Fish oil supplementation and arrhythmias.
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Arrhythmias, Cardiac↗
Biomedical subjects
Paul Dorian
Publications and source records attributed to Paul Dorian.
Downward delegation of implantable cardioverter defibrillator decision-making in a restricted-resource environment: the pitfalls of bedside rationing.
Implantable cardioverter defibrillators have been shown to reduce all-cause mortality in some patient populations at risk of sudden death. New Canadian guidelines recommend implantable cardioverter defibrillator therapy for these patients. However, the need for these devices exceeds the funded volumes in many Canadian jurisdictions. As a result, rationing of this resource has been necessary. While rationing at the macro (Ministry of Health) and meso (hospital) levels has achieved some level of acceptance by society, the responsibility for the decisions taken at the micro (individual) patient level actually rests with the physician at the bedside. This 'bedside rationing' creates a moral dilemma for physicians, who are torn between their traditional fiduciary role as 'patient advocate' and the competing role of 'gatekeeper'. This 'downward delegation' of rationing decision-making obscures the reality that rationing occurs, and encourages covert, opaque and inconsistent approaches. The remedy is the development of fair, legitimate procedures for making rationing decisions that include guidelines that structure and constrain those decisions. Macro- and meso-level stakeholders must also recognize and take responsibility for their part in restricting resources in a broadly inclusive and transparent process.
Canada↗
Design of the SHock Inhibition Evaluation with Azimilide (SHIELD) study: a novel method to assess antiarrhythmic drug effect in patients with an implantable cardioverter-defibrillator.
This report presents the rationale and study design details of the SHock Inhibition Evaluation with Azimilide study, which is recruiting 624 patients with implantable cardioverter-defibrillators (ICDs) who are at risk for life-threatening ventricular arrhythmia, randomized to azimilide 75 mg, azimilide 125 mg, or placebo and followed for 1 year. The objective of this study is to determine the effect of azimilide versus placebo on the symptomatic ventricular arrhythmia burden using a unique statistical analysis based on the unusual temporal distribution of symptomatic ICD therapies. The primary efficacy end points are time to all-cause shocks and time to all-cause shocks plus symptomatic ventricular arrhythmic events triggering antitachycardia pacing measured from randomization.
Anti-Arrhythmia Agents↗
Approach to antiarrhythmic therapy in patients with ICDs and frequent activations.
Patients with an implantable defibrillator may require concomitant antiarrhythmic drug therapy to reduce therapy from the device, especially shocks from the device. New evidence suggests that amiodarone, in combination with b-blockade, is the most effective treatment to reduce the frequency of defibrillator therapies, but sotalol and azimilide have also been shown to be effective. Electrical storm is a serious condition that occurs in 20% of patients living with a defibrillator, and its management requires a complex approach to the patient.
Anti-Arrhythmia Agents↗
Progression to chronic atrial fibrillation after the initial diagnosis of paroxysmal atrial fibrillation: results from the Canadian Registry of Atrial Fibrillation.
BACKGROUND: After its initial diagnosis, atrial fibrillation (AF) may progress from paroxysmal to chronic AF (CAF). The rate of progression and risk factors for progression are not clearly defined. METHODS: The Canadian Registry of Atrial Fibrillation (CARAF) enrolled patients from 6 Canadian cities at the time of their first electrocardiographic diagnosis of AF. Comprehensive clinical and echocardiographic data were collected and patients were followed annually, carefully documenting clinical outcomes, recurrence of paroxysmal AF, and progression to CAF. Baseline clinical, electrocardiographic, and echocardiographic variables were evaluated by univariate Cox proportionate hazards analysis. A stepwise approach was used to model the association between echocardiographic and clinical variables with progression to CAF. RESULTS: A total of 757 patients with a baseline diagnosis of paroxysmal AF were evaluated. Median follow-up was 8.0 years (range 2 days to 11.1 years). The probability of progression to CAF by 1 year was 8.6% and thereafter there was a slow but steady progression to 24.7% by 5 years. By 5 years, the probability of documented recurrence of any AF (chronic or paroxysmal) was 63.2%. Increasing age, significant aortic stenosis or mitral regurgitation, left atrial enlargement, and diagnosis of cardiomyopathy were independently associated with progression to CAF. A more rapid heart rate during AF was associated with decreased risk of progression. CONCLUSIONS: After the initial diagnosis of paroxysmal AF, there is a slow but steady progression to CAF. Baseline echocardiographic variables, age, cardiomyopathy, and heart rate were independently associated with progression to CAF.
