Relationship between juvenile obesity, dietary energy and fat intake and physical activity.

OBJECTIVE: To determine the relationship of juvenile obesity to dietary fat, particularly saturated fat, and with dietary energy (controlling for activity patterns). DESIGN: Cross-sectional, evaluation of diet and activity patterns of obese and non-obese children and adolescents. SUBJECTS: A total of 181 children, aged 4-16 y. Subjects were divided into two groups: obese (body mass index, BMI, > 95th percentile for age and sex), 40 males and 51 females; and non-obese (BMI < 75th percentile for age and sex), 35 males and 55 females. MEASUREMENTS: Dietary intake was analyzed with a dietary history interview; activity patterns were analyzed with an activity interview and body fat was measured with bioelectrical impedance analysis. RESULTS: The obese subjects consumed significantly more total calories, total fat in grams and saturated fatty acids (SFA) in grams than did the non-obese subjects. Based on step-wise multiple regression, the total energy consumed, not total fat or SFA, had the strongest relationship to the subject's percentage body fat, controlling for activity levels. CONCLUSION: We suggest that, although obese children and adolescents consume more dietary energy and fat than non-obese children and adolescents, there is a stronger relationship between total energy consumed and juvenile adiposity than with dietary fat or type of dietary fat consumed.

Relationship between pacemaker dependency and the effect of pacing mode on cardiovascular outcomes.

BACKGROUND: A recently completed trial, the Canadian Trial of Physiological Pacing (CTOPP), showed that physiological pacing did not significantly reduce mortality, stroke, or heart failure hospitalization, but it did show that atrial fibrillation occurred less frequently in patients with physiological pacing. Many pacemaker patients experience only transient bradyarrhythmias with an adequate unpaced heart rate (UHR) and are not pacemaker-dependent. The purpose of the present analysis was to determine if pacemaker-dependent patients have an increased benefit from physiological pacing compared with non-pacemaker-dependent patients. METHODS AND RESULTS: Of 2568 patients included in the CTOPP trial, 2244 patients had a pacemaker dependency test performed at the first follow-up visit. The yearly event rate of cardiovascular death or stroke steadily increased with decreasing UHR in the ventricular pacing group, but it remained constant in the physiological pacing group. When the patients were subdivided to UHR 60 bpm, there was an interaction between pacing mode treatment and UHR subgroup. The Kaplan-Meier plot confirmed a physiological pacing advantage only in the UHR

Patients at lower risk of arrhythmia recurrence: a subgroup in whom implantable defibrillators may not offer benefit. Antiarrhythmics Versus Implantable Defibrillator (AVID) Trial Investigators.

OBJECTIVES: The goal of this study was to identify subgroups of arrhythmia patients who do not benefit from use of the implantable cardiac defibrillator (ICD). BACKGROUND: Treatment of serious ventricular arrhythmias has evolved toward more common use of the ICD. Since estimates of the cost per year of life saved by ICD therapy vary from $25,000 to perhaps $125,000, it is important to identify patient subgroups that do not benefit from the ICD. METHODS: Data for 491 ICD patients enrolled in the Antiarrhythmics Versus Implantable Defibrillators Study were used to create a hazards model relating baseline factors to time to first recurrent arrhythmia. The model was used to predict the hazard for recurrent arrhythmia among all trial patients. A priori cut points provided lower and higher recurrent arrhythmia risk strata. For each stratum the incremental years of life due to ICD versus antiarrhythmic drug therapy were calculated. RESULTS: Factors that predicted recurrent arrhythmia were: ventricular tachycardia as the index arrhythmia, history of cerebrovascular disease, lower left ventricular ejection fraction, a history of any tachyarrhythmia before the index event and the absence of revascularization after the index event. Survival times (over a follow-up of three years) were identical in each arm of the lowest risk sextile (survival advantage 0.03 +/- 0.12 [se] years), while the survival advantage for patients above the first sextile was 0.27 +/- 0.07 (se) years (two-sided p = 0.05). CONCLUSIONS: Patients presenting with an isolated episode of ventricular fibrillation in the absence of cerebrovascular disease or history of prior arrhythmia who have undergone revascularization or who have moderately preserved left ventricular function (left ventricular ejection fraction > 0.27) are not likely to benefit from ICD therapy compared with amiodarone therapy.

