Lignocaine given prophylactically to patients with acute myocardial infarction

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 The evidence is out of date, and considerable uncertainty remains about the effects of prophylactic use of lidocaine on all-cause mortality, in particular, in patients with suspected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.

Significance of cardiac arrhythmias preceding first cardiac arrest in patients with acute myocardial infarction

In 417 consecutive cases of acute myocardial infarction (AMI) within a minimum of 21 days' stay in the Coronary Care Unit (CCU), primary cardiac arrest occurred in 41 patients (9.9%), the first episode occurring during ECG monitoring in 24 patients. After cessation of ECG monitoring, and within 2-25 days after admission, it occurred in 17 patients. Cardiac arrhythmias before the first cardiac arrest were analysed in these two groups of patients, and compared with the occurrence of cardiac arrhythmias within the first 5 days in 100 consecutive patients with AMI without complicating cardiac arrest. No significant difference in the frequency of cardiac arrhythmias could be demonstrated between the two groups with cardiac arrest and the control series. Moreover, complete absence of rhythm disturbances right up to the beginning of cardiac arrest was as frequent in the patient groups as in the control series (around 20%). As there is not sufficient evidence that treatment with antiarrhythmic drugs can provide safe prophylaxis against the occurrence of cardiac arrest, it is concluded that all patients with AMI should be kept in the CCU and monitored, by cable or by telemetry, for the duration of their stay. To achieve this, the cost in financial terms, manpower and reorganization is not a deterrent. Furthermore, this study does not give any support to the usual practice of confining possible attempts of prophylactic antiarrhythmic treatment to patients with arrhythmias of certain frequencies and/or types.

Effect of timolol on late ventricular arrhythmias after acute myocardial infarction

This is a subproject of the Norwegian timolol myocardial infarction study carried out at one of the clinical centers. High risk patients surviving either a reinfarction or large initial infarction were randomized to placebo (44 pts) or timolol (37 pts). A 24 hour ECG was obtained the day before randomization (at baseline, 7-28 days after the acute attack) then 3 days, 1 month and 6 months after start of therapy. During this period the number of patients with one or more of ventricular couplets, bigemini, ventricular tachycardia or early cycle premature ventricular contractions (PVC) (i.e. complex ventricular arrhythmias) and the average number of PVC per hour increased significantly in the placebo group but not in the timolol group. The results indicate that there is an increased severity and incidence of ventricular arrhythmias in the first 6 months after myocardial infarction. Timolol effectively inhibited this trend. The importance of timolol as an antiarrhythmic agent may therefore be to prevent subclinical infarction extension and secondary ventricular arrhythmias related to the size of the myocardial damage.

Effects of lidocaine on isolated, blood-perfused ventricular contractility in the dog

Direct inotropic effects of lidocaine on ventricular muscle were investigated in isolated canine left ventricular preparations which were perfused with a donor dog's arterial blood. Intravenous administration of lidocaine in doses of less than 1 mg/kg did not cause any significant hemodynamic or cardiac changes in the donor dog and in the isolated ventricular preparation. A large dose of 10mg/kg of lidocaine produced a marked depressor response in the donor and a negative inotropic effect in the isolated ventricle. Direct injection of lidocaine (1-30 micromol) to the isolated preparation induced a dose-related decrease in the ventricular contractile force. Infusion of lidocaine (3 micromol/ml per min) did not influence norepinephrine- or calcium chloride-induced positive inotropic effects. In the frequency-force relationship, lidocaine generally depressed the contractility, exhibiting the positive staircase phenomenon. On the other hand, a calcium entry inhibitor, diltiazem, readily caused the negative staircase. From these results, it is concluded that (1) a large amount of lidocaine has a cardiac depressant property, (2) lidocaine has no antiadrenergic properties, and (3) the action of lidocaine may probably be due to the effect of intracellular calcium movement but not to a modification of Ca inward currents.

Prophylactic lidocaine use in acute myocardial infarction: incidence and outcomes from two international trials. The GUSTO-I and GUSTO-IIb Investigators

BACKGROUND

Early meta-analyses suggested that prophylactic lidocaine use reduces ventricular fibrillation but increases mortality rates after acute myocardial infarction. We determined the frequency and effect on clinical outcomes with its use in the thrombolytic era.

METHODS AND RESULTS

We studied 43,704 patients enrolled in GUSTO-I or GUSTO-IIb who had ST-segment elevation, underwent thrombolysis, and survived at least 1 hour after enrollment. Odds ratios (OR) and confidence intervals (CI) were calculated for the risk of asystole, atrioventricular block, ventricular fibrillation, and ventricular tachycardia during hospitalization; for 24-hour, in-hospital, and 30-day mortality rates; and for 24-hour and 30-day mortality rates after adjustment for baseline predictors of death. In GUSTO-I and GUSTO-IIb, 16% and 3.5% of patients, respectively, received prophylactic lidocaine. They had a lower risk of death at 24 hours (OR 0.81, 95% CI 0.67 to 0.97) and trends toward lower odds of in-hospital death (OR 0.90, 95% CI 0.81 to 1.01) and death at 30 days (OR 0.92, 95% CI 0.82 to 1. 02). After adjustment for baseline characteristics, however, the odds of death were similar with or without lidocaine (OR 0.90 and 0. 97, respectively). Outside the United States, lidocaine was associated with higher incidences of all serious arrhythmias, but in US patients it conferred a lower likelihood of ventricular fibrillation and no increase in asystole, atrioventricular block, or mortality rates.

