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Biomedical subjects

Jan A Kors

Publications and source records attributed to Jan A Kors.

At least 19 recordsLinked to original sources
PubMed2005

Mild renal dysfunction is associated with electrocardiographic left ventricular hypertrophy.

BACKGROUND: Both renal dysfunction and left ventricular hypertrophy (LVH) are signs of end-organ damage, risk markers of cardiovascular (CV) disease and chronic heart failure. In selected populations such as those with diabetes or hypertension, renal dysfunction was found to be related to LVH. We studied the relation between renal dysfunction and LVH in a cross-sectional study in 8592 inhabitants from Groningen, The Netherlands. METHODS: Standard 12-lead electrocardiograms were recorded, and LVH was classified using the Cornell voltage duration product. Renal dysfunction was defined as creatinine clearance <60 mL/min/1.73 m(2) or microalbuminuria (30 to 300 mg/24 h). RESULTS: Electrocardiographic signs of LVH were present in 396 of subjects (5.3%). Subjects with LVH were older and had a more extensive CV risk profile. We found that LVH was more prevalent in subjects with renal dysfunction than in those without (8% v 4%, P < .001). Multivariate regression analysis demonstrated that renal dysfunction was independently related to a 1.47-fold increased risk of the presence of LVH (95% CI = 1.15 to 1.88, P = .009). In addition, both creatinine clearance (OR = 1.56, 95% CI = 1.07 to 2.2, P = .044) and microalbuminuria (OR = 1.37, 95% CI = 1.04 to 1.80, P = .024) were independently associated with the presence of LVH. CONCLUSION: Subjects with mild renal dysfunction have a substantially higher risk of LVH on electrocardiography than those without renal dysfunction.

Adult↗
PubMed2005

Identification of optimal electrocardiographic criteria for the diagnosis of unrecognized myocardial infarction: a population-based study.

BACKGROUND: Despite using the same tool (ECG), the proportion of myocardial infarctions that goes unrecognized varies from 20% to 60% in population-based studies. The reasons for such wide variations have not been studied. We sought to evaluate the effect of ECG-MI criteria and study methodology on the prevalence of unrecognized myocardial infarction (UMI) and to identify the optimal ECG-MI criteria for UMI detection in epidemiologic studies. METHODS: A random population-based sample of 2042 adults, age > or = 45 years, underwent history, medical record abstraction and ECG. Six different ECG-MI criteria and two subjective recognized myocardial infarction (RMI) identification criteria, from different published studies, were applied to the same survey ECG. The operating test characteristics of different criteria were compared with the objective criterion standard of a RMI by Gillum criteria. RESULTS: The UMI proportion estimates varied from 32% to 61% due to variation in ECG-MI criteria, while keeping the study population, MI recognition criteria, and ECG constant. Subjective criteria for MI recognition had limited value (positive predictive value of 44-93%) in picking up RMI. Depending on the ECG abnormality used to define MI, ECG reading had widely varying sensitivity (21-37%; P < 0.0001) with consistently high specificity (92-97%) for detection of RMI. CONCLUSIONS: The prevalence estimates of UMI vary widely and are strongly dependent on the ECG-MI and MI recognition criteria. Future studies of UMI should explicitly recognize this variation and select the ECG-MI criteria that match their study aims.

Cross-Sectional Studies↗
PubMed2004

Drug-induced atrial fibrillation.

Atrial fibrillation (AF) is the most common sustained rhythm disorder observed in clinical practice and predominantly associated with cardiovascular disorders such as coronary heart disease and hypertension. However, several classes of drugs may induce AF in patients without apparent heart disease or may precipitate the onset of AF in patients with preexisting heart disease. We reviewed the literature on drug-induced AF, using the PubMed/Medline and Micromedex databases and lateral references. Successively, we discuss the potential role in the onset of AF of cardiovascular drugs, respiratory system drugs, cytostatics, central nervous system drugs, genitourinary system drugs, and some miscellaneous agents. Drug-induced AF may play a role in only a minority of the patients presenting with AF. Nevertheless, it is important to recognize drugs or other agents as a potential cause, especially in the elderly, because increasing age is associated with multiple drug use and a high incidence of AF. This may contribute to timely diagnosis and management of drug-induced AF.

