Biomedical subjects
Publications and source records attributed to R M Gow.
Electrocardiograms taken at rest of 2 children with transplacental exposure to anti-Ro antibody but 1:1 atrioventricular conduction demonstrated sinus node disease. Treadmill exercise testing of 28 patients with congenital complete heart block found 3 patients with chronotropic incompetence of the sinus node.
We report the successful excision of a large left atrial rhabdomyoma producing complete obstruction of both inflow and outflow to the left ventricle. Systemic perfusion was dependent on anterograde ductual flow. The resultant univentricular physiology was initially managed medically, with spontaneous tumor regression contemplated as a means of possible long-term "cure." Failure to achieve hemodynamic stability compelled urgent surgical excision. This neonate was successfully discharged home with an in-series biventricular circulation.
BACKGROUND: There is a paucity of information to guide the management of the child with Down's syndrome and congenital heart disease in whom biventricular repair is precluded. METHODS: Through the cardiology and cardiovascular surgery databases of The Hospital for Sick Children and Toronto Congenital Cardiac Centre for Adults, we identified patients with trisomy 21 and ventricular hypoplasia who had undergone a Fontan procedure (or modification). RESULTS: Of 533 patients who had undergone a Fontan operation between 1976 and 1997, 4 had trisomy 21. All 4 patients had unbalanced complete atrioventricular septal defect with right ventricular hypoplasia in 3 and left ventricular hypoplasia in 1. Three patients survived, and 1 died of endocarditis. The 3 survivors have done well in the short term and medium term without complications related to the pulmonary vasculature. CONCLUSIONS: We suggest that in appropriately selected patients with trisomy 21 and ventricular hypoplasia who are unsuitable for two or one and a half ventricle repair, the Fontan procedure is not contraindicated and provides short-term and medium-term benefit.
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An increase in the incidence of primary cardiac tumors has been reported since the development or enhancement of noninvasive imaging modalities. We identified 56 children with primary cardiac tumors. Forty-four (78%) children had rhabdomyomas, 6 (11%) fibromas, 1 (2%) pericardial teratoma, 1 (2%) epicardial lipoma, 1 (2%) multicystic hamartoma, and 3 (5%) unspecified tumors. The mean age at diagnosis was 19 +/- 35 months (median 4.7 months, range 0.03 to 204 months), excluding 12 patients who were given the diagnosis before birth. Among 27,640 patients assessed for cardiac disease, the incidence of tumors was 0.06% (1980 to 1984), 0.22% (1985 to 1989), and 0.32% (1990 to 1995). Diagnosis was made in 55 of 56 patients by echocardiography. Catheterization was performed in five patients and magnetic resonance imaging in nine. No tumor-related deaths occurred. Nine patients had surgery because of hemodynamically significant obstruction or arrhythmias. Partial or complete regression occurred in 24 (54%) of 44 patients with rhabdomyomas. Overall, the prognosis was excellent. Individualized surgery allowed early safe treatment of symptomatic tumors.
Twenty-five neonates (16 boys and 9 girls) who had atrial flutter were identified. Diagnosis was made on or before the first day of life in 18 (72%). Heart failure were present in 9 patients, and hydrops fetalis was present in another 5. Atrial and ventricular rates did not differ between symptomatic and asymptomatic patients. Atrioventricular conduction was variable in 16 patients, and documented 1:1 conduction occurred in 5. Digoxin was the initial drug therapy given to 21 patients, with 7 reverting to sinus rhythm. Electrical cardioversion (pacing or synchronized shock) was attempted in 13 of the 14 cases in which digoxin was not successful and was attempted as the first treatment in 3 cases. Sustained sinus rhythm was achieved in 9. Two infants died of complications from prematurity but without having been successfully converted to sinus rhythm. No patient had atrial flutter during long-term follow-up (median 23 months). Neonatal atrial flutter has significant morbidity but an excellent long-term prognosis.