CONCLUSIONS

Prophylactic lidocaine use has decreased with the advent of thrombolysis, although its use may not be associated with increased mortality rates.

Multicenter randomized trial and a systematic overview of lidocaine in acute myocardial infarction

BACKGROUND

More than 20 randomized trials and 4 meta-analyses have been conducted on the use of prophylactic lidocaine in acute myocardial infarction (MI). The results suggest that lidocaine reduces ventricular fibrillation (VF) but increases mortality rates in acute MI.

METHODS AND RESULTS

Patients with ST-elevation MI who were examined <6 hours after symptom onset (n = 903) were randomly assigned to either lidocaine or no lidocaine and to either streptokinase and heparin or heparin alone. Lidocaine was given as 4 boluses of 50 mg each every 2 minutes, then an infusion of 3 mg/min for 12 hours, then 2 mg/min for 36 hours. We compared the incidence of in-hospital death and ventricular arrhythmias. We then performed a meta-analysis of prophylactic lidocaine in acute MI that included these and prior trial results. The rates of VF and death with and without lidocaine were calculated for each trial, then odds ratios (OR) with confidence intervals (CI) were calculated for the risk of these events overall with and without lidocaine. Patients given lidocaine in the randomized study had significantly less VF (2.0% vs 5.7% without lidocaine, P =.004) and a trend toward increased mortality rates (9.7% vs 7.0%, P =.145). Meta-analysis revealed nonsignificant trends toward reduced VF (OR 0.71, 95% CI 0.47 to 1. 09) and increased mortality rates (OR 1.12, 95% CI 0.91 to 1.36) with lidocaine.

CONCLUSIONS

Lidocaine reduces VF but may adversely affect mortality rates. The routine use of prophylactic lidocaine in acute MI is not recommended.

Lidocaine prophylaxis for fatal ventricular arrhythmias after acute myocardial infarction

OBJECTIVE

To compare the efficacy and safety of a 40-hour lidocaine infusion after completion of a 8-hour open-label infusion for prophylaxis of primary ventricular fibrillation in patients with uncomplicated acute myocardial infarction.

METHODS

This was a double-blind, randomized placebo-controlled trial held in the coronary care unit of a large nonprofit hospital. We studied 200 patients with uncomplicated acute myocardial infarction in Killip class I or II who came to the hospital within 6 hours of onset of symptoms and 22 patients who had ventricular fibrillation before the start of the study. Intervention consisted of an 8-hour lidocaine infusion followed by placebo or lidocaine for an additional 40 hours. The infusion rate was adjusted in patients > or = 70 years old and in those < 50 kg or > or = 90 kg. Measurements recorded were baseline demographic characteristics, incidence of ventricular arrhythmias, adverse reactions, and death.

RESULTS

New congestive heart failure developed during the randomized phase in 9% of patients receiving lidocaine and in 2% of patients receiving placebo (p = 0.03). Ventricular fibrillation did not occur during the treatment period, and sustained ventricular tachycardia developed in one patient receiving placebo. The in-hospital mortality rate was comparable in both groups (4% versus 2%; p = 0.68) but was much higher (13.6%) in patients with initial ventricular fibrillation not included in the randomized study.

CONCLUSIONS

A 40-hour age- and weight-adjusted lidocaine infusion administered after an initial 8-hour infusion provoked more congestive heart failure than placebo. In view of the absence of ventricular fibrillation episodes with both infusions, caution should be used when lidocaine is administered for longer than 8 hours in patients with uncomplicated myocardial infarction.

Early out-of-hospital lidocaine administration decreases the incidence of primary ventricular fibrillation in acute myocardial infarction

This study was designed to assess the effectiveness of early prehospital intravenous administration of lidocaine in preventing primary ventricular fibrillation (PVF) in patients with suspected acute myocardial infarction (AMI). Sixty patients with suspected AMI, seen by the Mobile Coronary Care Unit (MCCU) of Florence, were randomly allocated at home to treatment with lidocaine (bolus i.v. of 1 mg/kg, followed by an infusion of 4 mg/min) or placebo (infusion of saline at a rate of 1 mL/min), respectively. The lidocaine group (27 patients) and the control group (33 patients) were not significantly different in age, clinical condition, or time of randomization. The diagnosis of AMI was confirmed in all 60 patients during the hospital stay. Ventricular fibrillation (VF) occurred in 5 patients in the control group in comparison to none in the lidocaine group (P < 0.05). Three patients experienced VF at home and were successfully resuscitated by an MCCU cardiologist. In another two patients, VF occurred during the first 4 hours after onset of symptoms. No major side effects were observed after the infusion of lidocaine. Our findings support the effectiveness of the prophylactic administration of lidocaine in preventing PVF in the prehospital phase of AMI and suggest that the drug can be safely administered in this setting by prehospital personnel.

