Hermann K. Wolf

Electrocardiographic estimate of left ventricular mass versus radiographic cardiac size and the risk of cardiovascular disease mortality in the epidemiologic follow-up study of the first national health and nutrition examination survey

The prognostic value of a left ventricular (LV) mass index (g/m2) estimated from an electrocardiographic model and radiographic estimates of the relative heart volume (ml/m2) and cardiothoracic ratio for predicting the risk of cardiovascular disease mortality were investigated using Cox regression analysis to adjust for age, systolic blood pressure and history of heart attack in 1,807 men (1,609 white, 198 black) and 2,143 women (1,884 white, 259 black). The study population (ages 35 to 74 years at baseline) was followed from 5 to 12 years (average 9.5 years) for cardiovascular disease mortality. LV mass index and relative heart volume were independent predictors of cardiovascular disease mortality among white men. All 3 cardiac size estimates were independent predictors for cardiovascular disease mortality among white and black women. When LV mass index was used as a dichotomized variable to indicate the presence or absence of LV hypertrophy, the age-adjusted relative risk of cardiovascular disease mortality was 2.48 (95% confidence interval 1.77 to 3.46) for white men, 3.03 (1.49 to 6.16) for black men, 1.86 (1.21 to 2.87) for white women and 2.05 (0.83 to 5.05) for black women. The corresponding prevalence of LV hypertrophy was 15.4% for white men, 36.6% for black men, 20.1% for white women and 17.4% for black women. It is concluded that the electrocardiographic estimate of LV mass index can identify a substantially larger fraction of persons at increased risk for cardiovascular mortality than conventional electrocardiographic criteria for LV hypertrophy and that LV mass index estimated by electrocardiogram is a valuable supplement to radiographic cardiac size estimates in epidemiologic applications.

A simple procedure for positioning precordial ECG and VCG electrodes using an electrode locator

Methodological differences in the placement of precordial ECG electrodes are a major problem in multicenter clinical trials and epidemiological studies. Trend analysis and realization of the full potential of computer programs for serial comparison demands reduction of technical sources of variation in the electrocardiogram (ECG) and vectorcardiogram (VCG) and particularly errors in locating ECG electrodes. The ECG electrodes locator described here reduces a major precordial uncertainty in the identification of the midclavicular and the anterior axillary lines. It simplifies positioning and provides a numeric record of the key precordial electrode positions, facilitating control of electrode placement errors in serial recordings.

Trends in five-year survival of patients discharged after acute myocardial infarction

BACKGROUND It has previously been shown that the increased use of therapeutic intervention may not reduce patient fatality if there is a simultaneous increase in case severity. The present study was designed to extend the relationship between case severity and therapeutic interventions to long-term survival in the same study population. OBJECTIVE To compare five-year survival of patients discharged after acute myocardial infarction from 1984 to 1988 and from 1989 to 1993, and to evaluate possible reasons for survival differences. METHODS The present study was population-based. Survival time was determined by record linkage into the Canadian Mortality Database. Association of five-year survival with patient characteristics, in-hospital treatment and discharge medications was assessed by logistical regression analysis. Case severity was calculated as the probability of death within five years, given the patient profile and excluding any interventions. RESULTS Between the two study periods, most patient characteristics and treatment intensity changed, but case severity for the study population remained constant. Five-year survival improved from 74.8% to 79.2% (P(chi2)=0.001). The improvement was adequately described by the combination of changes in patient profile and treatment without residual period effect (P(goodness-of-fit)=0.752). The treatments significantly associated with five-year survival were coronary artery bypass graft surgery (OR 2.74; 95% CI 1.86 to 4.05), percutaneous coronary intervention (OR 2.63; 95% CI 1.67 to 4.14) and thrombolysis (OR 1.98; 95% CI 1.50 to 2.62) during admission, as well as acetylsalicylic acid (OR 1.39; 95% CI 1.15 to 1.68) or beta-blocker (OR 1.60; 95% CI 1.34 to 1.92) prescription at discharge. CONCLUSIONS Changes in patient profile did not affect long-term prognosis; instead, treatment modalities accounted for the observed improvement in five-year survival.

