Outcomes of emergent cardiac catheterization following pediatric cardiac surgery.

BACKGROUND: Although there is agreement of the importance of cardiac catheterization, especially interventional procedures, cardiac catheterization in postoperative critical care unit (CCU) period is often debated. The focus of this study was to explore the indications for and determinants of outcome after cardiac catheterization in this setting. METHODS: Between March 2004 and October 2006, 49 children (2.8% of cardiac surgeries) underwent 62 catheterizations before discharge from the CCU. Morphological, surgical, and catheterization data were accrued and analyzed using parametric competing risks models and multivariable risk-hazard analysis. RESULTS: Median age at surgery was 167 days (0-13.5 years) and time to catheterization was 8.5 (0-84) days following surgery. Catheterization procedures were either interventional (n = 35) or noninterventional (n = 27). Children who required a more urgent investigation following initial surgery more often had deployment of a stent at catheterization (P = 0.01) or subsequent surgical pulmonary artery augmentation (P < 0.01). Surgical reoperation was required following 23 (37%) catheterizations and was more common following index surgery involving a cavopulmonary shunt. Overall mortality was high (43%). Delayed invasive investigation beyond 2-3 weeks (P = 0.04) or a splinted sternum (P < 0.001) were risk factors for death. In addition, reoperation after a noninterventional catheterization predicted worse survival (P < 0.001). CONCLUSIONS: The need for invasive investigation in the immediate CCU period is associated with a poor outcome, especially when the investigation is delayed or an intervention is not possible. Identification of at-risk patients may improve outcomes. Best outcomes follow expedient catheterization with definitive management (often stent deployment or pulmonary artery augmentation).

The scoring of cardiac events during sleep.

Standardized guidelines for polysomnography (PSG) have not specified methods for acquiring or interpreting electrocardiographic (ECG) data. The practice of single lead ECG monitoring during PSG may allow identification of simple measures of cardiac rhythm but reduces the ability to detect myocardial ischemia and to define cardiac intervals. Although simple measures of cardiac rhythm such as heart rate and cardiac pauses are inherently reliable, there is limited data regarding outcome measures relative to sleep related heart rates and cardiac events during sleep. Several observational and cross-sectional studies demonstrate that average heart rate drops nearly 50% from infancy through young adulthood and that the average heart rate slows during sleep compared with wakefulness; the definitions of sinus bradycardia and sinus tachycardia should therefore be lower during sleep than wakefulness. Asystoles of up to 2 seconds are seen in normal populations during sleep. Although there may be an increased risk of certain arrhythmias at night, particularly in sleep disordered breathing, there is no evidence that supports different definitions for these arrhythmias during sleep compared with wakefulness. When the quality of tracings permits, the standard definitions of narrow- and wide-complex tachycardias and atrial fibrillation may be employed. In the future, expansion to multiple ECG leads and the use of alternative tools may provide better definition of heart rates and cardiac events during sleep.

Automatic atrial tachycardia in an infant following general anesthesia.

Automatic atrial tachycardia (AAT) is a rare supraventricular tachyarrhythmia (<10% of all supraventricular tachycardias), which can present in infants or young children. There are no published reports of AAT occurring in an infant or child following noncardiac surgery and general anesthesia. This report describes the management of a previously healthy 5-month-old infant, who developed AAT in the postanesthesia care unit following an uneventful circumcision under general anesthesia.

Asystole and severe bradycardia in preterm infants.

UNLABELLED: Transient episodes of apnea and bradycardia are common in preterm infants. Pronounced asystole or sinus arrest, however, is relatively rare and the clinical significance of such events is unknown. OBJECTIVE: The purpose of our study was to: (1) evaluate the prevalence of severe bradycardic and asystolic events in infants studied with polygraphic cardiorespiratory monitoring, (2) characterize these events, and (3) correlate the events with other clinical findings. METHODS: A total of 583 studies were performed in 454 preterm infants at a post-conceptional age 37.4 +/- 2.5 (range 34-42 weeks). Asystolic pauses were defined as no QRS complex for >or=3 s consistent with a heart rate <20 beats per minute (bpm). Severe bradycardia was defined as no QRS for >or=2 s consistent with a heart rate of 21-30 bpm. RESULTS: Eight infants (29.5 +/- 3.9 weeks' gestational age, birth weight 1,283 +/- 445 g) met the criteria of having had at least 1 asystolic event (heart rate

Protected circumferential conduction in the posterior atrioventricular vestibule of the left atrium: electrophysiologic and anatomic correlates.

