Sudden cardiac death

Prognostic value of heart rate variability and ventricular arrhythmias during 13-year follow-up in patients with mild to moderate heart failure

BACKGROUND

In contrast to patients with moderate to severe chronic heart failure (CHF), data regarding long-term outcome in patients with mild CHF are scarce. We examined the place of Holter monitoring to study the prognostic value of ventricular arrhythmias and heart rate variability (HRV) in patients with mild to moderate CHF during long-term follow-up.

METHODS

We studied 90 patients with mild to moderate CHF and NYHA class II who had been enrolled in the Dutch Ibopamine Multicenter Trial. At baseline their mean age was 60.5 +/- 8.0 years, left ventricular ejection fraction (LVEF) was 0.29 +/- 0.09, and 85% were males. At the start of the study, patients were only using diuretics, while digoxin, and particularly ACE inhibitors and beta-blockers were initiated later. Univariate and multivariate proportional hazard analyses were performed.

RESULTS

At baseline 80% of patients were in NYHA class II, and 20% were in class III; their mean age was 60 years, mean LVEF was 0.29, and 85% were men. During a follow-up of 13 years, 47 patients (53%) died. Cardiovascular (CV) death occurred in 39 patients, of which 28 were sudden cardiac death (SCD). For both CV death and SCD, LVEF <30% and ventricular premature beats/h (>20) were independent risk markers. Of the HRV parameters, total power (>2,500 ms(2)) was an important risk marker for CV death, but not for SCD.

CONCLUSION

The present 13-year follow-up study in 90 patients with mild to moderate CHF showed that ventricular premature beats and HRV may have important value in predicting outcome.

Prognostic importance of renal function in patients with early heart failure and mild left ventricular dysfunction

We evaluated the prognostic value of renal function in an initially "untreated" population with mild heart failure and compared the prognosis of this population with a matched controlled population. During a follow-up of 13 years (mean 11.7), 90 patients (56%) died. Mortality was higher compared with a matched controlled population. Multivariate Cox regression analysis demonstrated that beside the well-established risk markers of left ventricular ejection fraction and heart rate, renal function (estimated glomerular filtration rate, hazard ratio 1.16/10 ml/min/1.73 m(2), p = 0.003) was the only additional independent predictor of cardiovascular mortality in patients with early heart failure.

Increased ubiquitin immunoreactivity in unstable atherosclerotic plaques associated with acute coronary syndromes

OBJECTIVES

The current study was designed to examine whether ubiquitin expression is higher in unstable than in stable lesions of patients with acute coronary syndrome (ACS).

BACKGROUND

The ubiquitin system has been identified as the nonlysosomal pathway of protein degradation; it is involved in a number of biologic processes crucial to cell and tissue integrity and therefore, might be potentially involved in the rupture of unstable coronary plaques.

METHODS

We conducted an autopsy-based study of 25 consecutive patients with fatal ACS. Lesions of both infarct-related and noninfarct-related segments from the same patients were examined for the expression and localization of ubiquitin by use of immunohistochemistry and a semiquantitative grading scale.

RESULTS

Ubiquitin immunoreactivity was higher in infarct-related than in noninfarct-related lesions (1.4 +/- 0.5 vs. 1.1 +/- 0.6, p = 0.03). Compared with areas adjacent to the plaque (0.6 +/- 0.7), ubiquitin immunoreactivity was higher in areas around the lipid core (2.5 +/- 0.8, p < 0.001), plaque shoulders (1.6 +/- 1.1, p < 0.001), and fibrous cap regions (1.6 +/- 1.1, p < 0.001). Within the plaque area, co-localization of ubiquitin immunoreactivity with T cells and macrophages was found. In areas adjacent to the plaque, ubiquitin immunoreactivity co-localized with neointima cells and media smooth muscle cells.

CONCLUSIONS

In patients with ACS, ubiquitin immunoreactivity is enhanced in unstable, infarct-related lesions, predominantly in plaque regions of tissue degradation. Based on these findings, this study suggests a role for the ubiquitin system in the destabilization and rupture of coronary atherosclerotic plaques in humans.

