John P. DiMarco, M.D., Ph.D., received his M.D. and Ph.D. (Pharmacology) at Case Western Reserve University. He then completed an internal medicine residency and a cardiologv fellowship at Massachusetts General Hospital. Since 1981, he has been director of the Cardiac Electrophysiology Laboratory at the University of Virginia, where he is currently a professor of medicine. His major research interests are in the mechanisms and management of cardiac arrhythmias.
David E. Haines, M.D., received his MD. from the University of Rochester. He completed his internal medicine training at the University of Vermont, followed by a cardiology fellowship at the University of Virginia. After the fellowship, he joined the faculty of the University of Virginia and is currently an assistant professor of medicine and co-director of the Cardiac Electrophysiology Laboratory. He has a major research interest in the use of ablation techniques in the treatment of cardiac arrhythmias. Cur-r
Probl
Cardioi,
April
1990
SUDDEN
CARDIAC
DEATH
It is estimated that more than 350,000 people in the United States die suddenly each year from cardiovascular causes.l Until 25 years ago, sudden death was a final disease process, and little was understood about the mechanisms responsible for its occurrence. When external cardiac defibrillation was developed, cardiac arrest became a potentially treatable disorder. In-hospital coronary care units were organized to care for patients with myocardial infarction who were recognized to be at high risk for cardiac arrest. Emergency medical programs that enabled patients to be resuscitated from episodes of cardiac arrest before hospital admission were established in many communities. As more survivors of cardiac arrest have become available for study, much has been learned about the etiology and treatment of this dreaded syndrome. As we have learned more about the diseases that can lead to sudden death and have begun to appreciate the measures necessary to prevent both initial and recurrent episodes of unexpected cardiac arrest, the sudden death mortality rate in the United States has steadily declinedlP4 (Fig 1). Despite these advances, however, sudden out-of-hospital cardiac death remains the most common mechanism of death in patients with heart disease. DEFINITIONS
OF SUDDEN
DEATH
One of the major problems hampering our understanding of sudden death has been the lack of criteria for making an unambiguous diagnosis. World Health Organization WHOI criteria classify deaths within 24 hours of the onset of, symptoms as “sudden.” Many authors have used 1 hour as the time cutoff for classifying a death as sudden, while others have preferred to include only “instantaneous” deaths.’ Any time-based definition has limitations if we try to correlate time and mechanism. A significant proportion of cardiac deaths either occur during sleep or are unwitnessed, and accurate timing of death in relation to the onset of symptoms is impossible. Cardiac arrest victims may be resuscitated initially but die hours or days later either from recurrent arrhythmia or from neurologic, hemodynamic,
400
g Q 8 ii
E
a00 1uo
too
100
0
FIG 1. Trends in sudden cardiac death mortality over time. lum’ and Gillum et al.* and represent out-of-hospital ischemic heart disease. (ICD-9 Codes 410-414.)
Data shown were selected from Giland emergency room deaths due to
or ischemic sequelae of the initial event. Symptoms preceding the event may also be misleading. Chest pain preceding collapse may represent unstable angina or myocardial infarction without arrhythmia, or it may be merely a consequence of a rapid ventricular rate during an ,atrial or ventricular tachyarrhythmia. Other nonspecific symptoms such as increasing fatigue, weakness, or dyspnea may also cloud the picture since they may either be directly caused by or totally unrelated to the disease process causing the arrest. The most commonly used classification schema for cardiac death has been that proposed by Hinkle and Thaler6 (Table 1). In a study of 743 men between the ages of 50 and 65 years, these authors classified 58% of all deaths as due to arrhythmia, with 45% of these in the setting of either nondisabling or disabling congestive heart failure. Ninety percent of the arrhythmic deaths occurred in the setting of known underlying cardiac disease. Forty-two percent of the total deaths were classified as nonarrhythmic, with 64% of these due to noncardiac disease. In this series there were significant discrepancies between this classification of mechanism and one based on duration of symptoms prior to death. All of the 37 deaths that occurred within 5 minutes of the onset of symptoms and nearly all the deaths (49 of 53) within 1 hour of symptom onset were classified as arrhyth188
CurrProid
Cardiol,
April
1999
TABLE 1. Classification
of Mechanisms
of Baths
Hinkle-Thaler Arrhythmic deaths Not preceded by impairment of circulation Preceded by nondisabling congestive heart failure Preceded by disabling congestive heart failure Deaths in circulatory failure Failure of peripheral circulation Myocardial failure Nonclassiliable CAPS Investigators Ambytbmic death.-Abrupt cessation of respiration and pulse with loss of consciousnesS in the absence of a progressive severe medical condition likely to cause death within 4 months Proven Unproven Nonarrhythmic death.-Severe symptoms prior to cardiac arrest or expected survival
