[Catheter ablation for persistent atrial fibrillation: looking for the best strategy]

Drug-refractory atrial fibrillation (AF) can be highly symptomatic and warrant invasive ablation targeting the pulmonary veins. Although limited ablation for paroxysmal AF is associated with a high success rate, more extensive ablation appears to be indicated for persistent AF. The Substrate and Trigger Ablation for Reduction of Atrial Fibrillation Trial Part II (STAR AF II) showed that the addition of complex fractionated atrial electrogram (CFAE) ablation or linear ablation lesions did not result in an improved ablation outcome. However, novel techniques that allow assessment ]\of AF substrate, rotor mapping and AF trigger ablation have been associated with improved ablation outcome and randomised studies evaluating these techniques are currently being designed.

Conventional radiofrequency catheter ablation compared to multi-electrode ablation for atrial fibrillation

BACKGROUND

Limited data is available on long-term atrial fibrillation (AF) free survival after multi-electrode catheter pulmonary vein isolation (PVI). The aim of this study was to compare point-by-point PVI to multi-electrode PVI in terms of procedural characteristics and long-term AF free survival.

METHODS AND RESULTS

460 consecutive patients were randomly allocated: 230 patients underwent conventional, point-by-point ablation with a radiofrequency ablation catheter (cPVI group) and 230 patients underwent multi-electrode, phased radiofrequency ablation (MER group). Median follow-up was 43 months. Mean age was 56 years, 82% of patients had paroxysmal AF. Baseline characteristics did not differ among catheter groups. Acute electrical PVI was achieved in 99.7% of pulmonary veins, with no differences among catheter groups. Procedure time and ablation time were significantly shorter in the MER group. There were significantly less complications in the MER group (4.8% vs. 1.3%, P=0.025). After a mean of 1.5 procedures, AF free survival without the use of antiarrhythmic drugs was 74% at 1 year and 46% at 5 years follow-up and did not differ among catheter groups (cPVI group 45%, MER group 48%, P=0.777). In multivariate analysis, BMI, AF duration and CHADSVASc score were predictors of AF free survival.

CONCLUSION

Multi-electrode ablation was superior in procedure duration and ablation time, with less complications. However, both conventional point-by-point PVI and multi-electrode PVI achieved a high acute PVI success rate and showed a comparable long-term AF free survival.

ChronOS inject in children with benign bone lesions--does it increase the healing rate?

OBJECTIVE

Benign bone lesions in children although rare, can result in a pathological fracture. Although their etiology and pathogenesis are not yet entirely clear, the phenomenon of spontaneous healing is well known. Nevertheless, some benign bone lesions are unlikely to heal spontaneously due to the patient's age or high risk of fracture and deformity due to the lesion's location or size. The following study presents our results after treatment of these bone cysts with chronOS Inject.

METHODS

From June 2004 to May 2007 23 patients with 24 benign bone cysts were treated with chronOS Inject, an injectable tricalcium phosphate, using a minimally invasive technique at two pediatric surgery departments. Postoperative follow-up examined bone healing, remodeling, chronOS Inject resorption and adverse effects.

RESULTS

15 males and 9 females, mean age 11 years at time of diagnosis, were treated with chronOS Inject. The humerus was affected 13 times, the femur 7 times, the tibia twice and the radius, the fibula and talus once each. Except for one case, all pathological fractures healed within five weeks post-injection. Two children had cystic residues. No severe adverse effects were seen.

CONCLUSIONS

These preliminary results indicate that chronOS Inject could provide an alternative treatment for benign bone cysts that are unlikely to heal spontaneously due to the patient's age, high risk of instability or pathological fracture due to the lesion's size or location, or lesions that have already been treated several times using other methods without success.

A multicenter evaluation of gentamicin therapy in the neonatal intensive care unit

STUDY OBJECTIVE

To evaluate traditional nomogram (TN) versus individualized pharmacokinetic gentamicin dosing practices in neonatal intensive care units, focusing on achieving target therapeutic concentrations (peak > 8 microg/ml, trough < 2 microg/ml), number of dosing changes, number of concentrations obtained, and evidence of nephrotoxicity.