Circadian variation of paroxysmal atrial fibrillation. PA3 Investigators. Atrial Pacing Peri-ablation for Prevention of Atrial Fibrillation Trial.

The circadian variation of paroxysmal atrial fibrillation (AF) was studied in 67 patients who received a dual-chamber pacemaker 3 months before a planned atrioventricular node ablation. A distinct circadian variation of AF was observed with 2 time peaks in initiation (1 in the early morning and 1 in the early evening hours), which was modulated by atrial pacing, the duration of AF, and the use of beta-adrenergic blocking agents.

Influence of threonine intake on whole-body protein deposition and threonine utilization in growing pigs fed purified diets.

The relationship between available threonine (Thr) intake and whole-body protein deposition (PD) was established using the serial slaughter method in 36 individually housed growing gilts between 39 and 77 kg live BW. Pigs were prescreened for their maximum PD (PDmax), based on a N balance starting at 25 kg BW while they consumed semi-ad libitum a nonlimiting diet. Pigs were fed combinations of a casein and cornstarch-based diet that was confirmed to be first-limiting in Thr and a protein-free diet starting at approximately 30 kg BW. Casein-bound Thr was provided at 60, 70, 80, 90, 100, or 120% of estimated Thr requirements for PDmax. Energy intake was kept constant across treatments and exceeded requirements for PDmax. Pigs were fed three equal meals per day; feeding levels were adjusted weekly based on BW. Pigs were killed at either 39 kg BW (n = 2 per treatment) or 77 kg BW (n = 4 per treatment) for determining chemical body composition. Composition of 39-kg BW pigs was not different across treatments (P > 0.10); therefore, an overall mean initial body composition was used to estimate body protein content at the initial BW. Across treatments, mean daily ME intake was 25.3 (SE 0.08) MJ/d and did not differ (P > 0.10) among treatments. Average daily true ileal digestible Thr intake varied between 5.33 and 9.66 g/d, representing means for pigs on the lowest and the highest Thr intakes, respectively. Mean PD was 93, 102, 118, 124, 139, and 133 (SE 4.2) g/d for pigs on the six respective treatments. Dietary Thr intake did not influence (P > 0.10) Thr content of body protein at the final BW or the partitioning of body protein between carcass, viscera, and blood. The efficiency of Thr utilization for PD was lowest (P < 0.05) at the highest Thr intake level and highest (P < 0.05) at the lowest Thr intake level. It was similar (P > 0.10) at the four intermediate Thr intake levels, in which the relationship between true ileal digestible Thr intake and PD was linear. Based on these four treatments, calculated Thr disappearance, which is closely associated with inevitable Thr catabolism, was 23.5 (SE 0.55)% of available Thr intake. This value is consistent with an efficiency of using available Thr intake above maintenance Thr requirements (54 mg/kg BW0.75) for Thr retention with PD of 73.4 (SE 1.11)%. Based on N balances conducted at approximately 40 and 75 kg BW, the marginal efficiency of Thr utilization was not influenced by BW.

Randomized crossover comparison of DDDR versus VDD pacing after atrioventricular junction ablation for prevention of atrial fibrillation. The atrial pacing peri-ablation for paroxysmal atrial fibrillation (PA (3)) study investigators.

BACKGROUND: Some clinical data suggest that atrial-based pacing prevents paroxysmal atrial fibrillation (AF). This study tested the hypothesis that DDDR pacing compared with VDD pacing prevents AF after atrioventricular (AV) junction ablation. METHODS AND RESULTS: Patients were randomized to DDDR pacing (n=33) or to VDD pacing (n=34) after AV junction ablation and followed every 2 months for 6 months. Patients then crossed over to the alternate pacing mode and were followed for an additional 6 months. Primary analysis included the time to first recurrence of sustained AF (duration >5 minutes), total AF burden, and the development of permanent AF. The time to first episode of AF was similar in the DDDR group (0.37 days, 95% CI 0.1 to 1.3 days) and the VDD pacing group (0.5 days, 95% CI 0.2 to 1.7 days, P=NS). AF burden increased over time in both groups (P<0.01). At the 6-month follow-up, AF burden was 6.93 h/d (95% CI 4. 37 to 10.96 h/d) in the DDDR group and 6.30 h/d (95% CI 3.99 to 9.94 h/d) in the VDD group (P=NS). Twelve (35%) patients in the DDDR group and 11 (32%) patients in the VDD group had permanent AF within 6 months of ablation. Within 1 year of follow-up, 43% of patients had permanent AF. CONCLUSIONS: DDDR pacing compared with VDD pacing does not prevent paroxysmal AF over the long term in patients in the absence of antiarrhythmic drug therapy after total AV junction ablation. Many patients have permanent AF within the first year after ablation.