Long-term mortality among patients discharged alive after out-of-hospital cardiac arrest does not differ markedly compared with that of myocardial infarct patients without out-of-hospital cardiac arrest

The aim of our research was to study the long-term prognosis among patients discharged alive after an out-of-hospital cardiac arrest (OHCA) in comparison with patients discharged alive after acute myocardial infarction (AMI) without OHCA, and also to study the long-term influence of AMI in connection with OHCA. Our research was conducted in the municipality of Göteborg. We retrospectively studied patients discharged from hospital 1990-91 after an OHCA of cardiac aetiology and patients discharged after an AMI without prehospital cardiac arrest. During 1980-98, we studied all patients discharged alive after OHCA of cardiac aetiology, divided into groups of precipitating AMI and no AMI. The study includes 48 patients discharged alive after an OHCA 1990-91, 30 (62%) of whom had a simultaneous AMI and 1425 patients with an AMI without OHCA. Compared with AMI survivors, survivors of an OHCA of cardiac origin were younger but had more frequently a history of congestive heart failure. Their mortality rate during the subsequent 5 years was 46%, compared with 40% among survivors of an AMI (NS). The 5-year mortality rate among patients with an OHCA precipitated by an AMI was 40%. When correcting for differences at baseline, the adjusted risk ratio for death among patients with an OHCA of cardiac origin was 1.2 (95% CI 0.8-1.8) compared with patients with an uncomplicated AMI. During 1980-98, 215 patients were judged as having an OHCA precipitated by an AMI and 115 patients had an OHCA of cardiac aetiology but no simultaneous AMI. Five-year mortality was 54% and 50% respectively (NS). It is concluded that survivors of an OHCA of cardiac origin differed from survivors of an uncomplicated AMI in that they were younger and more frequently had a history of cardiovascular disease. Their 5-year mortality after discharge was similar to that of survivors of an AMI without a prehospital cardiac arrest, even after adjusting for differences at baseline.

EMS characteristics in an Asian Metropolis

A prospective citywide cohort study was conducted from August 1, 1993, through May 31, 1994 to analyze the epidemiological characteristics of emergency medical services (EMS) in an Asian city. Of 5,459 studied cases, the leading 3 causes were trauma (49.7%), alcohol intoxication (8.6%), and altered mental status (AMS) (6.9%). Half of the studied cases needed no prehospital care and 16.4% needed advanced life support (ALS) care. Traffic accidents accounted for 68% of trauma cases. Of 897 cases requiring ALS care, the two most common causes were AMS and dead on arrival (DOA) (32.1% and 21.2% in medical group, 10.1% and 4.5% in trauma group, respectively). The response time, time on scene, and transportation time were 4.6, 4.3, and 9.4 minutes, respectively. This Oriental EMS system experienced very short prehospital times, many traffic accidents, and extremely few DOA cases. Because few patients required ALS care, an emergency medical technician-based EMS system would probably be able to handle the majority of prehospital patients.

A new system for classification of cardiac death as arrhythmic, ischemic, or due to myocardial pump failure

Existing classifications of cardiac death fail to incorporate current understanding of the pathophysiology of sudden cardiac death. We developed a new scheme for classifying cardiac death that defines 3 categories of underlying mechanism: primary arrhythmia, acute myocardial ischemia/infarction, and myocardial pump failure. Using this new system, we classified the mechanism of 106 definite cardiac deaths from the Recurrent Coronary Prevention Project. Fifty deaths (47%) were classified as arrhythmic, 46 (43%) as ischemic, and 9 (8%) as due to myocardial pump failure (1 death was not classifiable). All 36 witnessed arrhythmic deaths were sudden and 8 of 9 witnessed myocardial pump failure deaths were nonsudden. The 38 witnessed ischemic deaths were split evenly between sudden and nonsudden. Interrater agreement for the classification of mechanism was 100%. This classification scheme, if validated in subsequent studies, will provide a useful algorithm for classifying deaths by underlying mechanism.

Predictors of mortality in patients with sustained ventricular tachycardias or ventricular fibrillation and depressed left ventricular function: importance of beta-blockade

To study prognostic factors in patients with sustained ventricular tachycardias (VT) or ventricular fibrillation (VF) complicated by left ventricular dysfunction, we evaluated the predictive value of demographic, clinical, and hemodynamic parameters for cardiac mortality and sudden cardiac death in 85 patients with VT or VF and left ventricular ejection fraction < 0.45 (mean 0.27 +/- 0.10). Patients underwent serial drug testing and received appropriate antiarrhythmic treatment, with amiodarone given as last-resort therapy. During a follow-up of 24 +/- 13 months, 23 patients died of cardiac causes, and 18 of them died suddenly. Left ventricular ejection fraction < or = 0.27 and amiodarone treatment were related to greater cardiac mortality and increased risk of sudden cardiac death, whereas beta-blockade was associated with improved survival. In the multivariate model cardiac mortality was best predicted by a left ventricular ejection fraction < or = 0.27, and absence of beta-blockade and severe left ventricular dysfunction were the strongest predictors of sudden cardiac death. We conclude that severe left ventricular dysfunction predicts increased cardiac mortality and high risk of sudden cardiac death. Moreover, beta-blocking treatment is associated with lower cardiac mortality and a reduced risk of sudden cardiac death in patients with sustained VT or VF and depressed left ventricular function. beta-Blocking agents may therefore be an important addition to conventional antiarrhythmic treatment in patients with VT or VF and left ventricular dysfunction.