Anti-Arrhythmia Agents↗
PubMed2004

The electrical T-axis and the spatial QRS-T angle are independent predictors of long-term mortality in patients admitted with acute ischemic chest pain.

OBJECTIVE: To investigate whether the orientation of the electrical T-axis and the spatial QRS-T angle provide independent diagnostic and prognostic information in patients presenting with acute chest pain. METHODS: Patients with symptoms suggestive of acute cardiac pathology, who were seen by a general practitioner and for whom a prehospital electrocardiogram (ECG) was recorded by the ambulance service between 1992 and 1994 were investigated. The ECGs (n = 2,261) for our study population were stored for off-line analysis by the Modular ECG Analysis System. QRS- and T-axes were computed from the reconstructed vectorcardiographic X, Y and Z leads. During the year 2000, a follow-up of the entire cohort was performed, and the vital status of the patients was determined via the civil registrar's office. Cox multivariable regression analyses were performed to evaluate the relation between the orientation of the T-axis, the spatial QRS-T angle and long-term mortality. RESULTS: An abnormal orientation of the T-axis and the spatial QRS-T angle were associated with an increased likelihood of cardiac diseases and an increased risk of all-cause mortality during short- and long-term follow-up. CONCLUSIONS: We conclude that the frontal T-axis and the spatial QRS-T angle are important determinants of diagnosis and prognosis in patients presenting with acute chest pain. The reintroduction of vectorcardiography in routine clinical practice might therefore be reconsidered.

Aged↗
PubMed2004

Defining unrecognized myocardial infarction: a call for standardized electrocardiographic diagnostic criteria.

BACKGROUND: Unrecognized myocardial infarctions (UMI) are detected by surveillance electrocardiograms (ECGs). In epidemiologic studies, different sets of ECG criteria have been used to define myocardial infarction, possibly contributing to significant differences in prevalence estimates and risk factor associations. We sought to summarize the rationale behind the various UMI-ECG definitions and to suggest an approach to develop uniform criteria. METHODS: A comprehensive review of relevant publications from 1966 to 2002 was conducted. RESULTS: Out of 14 major studies, the occurrence of UMI as a proportion of all infarctions varied from 4% to 44%, with markedly varying ECG criteria. No study directly addressed the rationale behind selection of ECG criteria. Computerized ECG analysis appears superior to visual reading due to better reliability, speed and cost while maintaining a similar predictive validity. Criteria requiring only major Q waves have the highest specificity for ECG-MI and for prediction validity for future coronary heart disease in middle-aged white men. The addition of minor Q waves and ST-T abnormalities improves predictive validity in middle-aged women and elderly men. Minor Q waves can have their diagnostic accuracy improved by several strategies, including use of ST-T wave changes, Washington Code, vector cardiogram, chronic obstructive pulmonary disease-ECG criteria, and serial ECG analysis. CONCLUSION: Currently the most cost-effective and valid method for detecting UMI in epidemiologic studies appears to be computerized ECG analysis using major Q waves in middle-aged white men. Issues needing further research include morphologic validation of ECG-UMI criteria and the influence of age, sex, and race on ECG-MI criteria.

Adult↗
PubMed2004

Reconstruction of the 12-lead electrocardiogram from reduced lead sets.