OBJECTIVES: Our purpose was to assess the risk factors for late mortality, loss of sinus rhythm and atrial flutter after the Mustard operation. BACKGROUND: The Mustard operation provides correction of cyanosis with low surgical risk in transposition of the great vessels. However, right ventricular failure, loss of sinus rhythm, atrial flutter and death are frequent long-term complications. METHODS: Records of 534 children who underwent the Mustard operation at a single center since 1962 were reviewed for demographic, anatomic, electrocardiographic and physiologic predictors and outcomes. RESULTS: There were 52 early deaths (9.7%). Survival analysis was undertaken for 478 early survivors with a mean follow-up interval of 11.6 +/- 7.2 years. There were 77 late deaths (16.1%), with sudden death (n = 31) the most frequent cause. Survival estimates were 89% at 5 years and 76% at 20 years of age. Risk factors were an earlier date of operation, operative period arrhythmia and an associated ventricular septal defect. Risk (hazard) of late death declined in the first decade, with further peaks in the second decade. Sinus rhythm was present in 77% at 5 years and 40% at 20 years. Loss of sinus rhythm was associated with previous septectomy, postoperative bradycardia and late atrial flutter. Freedom from atrial flutter was 92% at 5 years and 73% at 20 years of age. Risk factors for atrial flutter were the occurrence of perioperative bradyarrhythmia, reoperation and loss of sinus rhythm during follow-up. Risk of atrial flutter demonstrates a late increase. CONCLUSIONS: Ongoing loss of sinus rhythm and late peaks in the risk of atrial flutter and death necessitate continued follow-up.
To determine the incidence and risk factors for venous obstruction in children with transvenous pacing leads, 63 children were evaluated clinically and echocardiographically. Patients with abnormal clinical and/or echocardiographic findings were further investigated by venography. Thirteen patients (21%) had evidence of venous obstruction. Venography in 11 (2 refused) showed that severity of obstruction (as defined by percentage of luminal narrowing) was complete (100%) in 3, severe (> 90%) in 4, and moderate (60%-90%) in 5 (1 patient having 2 sites of obstruction). Risk factors for obstruction in 55 patients with single implantation procedures (10 with obstruction; 18%) were sought. Total cross-sectional area of lead(s) was indexed to body surface area at implantation (INDEX). Patients with obstruction had a higher mean INDEX (7.6 +/- 1.6 mm2/m2) than patients without obstruction (4.9 +/- 2.0 mm2/m2); P < 0.0002). Receiver-operator characteristic curves showed an INDEX > 6.6 mm2/m2 to best predict obstruction, with a sensitivity of 90% and specificity of 84%. Since pacing is lifelong, sizing of transvenous leads to the child is important to prevent obstruction and preserve venous access.
The Oscor MP52V and Medtronic 4951 leads have similar construction and intended application. To determine if one of these designs was more suited to pediatric pacing, we reviewed implant, 3 month, and 12 months follow-up thresholds for all 18 MP52V implants at our institution from December 1989 to April 1991 and compared them to the 4951 implants from January 1982 to October 1989. Lead survival for the MP52V implants was compared to the most recent 36 4951 implants. Patients ranged in ages from 2 days-16 years (median = 4 years) and required antibradycardia pacing for congenital or acquired heart disease. Patients were compared for weight and proportion of atrial leads in each group by t-test and Fisher exact tests respectively. Energy thresholds were assessed in microJ and compared by t-test. Lead survival was defined by abandonment or replacement for any reason. Kaplan & Meier survival curves were plotted and compared by Gehan's Wilcoxan Test. There were no significant differences between the MP52V and 4951 groups for age at implant (53 months vs 80 months) or proportion of atrial implants (5/18 vs 11/36). Lead survival was poor but did not differ significantly (70% vs 78% cumulative survival at 3 years), usually failing by exit block. Implant and follow-up thresholds did not differ significantly between leads. The MP52V did not provide significant improvement in performance over the 4951. New epicardial lead designs are needed to improve lead survival and thresholds in children.