Adolescent↗
Systematic evaluation of the determinants of defibrillation efficacy.
OBJECTIVES: We studied the effect of varying shock capacitance, shock impedance, and pulse duration on defibrillation efficacy in a randomized, crossover manner for biphasic shocks. BACKGROUND: The relationship between the electrical determinants of defibrillation efficacy is incompletely understood. METHODS: Biphasic shocks were delivered to 12 dogs through epicardial patches (to vary impedance) after 15 seconds of ventricular fibrillation using one of 100- or 155-muF capacitors at each of four pulse durations (2.5, 5, 10, 20 ms), in a balanced random order. There were two impedance groups: six with higher impedance (mean 97 +/- 15 Omega, range 80-120) and six with lower impedance (mean 39 +/- 3 Omega, range 34-44). Voltage requirements were estimated as the average of three defibrillation threshold (DFT) tests. RESULTS: Shock capacitance, resistance, and pulse duration all had significant effects upon the minimum voltage DFT (P = .0065, P = .0066, and P = .0001, respectively). The tilt associated with the lowest voltage and current requirement for each of the four capacitance/resistance combinations varied widely, between 34 +/- 5% and 63 +/- 3%, depending on capacitance and impedance. The optimal pulse duration associated with minimum DFT lies between 5.11 and 5.34 ms. CONCLUSIONS: Defibrillation voltage requirements for biphasic shocks are affected by pulse duration, capacitance and impedance, but not "tilt."
Animals↗
Out-of-hospital cardiac arrest rectilinear biphasic to monophasic damped sine defibrillation waveforms with advanced life support intervention trial (ORBIT).
BACKGROUND: Although biphasic defibrillation waveforms appear to be superior to monophasic waveforms in terminating VF, their relative benefits in out-of-hospital resuscitation are incompletely understood. Prior comparisons of defibrillation waveform efficacy in out-of-hospital cardiac arrest (OHCA) are confined to patients presenting in a shockable rhythm and resuscitated by first responder (basic life support). This effectiveness study compared monophasic and biphasic defibrillation waveform for conversion of ventricular arrhythmias in all OHCA treated with advance life support (ALS). METHODS AND RESULTS: This prospective randomized controlled trial compared the rectilinear biphasic (RLB) waveform with the monophasic damped sine (MDS) waveform, using step-up energy levels. The study enrolled OHCA patients requiring at least one shock delivered by ALS providers, regardless of initial presenting rhythm. Shock success was defined as conversion at 5s to organized rhythm after one to three escalating shocks. We report efficacy results for the cohort of patients treated by ALS paramedics who presented with an initially shockable rhythm who had not received a shock from a first responder (MDS: n=83; RLB: n=86). Shock success within the first three ascending energy shocks for RLB (120, 150, 200J) was superior to MDS (200, 300, 360J) for patients initially presenting in a shockable rhythm (52% versus 34%, p=0.01). First shock conversion was 23% and12%, for RLB and MDS, respectively (p=0.07). There were no significant differences in return of spontaneous circulation (47% versus 47%), survival to 24h (31% versus 27%), and survival to discharge (9% versus 7%). Mean 24h survival rates of bystander witnessed events showed differences between waveforms in the early circulatory phase at 4-10 min post event (mean (S.D.) RLB 0.45 (0.07) versus MDS 0.31 (0.06), p=0.0002) and demonstrated decline as time to first shock increased to 20 min. CONCLUSION: Shock success to an organized rhythm comparing step-up protocol for energy settings demonstrated the RLB waveform was superior to MDS in ALS treatment of OHCA. Survival rates for both waveforms are consistent with current theories on the circulatory and metabolic phases of out-of-hospital cardiac arrest.
Adult↗
Epinephrine and vasopressin during cardiopulmonary resuscitation.