BACKGROUND: The anatomic substrate for protected isthmus conduction in the right atrium has been well defined. Little is known of similar substrates in the left atrium (LA). METHODS: Patients (pts) with reentrant tachycardia (AVRT) supported by a single left-sided accessory pathway were studied retrospectively (n = 64) and prospectively (n = 31). Intracardiac electrograms were recorded from the His bundle position and coronary sinus (CS). The LA was mapped with a steerable catheter using the transseptal approach. LA anatomy was examined grossly and histologically in six cadaver hearts after removal of endocardium. RESULTS: A distal-to-proximal CS activation sequence during AVRT was seen in all patients with a left lateral accessory pathway before ablation. After one to three radiofrequency (RF) energy deliveries that did not interrupt accessory pathway conduction, the CS activation sequence was reversed in three patients in the retrospective group and bidirectional conduction block in the posterior atrioventricular vestibule of the LA (PAVV) was demonstrated in nine patients in the prospective group. Four of the six cadaver hearts showed a distinct circumferential inferoposterior myocardial bundle that coursed parallel to the CS in the PAVV. CONCLUSIONS: We described evidence of bidirectional intraatrial block in the PAVV after application of RF energy during accessory pathway ablation. Such conduction block may mimic the presence of a second accessory pathway. Our data suggest that circumferential conduction in the PAVV may be poorly coupled to the rest of the LA and may be involved in the macro-reentrant circuit around the mitral annulus. The circumferential inferoposterior myocardial bundle may serve as the underlying anatomic substrate.

Comparative effects of single- and linear triple-site rapid bipolar pacing on atrial activation in canine models.

Nonuniform conduction may cause block and/or delay, thereby providing a substrate for the onset and maintenance of reentrant atrial arrhythmias. We tested the hypothesis that linear triple-site, bipolar, rapid pacing (LTSBRP) of the right atrium generates more uniform wave-front propagation compared with single-site, bipolar, rapid pacing (SSBRP), thereby reducing and/or eliminating conduction block and delay that is otherwise present. Five dogs with pericarditis and three normal dogs were studied. Three plunge-wire electrode pairs were placed 5-7 mm apart in both perpendicular and parallel configurations at the superior aspect of the crista terminalis and were used to pace at 200- and 300-ms cycle lengths for < or =6 s. During pacing, 380 electrograms were recorded simultaneously from electrode arrays placed epicardially on the atria, which produced activation sequence maps for each pacing episode. Local conduction-velocity vectors were computed for each site during each episode. Histograms of absolute velocity vector angles from the x-axis (of the crista terminalis) were plotted to assess uniformity of wave-front propagation, and the magnitude of each vector was computed to assess the local speed. LTSBRP showed 1) more uniform linear activation wave fronts compared with SSBRP, 2) velocity vectors with a more uniform magnitude and direction compared with SSBRP, 3) a predominant absolute velocity vector angle vs. a scattered angle distribution with SSBRP, and 4) shorter right atrial activation time and faster mean epicardial speed than SSBRP for each pacing cycle length. LTSBRP created a more uniform wave-front propagation with less or no conduction block and/or delay compared with SSBRP.

Localization and radiofrequency ablation of atriofascicular pathways using electroanatomic mapping.

Atriofascicular pathways supporting antidromic reentrant tachycardia are uncommon, and may be difficult to ablate. Traditional mapping can be associated with traumatic loss of atriofascicular conduction. Atriofascicular fibers can insert into the right bundle and will, therefore, first activate the right ventricle. In contrast to initial activation of the ventricle near the tricuspid annulus that can be seen in patients with right-sided decremental atrioventricular pathways. We used electroanatomic mapping to map and ablate the ventricular insertion of atriofascicular pathways in two patients during sinus rhythm and during atrial pacing. In our 2 cases an atriofascicular potential was recorded from below the tricuspid valve annulus and tagged. At this site, each pathway was ablated with one radiofrequency lesion. We describe 2 cases where electroanatomic mapping of the right ventricle was used to map and ablate atriofascicular pathways.

Can current minute ventilation rate adaptive pacemakers provide appropriate chronotropic response in pediatric patients?

Since children have different activity patterns and exercise responses, uncertainty exists as to whether minute ventilation (MV) sensors designed for adults provide adequate chronotropic response in pediatrics. In particular, high respiratory rates (RR > 48 breaths/min), which are characteristic of the ventilatory response to exercise in children, cannot be sensed by MV rate responsive pacemakers. The purpose of this study was to evaluate the MV sensor rate response of the Medtronic Kappa 400 using exercise data from healthy children in a computer simulation of its rate response algorithm. Thirty-eight healthy children, ages 6-14, underwent a treadmill maximal exercise test. Subjects were divided based on body surface area (BSA) and MV rate response parameters were selected. Respiratory rates and tidal volumes were entered into the Kappa 400 rate response algorithm to calculate sensor-driven rates. Intrinsic heart rate (HR), oxygen uptake, and sensor-driven rates were normalized to HR reserve (HRR), metabolic reserve (MR), and sensor-driven reserve to compare across groups. Linear regression analysis among sensor-driven rate reserve, HRR, and MR was performed as described by Wilkoff. The mean slopes (+/- SD) of the relationships between the sensor-driven rate reserve and HRR were 1.06 +/- 0.34, 1.07 +/- 0.28, and 1.01 +/- 0.19 for children with BSA < 1.10 m2, 1.10 < BSA < 1.40 m2, and BSA > 1.40 m2, respectively. High correlations were found between sensor-drive rates and HR responses and between sensor-drive rates and MV throughout exercise. No significant differences were noted between sensor-drive rates and HR using the Wilkoff model. From this study the authors conclude that: (1) MV is a good physiological parameter to control heart rate and (2) simulated sensor-driven rates closely match intrinsic HRs during exercise in healthy children, which supports the appropriateness of clinical validation in pediatric pacemaker patients.