Comparison of cardiac refractory periods in children and adults

Biomimetic cultivation of atrial tissue slices as novel platform for in-vitro atrial arrhythmia studies

Living myocardial slices (LMS) are beating sections of intact human myocardium that maintain 3D microarchitecture and multicellularity, thereby overcoming most limitations of conventional myocardial cell cultures. We introduce a novel method to produce LMS from human atria and apply pacing modalities to bridge the gap between in-vitro and in-vivo atrial arrhythmia studies. Human atrial biopsies from 15 patients undergoing cardiac surgery were dissected to tissue blocks of ~ 1 cm² and cut to 300 µm thin LMS with a precision-cutting vibratome. LMS were placed in a biomimetic cultivation chamber, filled with standard cell culture medium, under diastolic preload (1 mN) and continuous electrical stimulation (1000 ms cycle length (CL)), resulting in 68 beating LMS. Atrial LMS refractory period was determined at 192 ± 26 ms. Fixed rate pacing with a CL of 333 ms was applied as atrial tachyarrhythmia (AT) model. This novel state-of-the-art platform for AT research can be used to investigate arrhythmia mechanisms and test novel therapies.

Resting membrane potential is less negative in trabeculae from right atrial appendages of women, but action potential duration does not shorten with age

AIMS

The incidence of atrial fibrillation (AF) increases with age. Women have a lower risk. Little is known on the impact of age, sex and clinical variables on action potentials (AP) recorded in right atrial tissue obtained during open heart surgery from patients in sinus rhythm (SR) and in longstanding AF. We here investigated whether age or sex have an impact on the shape of AP recorded in vitro from right atrial tissue.

METHODS

We performed multivariable analysis of individual AP data from trabeculae obtained during heart surgery of patients in SR (n = 320) or in longstanding AF (n = 201). AP were recorded by sharp microelectrodes at 37 °C at 1 Hz. Impact of clinical variables were modeled using a multivariable mixed model regression.

RESULTS

In SR, AP duration at 90% repolarization (APD₉₀) increased with age. Lower ejection fraction and higher body mass index were associated with smaller action potential amplitude (APA) and maximum upstroke velocity (V_max). The use of beta-blockers was associated with larger APD₉₀. In tissues from women, resting membrane potential was less negative and APA as well as V_max were smaller. Besides shorter APD₂₀ in elderly patients, effects of age and sex on atrial AP were lost in AF.

CONCLUSION

The higher probability to develop AF at advanced age cannot be explained by a shortening in APD₉₀. Less negative RMP and lower upstroke velocity might contribute to lower incidence of AF in women, which may be of clinical relevance.

Assessment of age, gender, and anxiety on ECG waveform morphology in a large population of domestic dogs

Cardiovascular diseases are major causes of death in the western world and this incidence increases in the elderly population. With aging, there are physiologic changes to the cardiac structure secondary to adipose tissue deposition, calcification of valve leaflets and changes in the structure of the heart including atrial remodeling. Such changes can make the myocardium more susceptible to stress leading to a higher prevalence of cardiovascular diseases in the aging population. Studies in healthy humans have shown that these structural and molecular changes in the heart are manifested as changes on an electrocardiogram (ECG). Using animal models, similar ECG changes have been found in guinea pigs, rabbits, and mice. No veterinary study has specifically evaluated if comparable aging changes occur in canine species. In this cross-sectional retrospective study, 12,026 ECGs from apparently healthy dogs were obtained and evaluated. Age was observed to have both linear and non-linear associations with multiple ECG variables, including P wave amplitude and duration, R amplitude and QRS duration. This study confirmed that, like humans, there may be ECG changes secondary to normal physiological cardiac aging. Further studies are warranted to confirm and elaborate on these findings as canines may be a useful model for cardiac aging in humans.

Pattern of recovery for transient complete heart block after open heart surgery for congenital heart disease: duration alone predicts risk of late complete heart block

Transient complete heart block (TCHB) is defined as complete interruption of atrioventricular conduction (AVC) after cardiac surgery followed by return of conduction. This study aimed to assess the risk for the development of late complete heart block (LCHB) after recovery of TCHB and to examine the electrocardiographic and electrophysiologic properties of the AVC system after TCHB. Of the 44 patients in this study who experienced TCHB, 37 recovered completely. Seven patients progressed from TCHB to intermittent CHB or LCHB requiring pacemaker implantation. Preoperative, early postoperative, and late postoperative electrocardiograms as well as postoperative atrial stimulation were obtained. The results showed that the median duration of TCHB was 5 days in the TCHB group compared with 9 days in the LCHB group (p = 0.01). All 37 subjects with TCHB recovered AVC within 12 days, but only two with LCHB did so (p = 0.02). The risk of LCHB for the patients with 7 days of postoperative TCHB or longer was 13 times greater than for the patients with fewer than 7 days of TCHB (p = 0.01). The median late postoperative PR interval was slightly but significantly longer in the LCHB group than in the TCHB group (p = 0.02). In contrast, the electrophysiologic properties between the two groups did not differ significantly. From those findings, we concluded that delayed recovery of AVC after surgical TCHB (≥7 days), but not electrophysiologic properties of recovered AVC assessed early in the postoperative period strongly, predicts risk of LCHB. Follow-up evaluation of AVC is particularly indicated for the delayed recovery group.

Electroanatomic remodelling of the pulmonary veins associated with age

AIMS

Increasing age is a significant risk factor for developing atrial fibrillation (AF). Pulmonary vein (PV) triggers are critical in the mechanism of AF, but little is known of the substrate changes that occur within the PVs with ageing. Therefore, we sought to identify whether ageing is associated with electroanatomic changes within the pulmonary veins.

METHODS AND RESULTS

Twenty-five patients undergoing ablation for left-sided supraventricular tachycardia had high-density 3D electroanatomic maps of all four PVs created. Patients were divided into two groups: group 1 aged <50 years and group 2 aged >50 years. Mean-voltage (MV), % low-voltage (LV < 0.5 mV), conduction, signal complexity, and PV muscle sleeve length and diameter were assessed. Age was 33 ± 8 vs. 66 ± 8 years for groups 1 and 2, respectively (P < 0.001). Group 2 demonstrated: (i) lower MV within the PVs (1.66 ± 1.1 vs. 1.88 ± 1.1 mV, P < 0.001); (ii) increased % LV (5.0 vs. 1.1%, P < 0.001), and increased voltage heterogeneity within the PVs (65 ± 14 vs. 55 ± 8%, P < 0.05); (iii) regional and global conduction slowing in the PVs; and (iv) increased % complex signals within the PVs (1.4 vs. 0.4%, P = 0.009). There was no difference in PV sleeve length or diameter.