Epinephrine (adrenaline) and vasopressin have been by far the most commonly studied vasopressors in experimental cardiac arrest. Despite animal experimental studies suggesting improved outcomes in experimental cardiac arrest, clinical trials of pressor agents have failed to show clear cut benefit from either vasopressin or epinephrine, although few, if any, trials compared pressor agents to a placebo. The action of vasopressors in the heart, particularly beta1-adrenergic stimulation, is associated with adverse cardiac effects including post-resuscitation myocardial dysfunction, worsening ventricular arrhythmias, and increasing myocardial oxygen consumption. Alpha2-adrenergic agonists, in experimental studies, show great promise in improving outcomes in experimental cardiac arrest, but have not been studied in humans. The combination of epinephrine and vasopressin may be effective, but has been incompletely studied. Clinical trials of vasopressor agents, which minimize direct myocardial effects are needed.
Animals↗
Antiarrhythmic action of beta-blockers: potential mechanisms.
Sympathetic nervous system overactivity has been linked to ventricular tachyarrhythmias and sudden death. It has been hypothesized that the extent and nature of the arrhythmogenic effect of sympathetic stimulation depends on the underlying myocardial substrate, the mechanism of the arrhythmia, and the integrated effects of sympathetic stimulation in the particular individual circumstance. Multiple direct and indirect mechanisms of adrenergic action on the heart may benefit from the known antiarrhythmic actions of beta-blocker therapy and other interventions that decrease sympathetic tone. The antiarrhythmic mechanism of beta-blockade (and possibly alpha-blockade) will depend on the specific mechanism of the individual arrhythmia and will differ for those arrhythmias caused by tachycardia and ischemia, those caused by reentry and promoted by decreased conduction velocity and shortened refractoriness, and those caused by early or delayed afterdepolarizations, usually in the context of prolonged action potential duration. Antagonism of cardiac adrenergic activity by beta-blockade in particular is the best-established drug therapy to prevent ventricular arrhythmias.
Adrenergic beta-Antagonists↗
Update on advanced life support and resuscitation techniques.
PURPOSE OF REVIEW: This article is a review of the most recent findings in resuscitation techniques in advanced cardiac life support. The article focuses particularly on the period after July 1, 2003, but relevant new findings before this period are also included. RECENT FINDINGS: Randomized clinical trial results suggest that the current cardiopulmonary resuscitation and advanced cardiac life support guidelines may need to be modified. Early defibrillation during the electrical phase of cardiac arrest remains the most crucial intervention, but performing cardiopulmonary resuscitation before defibrillation may be more effective, as compared with immediate defibrillation, during the circulatory phase of cardiac arrest. Biphasic waveforms are superior to monophasic damped sine waveforms in achieving defibrillation. Novel cardiopulmonary resuscitation methods that increase negative intrathoracic pressure promote an increase in blood flow return to the heart. These devices have been correlated with improved short-term survival rates during the circulatory phase of cardiac arrest. Vasopressin administration, given alone or in combination with epinephrine, should be considered during the circulatory phase of out-of-hospital cardiac arrest, particularly in patients presenting with asystole as the initial rhythm. Induction of hypothermia during the metabolic phase in cardiac arrest survivors improves 6-month survival rates and neurologic outcomes. SUMMARY: Strategies to improve the low survival outcomes of cardiac arrest victims are available. Clinical trials testing these strategies suggest benefit from certain interventions but are not definitive. These different therapeutic interventions should be performed in a phase-specific-oriented fashion according to the three-phase time-sensitive model of cardiac arrest.
Amiodarone↗
Canadian Cardiovascular Society/Canadian Heart Rhythm Society position paper on implantable cardioverter defibrillator use in Canada.
The Canadian Heart Rhythm Society in conjunction with the Canadian Cardiovascular Society is committed to the promotion of evidence-based practice in Canada. Since the last Canadian guidelines on the management of sudden cardiac death were published in 2000, several well-conducted clinical trials evaluating the implantable cardioverter defibrillator have been completed and published. The Canadian Cardiovascular Society Council has granted permission to review and update guidelines for the indications for implantable cardioverter defibrillators. Furthermore, data are emerging on the potential benefits of biventricular pacing therapy (cardiac resynchronization) for heart failure; recommendations for the use of this therapy have been included in the present paper. Ethical considerations and the economic implications of these recommendations are also included. Canada's heart rhythm specialists, represented by the Canadian Heart Rhythm Society, have been joined by two heart failure specialists, a medical ethicist and an economist, to develop the present position paper. Members of the Canadian Heart Rhythm Society participated in the discussion of these recommendations in open forum meetings and by electronic communication.