The role of parasympathetic modulation of the reentrant arrhythmic substrate in the genesis of sustained ventricular tachycardia

The influence of parasympathetic activity on the reentrant arrhythmic substrate in the genesis of sustained ventricular tachycardia remains unclear. To assess this influence, we studied the heart rate variability in 59 patients referred for invasive electrophysiological testing. In addition, the presence of late potentials and high grade ventricular ectopy, and the left ventricular ejection fraction was determined. The 28 patients with inducible sustained ventricular tachycardia were found to have lower heart rate variability by time- and frequency-domain measurements over 24 hours when compared to the 31 subjects who were noninducible. PNN50 was 4% in the inducible patients, whereas it was 9% in the subjects who were noninducible (P = 0.03). Similarly, HFP24H was 9 and 14 msec, respectively (P = 0.02). MAXHFP1H also differed (20 vs 27 msec [P = 0.04]) but not MINHFP1H (5 vs 6 msec). There was no association between heart rate variability and late potentials, degree of ventricular ectopy, or left ventricular ejection fraction. Thus, vagal tone does not appear to correlate with the presence of late potentials, ventricular ectopy, or left ventricular dysfunction. Low mean as well as maximal vagal tone, in contrast to minimal vagal tone, predicts inducibility of sustained ventricular tachycardia. Our data suggest that the inability to modulate parasympathetic tone appears to be an important determinant in the genesis of reentrant sustained ventricular tachycardia.

Out-of-hospital cardiac arrest in an Oriental metropolitan city

To investigate the epidemiology of out-of-hospital cardiac arrest in Taipei City, Taiwan, a prospective chart review and follow-up study was conducted by collecting the prehospital cardiac arrest record from 10 designated responsible emergency departments (EDs) from August 1, 1992 through May 31, 1993. Cases with the restoration of spontaneous circulation (ROSC) were followed up until discharged from hospital. The information gathered included age, sex, bystander cardiopulmonary resuscitation, response time (time elapsed from receiving the call to arrival on the scene), advanced cardiac life support (ACLS) time (time elapsed from receiving the call to arrival at the ED), initial cardiac rhythm in the ED, ROSC, survival to discharge from the hospital, underlying disease, past history, personal history, and neurological outcome at discharge. Of 638 out-of-hospital cardiac arrests, 554 (86.7%) were nontraumatic. Response time, ACLS time, ROSC rates, and survival rates were 7.4 minutes, 21.6 minutes, 15.8%, and 1.4%, respectively. In comparing the trauma and nontrauma group, there were significant differences in age, sex, response time, and ACLS time. Between cases of patients who had ROSC and those who died, the data were statistically significant, P = .0143, showing that ACLS time was shorter in the ROSC group (19.5 v 21.9 minutes). In analysis of underlying disease, definite and probable cardiac-origin sudden deaths were found in only 120 patients, which may extend the annual sudden cardiac death rates to be 0.0053%. In conclusion, the low resuscitation and survival rates in this country were because of delayed initiation of both basic life support and ACLS.(ABSTRACT TRUNCATED AT 250 WORDS)

Implantable cardioverter defibrillator compared with antiarrhythmic drug treatment in cardiac arrest survivors (the Cardiac Arrest Study Hamburg)

In 1987, the Cardiac Arrest Study Hamburg (CASH), a prospective, multicenter, randomized controlled study, was started in survivors of sudden cardiac death resulting from documented ventricular tachyarrhythmias. Through December 1991, 230 survivors (46 women, 184 men; mean age 57 +/- 11 years) of cardiac arrest caused by ventricular tachyarrhythmias were randomly assigned to receive either oral propafenone (56 patients), amiodarone (56 patients), or metoprolol (59 patients) or to have an implantable defibrillator (59 patients) without concomitant antiarrhythmic drugs. The primary endpoint of the study was total mortality. In March 1992, the propafenone arm of CASH was stopped because of excess mortality compared with the implantable defibrillator group. This article presents preliminary results of the comparison of implantable defibrillator therapy with propafenone therapy. A significantly higher incidence of total mortality, sudden death (12%), and cardiac arrest recurrence or sudden death (23%) was found in the propafenone group compared with the implantable defibrillator-treated patients (0%, p < 0.05). It was concluded that, in survivors of cardiac arrest, propafenone treatment is less effective than implantable defibrillator treatment.