In clinical practice, continuous recording of all leads of the 12-lead electrocardiogram (ECG) is often not possible. We wanted to assess how well absent, noisy, or defective leads can be reconstructed from different lead subsets and how well lead reconstruction performs over time. A data set of 234 24-hour ECG recordings was divided into an equally sized training and test set. Precordial leads were systematically removed, and for all lead subsets including both limb leads and at least one precordial lead, the absent leads were reconstructed using general and patient-specific reconstruction templates. Reconstruction performance was measured by correlation between the original and reconstructed leads over the QRS and T waves, by average and maximum absolute ST differences, and by agreement when a clinical decision rule was applied. Reconstruction performance over time was evaluated at baseline, at 20 minutes, and 1, 6, 12 and 24 hours after the start of each recording. Reconstruction accuracy was high (correlation > or =0.932, average ST difference < or =30 microV, agreement > or =94.9%) with general reconstruction for lead sets with 1 or 2 precordial leads removed but was less satisfactory when more leads were missing. Patient-specific reconstruction performed well when up to 4 precordial leads were removed (correlation > or =0.967, average ST difference < or =26 microV, agreement > or =95.7%). Patient-specific reconstruction performance initially slightly decreased and then stabilized over time but remained much better than general reconstruction after 24 hours. Accurate reconstruction of the 12-lead ECG from lead subsets is possible over time. General reconstruction allows reconstruction of 1 or 2 precordial leads, whereas up to 4 leads can be reconstructed well using patient-specific reconstruction.

Angina, Unstable↗
PubMed2004

Hypertensive stress increases dispersion of repolarization.

Several electrocardiographic indices for repolarization heterogeneity have been proposed previously. The behavior of these indices under two different stressors at the same heart rate (i.e., normotensive gravitational stress, and hypertensive isometric stress) was studied. ECG and blood pressure were recorded in 56 healthy men during rest (sitting with horizontal legs), hypertensive stress (performing handgrip), and normotensive stress (sitting with lowered legs). During both stressors, heart rates differed <10% in 41 subjects, who constituted the final study group. Heart rate increased from 63 +/- 9 beats/min at rest to 71 +/- 11 beats/min during normotensive, and to 71 +/- 10 beats/min during hypertensive stress (P < 0.001). Systolic blood pressure was 122 +/- 15 mmHg at rest and 121 +/- 15 mmHg during normotensive stress, and increased to 151 +/- 17 mmHg during hypertensive stress (P < 0.001). The QT interval was larger during hypertensive (405 +/- 27) than during normotensive stress (389 +/- 26, P < 0.001). QT dispersion did not differ significantly between the two stressors. The mean interval between the apex and the end of the T wave (Tapex-Tend) of the mid-precordial leads was larger during hypertensive (121 +/- 17 ms) than during normotensive stress (116 +/- 15 ms, P < 0.001). The singular value decomposition T wave index was larger during hypertensive (0.144 +/- 0.071) than during normotensive stress (0.089 +/- 0.053, P < 0.001). Most indices of repolarization heterogeneity were larger during hypertensive stress than during normotensive stress. Hypertensive stressors are associated with arrhythmogeneity in vulnerable hearts. This may in part be explained by the induction of repolarization heterogeneity by hypertensive stress.

Adult↗
PubMed2003

The elusive U wave: a simple explanation of its genesis.

Of the various waveforms in the electrocardiogram (ECG), the U wave has been the most elusive. After the first description of a U wave by Einthoven several hypotheses were put forward as to its origin. Three of these are frequently quoted, ie: 1) the repolarization of the Purkinje fibres; 2) the prolonged repolarization of the M-cells in the midmyocardium; and 3) after-potentials, possibly caused by mechanical forces in the ventricular wall. However, none of these hypotheses has gained general acceptance. We present a simple multilayered digital model of the myocardium, which explains the formation of the U wave on the basis of known electrophysiological processes responsible for the electrical sources in the myocardium, and of the physical laws, formulated in the lead vector concept, which link the potentials in or on the body to these sources. A realistic action potential (AP) is assigned to each layer. The timing of the APs is such that a normal ventricular wall activation is simulated. The differences in APs between adjacent layers create current sources Di that contribute to the potential course at an arbitrary observation point P through the heart vector-lead vector relationship. Assuming a homogeneous infinite medium, without changing the AP shapes or durations and without introducing after potentials, different realistically shaped T and U waves are simulated. Their amplitudes and configurations are dependent on the value of L, viz. the relative distance of the observation point to the myocardium. The gradual and varying transition from T wave into the U brings into question the traditional view that the end of T wave represents the end of the myocardial repolarization: T and U together must be considered as one repolarization complex. The traditional concept of QT prolongation would then need revision.

Action Potentials↗
PubMed2003

Normal limits of the electrocardiogram in Chinese subjects.