High rate atrial tachyarrhythmia detections in implantable pulse generators: low incidence of false-positive detections. The PA Clinical Trial Investigators.

Some newer pulse generators have enhanced diagnostic features that provide information on the frequency, date, time of onset, and duration of atrial and/or ventricular tachyarrhythmias. However, the sensitivity and specificity of device-based atrial tachyarrhythmia detections may vary and depend, in part, on lead position and selected programming parameters. The prevalence of inappropriate detections of paroxysmal atrial fibrillation (PAF) was investigated in 97 patients who received a Thera DR pacemaker 3 months prior to a planned AV node ablation. Patients were randomized to no atrial or to rate adaptive atrial pacing therapy and followed for 3 months. Following a total AV node ablation, patients were randomized to DDDR versus VDD pacing and followed for 1 year. The high rate atrial episode diagnostic feature was used for detection of PAF and the diagnostic data were retrieved during follow-up visits. Criteria were developed to identify oversensing due to near-field P wave detections, far-field R wave detections, or competitive atrial pacing as causes of false-positive atrial tachyarrhythmia detections. A total of 1,636 detections of PAF were recorded in patients preablation. Only 48 episodes (2.9%) were characterized as false-positive detections; 25 episodes (1.5%) were classified as oversensing, and 23 episodes (1.4%) were classified as competitive atrial pacing. A total of 3,061 detections of PAF were recorded postablation. Only four episodes (0.1%) were classified as oversensing. Thus, the diagnostic atrial tachyarrhythmia detection feature in newer pacemakers is an effective method for evaluating the time course of PAF in patients with implantable pulse generators.

Temporal patterns of paroxysmal atrial fibrillation following DDDR pacemaker implantation.

Paroxysmal atrial fibrillation (AF) episodes have been reported to be randomly distributed. However, because patients are not always symptomatic, it has been difficult to study temporal patterns of AF. Newer implantable pulse generators have data-logging capabilities that permit the detection and analysis of temporal patterns of AF. This study tested the hypothesis that AF episodes occur in clusters over time and that these episodes are not randomly distributed in individual patients. The date and time of 582 episodes of AF were recorded from the data logs of 16 patients with a Medtronic Thera DR followed 6 weeks and 6 and 12 months after pulse generator implant. The probability of AF recurrence and the interevent intervals between successive episodes of AF were fitted to monoexponential and Weibull distributions. A Weibull distribution best described the nonrandom distribution of AF for 67% of follow-up visits. Temporal clustering of AF (interevent intervals <24 hours) declined during follow-up (95 +/- 10%, 90 +/- 11%, and 74 +/- 28% at the 6-week and 6- and 12-month visits, respectively; p <0.05). The average duration of an episode of AF tended to increase over time (0.31 hour, 95% confidence intervals [CI] 0.17 to 0.58 hours; 0.36 hours, 95% CI 0. 17 to 0.78 hours; 0.65 hours, 95% CI 0.29 to 1.45 hours [p = 0.07] at the 6-week and 6- and 12-month visits, respectively). Paroxysmal AF recurrence is nonrandomly distributed over the long term in many patients. The temporal patterns of AF change over time after pacemaker implantation. This has implications for the selection of study end points in AF clinical trials.

Influence of dietary lysine and energy intakes on body protein deposition and lysine utilization in the growing pig.

