Epidemiology of ventricular tachycardia/ventricular fibrillation and sudden cardiac death

Prophylactic lidocaine for myocardial infarction

BACKGROUND

Coronary artery disease is a major public health problem affecting both developed and developing countries. Acute coronary syndromes include unstable angina and myocardial infarction with or without ST-segment elevation (electrocardiogram sector is higher than baseline). Ventricular arrhythmia after myocardial infarction is associated with high risk of mortality. The evidence is out of date, and considerable uncertainty remains about the effects of prophylactic use of lidocaine on all-cause mortality, in particular, in patients with suspected myocardial infarction.

OBJECTIVES

To determine the clinical effectiveness and safety of prophylactic lidocaine in preventing death among people with myocardial infarction.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (2015, Issue 3), MEDLINE Ovid (1946 to 13 April 2015), EMBASE (1947 to 13 April 2015) and Latin American Caribbean Health Sciences Literature (LILACS) (1986 to 13 April 2015). We also searched Web of Science (1970 to 13 April 2013) and handsearched the reference lists of included papers. We applied no language restriction in the search.

SELECTION CRITERIA

We included randomised controlled trials assessing the effects of prophylactic lidocaine for myocardial infarction. We considered all-cause mortality, cardiac mortality and overall survival at 30 days after myocardial infarction as primary outcomes.

DATA COLLECTION AND ANALYSIS

We performed study selection, risk of bias assessment and data extraction in duplicate. We estimated risk ratios (RRs) for dichotomous outcomes and measured statistical heterogeneity using I(2). We used a random-effects model and conducted trial sequential analysis.

MAIN RESULTS

We identified 37 randomised controlled trials involving 11,948 participants. These trials compared lidocaine versus placebo or no intervention, disopyramide, mexiletine, tocainide, propafenone, amiodarone, dimethylammonium chloride, aprindine and pirmenol. Overall, trials were underpowered and had high risk of bias. Ninety-seven per cent of trials (36/37) were conducted without an a priori sample size estimation. Ten trials were sponsored by the pharmaceutical industry. Trials were conducted in 17 countries, and intravenous intervention was the most frequent route of administration.In trials involving participants with proven or non-proven acute myocardial infarction, lidocaine versus placebo or no intervention showed no significant differences regarding all-cause mortality (213/5879 (3.62%) vs 199/5848 (3.40%); RR 1.02, 95% CI 0.82 to 1.27; participants = 11727; studies = 18; I(2) = 15%); low-quality evidence), cardiac mortality (69/4184 (1.65%) vs 62/4093 (1.51%); RR 1.03, 95% CI 0.70 to 1.50; participants = 8277; studies = 12; I(2) = 12%; low-quality evidence) and prophylaxis of ventricular fibrillation (76/5128 (1.48%) vs 103/4987 (2.01%); RR 0.78, 95% CI 0.55 to 1.12; participants = 10115; studies = 16; I(2) = 18%; low-quality evidence). In terms of sinus bradycardia, lidocaine effect is imprecise compared with effects of placebo or no intervention (55/1346 (4.08%) vs 49/1203 (4.07%); RR 1.09, 95% CI 0.66 to 1.80; participants = 2549; studies = 8; I(2) = 21%; very low-quality evidence). In trials involving only participants with proven acute myocardial infarction, lidocaine versus placebo or no intervention showed no significant differences in all-cause mortality (148/2747 (5.39%) vs 135/2506 (5.39%); RR 1.01, 95% CI 0.79 to 1.30; participants = 5253; studies = 16; I(2) = 9%; low-quality evidence). No significant differences were noted between lidocaine and any other antiarrhythmic drug in terms of all-cause mortality and ventricular fibrillation. Data on overall survival 30 days after myocardial infarction were not reported. Lidocaine compared with placebo or no intervention increased risk of asystole (35/3393 (1.03%) vs 14/3443 (0.41%); RR 2.32, 95% CI 1.26 to 4.26; participants = 6826; studies = 4; I(2) = 0%; very low-quality evidence) and dizziness/drowsiness (74/1259 (5.88%) vs 16/1274 (1.26%); RR 3.85, 95% CI 2.29 to 6.47; participants = 2533; studies = 6; I(2) = 0%; low-quality evidence). Overall, safety data were poorly reported and adverse events may have been underestimated. Trial sequential analyses suggest that additional trials may not be needed for reliable conclusions to be drawn regarding these outcomes.

