Joel A. Kirsh

Pediatric Myocarditis: Emergency Department Clinical Findings and Diagnostic Evaluation

OBJECTIVE. The goal was to determine, in children with myocarditis, the frequency of various presenting symptoms and the sensitivity of clinical and laboratory investigations routinely available in the emergency department. METHODS. We performed a retrospective review of all patients <18 years of age who were diagnosed as having myocarditis at our institution between May 2000 and May 2006 and who initially presented to an emergency department. Patients were categorized as having definite myocarditis (positive endomyocardial biopsy results) or probable myocarditis(diagnosis assigned by a pediatric cardiologist on the basis of history, physical examination, and investigation results in the absence of an endomyocardial biopsy or in the presence of negative biopsy results). All patients were assigned a predominant category of symptoms at presentation on the basis of criteria defined a priori. RESULTS. There were 16 cases of definite myocarditis and 15 cases of probable myocarditis. The age distribution was nonnormal, with peaks among children ≤3 years and ≥16 years of age. Of 14 patients who were seen by a physician before being diagnosed with myocarditis, 57% were originally diagnosed as having pneumonia or asthma. Thirty-two percent of patients presented with predominantly respiratory symptoms, 29% had cardiac symptoms, and 6% had gastrointestinal symptoms. Although evidence of cardiac dysfunction was frequently present in the form of respiratory distress, only a minority of children had evidence of hepatomegaly or abnormal cardiac examination results. The sensitivities of electrocardiograms and chest radiographs as screening tests were 93% and 55%, respectively. Among laboratory tests studied, aspartate aminotransferase measurement was the most sensitive (sensitivity: 85%). CONCLUSIONS. Children with myocarditis present with symptoms that can be mistaken for other types of illnesses; respiratory presentations were most common. When clinical suspicion of myocarditis exists, chest radiography alone is an insufficient screening test. All children should undergo electrocardiography. Aspartate aminotransferase testing may be a useful adjunctive investigation.

Ventricular response to atrial fibrillation: Role of atrioventricular conduction pathways

Irregularity of the ventricular rhythm is a hallmark of patients with atrial fibrillation, yet the genesis of the irregularity is not yet fully understood. The role of the atrioventricular (AV) node in determining the irregularity of the ventricular response to atrial fibrillation was investigated by comparing the frequency distributions of the atrial (AA) and the ventricular (RR) intervals. Atrial electrograms and surface electrocardiographic leads were recorded during sustained atrial fibrillation in 12 patients with conduction over the AV node. The scaling factor (mean RR interval/mean AA interval) quantified the ability of the conduction pathway to scale the atrial input to a slower ventricular response and ranged from 2.55 to 5.92 (mean +/- SD 3.77 +/- 0.92). The coefficient of variation (SD/mean) measured the relative variability of the AA and RR interval distributions. The atrial and ventricular coefficients of variation were not significantly different (0.20 +/- 0.04 versus 0.21 +/- 0.03, p greater than 0.27). Similar recordings were analyzed in six patients with conduction over a accessory AV pathway. The scaling factor ranged from 1.54 to 2.46 (2.02 +/- 0.39) and, as was the case for patients with conduction over the AV node, the atrial and ventricular coefficients of variation did not significantly differ (0.24 +/- 0.08 versus 0.27 +/- 0.10, p greater than 0.6). For both groups of patients, ventricular variability and the maximal RR intervals were predicted by the product of the scaling factor and either atrial variability or maximal AA intervals, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Bipole Configuration on Atrial Electrograms During Atrial Fibrillation