A serial slaughter study was conducted to determine the effects of true ileally digestible lysine (IDLys) intake and metabolizable energy intake (MEI) on whole-body protein deposition (PD) and dietary lysine utilization in pigs between 45 and 75 kg live weight (LW). Conventional N balances were determined at the start and end of the serial slaughter study. Semisynthetic diets based on casein and cornstarch provided protein-bound lysine to support protein depositions of approximately 70% (Lys70%, IDLys 11.1 g/d) or 90% (Lys90%, IDLys 13.2 g/d) of a determined maximum PD. During the serial slaughter study and at Lys70%, pigs were fed one of six levels of MEI ranging from 14.1 to 23.5 MJ/d; at Lys90%, pigs were fed one of seven levels of MEI ranging from 15.6 to 26.4 MJ/d. The serial slaughter study and N balances indicated that MEI and IDLys had independent effects on PD and lysine utilization. Lysine utilization (calculated as the fraction of absorbed available lysine, over and above maintenance lysine requirements, that was retained in body protein) and PD increased with increasing MEI until plateau values were reached. At the plateaus, PD was determined by lysine intake. When lysine intake determined PD, lysine utilization did not decline (P > 0.10) with increasing lysine intake. Based on the N balance study, there was no effect (P > 0.1) of LW on lysine utilization. The marginal efficiency of using absorbed available lysine for PD was 0.75 and was not affected by LW, MEI, or IDLys.

Mechanism of ventricular defibrillation. The role of tissue geometry in the changes in transmembrane potential in patterned myocyte cultures.

BACKGROUND: The geometry of the myocardium may influence changes in transmembrane potential (DeltaVm) during defibrillation. To test this hypothesis, specific nonlinear structures (bifurcations, expansions, and curved strands or "bends") were created in patterned cultures of neonatal rat myocytes. METHODS AND RESULTS: Extracellular field stimuli (EFS; 7 to 11 V/cm field strength) were applied parallel to the strands. Changes in Vm were measured with microscopic resolution using optical mapping techniques. In bifurcations, EFS produced 2 DeltaVm maxima (so-called secondary sources) at the shoulder of each limb that were separated by a decrease of either hyperpolarization or depolarization at the insertion of the stem strand. In expansions, EFS produced a significant decrease in DeltaVm at the insertion site of the expansion compared with the DeltaVm maxima measured at the lateral borders. In 50% of experiments, tertiary sources of opposite polarity appeared in the strand due to local electrotonic currents. New action potentials were propagated from the sites of DeltaVm maxima located at the lateral borders of the expansions. In bends, the strand oriented in parallel to the field dominated electrotonically and partially cancelled the sources produced by the perpendicular segment. CONCLUSIONS: In electrically well-coupled nonlinear structures, EFS produced changes in Vm at resistive boundaries that were determined by the electrotonic interaction between sources of different, direction-dependent strength. In addition, the interaction between localized secondary sources at nonlinear boundaries generated local current circuits, which gave rise to further changes in Vm (tertiary sources).

Dietary fish oil supplementation adversely affects cortical bone morphology and biomechanics in growing rabbits.

Despite substantial evidence that fish oil-derived (n-3) polyunsaturated fatty acids (PUFA) may protect against cardiovascular disease, the effects of supplements containing (n-3) PUFA on the skeletal system are unknown. Here we investigated how a diet supplemented with 10 g/100 g fish oil affected tibial cortical morphology and mechanical properties in weanling rabbits. Rabbits were subdivided into a normal control (n = 10), a fish oil (n = 20), and a pair-fed (n = 20) group. The pair-fed group was energy restricted to match average body mass of the fish oil group. At completion of the 40 day dietary intervention, control rabbits were significantly heavier than the other two groups. Comparison between control and pair-fed rabbits revealed that energy restriction alone (30%) did not induce significant changes in tibial middiaphyseal morphology, but tibial longitudinal growth was significantly impaired. Most tibial mechanical properties were significantly degraded by energy restriction. Fish oil-supplemented rabbits had significantly smaller middiaphyseal areal properties and shorter tibiae than pair-fed rabbits. Tibial structural properties were significantly reduced in fish oil-fed rabbits, but tibial stress at the proportional limit (material property) was not significantly affected. Our data suggest that 10% fish oil supplementation in the presence of modest vitamin E supplementation can have detrimental effects on the skeleton of rapidly growing rabbits.

Effects of antiarrhythmic drugs on QT interval dispersion--relationship to antiarrhythmic action and proarrhythmia.

