3 beats of ventricular tachycardia. The unadjusted associations between initial ECG findings and NA are reported.

RESULT

Among 126 infants with ECGs and Holters performed, NA was observed in 38 patients (30%) and was similar whether PACs were present or not on the initial ECG (33% vs. no PACs: 29%, p = 0.6). However, NAs were identified more frequently based on the presence of PVCs on the initial ECG (83% vs. 25%, p < 0.01).

CONCLUSION

NAs were prevalent and both their etiologies and impact on infants warrant future study.

Bradycardia in perspective-not all reductions in heart rate need immediate intervention

According to Wikipedia, the word 'bradycardia' stems from the Greek βραδύς, bradys, 'slow', and καρδία, kardia, 'heart'. Thus, the meaning of bradycardia is slow heart rate but not necessarily too slow heart rate. If looking at top endurance athletes they may have a resting heart rate in the very low thirties without needing emergent intervention with anticholinergics, isoprenaline, epinephrine, chest compressions or the insertion of an emergency pacemaker (Figure 1). In fact, they withstand these episodes without incident, accommodating with a compensatory increase in stroke volume to preserve and maintain cardiac output. With this in mind, it is difficult for the authors to fully understand and agree with the general sentiment amongst many pediatric anesthesiologists that all isolated bradycardia portends impending doom and must be immediately treated with resuscitative measures.

REM-related bradyarrhythmia syndrome

Cardiac arrhythmias during sleep are relatively common and include a diverse etiology, from benign sinus bradycardia to potentially fatal ventricular arrhythmias. Predisposing factors include obstructive sleep apnea and cardiac disease. Rapid eye movement (REM)-related bradyarrhythmia syndrome (including sinus arrest and complete atrioventricular block with ventricular asystole) in the absence of an underlying cardiac or physiologic sleep disorder was first described in the early 1980s. Although uncertain, the underlying pathophysiology likely reflects abnormal autonomic neural-cardiac inputs during REM sleep. The autonomic nervous system (ANS) is a known key modulator of heart rate fluctuations and rhythm during sleep and nocturnal heart rate reflects a balance between the sympathetic-parasympathetic systems. Whether the primary trigger for REM-related bradyarrhythmias reflects abnormal centrally mediated control of the ANS during REM sleep or anomalous baroreflex parasympathetic influences is unknown. This review focuses on the salient features of the REM-related bradyarrhythmia syndrome and explores potential mechanisms with a particular assessment of the relationship between the ANS and nocturnal heart rate fluctuations.

Normal limits for heart rate as established using 24-hour ambulatory electrocardiography in children and adolescents

BACKGROUND

To the best of our knowledge, normal limits of heart rate with respect to gender, and as established using 24-hour ambulatory Holter electrocardiography, have yet to be published for the entire age range of children and adolescents.

OBJECTIVES

To establish the normal limits for heart rate in newborns, infants, children, and adolescents of both genders.

PATIENTS AND METHODS

We obtained 24-hour Holter recordings from 616 healthy subjects aged from birth to 20 years with structurally normal hearts. The subjects were not receiving medication, and had not been submitted to prior cardiac intervention. Off-line analysis was performed with Mars 8000 scanners, analysing 5 consecutive RR intervals by the software available for automatic calculation of heart rate. All subjects were in sinus rhythm. Best-fit non-linear regressions were applied to correlate age and gender with minimum and mean heart rate, as well as with maximal RR-interval, and to calculate the 5th, 25th, 75th and 95th percentiles.

RESULTS

We observed significant gender-dependent differences in heart rate for persons aged 10 years and older, with the males exhibiting lower minimal and mean heart rates, and higher RR-intervals, than the females. Correlation of heart rate with age and gender could be established with sufficient accuracy using non-linear regression (p less than 0.0001): Minimum heart rate (male: R(2)=0.778, female: R(2) = 0.664) and mean heart rate (male: R(2) = 0.820, female: R(2) = 0.736) decreased with age, while the maximal RR-interval prolonged (male: R(2) = 0.562, female: R(2) = 0.486). Age and gender-related graphs of centiles were constructed.

