Ventricular Arrhythmias in First Acute Myocardial Infarction: Epidemiology, Mechanisms, and Interventions in Large Animal Models

We sought to describe the incidence, characteristics and survival of out-of-hospital sudden cardiac arrest (SCA) in the Maastricht area of The Netherlands. Incidence and survival rates of out-of-hospital SCA in different communities are often based on the number of victims resuscitated by the emergency medical services. Our population-based study in the Maastricht area allows information on all victims of witnessed and unwitnessed SCA occurring outside the hospital. Incidence, patient characteristics and survival rates were determined by prospectively collecting information on all cases of SCA occurring in the age group 20 to 75 years between January 1, 1991 and December 31, 1994. Survival rates were related to the site of the event (at home vs. outside the home) and the presence or absence of a witness and rhythm at the time of the resuscitation attempt in out-of-hospital SCA. Five hundred fifteen patients were included (72% men, 28% women). In 44% of men and 53% of women, SCA was most likely the first manifestation of heart disease. In patients known to have had a previous myocardial infarction (MI), the mean interval between the MI and SCA was 6.5 years, with >50% having a left ventricular ejection fraction >30%. The mean yearly incidence of SCA was 1 in 1,000 inhabitants. Of all deaths in the age groups studied, 18.5% were sudden. Nearly 80% of SCAs occurred at home. In 60% of all cases of SCA a witness was present. Cardiac resuscitation, which was attempted in 51% of all subjects, resulted overall in 32 (6%) of 515 patients being discharged alive from the hospital. Survival rates for witnessed SCA were 8% (16 of 208 subjects) at home and 18% (15 of 85 subjects) outside the home (95% confidence interval 1% to 18.8%). The majority of victims of SCA cannot be identified before the event. Sudden cardiac arrest usually occurs at home, and the survival of those with a witnessed SCA at home was low compared with that outside the home, indicating the necessity of optimizing out-of-hospital resuscitation, especially in the at-home situation.

Despite previous randomised trials of early beta-blocker therapy in the emergency treatment of myocardial infarction (MI), uncertainty has persisted about the value of adding it to current standard interventions (eg, aspirin and fibrinolytic therapy), and the balance of potential benefits and hazards is still unclear in high-risk patients. 45,852 patients admitted to 1250 hospitals within 24 h of suspected acute MI onset were randomly allocated metoprolol (up to 15 mg intravenous then 200 mg oral daily; n=22,929) or matching placebo (n=22,923). 93% had ST-segment elevation or bundle branch block, and 7% had ST-segment depression. Treatment was to continue until discharge or up to 4 weeks in hospital (mean 15 days in survivors) and 89% completed it. The two prespecified co-primary outcomes were: (1) composite of death, reinfarction, or cardiac arrest; and (2) death from any cause during the scheduled treatment period. Comparisons were by intention to treat, and used the log-rank method. This study is registered with ClinicalTrials.gov, number NCT 00222573. Neither of the co-primary outcomes was significantly reduced by allocation to metoprolol. For death, reinfarction, or cardiac arrest, 2166 (9.4%) patients allocated metoprolol had at least one such event compared with 2261 (9.9%) allocated placebo (odds ratio [OR] 0.96, 95% CI 0.90-1.01; p=0.1). For death alone, there were 1774 (7.7%) deaths in the metoprolol group versus 1797 (7.8%) in the placebo group (OR 0.99, 0.92-1.05; p=0.69). Allocation to metoprolol was associated with five fewer people having reinfarction (464 [2.0%] metoprolol vs 568 [2.5%] placebo; OR 0.82, 0.72-0.92; p=0.001) and five fewer having ventricular fibrillation (581 [2.5%] vs 698 [3.0%]; OR 0.83, 0.75-0.93; p=0.001) per 1000 treated. Overall, these reductions were counterbalanced by 11 more per 1000 developing cardiogenic shock (1141 [5.0%] vs 885 [3.9%]; OR 1.30, 1.19-1.41; p<0.00001). This excess of cardiogenic shock was mainly during days 0-1 after admission, whereas the reductions in reinfarction and ventricular fibrillation emerged more gradually. Consequently, the overall effect on death, reinfarction, arrest, or shock was significantly adverse during days 0-1 and significantly beneficial thereafter. There was substantial net hazard in haemodynamically unstable patients, and moderate net benefit in those who were relatively stable (particularly after days 0-1). The use of early beta-blocker therapy in acute MI reduces the risks of reinfarction and ventricular fibrillation, but increases the risk of cardiogenic shock, especially during the first day or so after admission. Consequently, it might generally be prudent to consider starting beta-blocker therapy in hospital only when the haemodynamic condition after MI has stabilised.