Death, Sudden, Cardiac↗
Implanted cardioverter defibrillators for the prevention of sudden death.
Implantable cardioverter defibrillators (ICDs) are effective in preventing sudden death from ventricular arrhythmias. Recent clinical trials have demonstrated reductions in all-cause mortality in ICD-treated patients, especially those with severe left ventricular dysfunction. However, selecting appropriate patients for ICD implantation, especially for the primary prophylaxis of all-cause death, is a challenge. Patients with recent myocardial infarction (less than 40 days) or those that have just undergone coronary artery bypass graft surgery do not benefit from ICD implantation. On average, annual death rates are reduced by 1.5% to 3.0%, but the risk of death in an individual patient is hard to quantify. Poor left ventricular function is the best predictor of both mortality risk and ICD benefit. Other risk predictors need to be identified.
Death, Sudden, Cardiac↗
Etiology and initial investigation.
The initial evaluation of a patient with atrial fibrillation should include a comprehensive review of historical factors, a physical examination and initial investigations. This evaluation has many important purposes, including the development of a therapeutic strategy for symptom relief, the assessment and management of thromboembolic risks, and the identification of underlying etiology. This evaluation should also review management of risk factors for overall cardiovascular morbidity and the treatment of atrial fibrillation. Baseline history, appropriate laboratory tests, and 12-lead electrocardiogram and echocardiography results should be obtained in all patients to identify the potential etiology and other comorbidities, and to stratify for risk of stroke.
Atrial Fibrillation↗
Pharmacological and nonpharmacological methods for rate control.
In many patients with atrial fibrillation, the most appropriate strategy is 'rate control', designed to slow down the rapid ventricular rates often seen with atrial fibrillation. Based on the hypothesis that symptoms, especially palpitations and exercise intolerance, are due to rapid ventricular rates with activity, optimum rate control usually requires reducing ventricular rates at rest and during activity. Beta-blockers and nondihydropyridine calcium channel blockers are likely more effective than digoxin alone, and the adequacy of rate control is best assessed with heart rate measurement during activity or with ambulatory electrocardiographic monitoring. Taking a patient's symptoms into account, reasonable target ventricular rates are less than 80 beats/min at rest and less than 100 beats/min, on average, over 24 h.
Atrial Fibrillation↗
Prophylactic use of an implantable cardioverter-defibrillator after acute myocardial infarction.
BACKGROUND: Implantable cardioverter-defibrillator (ICD) therapy has been shown to improve survival in patients with various heart conditions who are at high risk for ventricular arrhythmias. Whether benefit occurs in patients early after myocardial infarction is unknown. METHODS: We conducted the Defibrillator in Acute Myocardial Infarction Trial, a randomized, open-label comparison of ICD therapy (in 332 patients) and no ICD therapy (in 342 patients) 6 to 40 days after a myocardial infarction. We enrolled patients who had reduced left ventricular function (left ventricular ejection fraction, 0.35 or less) and impaired cardiac autonomic function (manifested as depressed heart-rate variability or an elevated average 24-hour heart rate on Holter monitoring). The primary outcome was mortality from any cause. Death from arrhythmia was a predefined secondary outcome. RESULTS: During a mean (+/-SD) follow-up period of 30+/-13 months, there was no difference in overall mortality between the two treatment groups: of the 120 patients who died, 62 were in the ICD group and 58 in the control group (hazard ratio for death in the ICD group, 1.08; 95 percent confidence interval, 0.76 to 1.55; P=0.66). There were 12 deaths due to arrhythmia in the ICD group, as compared with 29 in the control group (hazard ratio in the ICD group, 0.42; 95 percent confidence interval, 0.22 to 0.83; P=0.009). In contrast, there were 50 deaths from nonarrhythmic causes in the ICD group and 29 in the control group (hazard ratio in the ICD group, 1.75; 95 percent confidence interval, 1.11 to 2.76; P=0.02). CONCLUSIONS: Prophylactic ICD therapy does not reduce overall mortality in high-risk patients who have recently had a myocardial infarction. Although ICD therapy was associated with a reduction in the rate of death due to arrhythmia, that was offset by an increase in the rate of death from nonarrhythmic causes.