CONCLUSIONS

Heart rate, as documented using Holter recodings, can be correlated with age and gender, permitting establishments of normal gender-specific limits for children and adolescents.

Study of Cardiac Rate and Rhythm Patterns in Ambulatory and Hospitalized Children

Our aim was to underline possible differences in heart rate and rhythm patterns between ambulatory and hospitalized children. Holter monitoring was performed on 264 healthy ambulatory children and on 112 children who were hospitalized for noncardiotoxic conditions. Maximal, mean and minimal heart rates decreased with age. Maximal heart rate was significantly higher in ambulatory schoolchildren and adolescents than in hospitalized ones. Sinus arrhythmia was noted on every recording. Some children had episodes of first- or second-degree atrioventricular block while sleeping. Supraventricular and uniform ventricular extrasystoles were common. The incidence of all types of arrhythmia and conduction disturbances was similar in ambulatory and hospitalized children. These data can be taken as a basis for the analysis of 24-hour electrocardiogram monitoring in ambulatory but also in hospitalized children.

Outcome of pregnancies in patients with anti-SSA/Ro antibodies: A study of 165 pregnancies, with special focus on electrocardiographic variations in the children and comparison with a control group

OBJECTIVE

Aside from congenital heart block (CHB), sinus bradycardia and prolongation of the corrected QT (QTc) interval have been reported in infants born to mothers with anti-SSA antibodies. To assess the pathologic nature of these manifestations, this study focused on electrocardiographic (EKG) variations in these children, comparing them with findings in a control group.

METHODS

We studied 165 consecutive pregnancies in 106 anti-SSA-positive women with connective tissue diseases (CTDs). EKGs obtained on 58 children of this group were compared with those obtained on 85 infants born to mothers with CTD who were negative for both anti-SSA and anti-SSB.

RESULTS

No statistically significant difference was seen between the 2 study groups with regard to gestational age, prematurity, birth weight, age of the children at the time of EKG, age of the mothers, or treatments received by the mothers during their pregnancies. Seven of 137 children developed cutaneous neonatal lupus syndrome; 1 child developed CHB (CHB risk of 1 in 99 [1%] if only the first prospectively observed pregnancy in women without a history of CHB is included in the analysis). For EKGs recorded during the first 2 months of life, the mean +/- SD PR interval was 96 +/- 16 msec in the anti-SSA-positive group and 96 +/- 13 msec in the anti-SSA-negative group (P = 0.84), with mean QTc values of 397 +/- 27 and 395 +/- 25 msec (P = 0.57) and mean heart rates of 141 +/- 23 and 137 +/- 21 beats per minute (P = 0.20), respectively. No difference in the PR interval, QTc interval, or heart rate was observed for EKGs obtained between 2 and 4 months of life. When EKGs obtained at 0-2 months were compared with those obtained at 2-4 months, a physiologic prolongation of the QTc interval was observed in both study groups. No sudden infant death or symptomatic arrhythmia occurred during the first year of life.

CONCLUSION

The EKG findings in children of anti-SSA-positive and anti-SSA-negative mothers were not significantly different. Our results suggest that the prolongation of the QTc interval and sinus bradycardia that have recently been reported in children of mothers with anti-SSA antibodies occur independently of the anti-SSA antibodies. The pathologic nature of these EKG variations was not confirmed by our controlled study.

Differential diagnosis and management of the fetus and newborn with an irregular or abnormal heart rate

This article separately discusses the differential diagnosis and management of irregular or abnormal heart rate in both the fetus and the newborn. Conditions covered include ectopic beats, tachyarrythmias,atrial flutter, bradyarrythmias, tachycardia, congenital atrioventricular block, long QT syndrome, and bradycardias,among others.

[Neonatal lupus syndrome: review of the literature]

PURPOSE

Neonatal lupus syndrome include skin lesions, hematological and hepatic disorders, and congenital heart block (CHB) in the absence of severe cardiac malformation. This rare disorder is closely linked to transplacental transport of anti-SSA/Ro and anti-SSB/La maternal antibodies.

