Challenges in cardiac arrest research: data collection to assess outcomes

Data-driven sudden cardiac arrest research in Europe: Experts' perspectives on ethical challenges and governance strategies

Background

Observational studies using large-scale databases and biobanks help improve prevention and treatment of sudden cardiac arrest (SCA) but the lack of guidance on data protection issues in this setting may harm patients' rights and the research enterprise itself. This qualitative study explored the ethical aspects of observational SCA research, as well as solutions.

Methods

European experts in SCA research, medical ethics and health law reflected on this topic through semi-structured interviews (N = 29) and a virtual roundtable conference (N = 18). The ESCAPE-NET project served as a discussion case. Findings were coded and thematically analysed.

Results

The first theme concerned the potential benefits and harms (at individual and group level) of observational data-based SCA studies and included the following sub-themes: societal value, scientific validity, data privacy, disclosure of genetic findings, stigma and discrimination, and medicalisation of sudden death. The second theme involved governance through 'privacy by design', 'privacy by policy' and associated regulation and oversight. Sub-themes were: de-identification of data, informed consent (broad and deferred), ethics review, and harmonisation.

Conclusions

Researchers and scientific societies should be aware that ethico-legal issues may arise during data-driven studies in SCA and other emergencies. These can be mitigated by combining technical data protection safeguards with appropriate informed consent policies and proportional ethics oversight. To ensure responsible conduct of data research in emergency medicine, we recommend the establishment of 'codes of conduct' which should be developed in interdisciplinary groups and together with patient representatives.

Visual assessment of interactions among resuscitation activity factors in out-of-hospital cardiopulmonary arrest using a machine learning model

Aim

The evaluation of the effects of resuscitation activity factors on the outcome of out-of-hospital cardiopulmonary arrest (OHCA) requires consideration of the interactions among these factors. To improve OHCA success rates, this study assessed the prognostic interactions resulting from simultaneously modifying two prehospital factors using a trained machine learning model.

Methods

We enrolled 8274 OHCA patients resuscitated by emergency medical services (EMS) in Nara prefecture, Japan, with a unified activity protocol between January 2010 and December 2018; patients younger than 18 and those with noncardiogenic cardiopulmonary arrest were excluded. Next, a three-layer neural network model was constructed to predict the cerebral performance category score of 1 or 2 at one month based on 24 features of prehospital EMS activity. Using this model, we evaluated the prognostic impact of continuously and simultaneously varying the transport time and the defibrillation or drug-administration time in the test data based on heatmaps.

Results

The average class sensitivity of the prognostic model was more than 0.86, with a full area under the receiver operating characteristics curve of 0.94 (95% confidence interval of 0.92–0.96). By adjusting the two time factors simultaneously, a nonlinear interaction was obtained between the two adjustments, instead of a linear prediction of the outcome.

Conclusion

Modifications to the parameters using a machine-learning-based prognostic model indicated an interaction among the prognostic factors. These findings could be used to evaluate which factors should be prioritized to reduce time in the trained region of machine learning in order to improve EMS activities.

Association of Physical Activity With Primary Cardiac Arrest Risk in the General Population: A Nationwide Cohort Study of the Dose-Response Relationship

OBJECTIVE

To quantify the dose-response relationship between moderate to vigorous physical activity and primary cardiac arrest (PCA).

PATIENTS AND METHODS

There were 504,840 participants older than 18 years who underwent the Korean National Health Screening Program, including a self-administered questionnaire for physical activity from January 1, 2009, through December 31, 2014. Physical activity levels were converted into metabolic equivalent tasks (METs) per week and categorized to correspond with multiples of public health recommendations. We evaluated the quantitative and categorical dose-response relationship between physical activity and PCA.

RESULTS

A curvilinear dose-response relationship between physical activity and PCA was observed; the benefits started at two-thirds (5 MET-hour/week) of the United States and World Health Organization guidelines-recommended minimum (7.5 MET-hour/week) and continued to 5 times (40 MET-hour/week) the recommended minimum (P nonlinearity <.001). The largest benefit was noted at a level of 2 to 3 times the recommended minimum (hazard ratio, 0.6; 95% CI, 0.4 to 0.8). In addition, there was no evidence of an increased PCA risk at a level more than 5 times the recommended minimum (hazard ratio, 0.7; 95% CI, 0.5 to 1.1). These associations were consistent regardless of age, sex, body mass index, comorbid conditions, and estimated 10-year risk for cardiovascular disease.