DESIGN

Retrospective chart review.

SETTING

Three neonatal intensive care units.

PATIENTS

Three hundred nine infants prescribed gentamicin.

INTERVENTION

None.

MEASUREMENTS AND MAIN RESULTS

Sixty-seven percent of patients receiving pharmacokinetic dosing had initial peak concentrations of 8 microg/ml or greater compared with 7% of patients receiving TN dosing (p<0.001). Trough concentrations exceeding 2 microg/ml were reported in 23% of patients receiving TN dosing compared with 2% of pharmacokinetic-dosed patients (p<0.001). Forty-two percent and 6%, respectively, required dosage adjustments (p<0.01). The mean number of concentrations obtained per patient was 2.8 and 2.1, respectively (p<0.01). Neither group had evidence of gentamicin-related nephrotoxicity.

CONCLUSION

Compared with TN dosing, administering gentamicin loading doses and performing initial pharmacokinetic analysis resulted in rapid attainment of desired concentrations and fewer dosage adjustments, and allowed for a decrease in the number of gentamicin concentrations.

Use of enoxaparin in a preterm infant

OBJECTIVE

To describe the use of enoxaparin to treat suspected thrombosis in a preterm neonate.

CASE DESCRIPTION

A 29-week-gestation white infant with a family history of protein S deficiency lost color and blood flow to the right hand several hours after removal of the umbilical artery catheter. Although normal color returned to all except the distal first, second, and third fingers after warming, Doppler flow showed a radial artery defect, indicating a lack of blood flow. Enoxaparin 1 mg/kg intravenously every eight hours was then started. Heparin concentrations measured via anti-Xa assay drawn four and eight hours after a dose were 0.78 and 0.39 units/mL, respectively. Pharmacokinetic parameters calculated from these concentrations using a one-compartment model were elimination half-life four hours, volume of distribution 0.13 L/kg, and clearance 0.022 L/kg/h. No adverse effects were noted. Blood flow eventually returned, leaving only the third fingertip chronically injured.

DISCUSSION

Differences between the neonatal and adult hemostatic systems contribute to an increased risk of thromboembolic events and an altered sensitivity to heparin anticoagulation in the neonate. Although heparin is currently the anticoagulant of choice, it may produce several adverse effects, such as hemorrhage and thrombocytopenia, which may be avoided by use of low-molecular-weight heparins (LMWHs). However, despite the efficacy and improved safety profile of LMWHs in adults, data regarding their use in children and neonates are scarce. This case demonstrates that enoxaparin can be used safely and effectively in a preterm infant through appropriate monitoring of heparin concentrations to adjust dosages. A larger volume of distribution of enoxaparin was noted in this neonate than in adults.

CONCLUSIONS

Enoxaparin 1 mg/kg intravenously every eight hours was used safely in this preterm infant with suspected thrombosis, suggesting that more than one dosing regimen may be appropriate in this population.

Comparing the delivery of albuterol metered-dose inhaler via an adapter and spacer device in an in vitro infant ventilator lung model

OBJECTIVE

To compare the delivery of an albuterol metered-dose inhaler (MDI) (Ventolin) via an Aerochamber (Monaghan) with an inline adapter (Medicomp Straight Swivel) in an in vitro infant lung model.

METHODS

An in vitro infant lung model was modified to compare the delivery of albuterol MDI 10 inhalations via an Aerochamber with an inline adapter. The adapter and Aerochamber were placed at the endotracheal tube. A 1000 mL intravenous bag filled with 500 mL deionized water was attached to a 3.5 mm endotracheal tube (10 cm length). An Infant Bear Cub ventilator was used at the following settings: positive inspiratory pressure 20 cm H2O, intermittent mandatory ventilation 40 breaths/min, positive end expiratory pressure 4 cm H2O, and inspiratory time 0.5 second. Each device was run at least 10 times and assayed in duplicate by HPLC. An unpaired Student's t-test was used to analyze the statistical significance of the data.