Preliminary results of the Cardiac Arrest Study Hamburg (CASH). CASH Investigators

Sodium channel blockers and class III antiarrhythmic compounds, as well as beta blockers, have been used in preventing recurrences of sudden cardiac death. In recent years, implantable cardioverter-defibrillators (ICDs) have been used increasingly, but no data from randomized trials comparing antiarrhythmic drug and ICD therapy have been reported in this setting. In 1987, the Cardiac Arrest Study Hamburg (CASH), a prospective, randomized trial, was initiated to compare metoprolol, amiodarone, propafenone, and ICD implantation in patients surviving sudden cardiac death due to documented ventricular tachycardia and/or ventricular fibrillation. The details of the study design and preliminary results are presented herein. The primary endpoint of the study is total mortality. The data reviewed in March 1992, representing a mean follow-up period of 11 months, indicated no significant differences among patients randomized to metoprolol, amiodarone, and ICDs. However, there was a significantly higher total mortality and cardiac arrest recurrence in patients randomized to propafenone compared with those randomized to the ICD treatment limb. The study continues with the deletion of the propafenone treatment limb.

Conventional heart rate variability analysis of ambulatory electrocardiographic recordings fails to predict imminent ventricular fibrillation

OBJECTIVES

The purpose of this report was to study heart rate variability in Holter recordings of patients who experienced ventricular fibrillation during the recording.

BACKGROUND

Decreased heart rate variability is recognized as a long-term predictor of overall and arrhythmic death after myocardial infarction. It was therefore postulated that heart rate variability would be lowest when measured immediately before ventricular fibrillation.

METHODS

Conventional indexes of heart rate variability were calculated from Holter recordings of 24 patients with structural heart disease who had ventricular fibrillation during monitoring. The control group consisted of 19 patients with coronary artery disease, of comparable age and left ventricular ejection fraction, who had nonsustained ventricular tachycardia but no ventricular fibrillation.

RESULTS

Heart rate variability did not differ between the two groups, and no consistent trends in heart rate variability were observed before ventricular fibrillation occurred.

CONCLUSIONS

Although conventional heart rate variability is an independent long-term predictor of adverse outcome after myocardial infarction, its clinical utility as a short-term predictor of life-threatening arrhythmias remains to be elucidated.

Current usefulness of the signal-averaged electrocardiogram

Signal-averaged electrocardiography is a relatively simple, noninvasive technique by which valuable information can be gained to help in the management of patients with cardiovascular disease. The presence of late potentials on the SAECG is a good marker for the presence of an arrhythmogenic substrate that is believed to be the source of ventricular tachycardia in patients with coronary artery disease. The value of the detection of late potentials has been studied best after myocardial infarction, when the absence of late potentials makes the occurrence of an arrhythmic event very unlikely. The positive predictive value for an arrhythmic event to occur in the presence of late potentials is low, however, comparable to the predictive value of decreased left ventricular function, complex ventricular ectopy, or abnormal autonomic tone. This appears to have its explanation in the complex pathophysiology behind the occurrence of arrhythmic events. Improved accuracy for the SAECG is achieved when the result of the test is interpreted with consideration of the presence or absence of other predictive markers. A thorough understanding of the signal-averaged electrocardiogram makes optimal clinical use of the information gained from this easily acquired test possible.

Sudden cardiac death. Support for a role of triggering in causation

Epidemiological studies have identified associations between time of day and risk of sudden cardiac death. The marked peak in the occurrence of sudden cardiac death after awakening suggests that the disease is triggered by changes that occur during this time period. Increased sympathetic stimulation is a likely cause of such triggering. In the light of the circadian variation of sudden cardiac death and the evidence linking physical activity or mental stress (both associated with activation of the sympathetic nervous system) to the disease, the role of potential triggering events should be investigated. Controlled studies are needed to determine the relative risk of activities that may trigger sudden cardiac death. Since such studies must rely on witnesses (or resuscitated patients), data quality must be closely scrutinized, and studies using case-control and case-crossover designs are needed. The epidemiological and pathophysiological data reviewed in the present article suggest a number of pathways through which activities may trigger sudden cardiac death. Different extrinsic stimuli may cause similar physiological changes that subsequently lead to acute pathological events, a decrease in the ventricular fibrillation threshold through a direct myocardial effect, or a harmful effect on the conduction system. Myocardial ischemia induced by plaque rupture and thrombosis may lead directly to myocardial electric instability. The presence of chronic structural abnormalities of the myocardial tissue or the conduction system may further lower the threshold for electric instability and ventricular fibrillation.(ABSTRACT TRUNCATED AT 250 WORDS)