The use of antiarrhythmics in advanced cardiac life support

Antiarrhythmic agents have been used to treat malignant ventricular arrhythmias in the setting of acute myocardial ischemia with proven efficacy for many years. Thus, it has been presumed that these agents would be efficacious for the treatment of cardiac arrest. Unfortunately, hard data supporting this contention are unavailable to date. Furthermore, some of the experimental data in this area are conflicting, especially regarding the relative effects of lidocaine and bretylium. Thus, little definitive can be said based on experimental information. In two randomized patient studies, lidocaine and bretylium performed comparably. Because of the frequent use of lidocaine and thus the familiarity of most health care professionals with its use, it makes educational sense to utilize lidocaine as the antiarrhythmic drug of first choice during the cardiac arrest sequence. Recent data suggesting that amiodarone may be efficacious in patients with recurrent arrhythmias require additional confirmation. Although antiarrhythmic agents have been shown to be effective in the treatment of malignant arrhythmias in patients with acute myocardial infarction, their use prophylactically for patients with suspected infarction (advocated in the past) has recently undergone reevaluation. It is now clear that despite a reduction in ventricular fibrillation, overall mortality may be increased. This may be because the prophylactic treatment of patients with suspected infarction includes a large number of patients not at risk for ventricular fibrillation who still may be at risk for drug toxicity. Thus, prophylactic administration of lidocaine to all patients with suspected acute myocardial infarction can no longer be recommended. There are inadequate data upon which to base a recommendation concerning the use of lidocaine in patients receiving thrombolytic therapy. The group most likely to benefit from lidocaine are patients with ST segment elevation who present early after the onset of acute myocardial infarction. The use of lidocaine in this group requires additional study. At present, despite enthusiasm for the prophylactic use of magnesium for the treatment of arrhythmias, data are inadequate to support its routine administration. However, given the importance of magnesium and potassium levels in the genesis of malignant arrhythmias, their levels in plasma should be assessed, and abnormalities should be promptly corrected. The potential uses of antiarrhythmic agents during advanced cardiac life support span a remarkably diverse number of applications. For the purpose of this review, only the use of these agents during CPR and during the early hours of acute or suspected acute myocardial infarction will be considered.

Lidocaine to prevent ventricular fibrillation in the prehospital phase of suspected acute myocardial infarction: the North-Norwegian Lidocaine Intervention Trial

The efficacy of lidocaine to prevent ventricular fibrillation during the prehospital phase of suspected acute myocardial infarction was assessed 3 hours after administration in a randomized controlled trial. A total of 204 patients examined within 6 hours after onset of symptoms were included, and acute myocardial infarction was later confirmed in 63% of these. Lidocaine, administered as a 100 mg intravenous bolus dose followed by a 300 mg intramuscular injection, failed to prevent ventricular fibrillation, which was observed in 2 (2.1%) of 96 patients in the lidocaine group and in 3 (3.0%) of 101 patients in the placebo group (p = 0.95; odds ratio 0.7, 95% confidence interval 0.4 to 1.3). In addition, sudden cardiac collapse with unknown heart rhythm was observed in three patients who received lidocaine (3.1%) compared with none in the placebo group (p = 0.23; odds ratio 7.6, 95% confidence interval 2.8 to 22.1). The results of this small study suggest that lidocaine, even when given in a high dose, is ineffective in preventing ventricular fibrillation when administered before hospitalization for suspected acute myocardial infarction. Prophylactic use of lidocaine in this situation may therefore not be warranted or advisable.

Declining incidence of ventricular fibrillation in myocardial infarction. Implications for the prophylactic use of lidocaine

BACKGROUND

The purposes of the present investigation were 1) to track the incidence of primary ventricular fibrillation (VF) in the control and lidocaine-treated groups in the randomized control trials (RCTs) of lidocaine prophylaxis against primary VF in acute myocardial infarction, with particular emphasis on the time frame of the randomized trial, and 2) to estimate the number of patients who must receive lidocaine currently to prevent one episode of VF.