CONCLUSION

The beneficial effect of physical activity on PCA started at two-thirds of the recommended minimum and continued to 5 times the recommended minimum. No excess risk for PCA was present among individuals with activity levels more than 5 times the recommended minimum regardless of cardiovascular disease or lifestyle risk factor presence.

Clinical Associations between Serial Electrocardiography Measurements and Sudden Cardiac Death in Patients with End-Stage Renal Disease Undergoing Hemodialysis

The rate of sudden cardiac death (SCD) for hemodialysis (HD) patients is significantly higher than that observed in the general population and have the highest risk for arrhythmogenic death. In this multi-center study, patients starting hemodialysis in each hospital were enrolled; they underwent regular check-ups in an open-patient clinic. We examined serial electrocardiography (ECG) data in patients undergoing HD and determined their associations with the occurrence of SCD. Of 678 enrolled subjects who underwent serial ECG before and after hemodialysis, 291 died and 39 developed SCD. In all subjects, the QT peak-to-end (QTpe) interval at all leads and QRS duration were shortened after hemodialysis. The SCD group showed a significant change in the QTpe interval of the inferior, anterior, and lateral leads before and after hemodialysis compared with the survivor group (p < 0.001). In the pre-hemodialysis ECG, SCD patients had significantly longer QTpe intervals in all leads (p < 0.001) and a longer QRS duration (92.6 ± 14.0 vs. 100.6 ± 14.9 ms, p = 0.015) than survivors. In conclusion, patients with a longer QTpe interval before hemodialysis and large changes in ECG parameters after hemodialysis might be at a higher risk of SCD. Therefore, changes in the ECG before and after hemodialysis could help to predict SCD.

Incidence and Outcomes of Out-of-Hospital Cardiac Arrest in Singapore and Victoria: A Collaborative Study

Background

Incidence and outcomes of out‐of‐hospital cardiac arrest (OHCA) vary between communities. We aimed to examine differences in patient characteristics, prehospital care, and outcomes in Singapore and Victoria.

Methods and Results

Using the prospective Singapore Pan‐Asian Resuscitation Outcomes Study and Victorian Ambulance Cardiac Arrest Registry, we identified 11 061 and 32 003 emergency medical services‐attended adult OHCAs between 2011 and 2016 respectively. Incidence and survival rates were directly age adjusted using the World Health Organization population. Survival was analyzed with logistic regression, with model selection via backward elimination. Of the 11 061 and 14 834 emergency medical services‐treated OHCAs (overall mean age±SD 65.5±17.2; 67.4% males) in Singapore and Victoria respectively, 11 054 (99.9%) and 5595 (37.7%) were transported, and 440 (4.0%) and 2009 (13.6%) survived. Compared with Victoria, people with OHCA in Singapore were older (66.7±16.5 versus 64.6±17.7), had less shockable rhythms (17.7% versus 30.3%), and received less bystander cardiopulmonary resuscitation (45.7% versus 58.5%) and defibrillation (1.3% versus 2.5%) (all P<0.001). Age‐adjusted OHCA incidence and survival rates increased in Singapore between 2011 and 2016 (P<0.01 for trend), but remained stable, though higher, in Victoria. Likelihood of survival increased significantly (P<0.001) with arrest in public locations (adjusted odds ratio [aOR] 1.81), witnessed arrest (aOR 2.14), bystander cardiopulmonary resuscitation (aOR 1.72), initial shockable rhythm (aOR 9.82), and bystander defibrillation (aOR 2.04) but decreased with increasing age (aOR 0.98) and emergency medical services response time (aOR 0.91).

Conclusions

Singapore reported increasing OHCA incidence and survival rates between 2011 and 2016, compared with stable, albeit higher, rates in Victoria. Survival differences might be related to different emergency medical services practices including patient selection for resuscitation and transport.