RESULTS

There was significantly greater delivery of albuterol with the Aerochamber (19.49 +/- 7.23 microg; 2.17% +/- 0.8%) as compared with an inline adapter (1.0625 +/- 1.36 microg; 0.12% +/- 0.15%) (p = 0.001).

CONCLUSIONS

The Aerochamber provides a greater delivery of albuterol metered-dose inhalations to the lung than the inline adapter in an in vitro infant lung model.

Evaluating the delivery of nebulized and metered-dose inhalers in an in vitro infant ventilator lung model

OBJECTIVE

To evaluate drug delivery to the lungs of nebulized and metered-dose inhalers (MDIs) in an in vitro infant lung model.

METHODS

An in vitro lung model was modified to study drug delivery. A 1000 mL intravenous bag filled with 500 mL deionized water was attached to a 3.5 mm (12 cm length) endotracheal tube. An inline Marquest Whisper Jet infant circuit nebulizer system delivered 2.5 mg/3 mL albuterol sulfate inhalation solution (Ventolin nebules) at a flow rate of 5 L/min. An Aerochamber (Monaghan) was placed at the endotracheal tube for the delivery of the MDIs. Albuterol MDI (Ventolin) 10 inhalations and beclomethasone MDI (Beclovent) 20 inhalations were delivered. A Servo 900C (Siemens-Elma) was used at the following ventilator settings: positive inspiratory pressure 30 cm H2O), intermittent mandatory ventilation 40 breaths/min, positive end expiratory pressure 4 cm H2O, inspiratory time 0.4 sec. Each formulation was run at least 10 times and assayed in duplicate by HPLC. An unpaired Student's t-test was used to analyze the statistical significance of the data.

RESULTS

There was a significantly greater percentage of drug delivery with MDI albuterol (1.96 +/- 0.50) as compared with nebulized albuterol (1.26 +/- 0.37) (p = 0.002) or beclomethasone diproprionate (0.51 +/- 0.24) (p = 0.001).

CONCLUSIONS

Albuterol MDI provides a more efficient delivery of drug to the lung as compared with nebulized albuterol and MDI beclomethasone diproprionate.

Antiretroviral medication compliance in patients with AIDS

The paradigm of AIDS patient care has evolved to that of a chronic disease that is manageable with combination antiretroviral therapy. Intermittent adherence to antiretroviral regimens, however, has been associated with the selection of HIV mutations, resulting in drug-resistant virus. Medication compliance has become a vital component in the care of HIV-infected patients. This study was designed to assess the degree of medication compliance with zidovudine (ZDV) over a 2-month period among a convenience sample of 23 ambulatory patients with HIV infection. Enrollment took place during February to March 1995, when monotherapy with ZDV was considered the standard of care. Medication compliance was assessed by three methods: patient self-report determined by questionnaire, pharmacy refill records from the 3 months immediately before entry in the study, and an electronic monitoring system (Medication Event Management Systems [MEMS], Aprex Corp., Fremont, CA), which records the date and time of each opening of the medication vials. MEMS was utilized among a subgroup of eight participants over a 2-month period. Despite greater than 95% (22 of 23) of the subjects reporting that they believed ZDV was life prolonging, a majority took < or = 75% of the prescribed doses of ZDV as identified by both refill and MEMS methods. The mean percentage compliance over a 2-month period of observation for MEMS and pharmacy refill record review methods was 66% and 78%, respectively (p = 0.294). Among the subgroup of eight in the MEMS evaluation, 88% reported taking their ZDV according to the directions, all of the time. These results demonstrate that reliance upon patient self-report of medication compliance is less accurate than MEMS or pharmacy refill records, and that reliance on self-reporting could lead to erroneous assumptions of the patient's true drug compliance. In addition, the study suggests that pharmacy refill records may provide a method of assessing compliance that is equivalent to MEMS but is less experimental, and can easily be followed and interpreted by pharmacists and other clinicians caring for patients infected with HIV. Most importantly, relatively poor compliance rates demonstrated by MEMS raises serious concern for widespread development of HIV resistance to the more complicated, multiple-drug regimens in present use.