CURRENT KNOWLEDGE AND KEY POINTS

The prevalence of CHB in newborns of anti-Ro/SSA positive women with known connective tissue disease is 2% and the risk of recurrence ranges from 10 to 17%. Skin and systemic lesions are transient, whereas CHB is definitive and is associated with significant morbidity and mortality (estimated at 16-19%). A pacemaker must be implanted in 2/3 of cases. Myocarditis may be associated or may appeared secondarily. Mothers of children with CHB are usually asymptomatic or have Gougerot-Sjögren, or undifferentiated connective tissue disease. Mothers of children with cutaneous manifestations may present with more severe disease and systemic lupus erythematosus. In anti-Ro/SSA positive pregnant women, echocardiograms should be performed at least every 2 weeks from 16 to 24 weeks gestation. Electrocardiogram should be performed for all children.

FUTURE PROSPECTS AND PROJECTS

The efficiency of prophylactic treatment of CHB is not established. Therapy for CHB detected in utero is not standardized and involves fluorinated steroids (especially betamethasone).

Treatment of fetal tachycardia with sotalol: transplacental pharmacokinetics and pharmacodynamics

OBJECTIVES

The aim of this study was to investigate the pharmacokinetics and pharmacodynamics of sotalol in the treatment of fetal tachycardia.

BACKGROUND

Maternally administered, intrauterine therapy of fetal tachycardia is dependent on the transplacental passage of the antiarrhythmic agent.

METHODS

In a prospective study of patients treated for fetal tachycardia with sotalol, concentrations of sotalol were determined in maternal and umbilical blood and in amniotic fluid, and the relationship between these concentrations and the occurrence of conversion to sinus rhythm was investigated.

RESULTS

Eighteen fetal patients were studied, nine with atrial flutter and nine with supraventricular tachycardia. Fourteen were treated with sotalol; 13 converted to sinus rhythm, of whom 2 relapsed. There was one intrauterine death. Four patients were treated with sotalol and digoxin, of whom two were treated successfully. Mean birth weight was 3,266 g. The daily maternal sotalol dose was linearly related to the maternal plasma concentration. The mean fetal/maternal sotalol plasma concentration was 1.1 (range 0.67 to 2.87, SD 0.63), and the mean amniotic fluid/fetal blood ratio of sotalol was 3.2 (range 1.28 to 5.8, SD 1.4). The effectiveness of sotalol therapy could not be extrapolated from maternal blood levels.

CONCLUSIONS

Sotalol is a potent antiarrhythmic agent in the treatment of fetal tachycardia. The placental transfer is excellent. Sotalol accumulates in amniotic fluid but not in the fetus itself. Therefore it seems that renal excretion in the fetus is efficient and greater than the oral absorption by fetal swallowing. The maternal blood level is not a reliable predictor of the chances of success of therapy. Sotalol is not associated with fetal growth restriction.

Neonatal bradycardia

Heart rate monitoring has become a ubiquitous part of fetal and neonatal assessment, and has made detection of bradycardia in the fetal and neonatal periods a frequent occurrence. Evaluation of a fetus or neonate with bradycardia requires an understanding of the mechanisms of bradycardia as well as the cardiac and non-cardiac causes of bradycardia. The mechanisms of bradycardia include sinus bradycardia, abnormalities of sinus node function and abnormalities of atrioventricular conduction. In the instances where sinus bradycardia is pathologic, it usually results from non-cardiac disease. Sinus node dysfunction is rare early in life but can arise from surgical interventions, congenital heart disease, or endovascular manipulations. Abnormalities of atrioventricular conduction have a similar etiology but are more common than sinus node disease. Atrioventricular nodal disease can also result from maternal collagen vascular disease, even in the absence of symptoms in the mother. In these cases, epidemiological issues such as heart block in subsequent pregnancies and the maternal risk of developing symptomatic collagen vascular disease become important. The approach to treatment and long-term prognosis for bradycardia in the neonate is highly dependent on the underlying etiology and on the presence of concurrent factors such as structural heart disease.