METHODS AND RESULTS

The following variables from RCTs published between 1969 and 1988 were entered into logistic regression models to predict the percent of patients developing VF: year of publication of the RCT, method of data analysis used in the RCT, route and technique of lidocaine administration, duration of monitoring for VF, and exclusion criteria before randomization (congestive heart failure/cardiogenic shock, ventricular tachycardia/VF, or bradycardia/atrioventricular block). Year of publication was a significant predictor of VF in both the control and lidocaine groups (p less than or equal to 0.002) even after adjusting for other covariates. Based on a univariate logistic regression model with year as the predictor variable, it was estimated that the incidence of primary VF in the control group fell from 4.51% in 1970 to 0.35% in 1990 and from 4.32% down to 0.11% for the lidocaine group over the same time period. Thus, about 400 patients would currently need prophylaxis with lidocaine to prevent one episode of VF.

CONCLUSIONS

Present estimates of the risk:benefit ratio of lidocaine prophylaxis should consider the low risk of VF in control patients and the large number who need lidocaine prophylaxis to prevent one episode of VF. When added to the previously reported trend toward excess mortality in lidocaine-treated patients, these data argue against the routine prophylactic use of lidocaine in patients with acute myocardial infarction.

Prehospital prophylactic lidocaine does not favorably affect outcome in patients with chest pain

STUDY OBJECTIVES

The purpose of our study was to determine the morbidity and mortality in initially stable patients presenting to paramedics with chest pain; to examine possible beneficial effects of its use, including reduction of sudden death syndrome in the prehospital and emergency department setting; and to determine if prophylactic lidocaine is associated with adverse effects in this patient population.

DESIGN AND SETTING

This was a randomized, prospective study using prophylactic lidocaine in patients complaining of chest pain who presented to our paramedic system between January 1984 and January 1988.

TYPE OF PARTICIPANTS

All patients aged 18 years or older with chest pain of suspected cardiac origin who presented to paramedics during the study period were included. Excluded were patients presenting with warning arrhythmias, second- or third-degree heart block, bradycardias of less than 50, hypotension of less than 90 mm Hg systolic, or known allergy to lidocaine.

INTERVENTIONS

Patients were randomized into two groups, the lidocaine-treated group and the control group. An initial bolus of 1 mg/kg IV lidocaine was administered to the lidocaine-treated group. A simultaneous 2 mg/min IV drip was established. Ten minutes after the first dose of lidocaine, a second bolus of 0.5 mg/kg was administered.

MEASUREMENTS AND MAIN RESULTS

During the study period, 1,427 patients were entered; 704 received lidocaine, and 723 did not. Discharge diagnoses included acute myocardial infarction (31%), unstable angina (33%), other cardiac problems (7%), and noncardiac problems (29%); overall mortality rate was 7.4%. There was an equal distribution of deaths between the lidocaine-treated group (57) and the control group (48). Six patients had a cardiac arrest in the prehospital setting, and 15 had a cardiac arrest in the ED. Malignant ventricular arrhythmias as the precipitating arrest rhythm in patients with acute myocardial infarctions were similar for the lidocaine-treated and control groups. The incidence of adverse effects, including hypotension, bradycardias, second- or third-degree heart blocks, tinnitus, and altered mental status, was similar in both groups.

CONCLUSION

There are no benefits from the administration of prehospital prophylactic lidocaine in stable patients with chest pain; therefore, routine use in this setting appears unwarranted.

Lidocaine in the early phase of acute myocardial infarction: the controversy over prophylactic or selective use

In acute myocardial infarction, lidocaine is considered the drug of choice for the treatment of malignant ventricular arrhythmias. While initially a so-called "selective" treatment strategy prevailed, in which lidocaine was administered only after the onset of certain "warning arrhythmias," the prophylactic use of lidocaine in acute myocardial infarction has been gaining wider usage in intravenous and intramuscular application in recent years. Both therapeutic applications have been found to be problematic of late, which has led to increasingly restrictive use of lidocaine. While in selective treatment forms, the definition and prompt recognition of the so-called warning arrhythmias created especially acute problems, the prophylactic therapeutic use is problematic due to the occurrence of sometimes serious side effects, which is to be expected as the size of the collective being treated increases. Both treatment forms also appear limited by the narrow preventive efficacy of lidocaine against malignant ventricular arrhythmias, especially against ventricular fibrillation. The current therapeutic recommendation for lidocaine in acute myocardial infarction should be limited to patients presenting with very frequent and complex ventricular arrhythmias, especially when these are elicited by an R-on-T phenomenon. Side effects and other therapeutic problems encountered when the therapeutic modality is switched or adjusted can be greatly reduced by careful dosing and selection of the optimal combination substances.