AUTHORS' CONCLUSIONS

This Cochrane review found evidence of low quality to suggest that prophylactic lidocaine has very little or no effect on mortality or ventricular fibrillation in people with acute myocardial infarction. The safety profile is unclear. This conclusion is based on randomised controlled trials with high risk of bias. However (disregarding the risk of bias), trial sequential analysis suggests that additional trials may not be needed to disprove an intervention effect of 20% relative risk reduction. Smaller risk reductions might require additional higher trials.

Primary outcomes for resuscitation science studies: a consensus statement from the American Heart Association

BACKGROUND AND PURPOSE

The guidelines presented in this consensus statement are intended to serve researchers, clinicians, reviewers, and regulators in the selection of the most appropriate primary outcome for a clinical trial of cardiac arrest therapies. The American Heart Association guidelines for the treatment of cardiac arrest depend on high-quality clinical trials, which depend on the selection of a meaningful primary outcome. Because this selection process has been the subject of much controversy, a consensus conference was convened with national and international experts, the National Institutes of Health, and the US Food and Drug Administration.

METHODS

The Research Working Group of the American Heart Association Emergency Cardiovascular Care Committee nominated subject leaders, conference attendees, and writing group members on the basis of their expertise in clinical trials and a diverse perspective of cardiovascular and neurological outcomes (see the online-only Data Supplement). Approval was obtained from the Emergency Cardiovascular Care Committee and the American Heart Association Manuscript Oversight Committee. Preconference position papers were circulated for review; the conference was held; and postconference consensus documents were circulated for review and comments were invited from experts, conference attendees, and writing group members. Discussions focused on (1) when after cardiac arrest the measurement time point should occur; (2) what cardiovascular, neurological, and other physiology should be assessed; and (3) the costs associated with various end points. The final document underwent extensive revision and peer review by the Emergency Cardiovascular Care Committee, the American Heart Association Science Advisory and Coordinating Committee, and oversight committees.

RESULTS

There was consensus that no single primary outcome is appropriate for all studies of cardiac arrest. The best outcome measure is the pairing of a time point and physiological condition that will best answer the question under study. Conference participants were asked to assign an outcome to each of 4 hypothetical cases; however, there was not complete agreement on an ideal outcome measure even after extensive discussion and debate. There was general consensus that it is appropriate for earlier studies to enroll fewer patients and to use earlier time points such as return of spontaneous circulation, simple "alive versus dead," hospital mortality, or a hemodynamic parameter. For larger studies, a longer time point after arrest should be considered because neurological assessments fluctuate for at least 90 days after arrest. For large trials designed to have a major impact on public health policy, longer-term end points such as 90 days coupled with neurocognitive and quality-of-life assessments should be considered, as should the additional costs of this approach. For studies that will require regulatory oversight, early discussions with regulatory agencies are strongly advised. For neurological assessment of post-cardiac arrest patients, researchers may wish to use the Cerebral Performance Categories or modified Rankin Scale for global outcomes.

CONCLUSIONS

Although there is no single recommended outcome measure for trials of cardiac arrest care, the simple Cerebral Performance Categories or modified Rankin Scale after 90 days provides a reasonable outcome parameter for many trials. The lack of an easy-to-administer neurological functional outcome measure that is well validated in post-cardiac arrest patients is a major limitation to the field and should be a high priority for future development.

Sex-related differences in the presentation and outcome of out-of-hospital cardiopulmonary arrest: a multiyear, prospective, population-based study

OBJECTIVE

To examine whether previously observed sex-related differences in coronary artery disease syndromes also apply to patients with out-of-hospital sudden cardiac arrest, a probable subset of patients with coronary artery disease who are easy to recognize and are treated in a standardized fashion.

DESIGN

Prospective, population-based study conducted over a 6-yr period.

SETTING

A large urban municipality (population, 1.1 million) served by a single emergency medical services system with centralized medical direction and standardized protocols.

PATIENTS

All patients with out-of-hospital, nontraumatic, primary cardiac arrest.

INTERVENTIONS

Standardized advanced cardiac life support protocols.

