Prophylaxis of primary ventricular fibrillation in acute myocardial infarction. The case against lignocaine

Treatment of ventricular arrhythmias in the coronary patient: what sort of patient? For which rhythm disorder? With which procedure?

In the patient with coronary artery disease, complex ventricular arrhythmias and frequent ventricular arrhythmias appear to be independent risk factors for subsequent death, particularly in patients who have had myocardial infarction. In patients with symptomatic arrhythmias, treatment must be instituted and tested during rigorous supervision of the patient. Using both the noninvasive Holter monitoring/exercise test procedure and invasive electrophysiologic testing, a beneficial antiarrhythmic response after institution of antiarrhythmic agents indicates improved prognosis. However, a negative treatment response during programmed stimulation does not necessarily indicate bad prognosis. This is particularly true for testing during amiodarone treatment. For unselected patients, routine antiarrhythmic treatment cannot currently be recommended. Continuing studies will show whether screening for electrical instability of the myocardium, and institution of antiarrhythmic therapy thereafter, will improve overall survival. If patients tolerate beta-blocking treatment, this should probably be instituted because reductions in mortality have been found, particularly in high-risk patients.

Arrhythmia prophylaxis after acute myocardial infarction: a decade of controversy

Primary ventricular fibrillation continues to be a major complication of acute myocardial infarction occurring in 5-9% of patients in the coronary care unit and in a higher percentage of pre-hospital admissions. Prophylactic anti-arrhythmic drugs can prevent primary ventricular fibrillation. Lidocaine has been used for this purpose and can be administered safely and effectively in most patients by following well-established programs based on pharmacokinetic and pharmacodynamic data. The in-hospital mortality for patients with primary ventricular fibrillation exceeds that of matched controls not having the arrhythmia, and many studies show a higher 1-, 3-, and 5-year mortality. Other studies have failed to confirm these long-term results and have produced controversy among cardiologists. I continue to recommend prophylactic antiarrhythmic drugs for all patients with acute infarction, especially in those undergoing early interventional therapy.

Ventricular fibrillation complicating acute myocardial infarction. Two distinct clinical and electrocardiographic features

Two distinct electrocardiographic patterns of ventricular fibrillation (VF) complicating acute myocardial infarction (AMI) were observed in 34 patients during the first 24 hours from initial symptoms. Type 1 (seven patients) was characterized by fast disorganized ventricular activity, small voltage, and no clear identifiable QRS complexes (fine VF). Type 2 (27 patients) was defined as multiform QRS configuration (greater than 300/min) with marked changes in the amplitude (polymorphous VF). Type 1 rhythm was seen mostly during the hyperacute ischemic phase, probably associated with total coronary vessel occlusion; type 2 was observed when Q waves were already present in the electrocardiogram.

Flecainide--an intravenous infusion regimen

An intravenous infusion regimen for flecainide was studied in 12 patients. Therapeutic drug levels were rapidly established and maintained throughout the 48-h infusion period. Two patients were withdrawn because of possible drug related problems, but in general the regimen seemed both effective and well tolerated.

Lidocaine causes a reversible, concentration-dependent increase in defibrillation energy requirements

To investigate the influence of lidocaine on the energy requirements for internal defibrillation, lidocaine (n = 8) or saline solution (n = 12) was administered by intravenous infusion to 20 pentobarbital-anesthetized dogs, and the likelihood of successful defibrillation was examined at various shock energy levels before and after treatment. After lidocaine administration to a mean steady state concentration of 5.6 +/- 2.7 micrograms/ml, the mean energy required to achieve 50 and 90% success in defibrillation (E50 and E90) increased by 61.1 +/- 34.1% (mean +/- SD, p less than 0.005) and 47.1 +/- 28.6% (p less than 0.005), respectively. The steady state log lidocaine concentration correlated positively with the observed increase in E50 (r = 0.887, p less than 0.01) over a concentration range from 1.95 to 9.8 micrograms/ml. In a related experiment, lidocaine infusion was administered to five dogs and then abruptly discontinued. At energy levels achieving a mean 90.0 +/- 10.0% success in defibrillation before treatment, only 43.3 +/- 23.4% success was achieved after 60 minutes of the lidocaine infusion (p less than 0.01) at a mean plasma concentration of 8.4 +/- 2.1 micrograms/ml. The percent of successful defibrillations returned to baseline value (92.0 +/- 18.0%, p less than 0.01) after drug washout at a time when mean lidocaine concentration had declined to 1.8 +/- 0.5 microgram/ml. Lidocaine causes a reversible, concentration-dependent increase in the energy requirements for successful defibrillation; recommendations to administer lidocaine to patients with ventricular fibrillation resistant to defibrillation may need to be reviewed.

Intramuscular lidocaine for prevention of lethal arrhythmias in the prehospitalization phase of acute myocardial infarction

In a randomized controlled study examining the value of an intramuscular injection of lidocaine in the prehospitalization phase of suspected acute myocardial infarction, paramedics used an automatic injector to administer 400 mg of the drug into the patient's deltoid muscle before transport to the hospital. In a 33-month period, 7026 patients with acute chest pain were seen. Of the 6024 patients randomized (2987 to the lidocaine group and 3037 to the control group), 1935 (32 per cent) proved to have an acute myocardial infarction. In the entire 60-minute period of observation by continuous electrocardiography, primary ventricular fibrillation was observed in 8 treated and 17 control patients (P = 0.08). However, from 15 minutes after randomization onward, when plasma lidocaine levels were in the therapeutic range, only 2 cases of ventricular fibrillation occurred in the treated group, as compared with 12 in the control group (P less than 0.01). Ventricular tachycardia terminated a mean of 10 minutes after injection in six of nine lidocaine-treated patients with acute myocardial infarction but in none of five control patients with infarction (P less than 0.02). Mean plasma lidocaine levels were 3 micrograms per milliliter 11 to 20 minutes after injection in 369 consecutive patients. In 65 patients, levels were below 2 micrograms per milliliter, and in 15 patients, levels were above 6 micrograms per milliliter. Side effects were rare and did not contribute to mortality. We conclude that intramuscular lidocaine may be useful if given by a paramedic, another person, or the patient himself when acute myocardial infarction is suspected outside the hospital.