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PubMedDate not supplied

Rate control vs rhythm control strategies in atrial fibrillation.

Rhythm management for atrial fibrillation is a subject of intense interest. In this review, the two main strategies for rhythm management in atrial fibrillation, the "heart rate control" strategy and the "heart rhythm control" strategy, are discussed under several headings. Some of the basic issues surrounding heart rate control and heart rhythm control and their study in clinical trials are reviewed. Seven published trials that deal with a comparison of these two strategies are reviewed in some detail. In summary, no distinct advantage of the rhythm control strategy has been identified so far. With respect to pharmacologic therapies and the type of patient studied in most of these trials, advantages seem to accrue to the rate control strategy. Those advantages include fewer adverse drug effects, fewer hospitalizations, and lower cost. Two trials studying quite different patients, and in one case quite different drug therapies, are currently in progress, and these two trials are also briefly reviewed. Current guidelines have not taken into account fully the findings of the studies described in this review, and comment is offered on the current guidelines. Finally, some of the possibilities for future research around this question are highlighted.

Anti-Arrhythmia Agents↗

PubMed1998

Long Term Management of Atrial Fibrillation: Maintenance of Sinus Rhythm vs. Rate Control and Anticoagulation.

Two strategies for treatment of atrial fibrillation in the elderly include rate control with anticoagulation, or cardioversion and maintenance of sinus rhythm. Rate controlling agents include digoxin, calcium blockers, and b-blockers, most effective during exercise, or nonpharmacologic control with AV nodal ablation and pacemaker implantation. Agents to maintain sinus rhythm in the elderly include class Ia and III antiarrhythmics, with 1 year efficacies of approximately 50%. Whether the overall benefits of pharmacologic maintenance of sinus rhythm outweigh the risks of proarrhythmia and other adverse effects is under debate, but will be better delineated by the ongoing AFFIRM trial and VA cooperative trial, both randomizing patients to one of these two strategies.

Journal Article↗

PubMed2005

Controlled-rate freezing of human ES cells.

A significant obstacle to using human embryonic stem cells (hESCs) arises from extremely poor survival associated with freezing, typically in the range of 1%. This report describes a slow controlled-rate freezing technique commonly used for mammalian embryo cryopreservation. Using a combination of surviving colony number and colony diameter; survival was determined relative to untreated hESCs. Using a dimethyl sulfoxide (DMSO) cryoprotectant and either a homemade controlled-rate freezing device or a commercial freezing device, survival rates of 20%-80% were obtained. To achieve the highest levels of survival, the critical factors were an ice crystal seed (at -7 degrees to -10 degrees C), a freeze rate between 0.3 degrees and 1.8 degrees C/min, and a rapid thaw rate using room temperature water. Slow controlled-rate cooling allows a rapid, simple, and reproducible means of cryopreserving hESCs.

Cell Survival↗

PubMed2000

Cost-effective management of acute atrial fibrillation: role of rate control, spontaneous conversion, medical and direct current cardioversion, transesophageal echocardiography, and antiembolic therapy.

Management strategies for the acute treatment of atrial fibrillation (AF) include: (1) the use of intravenous drugs for rate control, (2) drug termination, or (3) direct current (DC) cardioversion. Delays in cardioversion can promote atrial remodeling and add thromboembolic risk. Rate control awaiting spontaneous or pharmacologic conversion may be a cost-effective strategy in patients presenting with recent onset of symptoms. Early DC cardioversion can be cost-effective and minimize antiembolic therapy issues in the acute setting. In patients presenting with AF of unknown or >48 hours' duration, rate control and therapeutic warfarin for 3-4 weeks followed by medical or DC cardioversion is standard practice. However, delays in conversion promote atrial remodeling that makes restoration of sinus rhythm more difficult and increases the likelihood of postcardioversion AF recurrence. Transesophageal echocardiography can identify patients at low risk for a cardioversion-related embolic event and allows cardioversion to be performed earlier, thereby minimizing atrial remodeling.

Algorithms↗

PubMed2004

Atrial fibrillation: rate control often better than rhythm control.