CONCLUSION

Increasing age is associated with PV electroanatomic changes characterized by a significant reduction in PV voltage, conduction slowing, and increasing signal complexity. These observations provide new insights into the potential mechanisms behind the increased prevalence of AF with advancing age.

Functional characteristics and inducibility of atrioventricular nodal re-entry in rabbits of different ages

AIMS

Many issues regarding atrioventricular nodal re-entry (AVNR) remain unexplored; however, no stable animal model for the study of AVNR has yet been developed. Clinically, AVNR is found more commonly in adults than children. We attempt to characterize AV nodal functional properties and inducibility of AVNRT using rabbits of three different age groups since we hypothesize that the inducibility of AVNR may increase as the subject ages.

METHODS AND RESULTS

We evaluated the inducibility of AVNR and the functional characteristics of the AV node in 6-month-old (Group 1), 2-month-old (Group 2), and at 1-week-old (Group 3) rabbits using a well-established rabbit heart model. We found that the inducibility of AVNR was higher in the 2-month-old group, compared with the 1-week-old group (30%). There was no functional difference between the two older groups (6-month-old and 2-month-old groups), however the youngest group (Group 3) showed better AV nodal functional properties. Regarding the correlation between inducibility and nodal functional properties, subgroups with AVNR demonstrated a longer AH maximum (AHmax) compared with the non-re-entry group, although there is no difference in age-adjusted AHmax. Regarding the correlation between inducibility and nodal functional properties, for the 1-week-old rabbits, subgroups with AVNR demonstrated a shorter AH minimum compared with the non-re-entry group (39.0 vs. 61.0, P=0.017).

CONCLUSION

Our results demonstrate that both 2-month-old and 6-month-old rabbits represent stable models for AVNR. Longer AH conduction time may lead to greater re-entry inducibility.

Rate-dependent AV nodal refractoriness: a new functional framework based on concurrent effects of basic and pretest cycle length

The atrioventricular (AV) node filters atrial impulses. Underlying rate-dependent refractory properties are assessed with the effective (ERPN; longest nonconducted atrial cycle length) and functional (FRPN; shortest His bundle cycle) refractory period determined with premature protocols at different basic rates. Fast rates prolong ERPN and shorten FRPN, but these effects vary with subjects, age, and species. We propose that these opposite and variable effects reflect the net sum of concurrent cumulative and noncumulative effects associated with basic (BCL) and pretest cycle length (PTCL), respectively. To test this hypothesis, we assessed selective and combined effects of five BCL (S1S1) and six PTCL (S1S2) on ERPN, FRPN, and their subintervals (ERPN = A2H2 + H2A3 and FRPN = H2A3 + A3H3, where A is atrium and H is His bundle) with S1S2S3 protocols in six rabbit heart preparations. At control BCL, PTCL shortenings prolonged ERPN (113 ± 12 vs. 101 ± 14 ms, P < 0.01) as a net result of prolonged A2H2 and curtailed H2A3. At control PTCL, BCL shortenings increased ERPN (127 ± 20 vs. 101 ± 14 ms, P < 0.01) by prolonging A2H2. FRPN did not vary with BCL but decreased (163 ± 6 vs. 175 ± 10 ms, P < 0.01) with PTCL that curtailed H2A3. Equal BCL and PTCL shortenings as in standard protocols prolonged ERPN but left FRPN unchanged. Notably, ERPN and FRPN significantly correlated through their H2A3 subinterval. In conclusion, BCL and PTCL are both important determinants of AV nodal refractoriness and together account for rate-induced changes in ERPN and FRPN observed during standard premature protocols. ERPN and FRPN are related variables. Similar functional rules may govern nodal refractory behavior during supraventricular tachyarrhythmias.

Complete heart block due to Lyme carditis in two pediatric patients and a review of the literature

Carditis is a common manifestation of adult patients with Lyme disease affecting 4-10% of Lyme patients in the United States. However, children with Lyme disease rarely present with acute carditis. The management of pediatric patients with complete heart block (CHB) secondary to Lyme carditis has not been well described. We report the acute management of 2 pediatric patients that presented in CHB secondary to Lyme disease.

Atrioventricular nodal reentrant tachycardia in children

The purpose of this study was to identify the clinical and electrophysiological characteristics of children with atrioventricular reentry tachycardia (AVNRT) and to define the prognosis and the treatment strategy. Sixty-two children (28 males and 34 females mean age, 10.2 +/- 3.2 years) with AVNRT ("slow-fast" type) were included in the study. Patients were divided into two groups: 47 patients with severe symptoms (group A) and 15 with mild symptoms (group B). The severity of the symptoms was not related to the electrophysiological parameters. Females were more symptomatic than males. Patients in group B did not receive any treatment (except 1 because of parents' choice) nor did they develop symptoms, and 5 patients had resolution of palpitations. Forty-one of 46 patients in group A were successfully treated with medical therapy as initial treatment. Thirty-one patients in group A underwent slow pathway ablation. There were late recurrences of AVNRT in 6 patients. Typical AVNRT in young patients does not appear to be life threatening. Patients with mild or no symptoms do well without therapy. Medical therapy and slow pathway ablation appear to be effective in the more symptomatic patients. Age and electrophysiological variables are not related to the symptoms or response to treatment. Females with AVNRT are more symptomatic and more likely to present with syncope.

Electrophysiologic and electroanatomic changes in the human atrium associated with age

OBJECTIVES

The purpose of this study was to characterize the pattern of atrial remodeling seen with human aging.

BACKGROUND

Atrial fibrillation (AF) occurs in 3% to 4% of the population over 65 years of age. It is associated with thromboembolic complications, worsening heart failure, and increased mortality, yet the electrical and structural remodeling that occurs with human aging remains unknown.

METHODS

Thirteen patients (66.4 +/- 1.7 years) > or =60 years (group A), 13 patients (50 +/- 2.1 years) age 31 to 59 years (group B), and 15 patients (24.7 +/- 1.0 years) < or =30 years (group C) underwent conventional electrophysiologic studies and electroanatomic mapping. We measured atrial refractoriness (ERP) at the distal coronary sinus (CS); low and high lateral right atrium (LRA) and the high septal right atrium at 600, 500, and 400 ms; maximum corrected sinus node recovery time (CSNRT); P-wave duration (PWD); conduction time (CT) along the CS and LRA; and discrete double potentials (DP) along the crista.

RESULTS

Aging was associated with an increase in atrial ERP, prolonged CT along the CS, increased PWD and CSNRT. There was no significant change in dispersion of refractoriness or rate adaptation. Electroanatomic mapping revealed diffuse areas of low voltage with regional conduction slowing. Both techniques demonstrated a greater number of DPs and fractionated signals along the crista terminalis with aging.

CONCLUSIONS

Aging is associated with regional conduction slowing, anatomically determined conduction delay at the crista, and structural changes that include areas of low voltage. In addition, impairment of sinus node function and an increase in atrial ERP occurred with aging. This electrical and structural remodeling may explain the increased propensity to AF with aging.