MEASUREMENTS AND MAIN RESULTS

During the 6 yrs of the study, 4147 consecutive patients were studied, 42% of whom were women (p <.001). Although women were significantly older than men (mean age, 68.7 +/- 18 vs. 61.7 +/- 17 yrs; p =.001), there were no significant differences for the percentages of witnessed and unwitnessed arrests, response intervals, and the length and type of treatment provided. Although men were more likely to have ventricular fibrillation/ventricular tachycardia on presentation (41% vs. 30%), women had more asystole (8.8% vs. 7%) and (organized) pulseless electrical activity than men (24% vs. 18%; p <.001). Nevertheless, more women were resuscitated (13.5% vs. 10.7%; p =.005), particularly women with non-ventricular fibrillation/ventricular tachycardia presentation (12.6% vs. 9.6%; p <.02). These differences were more pronounced when controlling for age (95% confidence interval, 1.44 [1.25-1.74]).

CONCLUSIONS

In cases of out-of-hospital sudden cardiac arrest, women have significantly better resuscitation rates than men, especially when controlling for age, particularly among women with non-ventricular fibrillation/ventricular tachycardia presentations. Additional studies are required to validate these observations, not only for long-term survival and external validity, but also for other potential genetic factors and potential discrepancies with other studies.

Gamma-linolenic acid provides additional protection against ventricular fibrillation in aged rats fed linoleic acid rich diets

Ligation of the coronary artery in rats produces severe ventricular fibrillation (VF) and malignant cardiac arrhythmia. Mortality increases with the age of the animal. Diets rich in saturated fatty acids (SF) but low in linoleic acid (LA) increase, but diets high in LA and low in SF decrease the severity of VF and mortality in older animals. The effects of an LA enriched diet can be blocked by inhibition of cyclooxygenase suggesting that conversion of LA to eicosanoids is central to the development of VF. Conversion of LA to gamma-linolenic acid (GLA) via delta-6 desaturase is the first step in the process. The activity of delta-6 desaturase declines with age. Thus inclusion of GLA in the diet of older animals may provide an additional benefit over LA alone. Dietary supplements of evening primrose oil (EPO) to one year old rats reduced ischaemic VF more than a supplement of sunflower seed oil (SSO) without GLA. Substitution of borage oil (more GLA than EPO but less LA than either EPO or SSO) was without additional benefit.

Effects of gender on cardiac arrhythmias

The purpose of this study is to review published data regarding gender differences in cardiac electrophysiology and in the occurrence of clinical arrhythmias. ECG differences between men and women include a faster resting heart rate in women, a longer corrected QT interval, and a lower QT dispersion than in men. The faster resting heart rate in women appears to be primarily related to differences in physical conditioning. The mechanism for the longer corrected QT interval in women is not completely known, but does not appear to be related to acute effects of estrogen or progesterone or differences in autonomic innervation. Women also appear to have a lower incidence of atrial fibrillation, a difference in the age distribution of supraventricular tachycardia, and a lower incidence of sudden death than men. Much of the lower incidence of sudden death in women may relate to a difference in the prevalence of coronary artery disease, but other factors such as inherent differences in repolarization, which may be reflected by a gender difference in the corrected QT interval, also may be operative. The paradox of a longer corrected QT interval and higher incidence of torsades de pointes, but lower population-based incidence of sudden death in women, has not been completely resolved. Further studies will be required to help better understand the basic mechanisms involved in gender differences in electrophysiology and arrhythmias and determine the extent to which these differences have implications for clinical management of cardiac arrhythmias.