(1) The treatment aims in atrial fibrillation are to reduce patients' symptoms and to prevent both embolism and deterioration of any underlying heart disease. Therapy consists of anticoagulant or antiplatelet drugs, treatment of any underlying heart disease, and heart rate control. (2) Digoxin, betablockers, diltiazem and verapamil slow the heart rate but rarely restore sinus rhythm. Amiodarone, disopyramide, flecainide, quinidine and sotalol can be used to prevent relapse of atrial fibrillation after electrical cardioversion, but they all have potentially serious adverse effects. New trials of antiarrhythmic treatments have been published since our last review of this subject. (3) In one trial in 403 patients, amiodarone was more effective than sotalol and propafenone in restoring and maintaining sinus rhythm. After 15 months of follow-up, there were fewer strokes among patients treated with amiodarone, but there was no difference between the three drugs in the overall incidence of cardiovascular events. (4) A clinical trial with 4060 patients compared rhythm control (mainly with amiodarone, sotalol or propafenone; sometimes combined with electrical cardioversion) and rate control (with digoxin, betablocker, diltiazem or verapamil; systematically combined with anticoagulant therapy). The antiarrhythmic treatment restored sinus rhythm in more than half the patients in the long term. But rhythm control did not reduce the risk of death or serious cardiovascular events during a mean follow-up period of 3.5 years. Rhythm control caused more adverse events than rate control; subgroup analyses (weak evidence) suggest that rhythm control may also have caused more deaths among patients over 65 and among patients with coronary heart disease. (5) In another trial, electrical cardioversion followed by antiarrhythmic therapy (mainly sotalol) sustainably restored sinus rhythm in more than one-third of 522 patients. But, compared with rate control treatment plus anticoagulant therapy, rhythm control did not reduce the risk of cardiovascular events, and was associated with a larger number of serious adverse cardiac effects. (6) Other recent trials confirm the risk of serious adverse effects, including severe arrhythmia with sotalol (especially at the start of treatment), and adverse thyroid and pulmonary effects with amiodarone. (7) Combined radiofrequency ablation and cardiac stimulation improved symptoms in some patients with incapacitating atrial fibrillation who had not responded to other treatments. However, this approach carries a risk of serious adverse effects, and its impact on the risk of cardiovascular events and death is not known. (8) In practice, an attempt should be made to restore sinus rhythm with amiodarone and/or electrical cardioversion, in symptomatic, recent or paroxysmal atrial fibrillation in patients under 65 who have no signs or symptoms of coronary heart disease. In other situations, rate control is the first-line option, using digoxin, betablockers (other than sotalol) or calcium channel blockers (diltiazem or verapamil). Whatever the option, treatment must be combined with anticoagulant or antiplatelet therapy, and with treatment of any underlying heart disease.

Adult↗

PubMed1997

Conversion of atrial fibrillation to sinus rhythm and rate control by digoxin in comparison to placebo.

AIMS: A randomized, double-blind study with a high dose of digoxin administered intravenously for conversion of atrial fibrillation (not due to haemodynamic alternations) to sinus rhythm, and for rate control in converters and non-converters was set up. Outcome measures were conversion within 12 h; time to conversion; early rate control; and stable slowing within 12 h. METHODS: We studied 40 patients with recent onset (< 1 week) atrial fibrillation; controls received saline intravenously, the other patients digoxin 1.25 mg. RESULTS: One patient converted before digoxin administration. Conversion occurred in 9/19 patients on digoxin and in 8/20 on placebo (ns). The mean time to conversion tended to be shorter only for digoxin. Two late conversions on placebo were observed within 24 h. Heart rate during atrial fibrillation decreased after 30 min for converters and non-converters (P < 0.05). For all patients on digoxin, heart rate after 30 min was lower compared to baseline (P < 0.002) and to placebo (P < 0.02). Persistent, stable slowing occurred only in 3/10 non-converters on digoxin (P < 0.05), and two patients developed bradyarrhythmias. QTc was shortened immediately after conversion in all patients. Converters had baseline characteristics similar to those of non-converters. CONCLUSIONS: Intravenous digoxin offers no substantial advantages over placebo in recent onset atrial fibrillation with respect to conversion, and provides weak rate control.

Aged↗

PubMed1979

Development of physiological response patterns concomitant with the learning of voluntary heart rate control.