Maturational atrioventricular nodal physiology in the mouse

INTRODUCTION

Dual AV nodal physiology is characterized by discontinuous conduction from the atrium to His bundle during programmed atrial extrastimulus testing (A2V2 conduction curves), AV nodal echo beats, and induction of AV nodal reentry tachycardia (AVNRT). The purpose of this study was to characterize in vivo murine maturational AV nodal conduction properties and determine the frequency of dual AV nodal physiology and inducible AVNRT.

METHODS AND RESULTS

A complete transvenous in vivo electrophysiologic study was performed on 30 immature and 19 mature mice. Assessment of AV nodal conduction included (1) surface ECG and intracardiac atrial and ventricular electrograms; (2) decremental atrial pacing to the point of Wenckebach block and 2:1 conduction; and (3) programmed premature atrial extrastimuli to determine AV effective refractory periods (AVERP), construct A2V2 conduction curves, and attempt arrhythmia induction. The mean Wenckebach block interval was 73 +/- 12 msec, 2:1 block pacing cycle length was 61 +/- 11 msec, and mean AVERP100 was 54 +/- 11 msec. The frequency of dual AV nodal physiology increased with chronologic age, with discontinuous A2V2 conduction curves or AV nodal echo beats in 27% of young mice < 8 weeks and 58% in adult mice (P = 0.03).

CONCLUSION

These data suggest that mice, similar to humans, have maturation of AV nodal physiology, but they do not have inducible AVNRT. Characterization of murine electrophysiology may be of value in studying genetically modified animals with AV conduction abnormalities. Furthermore, extrapolation to humans may help explain the relative rarity of AVNRT in the younger pediatric population.

Age related changes in dual AV nodal physiology

Dual atrioventricular nodal (DAVN) physiology has been reported in up to 63% of pediatric patients with anatomically normal hearts, yet atrioventricular nodal reentrant tachycardia (AVNRT) accounts for only 13%-16% of supraventicular tachycardia (SVT) in childhood. The incidence of AVNRT increases with age and becomes the most common form of SVT by adolescence. We investigated the age related electrophysiological responses to programmed atrial and ventricular stimulation in 14 pediatric patients who underwent intracardiac electrophysiological study prior to radiofrequency catheter ablation for AVNRT and who exhibited DAVN physiology. Single atrial and ventricular extrastimuli were placed following drive trains with cycle lengths of 400-700 ms and 350-500 ms, respectively. Six children (mean age 8.2 years, range 5.2-11.5 years) were compared to eight adolescents (mean age 16.6 years, range 13.3-20.7 years). Adolescents were found to have a significantly longer fast pathway effective refractory period (ERP) (median 375 vs 270 ms, P = 0.03), slow pathway ERP (median 270 vs 218 ms, P = 0.04), atrio-Hisian (AH) during AVNRT (median 300 vs 225 ms, P = 0.007), and AVNRT cycle length (median 350 vs 290 ms, P = 0.03). There was a strong trend for the AH measured at the fast pathway ERP to be longer in adolescents than in children (median 258 vs 198 ms, P = 0.055). The AH at the fast pathway ERP was more strongly correlated with baseline cycle length than with age (r = 0.7, P = 0.01 vs r = 0.5, P = 0.7). There was no significant difference in the retrograde VA conduction between adolescents and children. These results demonstrate an age related difference in AV nodal response to programmed atrial stimuli in pediatric patients with DAVN physiology and AVNRT. These differences are consistent with mechanisms that may explain the increased incidence of AVNRT in adolescents compared to children.

Developmental changes of atrioventricular nodal recovery properties

Atrioventricular (AV) nodal recovery properties can be studied by a periodic premature stimulation protocol performed at a slow basic rate. Developmental aspects of these properties have not been determined. The purpose of this study was to determine the developmental changes of AV nodal recovery properties. Forty-three children and young adults (male:female ratio 25:18) without AV nodal disease (aged 3.3 to 21.9 years) were studied by delivering premature atrial extrastimuli coupled to basic driven atrial beats. The individual recovery curve was fitted to the equation: A2H2 = A0H0 + exp(alpha -H1A2/tau) for H1A2 > or =theta, where A0H0 is the minimum AH interval, H1A2 is any recovery interval that exceeds the nodal effective refractory period, A2H2 is the corresponding nodal conduction time at any given H1A2, alpha is a constant, tau is the recovery time constant, and theta is the nodal effective refractory period. We found that: (1) A0H0 and alpha constant did not change significantly with age; (2) both tau (r = 0.324; p <0.05) and theta (r = 0.401; p <0.05) had a positive correlation with age; and (3) the maximum change in A2H2 with a 10-ms decrement in H1A2 was 32 ms and did not change significantly with age. Our results suggest that AV nodal recovery properties are age-dependent and both the recovery time constant and effective refractory period lengthen with age.

Electrophysiologic properties of the atrioventricular node in pediatric patients

OBJECTIVES

The purpose of this study was to characterize anterograde and retrograde properties of the atrioventricular (AV) node in children and to determine the presence of ventriculoatrial (VA) conduction and dual AV node pathways.

BACKGROUND

Although AV node reentry is common in adults, it accounts for 13% of pediatric supraventricular tachycardia (SVT). The age-related changes in the AV node with development are poorly understood. The incidence of dual AV node pathways and VA conduction in the pediatric population is unknown.

METHODS

Electrophysiologic studies were performed in 79 patients with normal hearts and no evidence of AV node arrhythmias. Patients were classified into two groups by age: group I = 49 patients (0.39 to 12.8 years old, mean [+/- SD] age 8.5 +/- 3.6); group II = 30 patients (13.4 to 20.0 years old, mean age 15.6 +/- 1.8).

RESULTS

There was a significant difference (p < 0.05) in the cycle length (CL) at which anterograde AV block occurred between group I (305 +/- 63 ms) and group II (350 +/- 91 ms). Sixty-one percent of children had VA conduction with no age-related differences. There was no significant difference in the mean CL of retrograde VA block (360 ms). The incidence of dual AV node pathways in group I was 15% and 44% in group II (p < 0.05).

CONCLUSIONS

These findings suggest that AV node electrophysiology undergoes maturational changes. The increase in AV node reentrant tachycardia in adults may relate to changes in the relative refractoriness and conduction of the AV node or to differences in autonomic input into the AV node that allow dual pathway physiology to progress to SVT.