Prediction of left ventricular mass from the electrocardiogram

Multiple stepwise regression methods were used to derive electrocardiographic (ECG) models for prediction of the echocardiographic left ventricular (LV) mass index from standard 12-lead ECG measurements using data files of 203 men and 252 women. The correlation between echocardiographic and ECG estimates of LV mass index was R2 = 0.58 for men and R2 = 0.42 for women. A separate logistic regression model was derived for classification of LV hypertrophy as a dichotomized dependent variable. This classifier chose R (aVL), T (V6), and S (V1) for men and R (aVL), T (V6), and S (I) for women and produced a moderate sensitivity (53.7% for men and 63.4% for women) and specificity (94.9% for men and 92.9% for women). We conclude that the initial performance of these and other recently developed multivariate estimators of LV mass and LV hypertrophy classifiers is promising enough to subject them to further studies to evaluate their utility as risk predictors.

Mechanism of persistent S-T segment elevation after anterior myocardial infarction

Abstract Persistent S-T segment elevation after anterior myocardial infarction, reliably predicts the presence of advanced left ventricular asynergy. The genesis of this persistent S-T elevation is unknown, although recent observations suggest that ischemia within or surrounding the infarct zone might be involved. To explore this possibility, a body surface mapping system was utilized to assess the torso distribution of these repolarization potentials, as well as the responsiveness of the S-T segment elevation to three randomized interventions designed to alter the myocardial oxygen supply/demand ratio (40 percent oxygen, sublingual nitroglycerin and isometric exercise). S-T segment amplitude measured 75 msec after the J point (as well as two measurements from time-normalized ST-T segments) was not significantly altered by any intervention in 11 patients, thus indicating that ischemia was an unlikely cause of the persistent S-T elevation. Moreover, plots of the integrated area of the first three eighths of both the QRS complex (Q wave zone) and the ST-T segment (S-T segment) revealed that the initial repolarization maximum (corresponding to the persistent S-T segment elevation) was spatially concordant with the initial depolarization minimum (reflecting precordial Q waves). Because large Q waves usually indicate transmural scar, this surface distribution supports the conclusion that ischemia is not responsible for persistent S-T segment elevation and suggests that the sources for these repolarization potentials are not located in the infarcted area.

Decreasing Mortality from Acute Myocardial Infarctions: Effect of Attack Rates and Case Severity

Mortality from myocardial infarction (MI) has declined in many countries and the reasons for the decline have not been fully quantified. We used the database of the Halifax County MONICA Project to test the hypothesis that the decline of in-hospital mortality from MI can be explained by a trend toward less severe disease as opposed to improved treatment. During the study period 1984-1993, 14,130 people aged 25-74 had been admitted to hospital with suspected MI. Of these, 3774 were diagnosed as definite MI by standardized criteria (480 fatal). For each patient, clinical history, serial cardiac enzymes, and ECG treatment regimen during hospital stay were extracted from patient charts. Survival status 28 days after onset of symptoms was determined. A severity index predicting 28-day case fatality was derived from health status at admission time. During the study period the rate of definite MI in the MONICA target population showed a general downward trend from 221 to 179 per 100,000/year (p = 0.0002). The severity index increased during the observation time (p < 0.0001), predicting 25% higher mortality. Case fatality fluctuated, but showed a marginally significant decline. We conclude that part of the decreased in-hospital mortality from MI is due to lower attack rates. The remainder occurred despite increased case severity and is possibly due to improved in-hospital treatment.