A new approach to prevent critical cardiac accidents in athletes by real-time electrocardiographic tele-monitoring system: Initial trial in full marathon

The majority of marathon deaths are caused by sudden cardiac arrest (SCA), which occur in approximately 1 in 57,000 runners. Such deaths are more common among older males and usually occur in the last 4 miles of the racecourse. Although prompt resuscitation, including early use of an automated external defibrillator (AED), improves survival, the deployment of enough trained medical staff and AEDs is difficult due to increased cost. Moreover, most victims of exercise-related SCA have no premonitory symptoms. Therefore, we tried to use a novel approach to prevent sudden cardiac deaths (SCD) related to SCA using real-time electrocardiographic tele-monitoring system, as an initial trial to assess operative possibility in a full marathon. As a result, 3 out of 5 runners had reasonable measurement results and sufficient tele-monitoring without complications related to this trial was possible. However, many investigations and improvements, such as improving cost-effectiveness, reducing noise, and automating the monitoring system, are needed for practical application of these devices for athletes. As a next step, we would establish a novel strategy to reduce SCDs in athletes using next-generation devices, which include an alarm system associated with early application of AED. <Learning objectives: Sudden cardiac arrest (SCA) is a major problem in sports cardiology. Here we investigated a novel approach using a real-time tele-monitoring system of electrocardiogram (ECG) to prevent sudden cardiac deaths by making use of an advanced alarm system which responds to SCA risk. Three out of five cases we monitored showed reasonable measurement of ECG with centralized observation in full marathon. This is the first report of this method, which may lead to the effective application of automated external defibrillator in athletes.>.

Epidemiology and stratification of risk for sudden cardiac death

Sudden cardiac death (SCD) is a major cause of mortality in the United States. Approximately 65% of cases of SCD occur in patients with underlying acute or chronic ischemic heart disease. The incidence of SCD increases 2- to 4-fold in the presence of coronary disease and 6- to 10-fold in the presence of structural heart disease. Ventricular fibrillation (VF) precipitated by ventricular tachycardia (VT) is a common mechanism of cardiac arrest leading to SCD. Triggers for SCD include electrolyte disturbances, heart failure, and transient ischemia. Although a large percentage of patients with out-of-hospital SCD do not survive, successful resuscitation to hospitalization has improved in recent years. One of the challenges for preventing SCD lies in identifying individuals at highest risk for SCD within a lower-risk population. The progression from conventional risk factors of coronary artery disease to arrhythmogenesis and SCD can be represented as a cascade of changes associated with levels of increasing risk. At the first level is atherogenesis, followed by changes in atherosclerotic plaque anatomy, which may be mediated by inflammatory processes. Disruption of active plaque formed during a transitional state initiates the thrombotic cascade and acute occlusion, after which acute changes in myocardial electrophysiology become the immediate trigger for arrhythmogenesis and SCD. Each level of the cascade offers different opportunities for risk prediction. Among the classes of risk predictors are clinical markers, such as ECG measures and ejection fraction. Transient risk markers, such as inflammatory markers, are potentially useful for identifying triggers for SCD. In the future, genetic profiling is expected to allow better assessment of individual risks for SCD.

Diabetes, glucose level, and risk of sudden cardiac death

AIMS

The prevalence of diabetes mellitus in industrialized countries is rapidly increasing, and diabetes is suspected to carry a particular high risk for sudden cardiac death (SCD).

METHODS AND RESULTS

We conducted a population-based case-control study at Group Health Cooperative. Cases (n=2040) experienced out-of-hospital cardiac arrest due to heart disease between 1980 and 1994. Controls (n=3800) were a stratified random sample of enrollees. Diabetes status was classified into four exclusive groups: (i) no diabetes, (ii) borderline, (iii) diabetes without microvascular disease (retinopathy or proteinuria), and (iv) diabetes with microvascular disease. When compared with no diabetes, we observed progressively higher risk of SCD associated with borderline diabetes [Odds ratio (OR)=1.24 (0.98-1.57)], diabetes without microvascular disease [OR=1.73 (1.28-2.34)], and diabetes with microvascular disease [OR=2.66 (1.84-3.85)], after adjustment for potential confounders (P-value for trend <0.001). Higher glucose levels were also associated with the risk of SCD both in the absence and in the presence of microvascular disease. However, subjects with microvascular complications but with glucose level <7.7 mmol/L were not at significant increased risk of SCD.