Thirty-six male undergraduate students were instructed to raise or lower heart rate in a multiple-session biofeedback experiment. Systolic and diastolic blood pressure, frontalis electromyographic activity, and skin conductance level were simultaneously recorded throughout biofeedback training. Principal axes factor analyses showed that physiological response patterning concomitant with the development of heart rate control was different early in training (Training Session 1) than it was late in training (Training Session 4) for both speeding and slowing conditions. These results indicate that different heart rate control strategies were used by the subjects early and late in training. The factor patterns also indicated a tendency for greater heart rate response specificity as training progressed for both speeding and slowing. Heart rate speeding sessions were also found to be associated with a significant increase in perceived state anxiety as measured by the State-Trait Anxiety Inventory. No significant change in perceived anxiety state, however, was associated with heart rate slowing.

Adolescent↗

PubMed1996

Rate-controlling biopolymer membranes as transdermal delivery systems for nifedipine: development and in vitro evaluations.

Membrane permeation-controlled transdermal delivery devices for the controlled delivery of nifedipine were developed using collagen (which was extracted from calf fetus skin) and chitosan membranes as rate-controlling membrane. To increase the stability of nifedipine in the systems, alginate gel was used as drug reservoir. Transdermal devices were fabricated by adhesive sealing techniques. In vitro drug release studies were carried out using modified Franz diffusion cells. Drug release was found to depend on the type of membrane used to control the drug delivery, suggesting that drug delivery is efficiently controlled by the rate-controlling membranes.

Adhesives↗

PubMed1978

Clinical evaluation of a pre-set ultrafiltration rate controller available for single pass and hemodiafiltration systems.

Introduction of high flux-type dialyzers, such as the RP-6, makes it necessary to devise an ultrafiltration rate controller for a single pass system. For this purpose, a new pre-set ultrafiltration rate controller has been developed and examined experimentally and clinically. The controller has twin chambers, each of which is divided into two symmetrical parts by a vertically-placed diaphragm. The diaphragm shifts repeatedly from right to left, aspirating in and driving out fresh or used dialysate alternately. If one removes a certain amount of used dialysate from a branch of the efferent line, negative pressure develops and aspirates an equal amount of water from the dialyzer. Therefore, extra dialysate obtained by a pump precisely reflects ultrafiltration rate. The controller has been used on five patients. The scheduled ultrafiltration rate was easily obtainable. The apparatus is also available for hemodiafiltration. Initial clinical trial has been promising.

Body Fluids↗

PubMed2005

Rate control versus rhythm control--decision making.

The present review examines the data and presents recommendations concerning the selection of rate-control or rhythm-control strategies, as opposed to the selection of specific therapies for rate control or rhythm control. There are several trials completed and others in progress that address issues surrounding the comparison of the two strategies, primarily using pharmacological therapies. The main results and some subanalyses of these trials are briefly reviewed. Gaps in the available data are identified. On the basis of the data, there is no clear advantage of one strategy over the other, although each seems to have potential advantages in different subsets of patients. Accordingly, the main recommendations are that either approach is acceptable, and that selection of a rhythm-management strategy should be individualized. This recommendation is based on a primarily pharmacological approach because that is currently the most common form of therapy used for rhythm management and because the evidence base is composed of comparisons of drug therapies. A number of clinical factors are identified to help individualize therapy and, included in these, is patient preference. It is also recommended that treating physicians be prepared to cross over from one strategy to another or change to nonpharmacological therapies when treatment goals are not achieved or adverse effects prevail.

Atrial Fibrillation↗

PubMed1985

Relative contribution of aortic and carotid baroreflexes to heart rate control in man during steady state and dynamic increases in arterial pressure.