Atrial fibrillation in the elderly

The prevalence of atrial fibrillation is 11% in persons older than 70 years and rises to 17% in those aged 84 years or more. One-year mortality ranges from 0.2 to 16%, being highest in elderly patients, and is associated with a 4.8-fold increased risk of stroke. Atrial fibrillation can be cardioverted to normal sinus rhythm electrically or pharmacologically and rapid ventricular rate can be controlled with drugs. While anti-coagulation prevents embolic events in those with atrial fibrillation, the decision to anticoagulate should be based on an assessment of the risk/benefit ratio.

Age- and anesthesia-related changes in accessory pathway conduction in children with Wolff-Parkinson-White syndrome

The anterograde effective refractory period of the accessory pathway is age-dependent in pediatric patients with the WPW syndrome. Thus, age should be considered when developing electrophysiologic criteria for the risk of hypotensive arrhythmias in these patients. In addition, general anesthesia must also be considered in interpreting age-related changes in the anterograde APERP, especially in children.

Atrial tachycardia in infants and children: electrocardiographic classification and its significance

An electrocardiographic classification of atrial tachycardia and its significance in children has not been reported. We reviewed the clinical histories and 12-lead surface electro-cardiograms (ECG) of 21 children with atrial tachycardia. Atrial rate and P-wave axis were determined for each patient. Some patients had features of typical atrial flutter (AF). Tachycardia was classified by atrial rate < 340/min or atrial rate > 340/min. Children with atrial tachycardia rate > 340/min consistently responded to conservative treatment (digoxin and/or cardioversion) without recurrences (p < 0.05 and p > 0.025); whereas in children with atrial rate < 340/min, only one case responded to conservative therapy. P-wave axis had no prognostic significance for either group. Additionally, high atrial rate (> 340/min) during tachycardia was noted in early infancy, compared to older children and adults, and probably represents the function of age. Classification of atrial tachycardia by rate is clinically useful for planning therapy and predicting response in children.

Electrophysiological abnormalities before and after surgery for atrial septal defect

The authors evaluated the electrophysiological parameters, atrial-His interval, His-ventricular interval, Wenckebach cycle length, corrected sinus node recovery time (CSNRT), and sinoatrial conduction time (SACT) before and after operation in 28 children with atrial septal defect (ASD). Before operation, electrophysiological abnormalities were detected in 20 (79%) of the 28 patients. Preoperative comparison of the mean value in each parameter between the two age groups showed higher values in all parameters in the older group. In 17 patients who underwent operation, atrial-His interval, Wenckebach cycle length, CSNRT, and atrial effective refractory period (AERP) significantly decreased after operation; preoperatively abnormal Wenckebach cycle length, CSNRT, and AERP values were normalized in many of them. Thus, electrophysiological abnormalities were already present before operation in the ASD children and were severer in the older children, but were improved to some degree following operation.

Electrophysiologic findings after Fontan repair of functional single ventricle

Cardiac arrhythmias are well recognized sequelae of the Fontan operation for complex congenital anomalies. In this study the electrophysiologic effects of the Fontan procedure were evaluated in 30 patients who underwent cardiac catheterization with electrophysiologic study 1.9 +/- 1.3 years (mean +/- SD) after modified Fontan repair for functional single ventricle. Abnormalities of sinus node or ectopic pacemaker automaticity were detected in 50% (15 patients) by determination of a prolonged corrected sinus node or pacemaker recovery time. Total sinoatrial conduction time was prolonged in 50% of the patients with normal sinus rhythm. Sinus node or ectopic atrial pacemaker function was entirely normal in only 43% of patients. The predominant atrial rhythm was normal sinus in 70% and ectopic atrial or junctional in 30%. Abnormalities of atrial effective and functional refractory periods were noted in 43% of patients and were most pronounced at faster paced cycle lengths. Atrial endocardial catheter mapping revealed intraatrial conduction delays between adjacent sites in 76% of the patients tested and in eight of nine patients with inducible intraatrial reentry. Programmed atrial stimulation induced nonsustained supraventricular arrhythmias in 10% of the 30 patients and sustained arrhythmias in 27%. Intraatrial reentry was the most common inducible arrhythmia and was present in seven of the eight patients with sustained and two of the three patients with nonsustained atrial arrhythmias. Atrioventricular conduction abnormalities were noted in 10% (three patients). No patient had inducible ventricular arrhythmias with programmed ventricular stimulation. The electrophysiologic findings after Fontan repair include abnormal sinus node function, prolonged atrial refractoriness, delayed intraatrial conduction and inducible atrial arrhythmias.(ABSTRACT TRUNCATED AT 250 WORDS)

Bundle branch block during orthodromic reciprocating tachycardia onset in infants

Transesophageal electrophysiologic studies were performed in 58 infants (age less than or equal to 1 year, median 10 days) with electrocardiographically documented orthodromic reciprocating tachycardia (ORT). The aim was to evaluate the occurrence, type and electrophysiologic effects of bundle branch block (BBB) during ORT onset. Of the 58 infants, 25 (43%) had BBB with pacing-induced tachycardia onset. BBB was initiated by single or double premature atrial extrastimuli and by burst atrial pacing; 4 infants also demonstrated BBB with spontaneous ORT onset during transesophageal study. Two of 25 infants had BBB only after intravenous procainamide. Comparison of the 25 infants exhibiting BBB at ORT onset with the 33 infants not demonstrating BBB revealed that age was not statistically different in the 2 groups, but that severity of illness (based on a 1 to 3 scale) was greater (p less than 0.05) and normal QRS ORT cycle length was shorter (p less than 0.02) in the infants with BBB. Of the 25 infants with BBB at ORT onset, 17 had left BBB, 3 had right BBB and 5 had both left and right BBB. Ventriculoatrial interval or cycle length increases during ORT with BBB in 16 of 25 (64%) infants suggested left free wall-accessory atrioventricular connections.(ABSTRACT TRUNCATED AT 250 WORDS)

The asymptomatic child a long time after the Mustard operation for transposition of the great arteries

We studied 36 asymptomatic children 7.7 +/- 2.5 years after a Mustard operation. Fifteen children had sinus rhythm on all electrocardiograms made during follow-up. Only 2 had normal 24-hour Holter recordings throughout follow-up, 6 had periods of supraventricular tachycardia, and 3 had periods of atrial flutter. The electrophysiological evaluation of sinus node function was normal in 5 of the 31 children who were studied. The behavior of the atrial myocardium was electrophysiologically abnormal in most of the children. Atrioventricular node function, on the contrary, was normal in nearly all of the children. Eleven children had normal hemodynamics. Four had severe or complete obstruction of the superior vena cava, 1 had a severe pulmonary venous obstruction, 3 had a severe left ventricular outflow tract obstruction, and 2 had a large left-to-right shunt. Only 3 children had normal hemodynamic and electrophysiological studies. We conclude that the absence of symptoms and a normal routine examination of children a long time after a Mustard operation does not exclude hemodynamic and electrophysiological abnormalities, which can sometimes be severe. In view of these disappointing results, we decided to replace the Mustard operation with the arterial switch operation in children with transposition of the great arteries.