CONCLUSION

These results emphasize the role of diabetes as a strong risk factor for SCD and outline the importance of glucose level at every stage of diabetes severity.

Incidence of out-of-hospital cardiac arrest

Estimates of the incidence of out-of-hospital primary cardiac arrest (CA) have typically relied solely upon emergency medical service or death certificate records and have not investigated incidence in clinical subgroups. Overall and temporal patterns of CA incidence were investigated in clinically defined groups using systematic methods to ascertain CA. Estimates of incidence were derived from a population-based case-control study in a large health plan from 1986 to 1994. Subjects were enrollees aged 50 to 79 years who had had CA (n = 1,275). A stratified random sample of enrollees who had not had CA was used to estimate the population at risk with various clinical characteristics (n = 2,323). Poisson's regression was used to estimate incidence overall and for 3-year time periods (1986 to 1988, 1989 to 1991, and 1992 to 1994). The overall CA incidence was 1.89/1,000 subject-years and varied up to 30-fold across clinical subgroups. For example, incidence was 5.98/1,000 subject-years in subjects with any clinically recognized heart disease compared with 0.82/1,000 subject-years in subjects without heart disease. In subgroups with heart disease, incidence was 13.69/1,000 subject-years in subjects with prior myocardial infarction and 21.87/1,000 subject-years in subjects with heart failure. Risk decreased by 20% from the initial to the final time period, with a greater decrease observed in those with (25%) compared with those without (12%) clinical heart disease. Thus, CA incidence varied considerably across clinical groups. The results provide insights regarding absolute and population-attributable risk in clinically defined subgroups, information that may aid strategies aimed at reducing mortality from CA.

Digoxin therapy and the risk of primary cardiac arrest in patients with congestive heart failure: effect of mild-moderate renal impairment

BACKGROUND AND OBJECTIVE

The cardiac safety of digoxin therapy for congestive heart failure (CHF) is a source of concern, especially among those with renal impairment.

METHODS

Using a case-control design, we examined the risk of primary cardiac arrest (PCA) associated with digoxin therapy within three levels of renal function.

RESULTS

After adjustment for other clinical characteristics, digoxin therapy for CHF was not associated with an increased risk of PCA [odds ratio (OR)=0.97, 95% confidence interval (CI) 0.59-1.62] among patients with normal renal function (serum creatinine </=1.1 mg/dL). In contrast, digoxin therapy was associated with a modest increase in risk (OR=1.58, CI 0.89-2.80) among patients with mild renal impairment (serum creatinine=1.2-1.4 mg/dL); and a twofold increase in risk (OR=2.39, CI 1.37-4.18) among patients with moderate renal impairment (serum creatinine=1.5-3.5 mg/dL).

CONCLUSIONS

These findings suggest that the risks of digoxin may offset the benefits among patients with moderately impaired renal function, but not among patients with normal renal function.

Sudden death and myocardial infarction in first degree relatives as predictors of primary cardiac arrest

The hypothesis that family history (FH) of myocardial infarction (MI) and FH of sudden death (SD) are both independent risk factors for primary cardiac arrest (PCA) was examined in a case-control study. PCA cases were attended by paramedics (1988-1994) and community-based age and sex matched controls were identified. Subjects (25-74 years) were free of prior clinically-recognized heart disease and major co-morbidity. Interviewers obtained a detailed history of MI and SD in first-degree relatives from spouses of 235 cases and 374 control subjects. A parental history of early-onset SD (age <65) was associated with an increased risk of PCA (odds ratio (OR)=2.69, 95% CI=1.35-5.36), after adjustment for parental history of MI and other risk factors. A parental history of late-onset SD was not associated with PCA risk (OR=0.94, 95% CI=0.55-1.62). Additionally, parental history of SD was related to early-onset PCA (OR=1.89, 95% CI=1.08-3.30) but not to late-onset PCA (OR=0.89, 95% CI=0.49-1.61). In contrast, parental MI (early/late) was related to PCA (early/late), after adjustment for other risk factors and parental history of SD. Similar results were observed in first-degree relatives. Findings suggest a potential role of familial factors related to both MI and SD in PCA. Stronger findings for a familial patterning of PCA were noted for early onset disease in cases and their relatives.