Lipids and cardiac arrhythmia

In any discussion of lipids and heart disease it is beneficial from the outset to recognise that at least three different pathological processes may be involved. The first of these is atherosclerosis which involves the deposition of "fat" in the coronary vessels, another is thrombogenesis which describes the formation of blood clots in the coronary vessels, and the third is arrhythmia which refers to disorders in the beating of the heart which may become sufficiently serious to cause sudden cardiac death (SCD). Also it is this disturbance in the rhythmic beating of the heart which is responsible for much of the mortality from 'heart attacks' which occur 'outside-of-hospital' in societies like U.S.A., U.K. and Australia. It is this latter condition of cardiac arrhythmia which is the major concern of this review. Because it is often difficult to differentiate the role of lipids in 'heart disease' in man, it has frequently been assumed that all dietary fatty acids have similar effects on the different processes involved, and many unwarranted generalisations have been made which have led to conflicts of opinion amongst physicians and confusion in the lay public. From the animal studies discussed in this review, it is apparent that dietary fatty acids have an important role to play in determining the vulnerability of the myocardium to develop serious ventricular fibrillation (VF) and potentially lethal cardiac arrhythmia. In general, diets rich in saturated fatty acids promote a state of myocardial vulnerability, whilst diets rich in PUFA significantly diminish the probability of developing lethal disorders in cardiac rhythm when the heart is placed under pharmacological (or emotional) stress, or deprived of sufficient blood flow and supply of oxygen. Very recent experiments with the monounsaturated fatty acid (MUFA) oleic acid clearly demonstrate that, at least in rats subjected to ligation of their coronary artery, this acid is not 'neutral' as has been suggested by some for its role in atherosclerosis, but in fact is indistinguishable from saturated fatty acids in its effect in promoting arrhythmia during either regional ischaemia or reperfusion arrhythmia in this animal model of SCD.(ABSTRACT TRUNCATED AT 400 WORDS)

Unfavorable outcome in patients with primary electrical disease who survived an episode of ventricular fibrillation

BACKGROUND

Prognosis in patients with ventricular tachyarrhythmia without structural heart disease (primary electrical disease) has been described as excellent. However, prognosis may be less favourable in the subgroup surviving an episode of ventricular fibrillation.

METHODS AND RESULTS

We prospectively followed 19 consecutive patients (age, 13 to 66 years; mean age, 33 years) who had survived an episode of documented ventricular fibrillation. Structural heart disease, preexcitation, and long QT syndromes were excluded by thorough cardiologic evaluation. All patients underwent 24-hour Holter monitoring, exercise testing, and programmed electrical stimulation according to a standardized protocol. Holter monitoring revealed episodes of ventricular tachyarrhythmia in 5 patients. Exercise testing reproducibly provoked ventricular tachycardia in 2 patients. Baseline programmed electrical stimulation yielded inducibility of rapid ventricular tachyarrhythmia in 10 patients (53%) and noninducibility in 9 (47%). Nine patients were discharged on antiarrhythmic drug therapy. A defibrillator was implanted in 10 patients. During 43-month follow-up (range, 5 to 85 months; median, 41 months), major arrhythmic events recurred in 7 patients (37%). Four of these patients had noninducibility at baseline programmed electrical stimulation. Two patients on antiarrhythmic drugs had recurrent cardiac arrest: one died suddenly and the other was successfully resuscitated from ventricular fibrillation and subsequently underwent defibrillator implantation. In the other 5 patients, termination of (pre)syncopal episodes was associated with defibrillator shocks. Termination of ventricular fibrillation was documented by Holter recording in one of these patients. Specific markers predictive of a recurrent event could not be identified, although 6 of 7 patients with recurrent events had experienced at least one episode of cardiac arrest or (pre)syncope before the index episode.

CONCLUSIONS

Patients with primary electrical disease presenting with ventricular fibrillation are at high risk of recurrence of major arrhythmic events during long-term follow-up. Noninducibility at baseline study does not predict an uneventful course. Also, early defibrillator implantation should be considered in these patients.

Dietary fatty acids and protection against experimental cardiac arrhythmias in rats

Sudden cardiac death accounts for about 50% of total coronary disease mortality in westernized industrial countries. The lack of early symptoms for this disorder makes prevention the preferred strategy. In a rat model of cardiac ischemia, dietary n-6 (sunflower seed oil) and n-3 (fish-oil) polyunsaturated fatty acids were shown to protect against arrhythmia compared with saturated fat, with greatest protection observed with fish oil. The frequency of arrhythmia was similar with monounsaturated fat from olive oil and saturated fat.

Ventricular fibrillation in patients without significant structural heart disease: a multicenter experience with implantable cardioverter-defibrillator therapy

OBJECTIVES

This study was undertaken to characterize the outcome of survivors of ventricular fibrillation with no or minimal structural heart disease who received an implantable cardioverter-defibrillator.

BACKGROUND

The prognosis among survivors of ventricular fibrillation with minimal or no structural cardiac abnormalities remains unclear. Since the advent of implantable cardioverter-defibrillators, this question takes on added importance.