Functional abnormalities of the conduction system in children with an atrial septal defect

We performed an electrophysiologic study in 40 children with an atrial septal defect and analyzed their pre- and postoperative electrocardiograms and 24-hour Holter recordings. The electrophysiologic study showed a prolonged corrected sinus node recovery time in 83% and an abnormal sinuatrial conduction time in 25% of the children. An early Wenckebach response to atrial pacing was seen in 18%. Sixteen percent had a prolonged atrial conduction time. The atrial functional refractory period was abnormal in 35%. Two children developed nonsustained supraventricular tachycardia during the electrophysiologic study. The preoperative electrocardiogram showed first-degree atrioventricular block in 15% of the children; prolonged periods of accelerated atrial rhythm were found in 35% of the preoperative 24-hour Holter recordings. The incidence of first-degree atrioventricular block and accelerated atrial rhythm decreased postoperatively. We could not find a significant correlation between age or shunt size and the presence of electrophysiologic abnormalities or arrhythmias. These results indicate that the sinus node, atrioventricular node and atrial myocardium show some degree of dysfunction in patients with an atrial septal defect. An early operation may prevent further progression of electrophysiologic abnormalities and the development of symptomatic arrhythmias.

Electrophysiologic consequences of the arterial switch repair of d-transposition of the great arteries

Electrophysiologic studies were performed at 12.7 +/- 4 months postoperatively in 20 patients who had the arterial switch repair at 1 to 120 days (mean 13 +/- 26 [SD]) for d-transposition of the great arteries. Preoperative electrocardiograms (ECGs) at rest revealed an ectopic atrial rhythm in one patient. Postoperative rest ECGs revealed transient postoperative ectopic atrial or junctional rhythms in two patients, intermittent ectopic atrial rhythms in two and right bundle branch block in nine with a normal QRS axis. In addition, ambulatory monitor recordings revealed infrequent premature ventricular complexes in five patients. Catheter endocardial mapping revealed sinus rhythm in 18 patients and ectopic atrial rhythm in 1 patient. Atrial activation after the switch repair was comparable with normal atrial activation. Activation of all low atrial sites was significantly earlier after the switch repair than after the Mustard repair. Mild abnormalities of sinus node function were present and consisted of slight prolongation of corrected sinus node recovery time in six patients and slightly increased sinoatrial conduction time in four. The ratio of sinus node recovery time to sinus cycle length was normal in all 20 patients. Atrial effective and functional refractory periods were normal in all patients and no atrial arrhythmias could be induced by programmed stimulation. Atrioventricular (AV) node conduction was excellent with normal AV node effective and functional refractory periods. The only electrophysiologic abnormality of His-Purkinje function was distal right bundle branch block in nine patients. Programmed stimulation of the ventricle produced repetitive ventricular responses in four patients: bundle branch reentry in three and intraventricular reentry in one.(ABSTRACT TRUNCATED AT 250 WORDS)

Inducible atrial flutter after the Mustard repair of complete transposition of the great arteries

Atrial flutter is a common postoperative arrhythmia in patients with complete transposition of the great arteries (d-TGA) after the Mustard repair. Sixty patients with d-TGA who had the Mustard repair were evaluated by electrophysiologic studies. Thirty-three (55%) had inducible sustained atrial flutter; 17 of them developed spontaneous clinical episodes of atrial flutter (clinical atrial flutter group) and 16 did not (nonclinical atrial flutter group). In 6 of the 17 patients (35%) with clinical inducible atrial flutter, the condition was first documented in the electrophysiologic laboratory with subsequent development of spontaneous clinical episodes. Catheter endocardial mapping, used to determine atrial activation sequences and and conduction intervals, revealed intraatrial conduction delays with late activation of the low atrial sites in all patients. Abnormalities of atrial refractoriness were present, with a greater dispersion of atrial refractoriness found in the clinical atrial flutter group. Severe abnormalities of sinus nodal function appeared to a significantly greater degree among patients who had clinical episodes of atrial flutter. These electrophysiologic abnormalities and associated arrhythmias may predispose patients with d-TGA to sudden death.

Electrophysiologic consequences of the Mustard repair of d-transposition of the great arteries

This study describes the electrophysiologic effects of the Mustard repair of d-transposition of the great arteries on the sinus node and on conduction and refractoriness in the atrium, atrioventricular (AV) node and ventricle. Seventy-two electrophysiologic studies were performed on 64 patients after the Mustard operation. Standard rest and 24 hour ambulatory electrocardiograms were evaluated. Catheter endocardial atrial mapping, available in 67 of the 72 studies, revealed that sinus rhythm was present in the atria in 33 patients, ectopic atrial rhythm in 26 and junctional rhythm in 8. Intraatrial conduction delays with very late activation of the low medial, low lateral or low right atrium at the AV junction were present in 53 of 59 patients with atrial or sinus rhythm. Sinus node function was normal in only nine patients. Prolonged refractory periods were found in the right atrial portion of the new right atrium when compared with the left atrial portion of the new right atrium. Forty-one percent of the patients had prolongation of atrial refractoriness with shortening of the paced cycle lengths. Fifty-one percent developed sustained intraatrial reentry with programmed atrial stimulation. Forty-eight percent of these patients with inducible atrial tachycardia have since developed clinical episodes of atrial flutter. In summary, electrophysiologic studies revealed significant abnormalities of sinus node function and atrial conduction and refractoriness. Alone or in combination, these abnormalities, which result in severe bradycardia or rapid atrial arrhythmias, may lead to sudden death. The Jatene or arterial switch procedure may provide an appropriate alternative operation in this group of patients.

Sinus node shift after the Senning procedure compared with the Mustard procedure for transposition of the great arteries

To investigate the nature of the dominant intrinsic cardiac pacemaker activity after the Senning procedure, endocardial mapping of the systemic venous atrium was accomplished a mean of 13 months after operation in 10 patients, aged 22 +/- 6 months. Multiple endocardial sites were measured to find the earliest atrial electrical activity timed back from the QRS complex. These data were compared with data from endocardial mapping performed in 6 patients late after the Mustard procedure. In 8 of 10 patients who had undergone the Senning procedure, the earliest activation time, corresponding by definition to the origin of the intrinsic pacemaker, was located in the inferior medial portion of the superior limb of the systemic venous atrium. In the other 2 patients who had undergone the Senning procedure, the earliest activity was in the high superior limb of the baffle at its junction with the superior vena cava. In contrast, the earliest activity in all patients who underwent the Mustard operation was at the junction of the superior vena cava and the superior limb of the systemic venous atrium. In response to programmed extrastimulation, the electrophysiologic behavior of the intrinsic pacemaker in the Senning group was abnormal compared with known normal sinus node (SN) data in only 3 of 10 patients, whereas all patients in the Mustard group had SN dysfunction. Abnormal SN function was noted in both patients in the Senning group, in whom a shift in the position of the earliest endocardial activation point was not seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhomogeneity of cellular refractoriness in human atrium: factor of arrhythmia?