Effect of sampling frames on response rates in the WHO MONICA risk factor surveys

Sample surveys are used to investigate occurrence and determinants of diseases in populations. Their reliability is influenced by quality of sampling frame and response rate. We investigated relationship between sampling frame type and response rates and assessed their impact on non-response bias, using data from the WHO MONICA Project, where 37 centres in 20 countries conducted sample surveys, employing the best locally available sampling frame. Sampling frames fell into three categories: Population registers (PR), electoral registers (ER), and health care registers (HR). Response rate (rrs) was factored into components reflecting quality of sampling frame (contact rate cr) and characterizing willingness of sample members to participate (enrolment rate er). The mean quality score for the sampling frames was 92 for PR, 87 for HR and 85 for ER; they contributed on average 23, 20, and 26 to the respective non-response rates. For all frame types and both sexes the lowest quality score occurred in the age group 35–44, suggesting a reduced ability to track migration of a highly mobile population group. The patterns in the age/sex distribution of er indicate at least for males in PR and females in HR a potential for non-response bias. Estimation of non-response bias through an abbreviated questionnaire failed because of low item response. We found that contact rate characterizes sampling frame quality. For all frame types it had a major influence on response rate. It is likely that low er and low cr cause different kind of bias, requiring different measures to minimize their effects.

Trends in event rate and case fatality of patients hospitalized with myocardial infarction between 1984 and 2001.

Between 1984 and 1993, prevalence and case fatality of hospitalized acute myocardial infarction (AMI) had declined in the population of Halifax County. We aimed to determine whether these trends continued into the 21st century by investigating patient characteristics, treatment methods, and fatality for hospital admissions of residents of Halifax County, aged 25-74, during 1984-1989 (period 1), 1990-1993 (period 2), and 1998-2001 (period 3) and diagnosed as AMI that were extracted from databases for the Halifax County MONICA and ICONS (Improving Cardiovascular Outcomes in Nova Scotia) Studies. Trends in patient characteristics and treatment methods were assessed by chi2 statistics. Their association with 28-day fatality was determined by logistic regression. Event rate declined during 1984-1993 but not into 1998-2001 (p = 0.206). Compared with 1990-1993, fewer AMI patients during 1998-2001 were > or = 55 years (73.3% vs. 69.9%), cigarette smokers (49.8% vs. 42.9%), had a history of myocardial infarction (28.9% vs. 24.9%), and had an admission heart rate >100 (34.8% vs. 17.4%). Additionally, more patients had a history of diabetes (22.5% vs. 28.1%). Case fatality declined progressively over the 3 study time periods (16.6%, 13.1%, and 9.4%, respectively). Changes also occurred in prevalence of Killip class 4 status during admission (20.2%, 10.3%, and 13.3%, respectively), use of thrombolysis (9.0%, 30.9, and 32.6%, respectively), and percutaneous coronary intervention (PCI) (4.3%, 11.2%, and 22.4%, respectively) in the different periods. Significant associations were found between case fatality and patient history of diabetes, history of MI, age, elevated admission heart rate, Killip class 4 impairment, thrombolysis, and PCI. The ICONS registry of hospitalized acute myocardial infarctions was used to compare case fatality during 1998-2001 with that reported by the Halifax County MONICA Project for 1984-1993. Whereas the population rate of myocardial infarctions had declined between 1984-1993 but not subsequently, case fatality declined significantly throughout the study period. The continued decline in case fatality is likely explained by changes in patient profile on presentation and medical therapies, including the increased use of thrombolysis and PCI.

Heart Size Estimates Indexed Optimally to Body and Chest Size

The prognostic value of heart size estimates in prediction of cardiovascular disease (CVD) mortality was investigated in 1,807 men (1,609 white, 198 black) and 2,143 women (1,884 white, 259 black) in

An Epidemiological Model for Coronary Heart Disease (CHD)

Mortality from CHD has been on the increase in most countries until in the late sixties the trend reversed in a few countries such as the USA, Canada, and Australia (Cooper 1978, Nicholls 1981, Epstein 1979). Ever since then CHD mortality has been on the decline in these countries. Since it is not known whether the incidence of CHD has declined or whether the prognosis of patients with CHD has improved, several studies have been initiated to determine the cause of the trend reversal. The data emanating from these studies will be difficult to interpret unless one is cogniscant of the inherent dynamics of the CHD system. The aim of this communication is to propose a dynamic model for the CHD system and to perform some preliminary system analysis. The benefits to be derived from such a model extend beyond the interpretation of mortality observations. It should be particularly useful in simulating intervention programs, since they are not only difficult to conduct but also require a very long observation period.