Cardiac conduction abnormalities and rhythm changes after neonatal anatomical correction of transposition of the great arteries

Seventy three infants who underwent neonatal anatomical correction for transposition of the great arteries with or without a ventricular septal defect were reviewed for evidence of conduction and rhythm abnormalities on preoperative and postoperative 12 lead electrocardiograms and during 24 hour Holter monitoring. There was a partial right bundle branch block pattern in 47% (29/62) of all patients and in 60% (24/40) of those with simple transposition. Complete right bundle branch block was noted in 21% including 5% with simple transposition. Holter monitoring showed sinus rhythm in all patients except three: one had episodes of supraventricular tachycardia, another an intermittent second degree heart block, and a third a complete heart block. Atrial extrasystoles were noted in 47% (29/62) of patients but were frequent in only three patients. Occasional unifocal ventricular extrasystoles were encountered in 37% (23/62) of patients and were frequent in a further 3% (2/62). Only one patient (2%) developed multifocal ventricular extrasystoles. The frequency of important cardiac arrhythmias after neonatal anatomical correction of transposition of the great arteries was 5%, significantly less than that reported after atrial inflow diversion for the same malformation.

An electrocardiographic midterm follow-up study after anatomic repair of transposition of the great arteries

Prospective studies of rhythm and conduction, before and after 1-stage anatomic repair of simple transposition of the great arteries, were performed on 24 survivors. Pre- and postsurgical serial standard electrocardiograms were obtained on each patient. Fourteen patients underwent perioperative 24-hour electrocardiograms; all had follow-up 24-hour electrocardiograms. Rare atrial or occasional ventricular premature complexes were detected in 3 (11%) patients before operation. After surgery, 1 patient developed right bundle branch block. Two patients developed a left bundle branch block. One patient had a QS pattern in V6, which disappeared on follow-up electrocardiogram. Transient second-degree atrioventricular block was detected in 1 patient. A normal P-R interval and P-wave axis were present in all but 1 patient. Mild sinus bradycardia or rare atrial or ventricular premature complexes were detected in 4 of twenty-nine 24-hour electrocardiograms performed in the first 2 years after surgery. At 3 years after repair, 5 patients had a normal 24-hour electrocardiogram and 1 had low-grade ectopy (rare atrial and ventricular premature complexes). At 4 years, all 4 patients studied had normal 24-hour electrocardiograms. During a mean follow-up of 3 years, we have yet to document any symptomatic arrhythmias.

Cardiac arrhythmias in healthy children revealed by 24-hour ambulatory ECG monitoring

Ambulatory electrocardiographic monitoring was performed on 360 healthy children, from newborn infants to junior high school students. They were divided into five groups by age: group A, 63 newborn infants on the first day of life; group B, 50 infants aged 1-11 months; group C, 53 kindergarten pupils aged 4-6 years; group D, 97 primary school pupils aged 9-12 years; and group E, 97 junior high school students aged 13-15 years. The maximal and minimal heart rates were significantly greater in infants than in older children. Sinus arrhythmia was recorded in every child. One boy in group E had an episode of sinus arrest for three seconds without any symptoms. First-degree and Wenckebach type second-degree atrioventricular blocks were not detected in group A and group B, but were most frequent in group E, especially during sleep. Supraventricular premature contractions (SVPCs) were the most common type of arrhythmia detected in this study. More than half of the children had at least one SVPC per 24-h monitoring period, and there were many children with frequent SVPCs in group E. The incidence of ventricular premature contractions (VPCs) in children of groups A and E was rather higher than in the other groups. Ventricular tachycardia was not recorded in any child except one newborn infant who had a couplet of VPCs without symptoms. Each group had different types and incidences of arrhythmias. There was a rising incidence of arrhythmias with advancing age, except in the neonatal period.