Spatial inhomogeneity of refractory periods, as measured during clinical electrophysiological studies, is a known predisposing factor of arrhythmia. We studied effective refractory periods (ERP) and action potential duration (ADP90) on isolated human atrium. Twelve samples of right atrium obtained during cardiac surgery from patients with (n = 6) and without (n = 6) atrial fibrillation (AF) were studied by microelectrode technique. For each preparation, ERP were measured at basic cycle lengths (BCL) of 1,600, 1,200, 800, and 400 msec in five different cells located around (0.8 mm) the stimulating electrode. Dispersion of ERP was significantly greater in the AF group (96.7 +/- 9 versus 70.9 +/- 9 msec, p = 0.01). In the non-AF group, we observed a positive linear correlation between ERP and BCL (r = 0.86) ADP90 and BCL (r = 0.93). On the contrary, in the AF group this correlation was absent between ERP and BCL (r = 0.28), poor between ADP90 and BCL (r = 0.62). These results suggest that nonhomogeneous recovery of excitability (dispersion and poor adaptation) may be an important factor of arrhythmia. This inhomogeneity is present at the cellular level as well as in the entire heart.

Hemodynamic and electrophysiologic results of the Senning procedure for transposition of the great arteries

Of 24 patients, aged 6 days to 24 months, undergoing the Senning procedure for transposition of the great arteries, 2 patients died perioperatively (8% operative mortality): 1 patient, a neonate, from sepsis and 1 patient, born prematurely and with multiple anomalies, from congestive heart failure. One patient died late postoperatively from noncardiac causes. The 21 survivors are clinically well, and in 20 complete hemodynamic and electrophysiologic data were obtained by cardiac catheterization a mean of 13 months after repair. All patients have normal systemic arterial oxygen saturation. Left ventricular function and pulmonary artery pressures are normal in all. None had pulmonary venous obstruction. Narrowing at the junction of the superior vena cava and systemic venous atrium with mean pressure differences of 5 mm Hg or more was found in 4 of the 20 patients, but was clinically manifest in only 1 patient. No abnormality of atrioventricular conduction was seen in response to programmed electrical stimulation. Sinus node dysfunction was present in 6 patients, with abnormalities of both automaticity and sinoatrial conduction. Among these 6 patients were the 5 who were younger than 5 months at operation. The Senning procedure generally results in excellent hemodynamic and electrophysiologic status in patients who undergo operation after the newborn period. Identification of sinus node dysfunction, seen in patients in whom the procedure is performed in the first few months of life, is of concern and identifies a need for close follow-up of sinus node function in this cohort of patients.

Application of the Rosenblueth hypothesis to assess cycle length effects on the refractoriness of the atrioventricular node

In adults, the effective refractory period of the atrioventricular (AV) node is lengthened, whereas that of the atrium, His-Purkinje system or ventricular myocardium is shortened with a shorter atrial pacing cycle length. However, in children, the effective refractory period of the AV node at shorter cycle lengths is also shortened. Based on Rosenblueth's 1-step delay hypothesis, an index of refractoriness within the AV node is defined as the longest coupling interval at the level of step delay within the AV node of an impulse that cannot be conducted to the His bundle. The slopes relating cycle length and refractoriness of the AV node are determined by both the conventional and revised methods in 9 pediatric patients with heart disease. The slope is positive for all patients using the revised method. The difference in values between the 2 methods in older children is striking because the slope is converted from a negative to a positive value. It is concluded that the AV node has the same positive slope relating cycle length and refractoriness as other cardiac tissues.

Pre- and postoperative electrophysiologic assessment of children with secundum atrial septal defect

Sinus node (SN) and atrioventricular node (AVN) dysfunction after repair of atrial septal defect (ASD) may be caused by inherent nodal abnormalities and not related to altered hemodynamics. To assess the preoperative prevalence and postoperative persistence of nodal dysfunction, 21 consecutive children, mean age 5.4 years, underwent electrophysiologic evaluations before ASD repair. Preoperative SN recovery time was prolonged in 11 patients and was associated with abnormal AVN response to rapid atrial pacing in 5. There were no significant differences in age, hemodynamic values or shunt size between children with normal and those with abnormal nodal function. Atrial and AVN refractory periods were normal. The ASD was repaired in 9 children with SN dysfunction. Electrophysiologic studies performed 4 to 16 months after surgical correction showed improvement in all electrophysiologic values. However, SN function remained abnormal. Significant decreases were observed in atrial (p less than 0.05) and AVN (p less than 0.05) refractory periods, with increased atrial conduction velocity (p less than 0.01) and AVN Wenckebach response to atrial pacing (p less than 0.01). ASD repair improved nodal and atrial muscle electrophysiologic function, theoretically by relieving stress on atrial impulse propagation. SN and AVN dysfunction may persist as an inherent part of the ASD complex.

Electrophysiologic abnormalities of children with ostium secundum atrial septal defect

Sinus node (SN) and atrioventricular node (AVN) function were evaluated in 49 patients with secundum type atrial septal defect (ASD). Automaticity and conduction system function were assessed by intracardiac recording of the AH and HV intervals at rest, corrected SN recovery time, sinoatrial conduction time, AVN refractory period and the ability of the AVN to conduct rapidly paced atrial beats to the ventricles. Electrophysiologic abnormalities were found in 41% of the 34 patients who were studied before surgery. However, no preoperative abnormalities were present in children younger than 2.5 years. If only children older than 2.5 years were analyzed, the incidence of conduction abnormalities was similar for the patients studied before operation (62%) and those studied after operation (71%). The size and ejection fractions of the right and left ventricles, the magnitude of shunt flow and the size of the ASD did not differ between the patients with and those without electrophysiologic abnormalities. AVN dysfunction was present in 40% of the patients who were studied after surgical repair. While this frequency was more than twice the preoperative incidence of AVN dysfunction, it was not statistically significant. The data suggest that patient age is the major factor that influences the presence of conduction system dysfunction in patients with ASD.