We studied the contribution of carotid vs. extracarotid baroreceptors in control of heart rate in normal humans. We measured heart interval (HI) and arterial pressure during steady-state infusion of phenylephrine (PE). PE increased mean arterial pressure (MAP) by 13 +/- 2 mmHg (mean +/- SEM; n = 10) and thus stimulated both carotid and aortic baroreceptors. Neck pressure (NP) was applied during PE infusion to counter the increase in transmural carotid sinus pressure, thus leaving only aortic baroreceptors stimulated by the increase in arterial pressure. PE infusion alone prolonged HI by 230 +/- 24 ms (P less than 0.05). Application of NP attenuated the HI response to 65 +/- 22 ms above control (P less than 0.05 vs. PE alone). During these steady-state increases in arterial pressure, elimination of the carotid baroreflex contribution reduced the HI prolongation by 41-70% in five subjects and by greater than 93% in five subjects. We also measured the HI response to dynamic ramp elevation of systolic arterial pressure (SAP) using bolus administrations of PE. Baroreflex control was calculated from the slope of the regression correlating SAP to succeeding HI for PE alone (carotid and aortic baroreceptor activation) and for PE plus superimposed dynamic NP at levels equal to the increases in SAP (aortic baroreceptor activation). During PE alone, the baroreflex slope was 20.2 +/- 2.9 ms/mmHg (n = 10). During PE plus NP, the baroreflex slope was reduced by 30% to 14.1 +/- 2.8 ms/mmHg (P less than 0.02 vs. during PE alone). Thus, during dynamic increases in arterial pressure, eliminating the carotid baroreflex contribution reduced the HI response by 30%. These studies indicate that extracarotid (presumably aortic) and carotid baroreflexes both participate in control of heart rate in humans. Extracarotid (aortic) baroreflexes appear to have the greater role in control of heart rate during dynamic increases in arterial pressure.

Adult↗

PubMed2005

Atrial fibrillation: how to approach rate control.

The optimal management of atrial fibrillation is of considerable clinical importance, and with the recent publication of four studies suggesting the equivalence of rate and rhythm control strategies, new attention has been focused on rate control. Reasons for rate control include reduction of symptoms and the prevention of tachycardia-mediated cardiomyopathy; yet, evidence-based definitions of optimal rate control are lacking. This article examines an approach to rate control that includes serial assessment of heart rate and symptoms, both at rest and with exertion, and the use of therapy tailored to the individual and modified over time (as no single therapy demonstrates clear superiority). Often, multidrug regimens including digoxin and a calcium channel blocker or beta-blocker are required, and in a minority of patients atrioventricular nodal ablation and pacing are necessary. Several novel therapies currently under development are also discussed.

Adrenergic beta-Antagonists↗

PubMed1999

Bacterial filament formation, a defense mechanism against flagellate grazing, is growth rate controlled in bacteria of different phyla.

A facultatively filamentous bacterium was isolated from eutrophic lake water and was identified as Flectobacillus sp. strain MWH38 (a member of the Cytophaga-Flavobacterium-Bacteroides phylum) by comparative 16S rRNA gene sequence analysis. Filament formation by Flectobacillus sp. strain MWH38 and filament formation by Flectobacillus major, the closest known relative of strain MWH38, were studied in chemostat cultures under grazing pressure by the bacterivorous flagellate Ochromonas sp. strain DS and without predation at several growth rates. The results clearly demonstrated that filament formation by the two flectobacilli is growth rate controlled and thus independent of the presence of a predator. However, flagellate grazing positively influenced bacterial growth rates by decreasing bacterial biomass and thus indirectly stimulated filament formation. The results of investigations of cell elongation and filament formation by Comamonas acidovorans PX54 (a member of the beta subclass of the class Proteobacteria) supported the recent proposal that in this species the mechanism of filament formation is growth rate controlled. The finding that the grazing defense mechanism consisting of filament formation is growth rate controlled in the flectobacilli investigated and C. acidovorans PX54 (i.e., in bacteria belonging to divergent evolutionary phyla) may indicate that this mechanism is a phylogenetically widely distributed defense strategy against grazing.

Animals↗

PubMed1983

Phase I pilot study on fast neutron teletherapy for advanced carcinomas of the head and neck region. Final report on local control rate and survival.

A final report is presented on the local control rate and length of survival for 100 patients with advanced squamous cell carcinomas of the head and neck region who received fast neutron teletherapy at the University of Washington during the period 1973 through 1977. Sixty-two patients were treated with neutrons alone and 38 were treated with a combination of neutrons and photons as part of a mixed beam fractionation scheme. The overall initial complete remission rate was 68% for the mixed beam group and 44% for the group treated with neutrons alone. Initial complete remission rates for the two groups of patients are given as a function of T-stage and N-stage and acturarial curves are presented which show the time course of local control and survival for the two treatment groups. For T3 and T4 lesions the initial complete remission rate appears to be greater using the mixed beam form of treatment than using neutrons alone. Treatment to high-dose levels using neutrons alone gave rise to significantly greater morbidity--both acute and late effects--than resulted from the mixed beam form of treatment. Local control rates and survival rates are compared with similar groups of patients treated with neutrons at other institutions.