Despite an increasing body of work on the nature of fibrillatory rhythms, and the application of different bipole configurations in antifibrillatory devices, little published work has assessed the effect of bipole configuration on the endocardial recordings of fibrillatory rhythms. To address this issue, a specially designed 6 Fr decapolar catheter was used to record intra‐atrial electrograms during sustained atrial fibrillation in 15 patients. Simultaneous filtered (30–500 Hz) and unfilfered (0,05–5,000 Hz) recordings of atrial fibrillation were performed of four different bipole configurations: (a) 1‐mm interelectrode spacing adjacent to the atrial wall; (b) 10‐mm interelectrode spacing adjacent to the atrial wall; (c) 10‐mm inter‐electrode spacing 24 mm from the distal catheter tip; (d) 1‐mm interelectrode spacing 24 mm from the distal catheter tip. One minute of such data was recorded, and each 4.27‐second segment (X 14 segments) was analyzed for atrial rate, electrogram amplitude, amplitude probability density function (apdf), median frequency in the 2–9 Hz band, and elecfrogram morphology. Changes in bipole configuration resulted in profound changes in calculated afrial rate, amplitude, and apdf (P < 0.001 by two‐way ANOVA in each instance). Specifically, closer interbipole spacing and closer proximity to the atrial wall resulted in lower calculated atrial rates, higher electrogram amplitudes, and higher apdf values. In contrast, median frequency proved to be a more robust measure despite multiple configurations (P> 0.10 by two‐way ANOVA). These changes significantly affected the predictive value of previously published detection criteria for rate (P < 0.01) and apdf (P < 0.000001). Bipole location also affected morphology, with locations adjacent to the atrial wall and with closer interbipole spacing having more discrete electrograms and greater apparent organization (P < 0.0001). Further, when data segments from all patients and bipole configurations were grouped, rate and apdf were found fo be strongly inversely correlated (r = ‐0.808). In conclusion: (1) Bipole configuration has important effects on calculated atrial rate, electrogram amplitude, and apdf during atrial fibrillation; (2) Median frequency and frequency domain analysis may be a more robust way of characterizing atrial fibrillation despite the use of different bipole configurations; (3) Changes in bipole configuration affect the efficacy of detection criteria, and considerations about the level of organization of a cardiac rhythm; (4) Rate and apdf may be largely redundant measures of fibrillatory rhythms; and (5) Traditional estimates of atrial rates up to 700/min during atrial fibrillation, based on the unipolar or widely spaced bipolar leads of the surface electrocardiogram, reflect the effects of their recording methods. and are an overesfimation of the true atrial rate.

Utility of Exercise Testing in Children and Teenagers With Arrhythmogenic Right Ventricular Cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is increasingly recognized as an important cause of exertional sudden death in otherwise healthy young individuals and athletes. Graded exercise testing is routinely included in the evaluation of patients with suspected ARVC, but its diagnostic utility has not been systematically assessed. Using a single-center retrospective design, the rhythm response to graded exercise testing was examined in 33 tests performed in 16 young (aged <18 years) patients with established diagnosis of ARVC. Ventricular premature complexes (VPCs) were classified as absent (graded 0), as being isolated or in couplets (graded 1), or as comprising nonsustained ventricular tachycardia (graded 2) during pretest rest, at peak exercise, and during postexercise recovery. VPCs were absent at rest in 21 of 33 studies, subsequently appearing at peak exercise in 4 studies and during recovery in 2 studies. Isolated VPCs and couplets were present at rest in 9 of 33 studies, with subsequent exercise provoking higher grade ectopic activity in 2 instances at peak exercise and in 1 case during recovery, while VPCs decreased or remained unchanged in all other cases. In all 3 instances in which ventricular tachycardia was observed during pretest rest, there was either suppression (3 at peak exercise, 2 during recovery) or no change (1 case during recovery) in VPC grade. In conclusion, the exercise response of ventricular ectopic activity is highly variable in young patients with ARVC. The diagnostic utility of graded exercise testing is thus questionable in young patients with suspected ARVC, and the absence or suppression of VPCs during exercise should not be considered reassuring in terms of its diagnostic exclusion.

Cardiac Perforation 6 Weeks After Percutaneous Atrial Septal Defect Repair Using an Amplatzer Septal Occluder

A 14-year-old boy presented to the emergency department unaccompanied by his parents with a decreased level of consciousness, bradycardia, and hypotension after a syncopal episode. The patients electronic chart revealed a percutaneous closure of a secundum atrial septal defect using an Amplatzer septal occluder (AGA Medical, Golden Valley, MN) 6 weeks before this presentation. An urgent echocardiogram revealed a moderate pericardial effusion, and 320 mL of fresh blood was evacuated by subxiphoid pericardiocentesis. The child underwent surgical exploration and was found to have a perforation in the superior-posterior aspect of the right atrium, which was corrected. The septal occluder was extracted, and the atrial septal defect was closed with a pericardial patch. This case illustrates a rare but life-threatening complication of percutaneous closure of atrial septal defect using an Amplatzer septal occluder and the importance of timely access to patient records when available history and physical examination are limited.

Long QT Syndrome

1272 CMAJ, August 9, 2011, 183(11)