First- or second-degree atrioventricular block as a risk factor in idiopathic dilated cardiomyopathy

To evaluate the significance of clinical, hemodynamic and electrocardiographic risk factors in idiopathic dilated cardiomyopathy 94 patients were followed prospectively for 49 +/- 37 months. During follow-up, 30 patients died, 13 died suddenly, 13 died of congestive heart failure and 4 of other causes. Follow-up was completed in 85 patients, and overall cardiac mortality was 31%. Univariate analysis revealed left ventricular ejection fraction among 20 variables as the major indicator of risk of both cardiac death of all causes and sudden cardiac death separately. Multivariate overall analysis determined 3 independent risk factors in the following order for all causes of cardiac death: Ventricular pairs > 40/24 hours (RR 7.2, p < 0.0001), left ventricular ejection fraction < or = 35% (RR 6.5, p < 0.001) and first- or second-degree atrioventricular (AV) block (RR 3.1, p < 0.05). In the subset of patients with ejection fraction < or = 35% ventricular pairs > 40 per 24 hours (RR 10.7, p < 0.001), AV block (RR 3.9, p < 0.05), and the missing administration of vasodilators (RR 3.3, p < 0.05) were the most important. The chief risk factors for sudden cardiac death were age (RR 7.4, p < 0.01) and AV block (RR 4.6, p < 0.05) by adjustment for age, and ejection fraction < or = 35% (RR 7.1, p < 0.01) and AV block (RR 4.2, p < 0.05) if not adjusted for age. A differentiation into 4 risk groups was attempted. The additional independent prognostic importance of AV block was shown, especially in combination with reduced ejection fraction or a high incidence of ventricular pairs.(ABSTRACT TRUNCATED AT 250 WORDS)

A reduction in the correlation dimension of heartbeat intervals precedes imminent ventricular fibrillation in human subjects

Reduced reflexive control of heartbeat intervals occurs with advanced heart disease and is an independent risk factor for mortality. Based on a previous study of experimental myocardial infarction in pigs, we hypothesized that a deterministic measure of heartbeat dynamics, the correlation dimension of R-R intervals (D2), may be a better predictor of risk than a stochastic measure, such as the standard deviation (SD). We determined the point estimates of the heartbeat D2 (i.e., PD2s) in Holter electrocardiographic recordings from 11 high-risk patients who manifested ventricular fibrillation (VF) during the recording and in high-risk controls having only nonsustained ventricular tachycardia (14 patients) or premature ventricular complexes (13 patients). We found that PD2 reduction (i.e., PD2s < 1.2) precedes lethal arrhythmias by hours, but is not reduced in high-risk controls (p < 0.001; sensitivity, 91%; specificity, 85%). Heartbeat SD did not discriminate among the patients. Thus PD2 of heartbeat intervals may provide an important diagnostic test and early warning sign of VF.

Application of chaos theory to biology and medicine

The application of "chaos theory" to the physical and chemical sciences has resolved some long-standing problems, such as how to calculate a turbulent event in fluid dynamics or how to quantify the pathway of a molecule during Brownian motion. Biology and medicine also have unresolved problems, such as how to predict the occurrence of lethal arrhythmias or epileptic seizures. The quantification of a chaotic system, such as the nervous system, can occur by calculating the correlation dimension (D2) of a sample of the data that the system generates. For biological systems, the point correlation dimension (PD2) has an advantage in that it does not presume stationarity of the data, as the D2 algorithm must, and thus can track the transient non-stationarities that occur when the systems changes state. Such non-stationarities arise during normal functioning (e.g., during an event-related potential) or in pathology (e.g., in epilepsy or cardiac arrhythmogenesis). When stochastic analyses, such as the standard deviation or power spectrum, are performed on the same data they often have a reduced sensitivity and specificity compared to the dimensional measures. For example, a reduced standard deviation of heartbeat intervals can predict increased mortality in a group of cardiac subjects, each of which has a reduced standard deviation, but it cannot specify which individuals will or will not manifest lethal arrhythmogenesis; in contrast, the PD2 of the very same data can specify which patients will manifest sudden death. The explanation for the greater sensitivity and specificity of the dimensional measures is that they are deterministic, and thus are more accurate in quantifying the time-series. This accuracy appears to be significant in detecting pathology in biological systems, and thus the use of deterministic measures may lead to breakthroughs in the diagnosis and treatment of some medical disorders.