Catheter ablation in children and young adults: is there an additional benefit from remote magnetic navigation?

PURPOSE: Although rare, children and young adults can suffer from significant cardiac arrhythmia, especially in the context of congenital malformations and after cardiac surgery. METHODS: A total of 62 patients (32 female, median age 20 years) underwent an invasive electrophysiology study between 2008-2011: half had normal cardiac anatomy, whereas the remaining patients had various types of congenital heart disease. All patients were treated using either conventional techniques (CVN) or remote magnetic navigation (RMN). RESULTS: Patients treated with the RMN system differed substantially from patients in the CVN group with respect to presence of congenital heart disease (67 % vs. 37 %), previous cardiac surgery (59 % vs. 20 %) or failed previous conventional ablation (22 % vs. 9 %), respectively. Although these more complex arrhythmias resulted in longer median procedure duration (180 vs. 130 min, p = 0.034), the median overall fluoroscopy exposure in the RMN group was significantly lower (4.1 vs. 5.2 min, p = 0.020). Clinical outcome was comparable in both groups without complications caused by the ablation. CONCLUSIONS: Catheter ablation using remote magnetic navigation is safe and feasible in children and young adults and is especially valuable in patients with abnormal cardiac morphologies. RMN resulted in significantly lower radiation exposure compared with the conventional technique.

[Contribution of comparative x-rays for infantile traumatology]. / Intérêt des radiographies ostéo-articulaires comparatives en traumatologie de l'enfant.

PURPOSE OF THE STUDY: There is a controversy over whether or not routine comparative x-rays should be prescribed for young children with bone and joint trauma. We conducted a retrospective analysis to assess the contribution of such x-rays. MATERIAL AND METHODS: The series included 203 children aged less than fifteen years who had experienced bone and joint trauma. Two junior orthopedic surgeons, two senior orthopedic surgeons and two pediatric radiologists reread the x-rays to establish the diagnosis, using comparative x-rays to make any necessary correction of the diagnosis. The surgeons were asked to propose a therapeutic strategy for each diagnosis and the radiologists were asked to judge the value of the comparative x-rays. RESULTS: The comparative x-rays were found to be reliable in only 87.5% of the cases, and were useful for diagnosis in only 8.8%. There were statistically significant differences depending on the localization, the patient's age, and the physician's experience. DISCUSSION: Systematic use of comparative x-rays should be discouraged. Only trauma affecting the elbow in older children can, in particular cases, warrant prescription of comparative x-rays.

[A new, spontaneous method for assessing sympathetic baroreflex function in humans]. / Une nouvelle méthode spontanée pour l'évaluation du baroréflexe sympathique chez l'Homme.

In humans, assessment of the sympathetic component of the arterial baroreceptor reflex (sBRS) is usually based on microneurographic recordings of muscle sympathetic nerve activity (MSNA), while inducing reflex changes with intravenous administration of vasoactive drugs (modified Oxford method). This method has several limitations, among which its poor temporal resolution. Some studies have proposed alternative methods by using spontaneous changes in arterial pressure (AP) and MSNA, usually collected under baroreflex closed-loop conditions (AP alters MSNA while MSNA alters AP), which makes the results difficult to interpret. In rats, a method has been developed and validated (Kanbar et al., 2007 [1]), which uses oscillations of renal SNA at the frequency of the heart beat. At this frequency, the baroreflex operates under open-loop conditions because of the low-pass filter properties of the resistance vasculature. The goal of the present study was to examine whether this method is applicable in humans. Data were previously collected by Gujic et al. (2007) [2]. Briefly, MSNA and AP were recorded in 16 young healthy subjects during a 5-minute baseline resting period then during a modified Oxford test (sodium nitroprusside and phenylephrine administrations). Using the 5-minute baseline recordings, spontaneous sBRS was assessed through empirical mode decomposition over consecutive 20-second periods. Spontaneous sBRS was significantly related to pharmacological sBRS (R=0.67, n=16, P=0.004). During the 5-minute period, spontaneous sBRS exhibited variations (CV=21.7±1.7%) that were negatively correlated with AP in five subjects (R=-0.61±0.03, P<0.05) and positively correlated with MSNA in ten subjects (R=0.73±0.03, P<0.05). The new method is able to correctly estimate sBRS, and reveals the existence of previously unrecognized fast fluctuations of sBRS.