Modes of onset ("initiating events") for paroxysmal atrial tachycardia in infants and children

Observations of spontaneous onset of paroxysmal atrial tachycardia (PAT) in infants and children have been infrequently reported. This study reports on modes of spontaneous onset of PAT in 22 infants and 8 children in whom onset of PAT was recorded during continuous electrocardiographic recording. During PAT, all 30 patients used the normal specialized atrioventricular conduction system for ventricular activation, with atrial activation occurring through an accessory atrioventricular connection (orthodromic reciprocating tachycardia). Wolff-Parkinson-White syndrome was present in 7 patients. Analysis of the mode of onset of PAT revealed that infants initiated PAT with atrial extrasystoles or sinus acceleration (a gradual shortening of the P-P interval). In 10 infants more than 10 PAT onsets were recorded, and in these infants the mode of onset was sinus acceleration. In 7 infants, both atrial extrasystole and sinus acceleration were observed to initiate PAT. In the older children, onset of PAT followed atrial extrasystole (3 patients), ventricular extrasystole (2 patients), and sinus pause with junctional escape (3 patients). It has been previously recognized that the natural history of these "initiating events" varies with patient age. Variations in frequency of spontaneous episodes of PAT may relate to chronologic variations in frequency and type of initiating events.

The effect of caffeine on cardiac rate, rhythm, and ventricular repolarization. Analysis of 18 normal subjects and 18 patients with primary ventricular dysrhythmia

To determine clinical electrophysiologic effects of a moderate dose of caffeine, we compared prevailing cardiac rhythm and rate, the prevalence and frequency of ventricular dysrhythmia, and Q-T intervals in two populations over an initial 24-hour caffeine-free period and a subsequent 24-hour period in which caffeine was ingested in a dosage of 1 mg/kg of body weight at intervals of one half-life during waking hours. Group 1 was composed of 18 clinically normal subjects; group 2 was 18 subjects with frequent ventricular ectopic beats (VEBs) and no (n = 16) or minor (n = 2) cardiac disease. Sinus rhythm was the prevailing rhythm in all subjects at all times. For group 1, the mean sinus rate during the caffeine-free period was 77 +/- 10 beats per minute, compared to 73 +/- 9 beats per minute during the period of caffeine ingestion (not significant). Similarly, for group 2, the average sinus rate during the caffeine-free period was 76 +/- 11 beats per minute, not significantly different from the average sinus rate during the test period, 76 +/- 10 beats per minute. During abstention from caffeine, four of 18 subjects in group 1 had infrequent (less than 1/hr) VEBs, compared to nine of 18 during caffeine ingestion (not significant). In group 2, some 16 of the 18 subjects had VEBs during the caffeine-free period, with the frequencies varying from less than one VEB per hour to 1,449 VEBs per hour. During the test period, 14 of the 18 subjects in group 2 increased their VEB frequency, and the group's mean frequency rose from 207 +/- 350 VEBs per hour (control period) to 307 +/- 414 VEBs per hour (test period) (p less than 0.01). The Q-T interval in group 1, measured as the corrected Q-T interval (Q-Tc), averaged 0.430 +/- 0.027 during the caffeine-free period, not significantly different from the test period (0.425 +/- 0.019). The comparable Q-Tc values for group 2 were 0.424 +/- 0.018 during the caffeine-free period and 0.433 +/- 0.025 for the period of caffeine ingestion (not significant).(ABSTRACT TRUNCATED AT 400 WORDS)