Class IA, IC, and III antiarrhythmic drugs prolong ventricular repolarization (VR) which is manifest as QT interval prolongation on the surface electrocardiogram. These drugs may prolong VR in a spatially heterogeneous manner which results in increased dispersion of VR. This may be manifest as increased QT interval dispersion. Antiarrhythmic drug-induced decreases in QT interval dispersion are associated with antiarrhythmic efficacy in patients with the long QT syndrome and in patients with sustained ventricular tachycardia. Antiarrhythmic drug-induced increases in QT interval dispersion are associated with ventricular proarrhythmia secondary to torsades de points ventricular tachycardia. A number of factors may modulate the effects of antiarrhythmic drugs on dispersion of VR, including the disease state, transient ischemia, electrolyte abnormalities, changes in autonomic tone, and hemodynamic stress.

Guidelines for pacemaker follow-up in Canada: a consensus statement of the Canadian Working Group on Cardiac Pacing.

A survey on Canadian pacing practices conducted in 1997 revealed a widespread desire for national guidelines on pacemaker follow-up. The present guidelines for pacemaker follow-up are a consensus statement of the Canadian Working Group on Cardiac Pacing. Direct patient follow-up rather than transtelephonic monitoring is desirable. Patients should be assessed at a minimum of within 72 h of implantation, at two to 12 weeks and at six months following implantation, and annually thereafter. More frequent assessments may be required for some patients. This depends on associated cardiovascular problems and specific devices. A typical follow-up visit should include a targeted cardiovascular assessment, interrogation of the pacing system, review of telemetered data, assessment of the underlying rhythm, assessment of pacing and sensing thresholds, and appropriate reprogramming of pacing parameters to optimize device function and longevity.

Conduction time oscillations precede the spontaneous termination of human atrioventricular reciprocating tachycardia.

Prior clinical research indicates that conduction slowing is the primary mechanism leading to the spontaneous termination of reentrant tachycardia in humans. Yet, some experimental models indicate that cycle length oscillations and enhanced conduction are important prerequisites. The role of oscillations in conduction times and enhanced conduction in the spontaneous termination of human reentrant tachycardia has not been adequately investigated. The electrophysiologic features preceding the spontaneous termination of orthodromic atrioventricular (AV) reciprocating tachycardia (RT) were evaluated in 21 patients, each of whom had a sustained (>60 seconds) and a spontaneously terminating (>/=10 beats and

Pacing to prevent atrial fibrillation.

Present therapies for the treatment of atrial fibrillation (AF) are often ineffective or not well-tolerated. Atrial-based pacing reduces the development of AF in the general pacemaker population. Presently, a number of studies are exploring the role of atrial pacing for prevention of AF. This article reviews the rationale for atrial pacing as a treatment for AF and the results of recent studies evaluating atrial pacing for prevention of AF.

Effects of physiologic pacing versus ventricular pacing on the risk of stroke and death due to cardiovascular causes. Canadian Trial of Physiologic Pacing Investigators.

BACKGROUND: Evidence suggests that physiologic pacing (dual-chamber or atrial) may be superior to single-chamber (ventricular) pacing because it is associated with lower risks of atrial fibrillation, stroke, and death. These benefits have not been evaluated in a large, randomized, controlled trial. METHODS: At 32 Canadian centers, patients without chronic atrial fibrillation who were scheduled for a first implantation of a pacemaker to treat symptomatic bradycardia were eligible for enrollment. We randomly assigned patients to receive either a ventricular pacemaker or a physiologic pacemaker and followed them for an average of three years. The primary outcome was stroke or death due to cardiovascular causes. Secondary outcomes were death from any cause, atrial fibrillation, and hospitalization for heart failure. RESULTS: A total of 1474 patients were randomly assigned to receive a ventricular pacemaker and 1094 to receive a physiologic pacemaker. The annual rate of stroke or death due to cardiovascular causes was 5.5 percent with ventricular pacing, as compared with 4.9 percent with physiologic pacing (reduction in relative risk, 9.4 percent; 95 percent confidence interval, -10.5 to 25.7 percent [the negative value indicates an increase in risk]; P=0.33). The annual rate of atrial fibrillation was significantly lower among the patients in the physiologic-pacing group (5.3 percent) than among those in the ventricular-pacing group (6.6 percent), for a reduction in relative risk of 18.0 percent (95 percent confidence interval, 0.3 to 32.6 percent; P=0.05). The effect on the rate of atrial fibrillation was not apparent until two years after implantation. The observed annual rates of death from all causes and of hospitalization for heart failure were lower among the patients with a physiologic pacemaker than among those with a ventricular pacemaker, but not significantly so (annual rates of death, 6.6 percent with ventricular pacing and 6.3 percent with physiologic pacing; annual rates of hospitalization for heart failure, 3.5 percent and 3.1 percent, respectively). There were significantly more perioperative complications with physiologic pacing than with ventricular pacing (9.0 percent vs. 3.8 percent, P<0.001). CONCLUSIONS: Physiologic pacing provides little benefit over ventricular pacing for the prevention of stroke or death due to cardiovascular causes.