Adult↗

PubMed1998

A rate-controlled indentor for in vivo analysis of residual limb tissues.

A tissue tester was designed to enable rate-controlled indentation of the bulk soft tissues of lower extremity residual limbs. The tissue tester employs a digital linear actuator that implements rate-controlled indentation, and a load cell that measures the reaction force resulting from tissue indentation. Viscoelastic phenomena such as preconditioning, hysteresis and force relaxation can be assessed, and the effect of varying indentation rates on soft tissue stiffness can be investigated. The device accommodates indentor excursions up to 30 mm, indentation at rates of 0 to 10 mm/s, reaction forces up to 44 N, and multiple loading/unloading cycles. The tissue tester is controlled via a notebook personal computer with a PCMCIA data acquisition card. The tissue testing trials are automated and the entire test system is portable and amenable for use in a clinical or research environment. System output consists of force-displacement curves from cyclic loading, and force-time curves following ramped-step indentation. The mean indentor positioning error was 0.071 (+/-0.75)% of the desired displacement. This error varied as a function of indentation and was approximately independent of the indentation rate. Indentation rates were accurate to within 0.94(+/-0.68)% of the desired value and also varied with indentation. Indentation of a viscoelastic foam yielded force-displacement curves that were consistent with that obtained from an Instron universal testing machine.

Amputation Stumps↗

PubMed1994

[Pressure build-up in 2 rate-controlled syringe infusion pumps].

The use of rate controlled syringe infusion pumps has spread to departments where the need for accurate infusion exists. The simplicity in using these pumps has led to a false feeling of safety. A case of hazardous use of a syringe infusion pump has been reviewed. An Ohmeda 9000- and a Terumo STC 521 syringe pump was here tested, n = 20. The occlusion pressures of the two pumps were different. The occlusion pressure changed with different infusion rates for both pumps. The pressure was built up in a straight linear fashion. The bolus release depended on the occlusion pressure and the amounts given were in the range of 1.0-1.6 ml, both pumps included. The time from occlusion to alarm depended on the occlusion pressures. There might be an advantage in using a soft infusion system. It is recommended not to use syringe pump infusion via peripheral veins so as to avoid the risk of pressure build-up in the subcutaneous tissue in case of infiltration. In the event of occlusion disconnect the infusion system prior to reopening. Don't rely on the occlusion alarm. Use a smooth infusion system.

Child, Preschool↗

PubMed1989

Transdermal therapeutic systems and rate controlled drug delivery.

One of the key design features of transdermal therapeutic systems, namely the system rate-control, and its impact on systemic therapy, are reviewed. Specifically, TTS(scopolamine) and TTS(estradiol) are evaluated as examples of the rate-controlled transdermal products. The use of these TTS products has resulted in controlled plasma concentration of drug and reduced side effects by the use of TTS(scopolamine) and more physiologic estradiol to estrone ratio with the transdermal dosage form of estradiol.

Administration, Cutaneous↗

PubMed2002

Complexity of intercalation of hydrazine into kaolinite--a controlled rate thermal analysis and DRIFT spectroscopic study.

Controlled rate thermal analysis (CRTA) allows the separation of adsorbed and intercalated hydrazine. CRTA displays the presence of three different types of hydrogen-bonded hydrazine in the intercalation complex: (a) The first is adsorbed loosely bonded on the kaolinite structure fully expanded by hydrazine-hydrate and liberated between approx 50 and 70 degrees C (b) The second intercalated hydrazine is lost between approx 70 and 85 degrees C. (c) The third type of intercalated-hydrazine molecule is lost in the 85-130 degrees C range. CRTA at 70 degrees C enables the removal of hydrazine-water and results in the partial collapse of the hydrazine-intercalated kaolinite structure to form a hydrazine-intercalated kaolinite. Removal of the adsorbed hydrazine enables the DRIFT spectra of the hydrazine-intercalated complex without any adsorbed hydrazine to be obtained. A band at 3626 cm(-1) attributed to the inner surface hydroxyls of kaolinite hydrogen bonded to hydrazine is observed. The intercalation of hydrazine-hydrate into kaolinite is complex and results from the different types of surface interactions of the hydrazine with the kaolinite surfaces.

Journal Article↗