The pharmacokinetics of lignocaine and beta-adrenoceptor antagonists in patients with acute myocardial infarction

Lignocaine (lidocaine) and beta-adrenoceptor antagonists are widely used after acute myocardial infarction. The therapeutic value of these agents depends on the achievement and maintenance of safe and effective plasma concentrations. Lignocaine pharmacokinetics after acute myocardial infarction (MI) are controlled by a number of variables. The single most important is left ventricular function, which affects both volume of distribution and plasma clearance. Other major factors include bodyweight, age, hepatic function, the presence of obesity, and concomitant drug therapy. Lignocaine is extensively bound to alpha 1-acid glycoprotein, a plasma protein which is also an acute phase reactant. Increases in alpha 1-acid glycoprotein concentration occur after an acute MI, decreasing the free fraction of lignocaine in the plasma and consequently decreasing total plasma lignocaine clearance without altering the clearance of non-protein-bound lignocaine. Complex changes in lignocaine disposition occur with long term infusions, and therefore early discontinuation of lignocaine infusions (within 24 hours) should be undertaken whenever possible. Because the risk of ventricular tachyarrhythmia declines rapidly after the onset of an acute MI, lignocaine therapy can be rationally discontinued within 24 hours in most patients. Lignocaine has a narrow toxic/therapeutic index, so that pharmacokinetic factors are critical in dose selection. In contrast, beta-adrenoceptor antagonists' adverse effects are more related to the presence of predisposing conditions (such as asthma, heart failure, bradyarrhythmias, etc.) than to plasma concentration. The pharmacokinetics of beta-adrenoceptor antagonists are important to help assure therapeutic efficacy, to provide information about the anticipated time course of drug action, and to predict the possible role of ancillary drug effects (such as direct membrane action) and loss of cardioselectivity. Lipid solubility is the main determinant of the pharmacokinetic properties of a beta-adrenoceptor antagonist. Lipid-soluble agents like propranolol and metoprolol are well absorbed orally, and undergo rapid hepatic metabolism, with important presystemic clearance and a short plasma half-life. Water-soluble drugs like sotalol, atenolol, and nadolol are less well absorbed, and are eliminated more slowly by renal excretion. Clinical assessment of beta-adrenoceptor antagonism is more valuable than plasma concentration determinations in evaluating the adequacy of the dose of a particular beta-adrenoceptor antagonist.(ABSTRACT TRUNCATED AT 400 WORDS)

Complexity and contradiction in clinical trial research

Randomized clinical trials have become the accepted scientific standard for evaluating therapeutic efficacy. Contradictory results from multiple randomized clinical trials on the same topic have been attributed either to methodologic deficiencies in the design of one of the trials or to small sample sizes that did not provide assurance that a meaningful therapeutic difference would be detected. When 36 topics with conflicting results that included over 200 randomized clinical trials in cardiology and gastroenterology were reviewed, it was discovered that results of randomized clinical trials often disagree because the complexity of the randomized clinical trial design and the clinical setting creates inconsistencies and variation in the therapeutic evaluation. Nine methodologic sources of this variation were identified, including six items concerned with the design of the trials, and three items concerned with interpretation. The design issues include eligibility criteria and the selection of study groups, baseline differences in the available population, variability in indications for the principal and concomitant therapies, protocol requirements of the randomized clinical trial, and management of intermediate outcomes. The issues in interpreting the trials include the regulatory effects of treatments, the frailty of double-blinding, and the occurrence of unexpected trial outcomes. The results of this review suggest that pooled analyses of conflicting results of randomized clinical trials (meta-analyses) may be misleading by obscuring important distinctions among trials, and that enhanced flexibility in strategies for data analysis will be needed to ensure the clinical applicability of randomized clinical trial results.

Prophylactic lidocaine in the prehospital patient with chest pain of suspected cardiac origin

The prophylactic use of lidocaine in the patient with cardiac chest pain has been reported to reduce the incidence of sudden death from ventricular dysrhythmias in the hospital setting, but few studies have been done in the early prehospital phase. We conducted a randomized, prospective study comparing the effects of lidocaine versus no lidocaine in stable patients presenting with chest pain to a paramedic system. In a one-year period, 446 patients qualified for the study; 222 received lidocaine and 224 did not. The overall hospital mortality of the two groups was 8.1% and 6.7%, respectively (P = .35). Four patients in each group developed sudden death in the prehospital and emergency department settings with ventricular dysrhythmia as the precipitating rhythm. One hundred twenty-nine (29%) had an acute myocardial infarction. The lidocaine and control group contained 68 and 61 of the patients, respectively, with an overall mortality rate of 14.7% and 13.1% (P = .45). The development of significant dysrhythmias (frequent premature ventricular contractions, ventricular tachycardia, bradycardia, second- and third-degree heart blocks) after initiation into the study was similar in both groups of patients. The use of lidocaine was a factor in decreasing systolic blood pressure (P less than 0.03) but did not appear to be clinically significant. For stable patients presenting with chest pain of suspected cardiac origin, prophylactic lidocaine in the prehospital setting was not effective in preventing life-threatening dysrhythmias, but clinically significant side effects were not noted either.