BACKGROUND: Accurate normal limits of the electrocardiogram (ECG) are the basis on which diagnostic criteria are developed. The ECG, however, is subject to age- and sex-variations and may also be racially determined. Studies into normal ECG limits for the Chinese, comprising one fifth of the world population, are few and have their limitations. We have undertaken to establish normal limits of the ECG from a large sample of healthy Chinese subjects. METHODS: Standard simultaneous 12-lead ECGs from 5360 apparently healthy Chinese subjects (3614 men and 1746 women, ages ranging from 18 to 84 years) were collected with a modern digital recorder and processed with a well-validated ECG computer program. The medians, lower limits (2nd percentile) and upper limits (98th percentile) of various ECG measurements were calculated and age and sex differences examined. RESULTS: Significant age trends were present in, for example, P-wave duration, QTc interval, and frontal QRS axis, with concomitant changes of R amplitudes in the extremity leads. Sex differences existed for heart rate, interval durations, the Sokolow and Cornell indices, and QRS and ST-T amplitudes in different leads. Notably, left-precordial R-wave amplitudes in women increased with age; the Sokolow index showed a clearer age trend for men than for women, the reverse being true for the Cornell index. Some of these findings are at odds with established diagnostic ECG criteria. CONCLUSIONS: Normal ECG limits of Chinese subjects show marked age and sex differences. This merits the definition and use of age- and sex-specific ECG criteria for a Chinese population.

Adolescent↗
PubMed2003

Spatial QRS-T angle predicts cardiac death in a general population.

AIMS: The aim of this study was to assess the prognostic importance of the spatial QRS-T angle for fatal and non-fatal cardiac events. METHODS AND RESULTS: Electrocardiograms (ECGs) were recorded in 6134 men and women aged 55 years and over from the prospective population-based Rotterdam Study. Spatial QRS-T angles were categorized as normal, borderline or abnormal. Using Cox's proportional hazards model, abnormal angles showed increased hazard ratios of cardiac death (age-and sex-adjusted hazard ratio 5.2 (95% CI 4.0-6.8)), non-fatal cardiac events (2.2 (1.5-3.1)), sudden death (5.6 (3.7-8.5)) and total mortality (2.3 (2.0-2.7)). None of the classical cardiovascular and ECG predictors provided larger hazard ratios. After adjustment for these predictors, the association of abnormal spatial QRS-T angles with all fatal study endpoints remained strong, but the association with non-fatal cardiac events disappeared. Computation of Akaike's information criterion showed that the angle contributed significantly to the prediction of all fatal endpoints by classical cardiovascular and ECG predictors. CONCLUSION: The spatial QRS-T angle is a strong and independent predictor of cardiac mortality in the elderly. It is stronger than any of the classical cardiovascular risk factors and ECG risk indicators and provides additional value to them in predicting fatal cardiac events.

Aged↗
PubMed2003

Ambiguity of human gene symbols in LocusLink and MEDLINE: creating an inventory and a disambiguation test collection.

Genes are discovered almost on a daily basis and new names have to be found. Although there are guidelines for gene nomenclature, the naming process is highly creative. Human genes are often named with a gene symbol and a longer, more descriptive term; the short form is very often an abbreviation of the long form. Abbreviations in biomedical language are highly ambiguous, i.e., one gene symbol often refers to more than one gene. Using an existing abbreviation expansion algorithm,we explore MEDLINE for the use of human gene symbols derived from LocusLink. It turns out that just over 40% of these symbols occur in MEDLINE, however, many of these occurrences are not related to genes. Along the process of making an inventory, a disambiguation test collection is constructed automatically.

Algorithms↗
PubMed2003

Mining microarray datasets aided by knowledge stored in literature.

DNA microarray technology produces large amounts of data. For data mining of these datasets, background information on genes can be helpful. Unfortunately most information is stored in free text. Here, we present an approach to use this information for DNA microarray data mining.

Databases, Genetic↗
PubMed2002

Microalbuminuria modifies the mortality risk associated with electrocardiographic ST-T segment changes.