Differential effects of oral beta blockade on cardiovascular and sympathetic regulation.

In patients with hypertension, beta blockade decreases muscle sympathetic nerve activity (MSNA; micrographic technique) expressed in burst frequency (burst/min) but does not affect MSNA expressed in burst incidence (burst/100 heart beats), because reductions in blood pressure (BP) upon each diastole continue to deactivate the arterial baroreceptors, but at a slower heart rate (HR). We studied the effects of oral beta blockade on MSNA and baroreflex sensitivity (BRS) in normal participants. Bisoprolol (5 mg, 1 week) was administered in 10 healthy young adults, using a double-blind, placebo-controlled, randomized cross-over study design. The beat-to-beat mean RR interval (RR) and systolic blood pressure (SBP) series were analyzed by power spectral analysis and power computation over the very low frequency (VLF), low frequency, and high frequency (HF) bands. Baroreflex sensitivity was computed from SBP and RR cross-analysis, using time and frequency domain methods. Bisoprolol increased RR (P < .0005), decreased mean SBP and diastolic blood pressure values (P < .01), did not change the SBP and RR powers, except for RR power in VLF (P < .02) and SBP power in HF (P < .03). The MSNA variability (P > .13) and respiratory pattern (P = .84) did not change from placebo to bisoprolol condition. The bisoprolol-induced bradycardia was associated with higher burst/100 heart beats (P < .05) and bisoprolol did not affect burst/min (P = .80). Time domain BRS estimates were increased after bisoprolol (P < .05), while frequency domain ones did not change (P > .1). Oral bisoprolol induces differential effects on sympathetic burst frequency and incidence in normal participants. Peripheral sympathetic outflow over time is preserved as a result of an increased burst incidence, in the presence of a slower HR. Unchanged BP and HR and MSNA variability suggests that the larger burst incidence is not due to sympathetic activation.

Facial cooling and peripheral chemoreflex mechanisms in humans.

AIM: Reductions in arterial oxygen partial pressure activate the peripheral chemoreceptors which increase ventilation, and, after cessation of breathing, reduce heart rate. We tested the hypothesis that facial cooling facilitates these peripheral chemoreflex mechanisms. METHODS: Chemoreflex control was assessed by the ventilatory response to hypoxia (10% O2 in N2) and the bradycardic response to voluntary end-expiratory apnoeas of maximal duration in 12 young, healthy subjects. We recorded minute ventilation, haemoglobin O2 saturation, RR interval (the time between two R waves of the QRS complex) and the standard deviation of the RR interval (SDNN), a marker of cardiac vagal activity throughout the study. Measurements were performed with the subject's face exposed to air flow at 23 and 4 degrees C. RESULTS: Cold air decreased facial temperature by 11 degrees C (P < 0.0001) but did not affect minute ventilation during normoxia. However, facial cooling increased the ventilatory response to hypoxia (P < 0.05). The RR interval increased by 31 +/- 8% of the mean RR preceding the apnoea during the hypoxic apnoeas in the presence of cold air, compared to 17 +/- 5% of the mean RR preceding the apnoea in the absence of facial cooling (P < 0.05). This increase occurred despite identical apnoea durations and reductions in oxygen saturation. Finally, facial cooling increased SDNN during normoxia and hypoxia, as well as during the apnoeas performed in hypoxic conditions (all P < 0.05). CONCLUSION: The larger ventilatory response to hypoxia suggests that facial cooling facilitates peripheral chemoreflex mechanisms in normal humans. Moreover, simultaneous diving reflex and peripheral chemoreflex activation enhances cardiac vagal activation, and favours further bradycardia upon cessation of breathing.