Prophylactic lidocaine in the early phase of suspected myocardial infarction

Four hundred two patients with suspected myocardial infarction seen within 6 hours of the onset of symptoms entered a double-blind randomized trial of lidocaine vs placebo. During the 1 hour after administration of the drug the incidence of ventricular fibrillation or sustained ventricular tachycardia among the 204 patients with acute myocardial infarction was low, 1.5%. Lidocaine, given in a 300 mg dose intramuscularly followed by 100 mg intravenously, did not prevent sustained ventricular tachycardia, although there was a significant reduction in the number of patients with warning arrhythmias between 15 and 45 minutes after the administration of lidocaine (p less than 0.05). The average plasma lidocaine level 10 minutes after administration for patients without a myocardial infarction was significantly higher than that for patients with an acute infarction. The mean plasma lidocaine level of patients on beta-blocking agents was no different from that in patients not on beta blocking agents. During the 1-hour study period, the incidence of central nervous system side effects was significantly greater in the lidocaine group, hypotension occurred in 11 patients, nine of whom had received lidocaine, and four patients died from asystole, three of whom had had lidocaine. We cannot advocate the administration of lidocaine prophylactically in the early hours of suspected myocardial infarction.

Prophylactic antiarrhythmic therapy in acute myocardial infarction

Safe, effective prophylaxis of arrhythmias in acute myocardial infarction (AMI) is an important clinical goal. Despite rescue squads, out-of-hospital ventricular fibrillation (VF) has a poor prognosis. Even in-hospital VF has an important morbidity and mortality. Successful prophylactic therapy may also prevent infarct size enlargement associated with tachyarrhythmias. Several antiarrhythmic drugs have been investigated. In 3 studies, mortality was significantly reduced, but all of these have serious methodologic flaws and the validity of their conclusions is debatable. More reliance can be placed on 2 other studies which suggested that VF was significantly reduced by prophylactic therapy. However, in one of these studies, which used high-dose intravenous lidocaine, an unusually high incidence of VF was observed in the placebo-treated patients. The second study, reporting the use of metoprolol in AMI, was based on retrospective subset analysis. The reduction in VF was seen from the fourth day onwards and not during the acute phase of infarction. The favorable results with high-dose intravenous lidocaine are the basis for widespread use of prophylactic arrhythmia therapy in AMI. Uncontrolled observations provide some corroboration of the benefit. However, the claimed efficacy for lidocaine remains scientifically poorly substantiated and the safety of the high-dose regimen is controversial. Effective prophylaxis of arrhythmias in AMI could have important clinical benefit. However, the strategy would entail administration of a drug to many patients not at risk of arrhythmias (those without AMI) and to a number of patients in whom the complications of infarction are destined to develop.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of antiarrhythmic drugs on mortality after myocardial infarction

The theoretical potential for a preventive or prophylactic effect of antiarrhythmic drugs (excluding beta blockers) in the treatment of coronary patients with ventricular arrhythmias has not been realized. Randomized controlled clinical trials conducted during the early hospital phase after an acute myocardial infarction as well as after discharge have not demonstrated an effect on patient survival. Three possible explanations exist. First, treatment of ventricular arrhythmias does not improve prognosis. Although this explanation is supported by the overall trial results, it is contrary to massive evidence from animals, clinical and epidemiologic studies. Second, treatment of ventricular arrhythmias does prolong life but benefit has not been observed in the trials. Limitations in applied methods, including insufficient sample sizes, may have obscured a true favorable intervention effect. Third, control of ventricular arrhythmias helps some patients but harms others. Concomitant treatment with digitalis and diuretics and, possibly, arrhythmogenic properties of the investigational drugs themselves might have confounded the overall results. The second in particular, but also the third explanation, are the most plausible. Only 1 of the 20 controlled clinical trials considered for this review required presence of ventricular arrhythmias as an entry criterion. All trials were small; the largest number of patients enrolled in a single trial was 610 and the highest number of deaths in a trial was 49. To resolve the uncertainty, increased attention to methodologic issues, such as selection of appropriate study populations, intervention strategies and larger sample sizes, is required.(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment of cardiac arrhythmias in patients with acute myocardial infarction

Cardiac arrhythmias and conduction disturbances are commonly observed in patients with myocardial infarction. The available data suggest the administration of prophylactic lidocaine, either through a large intramuscular dose (300 mg), which is particularly suited for out-patient situations, or through intravenous loading doses followed by a constant lidocaine infusion. Patients with ventricular arrhythmia should be treated with direct-current countershock if hemodynamic deterioration is present. Drug therapy for patients with ventricular arrhythmias who are resistant to lidocaine include procainamide, bretylium, or intravenous amiodarone (experimental drug). Treatment of atrioventricular block in acute infarction depends on the site of atrioventricular block, the infarct location, and the hemodynamic status. Generally, atrioventricular block associated with inferior infarction and normal hemodynamic states generally does require insertion of a pacemaker. In contrast, patients with anterior myocardial infarction and Mobitz II or third degree atrioventricular block should be treated with emergent temporary insertion of a pacemaker. In addition, prophylactic pacing is clearly indicated for those with acute myocardial infarction complicated by the bifascicular block pattern of first degree atrioventricular block and new onset bundle branch block.