Two-dimensional and M-mode echocardiographic evaluation of fetal arrhythmia

Cardiac anatomy and rhythm were evaluated in the fetuses of 18 pregnant women (between 20 and 42 weeks of gestation) referred because of abnormal fetal heart rate or rhythm. Utilizing a 3 MHz two-dimensional scan head with M-mode capability, M-mode recordings were obtained at paper speeds of 50 and 100 mm/s from 16 fetuses. The arrhythmia of two fetuses was diagnosed using two-dimensional echo alone. Semilunar and atrioventricular valve opening and closing points, A waves, plus ventricular wall motion were used for timing purposes; and heart rate and rhythm were determined. Diagnoses made were atrial premature beats n = 3, ventricular premature beats n = 3, congenital heart block n = 4, supraventricular tachycardia n = 3, sinus bradycardia n = 1, and blocked atrial beats n = 1. In three fetuses no arrhythmia was identified. Cardiac anatomy was normal in 16 fetuses, with two (congenital heart block) felt to have univentricular hearts. Fourteen pregnancies went to term, two were delivered prematurely, and two fetuses with congenital heart block were stillborn. In three fetuses arrhythmia was confirmed during labor by fetal scalp electrode. Arrhythmia was absent after birth in 11 of 16 infants, with congenital heart block persistent in two infants, and supraventricular tachycardia, atrial premature beats, and blocked atrial premature beats remaining in one each. Intervention with medical management was attempted in four pregnancies, with successful termination of arrhythmia supraventricular tachycardia) in two fetuses. We conclude that combined two-dimensional M-mode capability is useful in the diagnosis of fetal rhythm disturbances, and perhaps in the selection of timing, and mode of intervention.

Cardiac rhythm, rate and ventricular repolarization properties in infants at risk for sudden infant death syndrome: comparison with age- and sex-matched control infants

Using 24-hour ambulatory electrocardiographic recordings and 120-lead body surface potential maps, prevailing cardiac rate and rhythm, incidence and frequency of dysrhythm and rate and pattern of ventricular repolarization at the body surface were compared in 17 infants at risk for sudden infant death syndrome (SIDS) and 17 age- and sex-matched control subjects. Sinus rhythm was the prevailing rhythm in both study groups and there were no intergroup differences in average overall awake or asleep sinus rates, nor in temporal variability of sinus rate. Atrial and ventricular ectopic activity were equally uncommon in both study groups. Although there were smooth and bipolar body surface distributions of ST-T and QRST time integrals in both study groups, the average rate of ventricular repolarization (QTc), measured from the 12-lead electrocardiogram, 120-lead body surface potential maps and 24-hour electrocardiography, was consistently shorter in the at-risk group than in the control group. However, temporal variability of QTc was not different between the 2 groups. Thus, significant cardiac dysrhythm and QT prolongation are not found in infants at increased risk for SIDS. Rather, there is an abbreviated ventricular repolarization interval in at-risk infants. In combination with the findings of intergroup similarity of average sinus rate and temporal variability of sinus rate and ventricular repolarization rate, the data suggest a subtle, constant difference in cardiac autonomic activity, most likely an increase in sympathetic tone, in at-risk subjects. The role of this altered cardiac autonomic activity in the causation of SIDS remains undetermined.

QT interval variability on the body surface

To assess the effects of measurement methodology on QT determinations and to define the spectrum of QT values, including interlead variability, on the body surface, we measured QT in each of 120 simultaneously-recorded, signal-averaged ECG leads in 10 normal subjects and 14 patients with QT prolongation (lead II QTc greater than 440). Two separate, but related, methods of QT measurement were utilized. Method A was a relatively conventional technique in which ST-T offset was defined as the time instant of return of the T wave to a P-P baseline, or as the point of U-on-T intersection. Method B was a more rigorous method, which defined ST-T offset in a similar manner, and in addition discarded from analysis all QT values from leads with monophasic ST-T waveform in which the QT values were greater than the longest QT from leads with definite U waves. Method B was utilized to minimize factitious prolongation of QT by inapparent U-on-T. By both methods the mean body surface QTc values were significantly greater (p less than 0.001) in the patient group (482 +/- 65 [S.D.] msec, method A; 447 +/- 43 msec, method B), than in the normal subject group (399 +/- 14 msec, method A; 396 +/- 12, method B). Interlead QTc variability (difference between the longest and shortest QT) was considerable with both methods and in both study groups. Expressed as percent of average body surface values, the mean interlead QTc variability in normal subjects averaged 22 percent with method A and 19 percent with method B; in the patient group, however, it averaged 32 percent with method A and only 18 percent with method B. In absolute terms, the mean variability in the patient group with method A (155 +/- 62 msec) was significantly greater (p less than 0.001) than that of the normal group (89 +/- 33 msec); with method B, interlead variability was the same (p = NS) in the normal (76 +/0 27 msec) and patient groups (80 +/- 44 msec). This latter finding suggests the possibility that the repolarization abnormality in patients with QT prolongation may occur relatively uniformly throughout the ventricular myocardium. Thus, measurement techniques are important in multiple-lead QT determinations. Although reduced by techniques designed to minimize factitious QT prolongation, interlead QT variation is considerable over the torso surface, in both normal subjects and patients with repolarization abnormalities.(ABSTRACT TRUNCATED AT 400 WORDS)