OBJECTIVES: We sought to investigate whether microalbuminuria, a proposed marker of generalized vascular damage, enhances the prognostic value of ST-T segment changes for all-cause and cardiovascular mortality in the general population. BACKGROUND: ST-T segment changes on the rest electrocardiogram (ECG) predict mortality in the general population. However, the excess risk seems to be low, particularly in nonhospitalized populations with a low cardiovascular risk profile. METHODS: In a population of 7,330 male and female subjects, a total of 89 deaths (1.2%) occurred during a median three-year follow-up. In 69 of these, the cause of death was obtained from the Central Bureau of Statistics: 25 subjects died of cardiovascular causes (36%). Using computerized Minnesota coding, ST-T segment changes were coded as 4.1-4 and 5.1-4. Microalbuminuria was defined as a urinary albumin excretion of 30 to 300 mg per 24 h. RESULTS: The combination of ST-T segment changes and microalbuminuria showed a higher hazard ratio (HR) for all-cause mortality (HR 8.6 [95% confidence interval [CI] 4.8 to 15.2, p < 0.0001), as compared with ST-T segment changes in the absence of microalbuminuria (HR 1.3 [95% CI 0.7 to 2.5]), which was independent of other cardiovascular risk factors (HR 3.3 [95% CI 1.5 to 7.1], p = 0.002). The combination showed a higher HR when only cardiovascular deaths were taken into account, as compared with all-cause mortality (HR 24.5 [95% CI 7.9 to 76.0], p < 0.0001), which also counted for ST-T segment changes alone (HR 4.4 [95% CI 1.4 to 14.5], p = 0.02). After controlling for other risk factors, the HRs were 10.4 (95% CI 2.5 to 43.6, p = 0.001) for the combination and 2.7 (95% CI 0.6 to 12.3) for ST-T segment changes alone. CONCLUSIONS: This study suggests that, in subjects with ST-T segment changes on their rest ECG, microalbuminuria could identify those at increased risk of all-cause and cardiovascular mortality.

Adult↗
PubMed2002

How many electrodes and where? A "poldermodel" for electrocardiography.

It is known that body surface potential maps (BSPMs) contain diagnostic information not easily retrieved from the standard 12-lead electrocardiogram (ECG). Alternate lead sets that can reconstruct the BSPM have been proposed, but they are impractical because they require more than the 10 electrodes of the standard ECG and use nonstandard positions. We propose a practical approach to increasing the diagnostic information content of the standard ECG by repositioning selected chest electrodes. Thus, in the best tradition of the Dutch "poldermodel," we have sought to strike a compromise between the demands of different parties, one that, while suboptimal for each, will be seen by all as the best attainable result. We used a set of 746 120-lead BSPMs from healthy individuals and patients with various abnormalities. Data were split in a learning and a test set. Using the learning set, a general transformation to reconstruct all BSPM leads from the standard 12-lead ECG was derived by linear regression. Similarly, BSPMs were reconstructed when 2 of electrodes V(3)-V(6) were moved to other positions on the anterior part of the chest. Reconstruction performance was assessed on the test set by correlation and similarity coefficients. Thanks to the redundancy of information in the precordial leads, 2 missing precordial leads can be reconstructed from the others, using general coefficients, to a high degree of accuracy, particularly when the missing leads were not adjacent. We chose to reposition V(4) and V(6) to different sites on the anterior thorax. From the many electrode sites that we explored, those at 2 intercostal spaces below and above V(2) yielded better BSPM reconstruction than was attainable from the standard electrode positions, in most parts of the anterior thorax, including regions that are known to contain important diagnostic information less well brought forward by the standard ECG. Slight variations in the new electrode positions did not appreciably change the results. The standard 12-lead ECG proved to produce better overall reconstructions than either the EASI configuration or vectorcardiographic lead systems. Repositioning electrodes V(4) and V(6) provides a simple, practical method by which to improve the sampling of diagnostic information from the body surface while maintaining the full diagnostic content of the standard 12-lead ECG. This approach also obviates the need to determine the precise location of V(4) electrode, which may be difficult in women.

Body Surface Potential Mapping↗