Adult↗
Placebo-controlled, randomized clinical trial of azimilide for prevention of ventricular tachyarrhythmias in patients with an implantable cardioverter defibrillator.
BACKGROUND: Although implanted cardioverter defibrillators (ICDs) effectively treat sustained ventricular tachyarrhythmias, up to 50% of ICD recipients eventually require concomitant antiarrhythmic drug therapy to prevent symptomatic arrhythmia recurrences and hence reduce the number of device therapies. METHODS AND RESULTS: A total of 633 ICD recipients were enrolled in a randomized, double-blind, placebo-controlled study to evaluate the effect of daily doses of 75 or 125 mg of azimilide on recurrent symptomatic ventricular tachyarrhythmias and ICD therapies. Total all-cause shocks plus symptomatic ventricular tachycardia (VT) terminated by antitachycardia pacing (ATP) were significantly reduced by azimilide, with relative risk reductions of 57% (hazard ratio [HR]=0.43, 95% CI 0.26 to 0.69, P=0.0006) and 47% (HR=0.53, 95% CI 0.34 to 0.83, P=0.0053) at 75- and 125-mg doses, respectively. The reductions in all-cause shocks with both doses of azimilide did not achieve statistical significance. The incidence of all appropriate ICD therapies (shocks or ATP-terminated VT) was reduced significantly among patients taking 75 mg of azimilide (HR=0.52, 95% CI 0.30 to 0.89, P=0.017) and those taking 125 mg of azimilide (HR=0.38, 95% CI 0.22 to 0.65, P=0.0004). Five patients in the azimilide groups and 1 patient in the placebo group had torsade de pointes; all were successfully treated by the device. One patient taking 75 mg of azimilide had severe but reversible neutropenia. CONCLUSIONS: Azimilide significantly reduced the recurrence of VT or ventricular fibrillation terminated by shocks or ATP in ICD patients, thereby reducing the burden of symptomatic ventricular tachyarrhythmia.
Anti-Arrhythmia Agents↗
Use of implantable cardioverter defibrillators after out-of-hospital cardiac arrest: a prospective follow-up study.
BACKGROUND: Survivors of out-of-hospital cardiac arrest are at high risk of recurrent arrests, many of which could be prevented with implantable cardioverter defibrillators (ICDs). We sought to determine the ICD insertion rate among survivors of out-of-hospital cardiac arrest and to determine factors associated with ICD implantation. METHODS: The Ontario Prehospital Advanced Life Support (OPALS) study is a prospective, multiphase, before-after study assessing the effectiveness of prehospital interventions for people experiencing cardiac arrest, trauma or respiratory arrest in 19 Ontario communities. We linked OPALS data describing survivors of cardiac arrest with data from all defibrillator implantation centres in Ontario. RESULTS: From January 1997 to April 2002, 454 patients in the OPALS study survived to hospital discharge after experiencing an out-of-hospital cardiac arrest. The mean age was 65 (standard deviation 14) years, 122 (26.9%) were women, 398 (87.7%) had a witnessed arrest, 372 (81.9%) had an initial rhythm of ventricular tachycardia or ventricular fibrillation (VT/VF), and 76 (16.7%) had asystole or another arrhythmia. The median cerebral performance category at discharge (range 1-5, 1 = normal) was 1. Only 58 (12.8%) of the 454 patients received an ICD. Patients with an initial rhythm of VT/VF were more likely than those with an initial rhythm of asystole or another rhythm to undergo device insertion (adjusted odds ratio [OR] 9.63, 95% confidence interval [CI] 1.31-71.50). Similarly, patients with a normal cerebral performance score were more likely than those with abnormal scores to undergo ICD insertion (adjusted OR 12.52, 95% CI 1.74-92.12). INTERPRETATION: A minority of patients who survived cardiac arrest underwent ICD insertion. It is unclear whether this low usage rate reflects referral bias, selection bias by electrophysiologists, supply constraint or patient preference.
Age Distribution↗
Applying the new STEMI guidelines: 1. Reperfusion in acute ST-segment elevation myocardial infarction.
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Anistreplase↗