Incidence and significance of primary abnormalities of cardiac rhythm in infants at high risk for sudden infant death syndrome

The exact relationship between cardiac arrhythmias and sudden infant death syndrome (SIDS) is uncertain. Several reports have implicated both ventricular and supraventricular arrhythmias in isolated cases, but there have been no studies of the incidence or type of arrhythmias that occur in populations at risk for SIDS. Of 1699 infants at high risk for SIDS, 60 (4%) were found to have a primary cardiac arrhythmia (i.e., not associated with disordered respiration or apnea). The incidence of atrial and ventricular premature beats, supraventricular tachycardia, and Wolff-Parkinson-White syndrome was similar to the incidence found in normal infants. Primary bradycardia (defined as a heart rate less than 60 for greater than 10 s not associated with abnormal respiration) was the most common arrhythmia, occurring with a frequency and severity not seen in normal infants. Thirty-two infants experienced periodic bradycardia. In 19 of these latter infants, there were symptoms associated with these bradyarrhythmias that necessitated treatment. Heart rates as low as 20 beats/min were recorded. One infant presented with an episode of ventricular fibrillation and on further evaluation was noted to have recurrent bradyarrhythmias. In no infant was there abnormal prolongation of the QT interval. Primary bradyarrhythmias are seen at an increased incidence in infants at high risk for SIDS and may play a causal role in this syndrome. Most symptomatic infants can be adequately controlled with sympathomimetic or parasympatholytic therapy. Other cardiac arrhythmias occur at a rate similar to that in normal infants and are therefore unlikely to play a major role in SIDS.

Frequent ventricular ectopic activity without underlying cardiac disease: analysis of 45 subjects

Forty-five subjects, aged 2 weeks to 62 years, who presented with frequent (greater than 100/day) ventricular ectopic beats (VEBs) and without evidence of underlying cardiac disease were studied. The spectrum of ventricular dysrhythmia was assessed by 24-hour ambulatory electrocardiography and exercise tolerance test. Sinus rhythm was the prevailing rhythm in all subjects. VEB frequency averaged 444 +/- 454 per hour (range 0 to 1,863) over the 24-hour monitoring period and was not significantly different during waking or sleeping periods. There was no simple correlation of VEB frequency with prevailing sinus rate (r = -0.0006; p = not significant [NS]). The prevalence of complex VEBs (multiform, R-on-T and repetitive) was relatively high (18 of 45 patients), and was equally distributed about the median VEB frequency of 314 VEBs/hour (7 of 18 versus 11 of 18; NS). Of the 43 subjects who had exercise tests, 37 had VEBs during the preexercise rest phase, compared with only 11 at peak exercise (p less than 0.0001). To assess the short-term natural history of the VEBs, 27 subjects had repeat clinical examinations and 24-hour electrocardiograms at a mean interval of 8 months. All remained well. Although there was considerable individual temporal variability of VEB frequency in this subgroup, there was no significant change in group mean values (415 +/- 409 VEBs/hour initially versus 401 +/- 383 VEBs/hour at follow-up study; NS). The relative temporal constancy of VEB frequency in the group as a whole was also reflected in a high linear correlation of VEB frequency at initial and follow-up studies (r = 0.816; p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)