Sinus node function and conduction system before and after surgery for secundum atrial septal defect: an electrophysiologic study

Arrhythmias are common in the natural history as well as in the late postoperative course of patients with atrial septal defect (ASD); electrophysiologic disturbances may result from the ASD itself or from surgery. Electrophysiologic studies were performed in 18 children (mean age 10 years) both before and after surgical closure of the ASD. Sinus node (SN) function, conduction intervals and refractory periods (atrial and atrioventricular [AV] nodal) were determined. Before surgery, corrected SN recovery time was prolonged in 14 patients; the mean value for the group was 357 +/- 163 ms. The AH interval was slightly prolonged, as were AV nodal refractory periods. Postoperatively, SN recovery time decreased in all patients who remained in sinus rhythm (p less than 0.02), but 5 patients had atrial ectopic rhythm. The AH interval decreased significantly (p less than 0.02), as did the refractory periods, mainly for the AV node (p less than 0.01). The pacing rate at which second-degree AV block occurred increased. Thus, closure of ASD improves AV conduction, decreases AV nodal refractory periods and improves SN function, probably by suppressing rightsided heart volume overload. However, SN function may be lost, probably as a result of the operative procedure.

Induction of nonsustained atrial flutter by programmed atrial stimulation in children: incidence, mechanisms, and clinical implications

Nonsustained atrial flutter was induced by programmed atrial extrastimulation in 6 (4%) of 137 children with preoperative congenital heart defects, who underwent electrophysiologic evaluation as part of cardiac catheterization. None of these patients had ECG or clinical evidence of arrhythmias. Atrial reentry was induced by programmed atrial extrastimulation in these six patients at coupling intervals slightly longer than the coupling interval at which flutter was induced. The flutter cycle length was similar to the atrial refractory periods. The duration ranged between 0.4 second and 60 seconds. The PA interval and the duration of the P wave were normal in all of the patients. Five of the six had normal PR intervals. It is concluded that nonsustained atrial flutter may be induced by programmed atrial extrastimulation in dysrhythmia-free children. The cycle length is determined by atrial refractoriness and, contrary to adults with clinical atrial flutter, prolonged PA and P wave duration are not predisposing factors.

Aging and atrial electrophysiologic properties in man

In order to assess the influence of age on atrial electrophysiologic properties, we studied 17 normal subjects, whose ages were homogeneously distributed between 17 and 78 years, measuring in each of them effective (ERP) and functional (FRP) refractory periods at 3 sites of the right atrium (high, middle and low in the lateral wall) at the same driven frequency (120/min). Twice threshold stimuli of 2 msec duration were applied. Dispersion of atrial refractoriness was measured as the longest minus the shortest refractory period. A significant direct correlation was observed between age and dispersion of atrial refractoriness (of ERP: r = 0.75, P less than 0.001; of FRP: r = 0.82, P less than 0.001). Moreover, age showed a significant direct correlation with refractoriness at high right atrium (ERP: r = 0.66, P less than 0.01; FRP: r = 0.76, P less than 0.001), but did not correlate with that at the other two sites. We suggest that ageing modifies atrial refractoriness in a non-uniform manner inducing a progressive increment of dispersion of atrial refractoriness. The impression is that a slow but continuous process takes place from juvenility to old age.

Maturational changes in ventriculoatrial conduction in the intact canine heart

This study reports on the changes in ventriculoatrial (VA) conduction that occur with maturation. Programmed atrial and ventricular premature extra-stimulation (coupled to a fixed paced cycle length) and rapid atrial pacing were performed in three groups of dogs: Group I = 8 neonates aged 5 to 14 days, Group II = 9 young dogs aged 6 to 9 weeks and Group III = 10 adult dogs. High right atrial, His bundle and right ventricular electrograms were recorded. There were no differences in the AH intervals at rest. In all but five animals, atrioventricular conduction was limited by the atrial functional refractory period (Group I, 109 +/- 12 ms; Group II, 152 +/- 22 ms; Group III, 167 +/- 19 ms). As expected, with rapid atrial pacing, Wenckebach conduction developed at a shorter cycle length in the younger animals (Group I, 145 +/- 20 ms; Group II, 153 +/- 15 ms; Group III, 200 +/- 25 ms, p less than 0.01). Ventriculoatrial conduction was documented in 87% of Group I puppies and 100% of Group II, but only 40% of Group III dogs. The effective and functional refractory periods of the VA conduction system were significantly shorter in the more immature groups of dogs (effective/functional: Group I, 124 +/- 27/168 +/- 22 ms; Group II, 139 +/- 23/202 +/- 13 ms; Group III, 270 +/- 28/326 +/- 25 ms; p less than 0.01). Relative to the adult dog, the immature heart showed a greater incidence of VA conduction and shorter VA refractory periods. This enhanced VA conduction may be of physiologic importance in the initiation and perpetuation of certain supraventricular arrhythmias.

Vasovagal syncope in children requiring pacemaker implantation

Four children presented with episodic loss of consciousness. Two of the children were siblings. Neurologic causes were initially suspected in all but extensive evaluations and EEGs excluded seizures. ECGs in one patient demonstrated first- and second-degree AV block and first-degree AV block in another. The QT and QTc intervals were normal in all. Eyeball pressure in all patients produced profound bradycardia. All patients became asymptomatic after the implantation of pacemakers, although one died 15 months afterward from another cause.

Arrhythmias in transposition of the great arteries after the Mustard operation

Disorders of rhythm or conduction in patients with transposition of the great arteries (TGA) after the Mustard operation have been widely reported. This study provides a systematic evaluation of the electrophysiologic function of 87 survivors of the Mustard operation at a single institution. Surface electrocardiograms were reviewed in all 87 patients, Holter monitoring data in 26 patients, exercise electrocardiograms in 21 patients, and invasive electrophysiologic data in 61 patients. Surface electrocardiograms showed normal sinus rhythm in 52%, sinus node dysfunction in 27%, and atrioventricular block in 16%. Holter monitoring was obtained in an unselected subgroup of 26 patients who had a mean age of 12 years and a mean interval from operation of 9 years. Sinus node dysfunction was found in 58%, atrioventricular block in 27% ventricular ectopy in 50%, supraventricular ectopy in 27%, and no abnormalities in only 8%. Intracardiac electrophysiologic evaluation showed a high frequency of abnormal sinus node recovery times and suboptimal response of the atrioventricular-conduction system to rapid atrial pacing. When all modalities used in this study were considered, sinus node dysfunction occurred in 47%, ectopy in 34% and atrioventricular block in 23%. Although only 30% of patients had no evidence of arrhythmia, symptoms of rhythm or conduction disturbances were rare.