METHODS

This 10-center retrospective study provided information on 28 survivors of ventricular fibrillation (mean age 42 years) with minimal or no structural abnormalities who were treated with an implantable cardioverter-defibrillator.

RESULTS

Ventricular tachyarrhythmias (polymorphic in all but one patient) were induced during baseline programmed stimulation in 39% of patients. During a median 30.6-month follow-up period after implantable cardioverter-defibrillator implantation, there were no cardiac deaths and two noncardiac deaths. Sixteen patients experienced 36 shock episodes (total 88 shocks). The majority of shocks were classified as "indeterminate"; one patient received 47 "spurious" shocks during one shock episode and each of four patients received one "appropriate" shock. Ventricular arrhythmias were not inducible in any of these latter four patients.

CONCLUSIONS

Survivors of ventricular fibrillation with minimal or no structural cardiac abnormalities receiving an implantable cardioverter-defibrillator have an excellent 3-year survival rate. The occurrence, albeit infrequent, of appropriate implantable cardioverter-defibrillator shocks in this group suggests that these patients have a potential risk of recurrent cardiac arrest whose fatal outcome may be avoided by implantable cardioverter-defibrillator therapy.

The effect of bidisomide (SC-40230), a new class Ia/Ib antiarrhythmic agent, on defibrillation energy requirements in dogs with healed myocardial infarctions

Bidisomide is a Class Ia/Ib antiarrhythmic agent with activity against ventricular and supraventricular arrhythmias. The potential for bidisomide to increase defibrillation threshold (DFT) was tested in anesthetized dogs with healed left ventricular infarcts (> or = 10 days). Defibrillation patches were attached to each ventricle and shocks were delivered via an external cardioverter/defibrillator. Three groups were studied: placebo (saline), canine therapeutic bidisomide (TB, 2-5 micrograms/mL plasma concentration) and supratherapeutic bidisomide (STB, 6-14 micrograms/mL). Each animal received only one treatment. An abbreviated DFT curve was determined before and after treatment. Heart rate, blood pressure, PR, QRS, infarct size, and hematocrit were also measured before and after treatment. DFT was significantly increased (average +3 to +5 joules [J], P < 0.05) by TB and STB. TB (5/5) did not increase DFT beyond 40 J. In 6/7 experiments, STB did not increase DFT beyond 40 J. Placebo (n = 6) had no significant effect on DFT. Infarct size (mean = 11% of the left ventricle) was not significantly different between groups. Heart rate and QRS were not significantly altered but blood pressure was significantly decreased (16%-31% systolic, 29%-45% diastolic) and hematocrit was significantly increased (19% to 25%) in all groups. PR was significantly increased by STB only.

CONCLUSION

therapeutic and supratherapeutic doses of bidisomide slightly but significantly increased DFT (3-5 J) in a canine infarcted heart model.

Idiopathic ventricular fibrillation

A review of the literature dealing with sudden death revealed 19 articles in which ostensibly healthy patients with documented VF unrelated to any known cardiac or noncardiac etiology are reported. Fifty-four patients fulfilling the criteria for idiopathic VF, including 14 patients investigated at our institution, are described. The mean age of patients for studies that reported age data was 36 years, with a male-to-female ratio of 2.5 to 1. Over 90% of the patients required resuscitation, while syncope due to nonsustained VF occurred in the rest. Diagnosis of VF was preceded by syncope in one fourth of the patients. Holter monitoring and exercise stress tests were often unrewarding. Available electrophysiologic data revealed a 69% inducibility rate of sustained ventricular tachyarrhythmias using nonaggressive protocols of ventricular stimulation in most cases. Induced tachyarrhythmias were poorly tolerated, and were mostly of polymorphic configuration. Class IA antiarrhythmic agents were highly effective in preventing reinduction of these arrhythmias. Available figures suggest an 11% rate of sudden death within 1 year of diagnosis. Appropriate antiarrhythmic therapy appears to improve prognosis. Reviewed data suggest that idiopathic VF represents an underestimated cause of sudden cardiac death in ostensibly healthy patients. An international registry of patients with idiopathic VF is warranted.