Emergency medical services information systems and a future EMS national database

Since the early 1970s, various publications and legislation have contributed to the development of emergency medical services (EMS) information systems and databases. Yet, even today, EMS systems vary in their ability to collect patient and systems data and to put these data to use. In addition, no means currently exists to easily link disparate EMS databases to allow analysis at local, state, and national levels. For this reason, the National Association of State EMS Directors is working with its federal partners at the National Highway Traffic Safety Administration (NHTSA) and the Trauma and EMS program of the Health Resources and Services Administration's (HRSA's) Maternal and Child Health Bureau to develop a national EMS database. Such a database would be useful in developing nationwide EMS training curricula, evaluating patient and EMS system outcomes, facilitating research efforts, determining national fee schedules and reimbursement rates, and providing valuable information on other issues related to EMS care.

Family history as a risk factor for primary cardiac arrest

BACKGROUND

The hypothesis that a family history of myocardial infarction (MI) or primary cardiac arrest (PCA) is an independent risk factor for primary cardiac arrest was examined in a population-based case-control study. In addition, we investigated whether recognized risk factors account for the familial aggregation of these cardiovascular events.

METHODS AND RESULTS

PCA cases, 25 to 74 years old, attended by paramedics during the period 1988 to 1994 and population-based control subjects matched for age and sex were identified from the community by random digit dialing. All subjects were free of recognized clinical heart disease and major comorbidity. A detailed history of MI and PCA in first-degree relatives was collected in interviews with the spouses of case and control subjects by trained interviewers using a standardized questionnaire. For each familial relationship, there was a higher rate of MI or primary cardiac arrest (MI/PCA) in relatives of case compared with relatives of control subjects. Overall, the rate of MI/PCA among first-degree relatives of cardiac arrest patients was almost 50% higher than that in first-degree relatives of control subjects (rate ratio [RR]=1.46; 95% CI=1.23 to 1.72). In a multivariate logistic model, family history of MI/PCA was associated with PCA (RR=1.57; 95% CI=1.27 to 1.95) even after adjustment for other common risk factors.

CONCLUSIONS

Family history of MI or PCA is positively associated with the risk of primary cardiac arrest. This association is mostly independent of familial aggregation of other common risk factors.

Out-of-hospital cardiac arrest in the 1990's: a population-based study in the Maastricht area on incidence, characteristics and survival

OBJECTIVES

We sought to describe the incidence, characteristics and survival of out-of-hospital sudden cardiac arrest (SCA) in the Maastricht area of The Netherlands.

BACKGROUND

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.

METHODS

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.

RESULTS

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%).

CONCLUSIONS

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.

Absence of association between insurance copayments and delays in seeking emergency care among patients with myocardial infarction

BACKGROUND

The requirement of copayments for emergency care is thought to control costs by reducing "inappropriate" visits to the emergency department. However, requiring copayments may lead to adverse outcomes if patients delay seeking care for emergency conditions. To determine whether such requirements are associated with delays in seeking care, we examined the length of time from the onset of symptoms to arrival at the hospital among patients with myocardial infarction who did or did not have required insurance copayments.

METHODS

All patients were enrolled in a single health maintenance organization (HMO) and presented with myocardial infarction at 1 of 19 hospitals in King County, Washington, from 1989 through 1994. There were 602 patients whose health insurance required a copayment for emergency department care (range, $25 to $100) and 729 patients with no copayment requirement. Data on the time to presentation were obtained from a review of ambulance and hospital records.