Evaluation of a sparse sampling strategy for determining vancomycin pharmacokinetics in preterm neonates: application of optimal sampling theory

OBJECTIVE

To use optimal sampling theory to determine the fewest vancomycin concentrations required and the appropriate sampling times to calculate vancomycin pharmacokinetic parameters in neonates.

DESIGN

Unblinded evaluation in neonates with presumed sepsis.

SETTING

Level 3 community-based neonatal intensive care unit.

PATIENTS

Eleven neonates with presumed sepsis.

INTERVENTIONS

Twelve courses of intravenous vancomycin 20 mg/kg were administered. Blood samples were collected 3 and 9 hours after initiation of a 1-hour infusion of the first dose.

MEASUREMENTS AND MAIN RESULTS

A two-compartment model was fit to vancomycin concentrations using iterative two-stage analysis. Pharmacokinetic parameter estimates were used for determination of optimal sampling times for two-, three-, and four-sample strategies with subsequent generation of two-, three-, and four-sample concentration data for 100 cases. Relative performance of strategies was compared through calculation and comparison of D efficiency for the determined strategies. Bias (median percent error) and precision (median percent absolute error) of pharmacokinetic parameter estimates for each strategy in the 100 simulated cases were determined.

CONCLUSIONS

For estimation of total clearance and volume in the central and peripheral compartments, all strategies performed similarly with no difference in efficiency or bias and precision of estimates. Our results suggest that for clinical evaluations two appropriately timed samples (0.5 h after a 1-h infusion, trough concentration) are adequate for estimation of vancomycin clearance in neonates.

Gentamicin pharmacokinetics in neonates with patent ductus arteriosus

OBJECTIVES

To determine the effect of patent ductus arteriosus on the pharmacokinetics of gentamicin in neonates and to examine whether any particular pharmacokinetic parameter is of value as a marker of patent ductus arteriosus.

DESIGN

Cohort study of neonates treated with gentamicin, according to a standard dosing protocol.

SETTING

A 24-bed, Level III, neonatal intensive care unit.

PATIENTS

Neonates treated with gentamicin at the time of admission to the neonatal intensive care unit, using a standard protocol, and who were < 36 wks of gestational age.

INTERVENTIONS

All patients received a gentamicin loading dose, and had gentamicin concentrations measured at 2 and 12 hrs after this dose, in order to determine pharmacokinetic parameters and calculate the optimum maintenance dose. Those neonates subsequently diagnosed to have patent ductus arteriosus, based on clinical suspicion and echocardiographic confirmation, were compared with those neonates without clinically suspected patent ductus arteriosus. Gentamicin pharmacokinetic parameters were calculated using a one-compartment model.

MEASUREMENTS AND MAIN RESULTS

A total of 322 courses of gentamicin were administered (patent ductus arteriosus, n = 106; control, n = 216). Gentamicin clearance was decreased in the patent ductus arteriosus group vs. the control group (40.02 vs. 44.73 mL/kg/hr; p < .0108). Volume of distribution was greater for patent ductus arteriosus patients (0.61 L/kg) than for controls (0.54 L/kg) (p < .0002). Also, volume of distribution was a useful marker for presence of patent ductus arteriosus, with a 92% specificity for patent ductus arteriosus.

CONCLUSIONS

Gentamicin dosing should be altered in neonates with patent ductus arteriosus to reflect the impact of higher volume of distribution and lower clearance. When the gentamicin volume of distribution exceeds 0.7 L/kg, it may be of predictive value for the presence of patent ductus arteriosus.

Recent advances in pediatrics

The challenging issues in pediatric pharmacotherapy are both profound and exciting. Microtechnologies for evaluating the impact of genetics in disease (e.g., using polymerase chain reactions) and the possibilities of therapeutic interventions create major clinical and ethical dilemmas that remain to be resolved. Inclusion of pediatric patients in drug development and marketing trials also remains a point of contention. Finally, well-established therapies should not be overlooked in favor of new but unestablished treatment approaches. Future columns will continue to use the current format, in which a few selected topics of high therapeutic importance are discussed. The research technologies, discussion of new drug therapy interventions, and preventive strategies most likely to benefit the health care of infants, children, and adolescents will remain the scope of this column.