Ventricular fibrillation complicating acute myocardial infarction: reasons against the routine use of lidocaine

Because of recent recommendations that lidocaine be used prophylactically in all coronary care unit (CCU) patients with suspected myocardial infarction (MI), an approach not used in our CCU, we analysed our experience with ventricular fibrillation (VF) occurring in the setting of an acute MI. The frequency of VF in all patients was 3.2%. In MI patients 5.7%, of primary ventricular fibrillation (PVF) 2.8%, and of complicating ventricular fibrillation (CVF) 6.8%. All patients with PVF were resuscitated immediately. There was an increased in-hospital mortality for patients with VF compared to patients without VF; however, the increased mortality did not seem to result directly from VF. The long-term survival of PVF patients who survived to discharge was excellent (80% at 58 months). The routine use of prophylactic lidocaine would have been of no potential benefit in 96.8% of our patients, subjecting them to extra expense and possible toxicity. Since we have found no compelling evidence that the prophylactic administration of lidocaine can reduce mortality, we do not recommend this therapy for acute MI patients in our CCU.

Intravenous antiarrhythmic drugs: newer aspects of therapy

The use of the intravenous form of antiarrhythmic drugs from the perspective of prophylaxis, urgency of therapy, and rapid assessment of effectiveness is reviewed. Examples of clinical relevance for each of these 3 variables are used to illustrate the relevance of these approaches. 1) In the human model of acute myocardial infarction, prophylaxis with lidocaine is proved and is safe, with toxicity minimized when accurate determinations of blood levels of drug are readily available. 2) When reversion is unsuccessful and ventricular response cannot be controlled with conventional therapy, rapid supraventricular tachyarrhythmias will often normalize in response to intravenous verapamil therapy, a calcium-blocking agent soon available for clinical use. 3) A long-term outpatient antiarrhythmic drug program guided by target blood levels can be defined rapidly by intravenous administration of drug; this approach enhances safety and simplifies the definition of an ongoing antiarrhythmic program. Disopyramide responsiveness can be defined using this technique.

Lignocaine prophylaxis in acute myocardial infarction: an evaluation of randomised trials

Although lignocaine has been used in coronary care units for almost two decades, its role in preventing ventricular fibrillation (VF) during acute myocardial infarction (MI) is still debated. Of fifteen randomised trials of lignocaine prophylaxis, most showed no apparent benefit. When the data from all fifteen trials were pooled and a summary relative risk estimate calculated, there was a significant benefit of lignocaine treatment in preventing VF. However, the trials had widely differing treatment schedules, modes of drug administration, and doses of lignocaine; to decrease the clinical heterogenity, minimum criteria for adequacy of treatment were established and the data from six trials which fulfilled these requirements were pooled. The summary relative risk estimate calculated from the pooled data of these six trials also demonstrated a significant prophylactic effect of lignocaine that was even greater when the two trials which treated patients with left ventricular failure and shock were excluded. From these analyses, it is concluded that lignocaine treatment provides prophylaxis against VF in acute MI. The failure of most trials to demonstrate such a prophylactic effect is due to small sample sizes and inadequate treatment protocols.

Placebo controlled study of prophylaxis of ventricular arrhythmias in acute myocardial infarction

Successful prophylaxis of ventricular arrhythmias in acute myocardial infarction might achieve a major reduction in mortality of this condition. No satisfactory drug is yet available, but many new antiarrhythmic agents are being tested in this role. Such placebo controlled investigations in the earliest phase of myocardial infarction encounter unique problems of study design, drug pharmacokinetics, study conduct, and data analysis.

Suppression of ventricular arrhythmias with intravenous disopyramide and lidocaine: efficacy comparison in a randomized trial

Twenty-six patients with clinically significant ventricular arrhythmias were randomly assigned to treatment with either intravenous disopyramide or lidocaine; crossover to the other agent was permitted in nine cases of primary drug failure. In addition, disopyramide was administered nonrandomly to seven patients with ventricular arrhythmias not controlled by lidocaine in standard doses. Arrhythmia control (greater than 50 percent reduction of premature ventricular complexes) was achieved in all 22 trials with disopyramide and in 9 of 13 trails with lidocaine in the random study, whereas clinical efficacy (arrhythmia control with absence of side effects) occurred respectively in 15 of 22, and 8 of 13 trials. In all 11 patients (7 nonrandom, 4 random) whose arrhythmia was not controlled with lidocaine the arrhythmia was controlled with disopyramide. Thus, the clinical efficacy of intravenous disopyramide ran parallel to that of lidocaine in patients with ventricular arrhythmias. Furthermore, intravenous disopyramide was an effective alternative agent for patients with arrhythmia not controlled by lidocaine.