RESULTS

The median length of time from the onset of symptoms to arrival at the hospital, as adjusted for age, sex, and race, was 135 minutes for the copayment group and 137 minutes for the group with no copayment (95 percent confidence interval for the difference, -19 to +16 minutes). There was no significant association between the presence or absence of a copayment requirement and the time to arrival at the hospital after adjustment for calendar year, income, educational level, cardiac history, or clinical symptoms. Since some patients may be unaware of their copayment requirement, we performed a subgroup analysis of data on patients who had a previous visit to the emergency department with the same copayment status - that is, of patients who were likely to know about their copayment. This analysis also showed no significant association between the requirement for a copayment and delays in seeking treatment.

CONCLUSIONS

For privately insured patients in this HMO, the requirement of modest, fixed copayments for emergency services did not lead to delays in seeking treatment for myocardial infarction.

Clinically silent electrocardiographic abnormalities and risk of primary cardiac arrest among hypertensive patients

BACKGROUND

Whether continuous ECG indexes that reflect the severity of left ventricular hypertrophy (LVHI), myocardial injury (CIIS), and QT-interval prolongation (QTI) are associated with the risk of primary cardiac arrest among hypertensive patients, independent of conventional binary ECG criteria, remains unknown.

METHODS AND RESULTS

We conducted a population-based case-control study among patients who were free of clinically recognized heart disease and who received care at a health maintenance organization. Cases (n = 131) were treated hypertensive patients who had had a primary cardiac arrest between 1977 and 1990. Controls (n = 562) were a stratified random sample of treated hypertensive patients. Resting ECGs were reviewed to estimate the severity of left ventricular hypertrophy, myocardial injury, and QT-interval prolongation on the basis of the algorithms of the Novacode ECG classification system. After adjustment for other risk factors and binary ECG criteria for the abnormalities, the LVHI, CIIS, and QTI scores were directly related to the risk of primary cardiac arrest. In a comparison of the 80th with the 20th percentile score for the LVHI, the risk was increased 40% (odds ratio, 1.4; 95% CI, 1.0 to 2.0); for the CIIS, the risk was increased 70% (odds ratio, 1.7; 95% CI, 1.2 to 2.5); and for the QTI, the risk was increased 80% (odds ratio, 1.8; 95% CI, 1.3 to 2.7).

CONCLUSIONS

Our findings suggest that continuous ECG indexes that reflect left ventricular hypertrophy, myocardial injury, and QT-interval prolongation are directly related to the risk of primary cardiac arrest among hypertensive patients without clinically recognized heart disease. Binary ECG criteria may underestimate the prognostic importance of these pathophysiological abnormalities.

Diastolic blood pressure and the risk of primary cardiac arrest among pharmacologically treated hypertensive patients

BACKGROUND

Previous studies have raised the concern that the reduction of diastolic blood pressure below 85 mm Hg among treated hypertensive patients may have cardiac hazards. However, these reports have not fully assessed potential confounding from coexisting cardiovascular disease.

METHODS

We conducted a population-based case-control study to examine the relation between treated diastolic blood pressure and the risk of primary cardiac arrest among hypertensive patients free of clinically diagnosed cardiovascular disease. Cases were hypertensive enrollees of the Group Health Cooperative of Puget Sound, an HMO, who had primary cardiac arrest between 1977 and 1990 (n = 80). Control patients were a stratified random sample of hypertensive enrollees (n = 426). Ambulatory-care records were reviewed to assess blood pressures and other clinical characteristics. Medication use was assessed through the HMO computerised pharmacy database.

RESULTS

Logistic regression models suggested a curvilinear relation between the level of treated diastolic blood pressure and the risk of primary cardiac arrest, after adjustment for pretreatment diastolic blood pressure, antihypertensive therapy, and other potential confounders. Compared with a treated diastolic blood pressure of 85 mm Hg, a treated diastolic blood pressure of 80 mm Hg was associated with a small increase in risk (relative risk [RR] 1.2; 95% confidence interval [CI] 1.0, 1.6), 75 mm Hg was associated with a modest increase in risk [RR 1.6; 95% CI 1.2, 2.1], and 70 mm Hg was associated with more than a twofold increase in the risk of primary cardiac arrest [RR 2.3; 95% CI 1.4; 3.8). There was little evidence of effect modification by pretreatment diastolic blood pressure.