The relationship between the pacemaker sensitivity safety factor (PSSF) and atrial under- or oversensing as documented by 24-hour Holter monitoring was examined. Our study comprised 78 transvenous fixed atrial leads implanted between 1983-1995 in 71 children. Overall, 210 Holter reports identified 143 (68%) Holters with normal atrial sensing function, 31 (15%) with undersensing, 32 (15%) with oversensing, and 4 (2%) with both problems. From 161 Holter reports in which the PSSF was available, the incidence of undersensing at a PSSF of 2.0 (range 1.5-2.4) was 25% (14/57). There was a dramatic decline in undersensing when the PSSF was > or = 3 (3%) compared to a PSSF < 3 (21%) (P < 0.001). A PSSF cut-off point of 2.0 best predicted occurrence of undersensing with a sensitivity of 79% and a specificity of 67%. Other variable were also examined by multiple logistic regression analysis, but only PSSF remained highly associated with undersensing (odds ratio [OR] = 0.6, P = 0.03). In contrast, PSSF did not have a significant role in predicting oversensing, but presence of sick sinus syndrome (OR = 10.5) or unipolar lead (OR = 5.6) were significantly associated with oversensing (P = 0.0001). The majority of undersensing problems can be avoided by routinely allowing for at least a threefold or more programmed sensitivity margin. Other factors may increase the risk of oversensing, regardless of the PSSF.
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Cardioverter-defibrillators were implanted in children aged 4 to 16 years over a 5-year period with no mortality and eventual clinically appropriate shocks in 6 of 11 patients. Both transvenous and epicardial implantable cardioverter-defibrillators were safe and effective in children resuscitated from sudden death or at high risk for sudden death.
We reviewed 40 infants and young children with VT. Median maximum VT rate was 214 beats/min (range 152 to 375 beats/min). A cause was defined in 20 (50%), the most common being cardiomyopathy or myocarditis in 8 (20%). There were six deaths (15%) related to VT, three of which occurred at diagnosis and in patients less than 1 week old. In 5 of 6 deaths related to VT, a cause was defined. At follow-up, 31 (91%) of 34 survivors did not have VT. The presence of symptoms was a predictor of death related to VT. The outlook for asymptomatic patients and those who survived more than 6 months after diagnosis and who do not have progressive myocardial disease appears good.
To obtain normative data for the childhood signal-averaged ECG (SAECG), we obtained SAECGs in 155 volunteers, aged 5-15 years, using Frank leads and a Fourier transform filter. Unfiltered QRS duration (QRSDU) and filtered QRS duration (QRSDF) were significantly longer in males, and the root mean square of the terminal 40 ms (RMS40) was significantly higher in females. There were no gender differences in the duration of high frequency low amplitude signals < 40 microV (DHFLA). All SAECG variables were significantly related to body surface area (BSA). Regression models were established for SAECG variables. For males, the predicted mean + 1.96 standard deviations (SD) for QRSDF (97.5th centile) ranged from 114 ms at BSA 0.70 m2 to 123 ms at 1.90 m2. For females, the predicted mean + 1.96 SD for QRSDF ranged from 110 ms at BSA 0.70 m2 to 119 ms at 1.90 m2. For males and females, the predicted mean + 1.96 SD for DHFLA ranged from 34 ms at 0.70 m2 to 38 ms at 1.90 m2. For males, the predicted mean - 1.96 SD (2.5th centile) for RMS40 (based on natural logarithm model) ranged from 30 microV at 0.70 m2 to 15 microV at 1.90 m2. For females, the predicted mean -1.96 SD for RMS40 ranged from 42 microV at 0.70 m2 to 20 microV at 1.90 m2. In children 5-15 years of age, both gender and BSA need to be taken into account when interpreting the SAECG.
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After spontaneously acquiring complete heart block, two children presented with torsade de pointes as a result of inappropriate prolongation of the QT interval. Although both remain well following pacemaker insertion, their cases illustrate the importance of QT interval assessment in patients with atrioventricular block, and demonstrate that syncopal episodes, and possibly sudden death, in children with acquired heart block can be due to bradycardia-induced ventricular tachyarrhythmias, rather than extreme bradycardia per se.
Cardiac fibromas in infants and children may present as intramural or intracavitary masses. Total or partial resection as well as transplantation have been reported as treatment for symptomatic patients. We report an infant, diagnosed prenatally, who underwent partial excision of a massive obstructive right ventricular fibroma and creation of a bidirectional cavopulmonary shunt. The palliative approach has allowed the child to be followed up with the option of transplantation should the tumor continue to increase in size.