The influence of age and dietary fat in an animal model of sudden cardiac death

The influence of dietary fat on myocardial vulnerability to arrhythmia was examined using coronary artery occlusion and reperfusion in the anesthetised rat as a whole animal model of ventricular fibrillation and sudden cardiac death. Animals were fed a reference (REF) diet alone or supplemented 12% by weight with tuna fish oil (TFO) (rich in n-3 fatty acids), sunflower seed oil (SSO) (rich in n-6 fatty acids) or sheep perirenal fat (SF) (rich in saturated fatty acids). Feeding periods of 6, 12, and 18 months and a total of 108 rats were used. The incidence of ventricular fibrillation in occlusion was reduced from 46% of REF animals to 6% and 21% in TFO and SSO groups respectively and increased to 68% in the SF-fed rats. The incidence of ventricular tachycardia was also reduced by TFO and SSO. The duration of arrhythmic episodes was increased by SF and reduced by TFO and SSO. The incidence of fibrillation on reperfusion of acutely ischemic myocardium (15 minutes occlusion) was significantly reduced by TFO only (12%, REF = 50%, SSO = 30%, SF = 70%). Severity of arrhythmias increased with age as did the extent of dietary influence. Mortality from fibrillation which only occurred in rats aged 12 months or older (REF = 13%) was increased by SF (43%) mainly in reperfusion (38%) but did not occur in TFO or SSO. These results indicate the potential benefit of dietary modification to include a higher proportion of polyunsaturated fat especially fish oil in reducing risk of sudden cardiac death.(ABSTRACT TRUNCATED AT 250 WORDS)

Implantable defibrillation: eight years clinical experience

Implantation of the first automatic defibrillator occurred in February 1980. Incorporation of cardioversion capability in 1982 resulted in the AICD automatic implantable cardioverter defibrillator. Between April 1, 1982 and April 15, 1988, 3610 patients in 236 U.S. and 84 international centers received AICD pulse generators. Patient population consisted of 2904 males and 683 females with recurrent ventricular tachycardia and/or fibrillation, mean age 59 yrs. (range 9-96 yrs.). Primary diagnoses reported for the patient group were: coronary artery disease (63.5%), nonischemic cardiomyopathy (12.9%), other (6.4%) and unspecified (17.2%). Mean reported LV ejection fraction was 32.8%. Follow-up averaged 12.2 mo. (range 0-72 mo.). Of 385 deaths, 94 (24%) were sudden. Cumulative percentage survival (+/- S.E.) from sudden cardiac death (SCD) was 98.0 +/- 0.3%, 96.5 +/- 0.5%, 95.2 +/- 0.7%, 93.7 +/- 1.0%, 93.7 +/- 1.0% and 89.7 +/- 4.0% at 12, 24, 36, 48, 60 and 72 months, respectively. Operative mortality (less than or equal to 30 days) was 2.5%. Reported side effects/complications were similar to those of pacemakers. To date, 33% of the patients received spontaneous device countershocks. AICD pulse generator survival from electrical and mechanical failures was 92.8 +/- 0.5%, 88.4 +/- 0.7%, 86.7 +/- 0.8% and 86.4 +/- 0.9% at 12, 18, 24 and 30 mos. Data analysis demonstrates that the AICD has had a significant impact on patient survival from SCD.

The premise, promise, and perils of the prevention of lethal ventricular tachyarrhythmias

Sudden cardiac death caused by ventricular tachyarrhythmias claims about 360,000 lives a year in the United States. The premature ventricular complex (PVC) hypothesis has been the cornerstone for understanding this problem, but it is now recognized as an incomplete explanation for this catastrophy. The recognition of the importance of structural heart disease in this process has led to the development of the Substrate Hypothesis as an alternative explanation. In this construct, PVCs may trigger lethal arrhythmias but only if an abnormal electrophysiologic substrate is present. This hypothesis more completely describes the pathophysiology of the process, provides the basis for understanding the value and limitations of the techniques used for risk assessment and management, and helps clarify the potential endpoints and potential adverse effects of therapy to prevent arrhythmias. Since no single diagnostic technique is ideal and no therapeutic modality is universally effective, an approach to the management of this problem must be multidimensional and based on a firm understanding of the actual risk of a life threatening arrhythmia, the potential but unproven benefits and uncertain endpoints of drug therapy, the cost, and the potential for arrhythmia exacerbation or significant side effect.