Prophylactic lidocaine in suspected acute myocardial infarction

The incidence of serious ventricular arrhythmias following acute myocardial infarction is highest during the first few hours after injury, and thereafter declines. Several investigations into the prophylactic use of lidocaine to prevent the development of arrhythmias have shown that lidocaine, given in therapeutic doses, is effective in preventing ventricular fibrillation and in reducing early mortality. Lidocaine was found to be effective when given either by the intravenous or by the intramuscular routes. The recommended dosage is 100 mg given as an intravenous bolus followed by 2 to 4 mg/min as an infusion, which should be given by infusion pump. Another recommendation is to use two 100 mg boluses 20 minutes apart, along with the same infusion. We recommend that lidocaine be started as soon as possible in all patients suspected of having suffered acute myocardial infarction.

Antiarrhythmic drug effect mimicked by spontaneous variability of ventricular ectopy

Twenty patients with frequent ventricular ectopic beats had a 5 1/2 hour ECG rhythm strip recorded. Individual patients showed a marked spontaneous variability from one half-hour to the next in the total number of ectopic beats (-99% to +1100%) and the occurrence of pairs or salvos. Although no patient received antiarrhythmic drugs, some patients showed a spontaneous change in arrhythmia which mimicked either drug suppression or drug-induced worsening of arrhythmias. If an antiarrhythmic drug had been given to these patients after the first half-hour, 65% would have been termed "drug responders," using the criteria of 50% reduction in ectopic beats and elimination of pairs or salvos during any half-hour period in the subsequent three hours. Spontaneous variability in ventricular ectopic beats causes serious problems when using ECG monitoring to evaluate antiarrhythmic drug response in individual patients. The arrhythmias averaged for the entire group remained stable during the recording period. Evaluating antiarrhythmic drugs by examining group response rather than individual patient response minimizes the effect of spontaneous variability.

Oral disopyramide for the prevention of arrhythmias in patients with acute myocardial infarction admitted to open wards

Patients with acute myocardial infarction admitted to open wards of three hospitals were given either oral disopyramide (100 mg four times daily) or matching placebo, prophylactically, for seven days. The drug was associated with a significant reduction in mortality (p = 0-0025) and in incidence of extension of infarction (p = 0-01), ventricular fibrillation (p = 0-05), and ventricular tachycardia (p = 0-01). Disopyramide was not associated with any particular complication or side-effect. Unitl information is available to the contrary, oral disopyramide should be given for the first seven days after myocardial infarction to all patients not managed in an intensive-care unit.

Beneficial effect of lidocaine on ventricular electrical stability and spontaneous ventricular fibrillation during experimental myocardial infarction

Several studies have questioned the efficacy of lidocaine in reducing the incidence of ventricular fibrillation shortly after acute myocardial infarction when arrhythmogenic mechanisms may be different from those operative several hours later. To determine whether lidocaine inhibits the occurrence of early ventricular fibrillation, the left anterior descending and septal coronary arteries were occluded at their origins in open chest anesthetized dogs. Fourteen of 16 control dogs died with ventricular fibrillation. Fifteen dogs received two different dose regimens of lidocaine before coronary occlusion. Of the 11 treated dogs maintaining lidocaine bl), 6 survived (P less than 0.05). Five dogs received the larger dose; all died, four having blood levels of 6.3 mug/ml or greater at the time of death. Ventricular fibrillation threshold also increased in six of eight dogs when lidocaine was administered after coronary occlusion. It is concluded that lidocaine at blood levels of 1.2 to 5.5 mug/ml significantly reduces the incidence of ventricular fibrillation early after coronary occlusion. Administration of this agent therefore may be of particular value in the early phase of acute myocardial infarction.

Oral disopyramide in prophylaxis of arrhythmias following myocardial infarction

Oral disopyramide given prophylactically following myocardial infarction has been compared with placebo in a double-blind trial using continuous-tape monoriting of the electocardiogram. It caused a significant reduction in the incidence of ventricular arrhythmias and of the various degrees of heart-block. There was a significant reduction of reinfarction during hospital stay in patients who had received disopyramide. Disopyramide appears to be a safe and effective oral therapy in the prevention of potentially serious arrhythmias following myocardial infarction.

Logical approach to lignocaine therapy

Plasma lignocaine concentrations were measured during and after lignocaine infusions administered for suppressing ventricular dysrhythmias. Twenty-four patients with a primary diagnosis of acute myocardial infarction without gross circulatory disturbance received, after a bolus of lignocaine, either 4 mg/min for 30 minutes, 2 mg/min for two hours, then 1 mg/min thereafter or 1 mg/min throughout. The higher dose regimen produced continous therapeutic levels of lignocaine, which were achieved only after four hours by the lower dose. On the other hand, in patients who had undergone cardiac surgery and who had circulatory and heptic dysfunction the lower dose regimen achieved therapeutic levels early. The plasma half life was longer in the surgical group (P less than 0.02). The higher initial infusion rate is recommended for patients with acute myocardial infarction without gross circulatory impairment.