Reevaluation of enhanced atrioventricular nodal conduction: evidence to suggest a continuum of normal atrioventricular nodal physiology

The syndrome of enhanced atrioventricular nodal (AVN) conduction has been defined arbitrarily by: AH interval during normal sinus rhythm (AH-NSR) less than or equal to 60 msec; shortest right atrial pacing cycle length (PCL) maintaining 1:1 AVN conduction (shortest PCL 1:1) less than or equal to 300 msec; and at the shortest PCL 1:1, an increase in the AH interval from AH-NSR (delta AH) less than or equal to 100 msec. We examined the relationship between AH-NSR, shortest PCL 1:1, and delta AH in 160 consecutively studied patients who did not have accessory AV pathways or second-degree AV block to determine whether a distinct subgroup of patients with unusually rapid AVN conduction properties could be identified. The frequency distribution of each of the variables was unimodal and continuous. Cluster analysis, combining the three variables, failed to reveal a distinct subgroup at the lower end of the spectrum. Sixty-six patients (41%) had AH-NSR less than or equal to 60 msec, 36 (23%) shortest PCL 1:1 less than or equal to 300 msec, 76 (48%) delta AH less than or equal to 100 msec, and 17 (11%) all three criteria. The shape of the AH vs atrial PCL curve was independent of shortest PCL 1:1. Neither delta AH nor the terminal slope of the curve for AH vs atrial PCL (measured over the 20-40 msec before Wenckebach block) was related to AH-NSR or shortest PCL 1:1. We conclude that a subgroup cannot be identified by AH-NSR, shortest PCL 1:1, and delta AH, and that enhanced AVN conduction as previously defined represents simply one end of the continuous spectrum of normal AVN physiology.

Preoperative secundum atrial septal defect with coexisting sinus node and atrioventricular node dysfunction

Sinus node dysfunction in patients after repair of the secundum atrial septal defect has been ascribed to surgical damage. We studied 15 consecutive patients with secundum atrial septal defect before operative intervention. Noninvasive testing included 34-hour electrocardiographic monitoring and a standard 13-lead ECG. Intracardiac electrophysiologic techniques included corrected sinus node recovery time, sinoatrial conduction time, His bundle recording to measure AH and HV intervals, the atrial pacing rate at which atrioventricular node Wenckebach occurred, and atrioventricular nodal refractory period. The ECG revealed an ectopic atrial rhythm in two patients. Intracardiac electrophysiology showed an abnormal corrected sinus node recovery time (range -40 to 800 msec) in 10 patients. Five patients had evidence of atrioventricular nodal dysfunction with prolonged AH interval or abnormal atrial pacing rate at which atrioventricular Wenckebach occurred. These data indicate that sinus node dysfunction or atrioventricular node dysfunction were present before surgical intervention.

Usefulness of the ajmaline test in patients with latent bundle branch block

Twelve patients were studied with intermittent bundle branch block whose conduction disturbance disappeared completely and could no longer be recorded even after provoked changes in heart rate. Premature atrial stimulation and atrial pacing at rapid rates were performed in nine patients; in none of these nine were these procedures able to evoke the complete bundle branch block pattern that all patients exhibited before the spontaneous normalization of conduction. In marked contrast, the administration of ajmaline (1 mg/kg body weight, intravenously in 90 seconds) caused the bundle branch block pattern to reappear in 10 (83.3 percent) of the 12 patients 30 to 120 seconds after the end of the injection, and in 11 patients (91.6 percent) when additional atrial stimulation was performed in 1 of the 2 "failures." This pharmacologic test was much more rapid and simple than electrophysiologic testing and it was noninvasive. Results of this study suggest that some form of subclinical fascicular injury was present (or had persisted) at a time when intraventricular conduction was persistently normal even though no significant physiologic alteration could be demonstrated by the atrial stimulation techniques. The ajmaline test may become a valuable tool for uncovering cases of latent bundle branch block and furthering our knowledge of the early natural history of intraventricular block.

Determinants of ventricular refractory periods in children with congenital heart disease: effects of cycle length and age

Ventricular effective refractory periods (ERP) and functional refractory periods (FRP) were determined by programmed ventricular extrastimulation in 53 pediatric patients with a spectrum of congenital heart disorders. Of these 63 children (ages 8 months to 18 years), 38 were preoperative, 17 had repair of their cardiac lesion via right ventriculotomy, and eight were postoperative without a ventriculotomy. We demonstrated that there was a linear relationship between the cycle length and ventricular refractory periods. The regression equations 73 + 0.29 x cycle length (msec) for the ventricular ERP (msec) and 80 + 0.30 x cycle length (msec) for ventricular FRP (msec) were found to define the determined properties of ventricular refractory periods (VRP) in children. These VRP characteristics were independent of age in children less than 13 years of age.

His-Purkinje responses and refractory periods during atrial extrastimulation in children with heart defects

During atrial extrastimulation, split His potentials, prolonged His-to-ventricular (H2V2) intervals and block distal to the His bundle deflection were observed in both preoperative and postoperative children with heart defects. His-Purkinje responses and refractoriness were identified in 31 of 78 (40%) pediatric patients (20 of 51 preoperative and 11 of 27 postoperative) during atrial extrastimulation coupled to sinus and/or paced cycle lengths. Split His potentials were found in 14 patients (eight preoperative and six postoperative) and His bundle relative refractory periods ranged from 250--490 msec. Prolonged H2V2 intervals were found in these and in an additional 16 patients (11 preoperative and five postoperative) and the relative refractory period of the His-Purkinje system ranged from 230--500 msec. Block distal to the His deflection occurred in seven patients (five preoperative and two postoperative) and the effective refractory period ranged from 230--510 msec. Split His potentials, long H2V2 intervals and block distal to the His bundle deflection produced by atrial extrastimulation were found in peroperative as well as postoperative children. These responses probably represent functional electrophysiologic characteristics of the pediatric cardiac conduction system.

Idiopathic recurrent sustained ventricular tachycardia in children and adolescents

The electrophysiologic characteristics of recurrent sustained ventricular tachycardia were studied in seven pediatric patients. The mechanisms of the ventricular tachycardia were evaluated using programmed electrical stimulation. Ventricular tachycardia could be reproducibly initiated in two patients and terminated in one patient in the basal state. It could be initiated in one additional patient and terminated in two additional patients after administration of a type IB drug. In four patients, ventricular tachycardia could not be initiated or terminated by programmed electrical stimulation. The site of origin of the ventricular tachycardia determined by catheter endocardial mapping was the right ventricular outflow tract in four patients, the interventricular septum in two patients and the inferior left ventricle in one patient. The ventricular tachycardia more frequently had an automatic than a reentrant mechanism, and originated more often in the right than in the left ventricle; it was not frequently associated with structural heart disease in this group of patients.

Dual atrioventricular nodal pathways: a benign finding in arrhythmia-free children with heart disease

The incidence and significance of dual atrioventricular (A-V) nodal pathways are described in 78 children with associated congenital or acquired heart disease. None of these patients had clinical or electrocardiographic evidence of arrhythmia. Dual A-V nodal pathways were observed in 35 percent of the preoperative group and in 33 percent of the postoperative group. Despite this substrate for A-V nodal reentry, supraventricular tachycardia was neither induced during electrophysiologic evaluation nor did it develop clinically over a follow-up period of 1 month to 15 years. It is concluded that dual A-V nodal pathways are common and may be a benign finding in arrhythmia-free children with heart disease.