EPIDEMIOLOGY OF SUDDEN CARDIAC DEATH

Giacinto Pettinati

Divisione di Cardiologia Ospedale “F.Ferrari” Casarano

Progress on diagnosis and treatment of cardiac arrhythmias - Atti Congresso MESPE - Taorminia 2002

Sudden cardiac death, wich is defined as an unexpected, usually arrhythmic  death occurring  in asymptomatic individuals shortly after the onset of symptoms, is responsible for more than half of the total cardiac mortality in developed countries throughout the world (1). At least half these deaths occur outside a hospital setting. So, the most important problem is the out-of-hospital sudden death.

INCIDENCE

The incidence of out-of-hospital cardiac arrest increases with age, and women have a lower incidence than men (2). Becker (3) noted the incidence of out-of-hospital cardiac arrest attended by Emegency Medical Services in 20 different communites to vary between 36 and 128/100.000 per year, and there was an association between a higher incidence and lower survival. The authors ascribed the differences to methodological differences and/or true variations between populations. In a population-based rather than emergency medical service-based report from Maastricht, the incidence of sudden out-of-hospital cardiac arrest was 97/100.000 per year in the age range 20-75 years (4). During childhood and adolescents (age <20 years), the incidence has been reported to be 1-4/year per 100.000 individuals (5). It has been estimated that 30 sudden cardiac deaths per million inhabitants occur every week in industrial countries. More recent data indicate an overall 10% increase in sudden cardiac death from 1989 to 1996 in the United States (6).

INITIAL ARRHYTMIA

The proportion of patients having ventricular fibrillation at the time of collaps has been estimated to be about 80-90% among patients who  suffer from cardiac arrest of cardiac aetiology (7). In the group with out-of-hospital cardiac arrest the occurrence of ventriculation fibrillation was only roughly calculated since the ambulance crew arrived with the patients several minutes after collapse. So, in fact, the true occurrence of ventricular fibrillation at the time of sudden cardiac arrest is not known.

Ventricular fibrillation seems to convert to asystole relatively slowly over time. Thus, 20 min. after collapse, about 25% of patients are still in ventricular fibrillation.

In some studies, asystole is the first recorded “rhytm” in more than half of patients with cardiac arrest outside hospital, but again, patient selection, EMS activation intervals and proportion of bystander CPR result in notable variations. Asystole is more common in cardiopulmonary collapse among infants and children (8). Very few studies have tried to assess the underlying aetiology of out-of-hospital asystole, but some studies indicate that in these patients more often there is a non cardiac origin to the cardiac arrest compared with patiens found in ventricular fibrillation (10).

Eisenberg and colleagues (12) reported  that ventricular fibrillation was more often connected to absence of prodromal symptoms before collapse. Several papers have reported on a connection between  chest pain before collapse and initial arrhytmia of ventricular fibrillation, and there is also a similar connection between dyspnoea before collapse and bradyarrhytmic cardiac arrest (13).

The aetiology behind PEA has rarely been studied, but existing data indicate that nearly half of the cases are of cardiac origin (38,44,45). In patients without heart failure and hospitalised for their first myocardial infarction, death in hospital with PEA seems, to be strongly related to left ventricular free wall rupture (11).

AETIOLOGY

Among all patients who die outside the hospital, 56-66% have cardiac aetiology (14) witch seems to be more common among men (15)

Causes of cardiac arrest in patients with cardiac disease are:

-                           Ischemia cardiac disease

-                           Non –atherosclerotic disease of coronary arteries

-                           Cardiomyopathies

-                           Valvular heart disease

-                           Infiltrative and infiammatory myocardial disease

-                           Congenital heart disease

-                           Primay electrical abnormalities

The predominant cause is coronary artery disease. The most frequent causes of sudden cardiac arrest of non cardiac aetiology are:

-                           Trauma

-                           Non-traumating bleeding

-                           Suicide

-                           Pulmonary embolism

-                           Lung disease

-                           Malignancy

-                           Drug overdose

-                           Soffocation

WHEN DOES SUDDEN DEATH OCCUR

Sudden death have a diurnal rhytm with a more frequent occurrence in the morning hours (16). Patients found in ventricular fibrillation are early also reported to peak in the afternoon or early evening (17). Recurrent cardiac arrests, do not occur at the same time of the day (17). Such data indicate that it is the patients activity or an environmental influence that triggers the arrest. The increased risk of sudden death in the first hour after rising may be due in part to morning increase in blood pressure and heart rate, increased vascular tone, changes in heart rate variability, elevated blood viscosity and platelet aggregability (18). Intake of toxic substances such as alcohol may trigger sudden death, as well as the first cigarette in the morning (19). Mental or psychological stress may also trigger sudden death as observed during the Iraqi missile attacks on Israel (20)

Exposure to cold is considered to be one of the main factors influencing morbidity and mortality from cardiovascular disease, including sudden death. It has been suggested that the circadian variation and seasonal variation are more pronounced in the elderly whereas the day of week differences are not influenced by age (16). The observation that sudden deaths occur more frequently on Mondays has been interpreted as caused by work induced stress (16).

WHERE DOES SUDDEN DEATH OCCURR

It is reported in cases where advanced cardiac life support was initiated by ambulance crew that more than 2/3 of all cases occurred in the patient’s home (21). As reported from a survey of 7185 patients with out-of-hospital cardiac arrest  in Seattle (22), the largest location category of out-of-hospital cardiac arrest in public places was outdoors. When all patients who suffer sudden cardiac arrest out of hospital are included, regardless of whether cardiopulmonary resuscitation was initiated or not, about 80% occur in the patients home. In a Finnish forensic study of sudden unexpected death, 63% of unwitnessed daths occurred in the patietns home (23).

PREDICTORS OF IMMEDIATE SURVIVAL

Among patients who suffer an out of hospital cardiac arrest, overall survival rates have been reported to vary between 1,4% in New York and 23% in Stavanger (24). A marked variability in survival rate has been reported from 5% (25) to 35% (26) in patients with an hospital arrest. For all patients who suffer from out of hospital cardiac arrest the most important  predictors of survival are:

1)                        whether the arrest was witnessed or not (27);

2)                        whether the patient was found in ventricular fibrillation  or not (27);

3)                        whether bystander cardiopulmonary resuscitation was performed or not (29).

For patients found in ventricular fibrillation the most important predictors of survival are:

1)                        the interval between collapse and defibrillation ;

2)                        bystander initiated cardiopulmonary resuscitation (29).

For patients found in asystole, predictors of survival are less frequently described in the literature. However, it was recently reported that for patients found in asystole, the arrest being witnessed and a younger age were predictors of an increased chance of survival (10). Few reports on predictors of survival are available regarding patients found in pulseless electrical activity. Organised atrial activity and normal QRS morphology on first ECG recording in PEA has been reported to predict a better outcome  in some studies (30).

There is a considerable amount of data on long term survival after successful resuscitation from out-of-hospital cardiac arrest (32). Unfortunately, there are often very different patient selection factors in these reports and the results are not always comparable. Five year-survival has varied between 77% and 41% (31).

In a multivariate analysis it has been reported that female sex is associated with an increased immediate survival (patients being hospitalized alive) but not with survival to discharge from hospital (33). These data agree with other observations that mortality in cardiac disease  out of hospital is higher in men than women but in hospital mortality is higher in women than in men. In patients hospitalized after out of hospital cardiac arrest, survival to discharge is higher in man than in woman (34). There are also some data suggesting that women have a worse long-term prognosis when discharged alive after  successful resuscitation with out-of-hospital cardiac arrest (31). Thus it seems women may be protected from immediate death when suffering a cardiac arrest. The mechanism behind this observation can only be speculated. In animal studies it has been reported that female gender is associated with an increase in vagal tone when a coronary artey is occluded. This might be one protective mechanism (35)

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