David E. Haines, M.D., received his MD. from the University of Rochester. He completed his internal medicine training at the University of Vermont, followed by a cardiology fellowship at the University of Virginia. After the fellowship, he joined the faculty of the University of Virginia and is currently an assistant professor of medicine and co-director of the Cardiac Electrophysiology Laboratory. He has a major research interest in the use of ablation techniques in the treatment of cardiac arrhythmias. Cur-r
Probl
Cardioi,
April
1990
SUDDEN
CARDIAC
DEATH
It is estimated that more than 350,000 people in the United States die suddenly each year from cardiovascular causes.l Until 25 years ago, sudden death was a final disease process, and little was understood about the mechanisms responsible for its occurrence. When external cardiac defibrillation was developed, cardiac arrest became a potentially treatable disorder. In-hospital coronary care units were organized to care for patients with myocardial infarction who were recognized to be at high risk for cardiac arrest. Emergency medical programs that enabled patients to be resuscitated from episodes of cardiac arrest before hospital admission were established in many communities. As more survivors of cardiac arrest have become available for study, much has been learned about the etiology and treatment of this dreaded syndrome. As we have learned more about the diseases that can lead to sudden death and have begun to appreciate the measures necessary to prevent both initial and recurrent episodes of unexpected cardiac arrest, the sudden death mortality rate in the United States has steadily declinedlP4 (Fig 1). Despite these advances, however, sudden out-of-hospital cardiac death remains the most common mechanism of death in patients with heart disease. DEFINITIONS
OF SUDDEN
DEATH
One of the major problems hampering our understanding of sudden death has been the lack of criteria for making an unambiguous diagnosis. World Health Organization WHOI criteria classify deaths within 24 hours of the onset of, symptoms as “sudden.” Many authors have used 1 hour as the time cutoff for classifying a death as sudden, while others have preferred to include only “instantaneous” deaths.’ Any time-based definition has limitations if we try to correlate time and mechanism. A significant proportion of cardiac deaths either occur during sleep or are unwitnessed, and accurate timing of death in relation to the onset of symptoms is impossible. Cardiac arrest victims may be resuscitated initially but die hours or days later either from recurrent arrhythmia or from neurologic, hemodynamic,
400
g Q 8 ii
E
a00 1uo
too
100
0
FIG 1. Trends in sudden cardiac death mortality over time. lum’ and Gillum et al.* and represent out-of-hospital ischemic heart disease. (ICD-9 Codes 410-414.)
Data shown were selected from Giland emergency room deaths due to
or ischemic sequelae of the initial event. Symptoms preceding the event may also be misleading. Chest pain preceding collapse may represent unstable angina or myocardial infarction without arrhythmia, or it may be merely a consequence of a rapid ventricular rate during an ,atrial or ventricular tachyarrhythmia. Other nonspecific symptoms such as increasing fatigue, weakness, or dyspnea may also cloud the picture since they may either be directly caused by or totally unrelated to the disease process causing the arrest. The most commonly used classification schema for cardiac death has been that proposed by Hinkle and Thaler6 (Table 1). In a study of 743 men between the ages of 50 and 65 years, these authors classified 58% of all deaths as due to arrhythmia, with 45% of these in the setting of either nondisabling or disabling congestive heart failure. Ninety percent of the arrhythmic deaths occurred in the setting of known underlying cardiac disease. Forty-two percent of the total deaths were classified as nonarrhythmic, with 64% of these due to noncardiac disease. In this series there were significant discrepancies between this classification of mechanism and one based on duration of symptoms prior to death. All of the 37 deaths that occurred within 5 minutes of the onset of symptoms and nearly all the deaths (49 of 53) within 1 hour of symptom onset were classified as arrhyth188
CurrProid
Cardiol,
April
1999
TABLE 1. Classification
of Mechanisms
of Baths
Hinkle-Thaler Arrhythmic deaths Not preceded by impairment of circulation Preceded by nondisabling congestive heart failure Preceded by disabling congestive heart failure Deaths in circulatory failure Failure of peripheral circulation Myocardial failure Nonclassiliable CAPS Investigators Ambytbmic death.-Abrupt cessation of respiration and pulse with loss of consciousnesS in the absence of a progressive severe medical condition likely to cause death within 4 months Proven Unproven Nonarrhythmic death.-Severe symptoms prior to cardiac arrest or expected survival