CONCLUSIONS

Our findings support available evidence that among hypertensive patients a treated diastolic blood pressure level below 85 mm Hg is associated with cardiac hazards.

Further prospective evidence of a circadian variation in the frequency of call for sudden cardiac death. Belgian Cardiopulmonary Cerebral Resuscitation Study Group

OBJECTIVE

To determine whether in a larger data base call for sudden cardiac death exhibits a specific circadian rhythm similar to that recently demonstrated by Levine et al.

DESIGN AND SETTING

The time of the day of calls received for out-of-hospital cardiac arrests (OOHCA) prospectively registered between 1983 and '90 by 7 major Belgian pre-hospital EMS-MICU services. Chrono-biologic assessment was made by two-harmonic linear regression analysis of the data tabulated by hour of the day. The hourly distribution of calls for OOHCAs was subjected to Fourier transformation resulting in a periodogram.

PATIENTS

3471 OOHCAs with presumed cardiac etiology and age of more than 18 years versus 2007 inpatients registered in the same period.

MEASUREMENTS AND RESULTS

Significant and remarkably similar circadian patterns were found (R-square = 0.84) for the cardiac origin OOHCAs and the ventricular fibrillation OOHCAs. There is a low incidence during the night and an increased incidence from 6 a.m. until noon with an additional early afternoon-peak. The data were always better fitted when applying sinusoids with periods of 8 and 24 h instead of 12 and 24 h. Our observed circadian distribution resembles the reported circadian variation of ischaemic episodes, ventricular tachycardia and acute myocardial infarction in the awake hours. The time distribution of OOHCA (cardiac origin) differs significantly from OOHCA (non-cardiac origin) and from in-hospital cardiac arrests. The in-hospital CA pattern shows less deviation. The age dependent variation in the incidence of cardiac origin OOHCAs, was not obvious for the ventricular fibrillation subgroup.

CONCLUSION

Knowledge about the cyclical nature of incidence of cardiac arrests is useful to improve intersystem comparisons and make sound decisions about prophylaxis, treatment and allocation of resources.

Diuretic therapy for hypertension and the risk of primary cardiac arrest

BACKGROUND

The results of trials of the primary prevention of coronary heart disease have suggested that treating hypertension with high doses of thiazide diuretic drugs might increase the risk of sudden death from cardiac causes. In contrast, treatment with low doses of thiazide reduces the risk of coronary heart disease.

METHODS

To examine the association between thiazide treatment for hypertension and the occurrence of primary cardiac arrest, we conducted a population-based case-control study among enrollees of a health maintenance organization. The case patients were 114 persons with hypertension who had a primary cardiac arrest from 1977 through 1990. The control patients were a stratified random sample of 535 persons with hypertension. The patients' treatment was assessed with the use of a computerized pharmacy data base. Records of their ambulatory care were reviewed to determine other clinical characteristics.

RESULTS

The risk of primary cardiac arrest among patients receiving combined thiazide and potassium-sparing diuretic therapy was lower than that among patients treated with a thiazide without potassium-sparing therapy (odds ratio, 0.3; 95 percent confidence interval, 0.1 to 0.7). As compared with low-dose thiazide therapy (25 mg daily), moderate-dose therapy (50 mg daily) was associated with a moderate increase in risk (odds ratio, 1.7; 95 percent confidence interval, 0.7 to 4.5), and high-dose therapy (100 mg daily) was associated with a larger increase in risk (odds ratio, 3.6; 95 percent confidence interval, 1.2 to 10.8) (P value for trend, 0.02). The addition of a potassium-sparing drug to low-dose thiazide therapy was associated with a reduced risk of cardiac arrest (odds ratio, 0.4; 95 percent confidence interval, 0.1 to 1.5).

CONCLUSIONS

Both the dose of thiazide drugs and the addition of potassium-sparing drugs influence the risk of primary cardiac arrest. These results may explain the differences in the effect of antihypertensive therapy on mortality from coronary heart disease in previous clinical trials.