Dispersion of ventricular repolarization and ventricular fibrillation in left ventricular hypertrophy: influence of selective potassium channel blockers.

This study tested the hypothesis that combination ion channel blockers of the transient outward current (I(to)) and the rapid component of the delayed rectifying current (I(Kr)) would produce greater prolongation of the ventricular action potential duration (APD) and increased dispersion of the APD in hypertrophied hearts compared with control hearts. Isolated rabbit hearts were studied 48 +/- 5 days postabdominal aortic banding. Left ventricular endocardial and epicardial APDs were significantly greater at baseline in the hypertrophied group than in controls (P <.05). The magnitude of APD prolongation induced by the I(to) blocker 4-aminopyridine (4-AP) and combination 4-AP and the I(Kr) blocker dofetilide was greater in the hypertrophied hearts than in the normal hearts (P <.01). Mean APD dispersion was significantly greater in the hypertrophied group than in the control hearts at baseline (P <.05). 4-AP increased APD dispersion by a similar magnitude in the hypertrophied hearts (10 +/- 10 ms) and the control hearts (8 +/- 8 ms, P = NS), whereas the combination 4-AP and dofetilide increased APD dispersion by a greater magnitude in the hypertrophied hearts (41 +/- 28 ms) than the control hearts (21 +/- 11 ms, P <.05). Ventricular fibrillation occurred spontaneously in four hypertrophied hearts (40%) during combination drug perfusion and in none of the control hearts (P <.05). Thus, combination I(to) and I(Kr) blockers cause greater prolongation APD and increased APD dispersion in left ventricular hypertrophy, and this is associated with the development of ventricular fibrillation.

Atrial pacing periablation for prevention of paroxysmal atrial fibrillation.

BACKGROUND: This study tested the hypothesis that rate-adaptive atrial pacing would prevent paroxysmal atrial fibrillation (PAF) in patients with frequent PAF in the absence of symptomatic bradycardia. METHODS AND RESULTS: Patients (n=97) with antiarrhythmic drug-refractory PAF received a Medtronic Thera DR pacemaker 3 months before planned AV node ablation. Patients were randomized to no pacing (n=48) or to atrial rate-adaptive pacing (n=49). After a 2-week stabilization period, patients were followed up for an additional 10 weeks. The time to first recurrence of sustained PAF, the interval between successive episodes of PAF, and the frequency of PAF were compared between the 2 groups in intention-to-treat analysis. Time to first episode of sustained PAF was similar in the no-pacing (4.2 days; 95% CI, 1.8 to 9.5) and the atrial-pacing (1.9 days; 95% CI, 0.8 to 4.6; P=NS) groups. PAF burden was lower in the no-pacing (0.24 h/d; 95% CI, 0.10 to 0.56) than in the atrial-pacing (0.67 h/d; 95% CI, 0.30 to 1.52; P=0.08) group. Paired crossover analysis in 11 patients revealed that time to first PAF was shorter during atrial pacing (1.6 days; 95% CI, 0.6 to 4.9) than with no pacing (6.0 days; 95% CI, 2.4 to 15.0; P=0.13), and PAF burden was greater during atrial pacing (1.00 h/d; 95% CI, 0.35 to 2.91) than with no pacing (0.32 h/d; 95% CI, 0.09 to 1.13; P<0.016). CONCLUSIONS: Atrial rate-adaptive pacing does not prevent PAF over the short term in patients with antiarrhythmic drug-resistant PAF without symptomatic bradycardia.