Prediction of the left ventricular mass from the electrocardiogram in systemic hypertension.

Although echocardiography provides a reliable method to determine left ventricular (LV) mass, it may not be available in all settings. Numerous electrocardiographic (ECG) criteria for the detection of LV hypertrophy have been developed, but few attempts have been made to predict the LV mass itself from the ECG. In a community-based survey program in the general population, 277 subjects were identified with untreated diastolic hypertension (diastolic blood pressure 95 to 115 mm Hg, 3 occasions) or isolated systolic hypertension (diastolic blood pressure <95 mm Hg and systolic blood pressure 160 to 220 mm Hg, 3 occasions). All subjects underwent ECG and echocardiography on the same day. A multiple linear regression analysis was performed using a random training sample of the data set (n = 185). The independent variables included both ECG and non-ECG variables. The resulting model was used to predict the LV mass in the remainder of the data set, the validation sample (n = 92). Using sex, age, body surface area, the S-voltage in V1 and V4, and the duration of the terminal P in V1 as independent variables, the model explained 45% of the variance (r = 0.67) in the training sample and 42% (r = 0.65) in the validation sample. This result exceeded that of 2 existing ECG models for LV mass (r = 0.40 and 0.41). The correlations between LV mass and combinations of ECG variables used for the detection of LV hypertrophy, such as the Sokolow-Lyon Voltage (r = 0.03) and the Cornell Voltage (r = 0.31), were comparatively low. In settings where echocardiography is not available or is too expensive and time-consuming, prediction of the LV mass from the ECG may offer a valuable alternative.

Fitting multistate transition models with autoregressive logistic regression: supervised exercise in intermittent claudication.

The purpose of this study was to develop a model that predicts the outcome of supervised exercise for intermittent claudication. The authors present an example of the use of autoregressive logistic regression for modeling observed longitudinal data. Data were collected from 329 participants in a six-month exercise program. The levels of the polytomous outcome variable correspond to states they defined in a Markov decision model comparing treatment strategies for intermittent claudication. Autoregressive logistic regression can be used to fit multistate transition models to observed longitudinal data with standard statistical software. The technique allows exploration of alternative assumptions about the dependence in the outcome series and provides transition probabilities for different covariate patterns. Of the alternatives examined, a Markov model including two preceding responses, time, age, ankle brachial index, and duration of disease best described the data.

Summary receiver operating characteristic curves as a technique for meta-analysis of the diagnostic performance of duplex ultrasonography in peripheral arterial disease.

RATIONALE AND OBJECTIVES: We summarized and compared the diagnostic performance of duplex and color-guided duplex ultrasonography in the evaluation of peripheral arterial disease. We present our research as an example of the use of summary receiver operating characteristic (ROC) curves in a meta-analysis of diagnostic test data. METHODS: A search of the English-language medical literature published between 1984 and 1994 retrieved 48 reports, 14 of which met the inclusion criteria. The analysis was limited to the aortoiliac and femoropopliteal segments because only two studies reported results of infrapopliteal arteries. Diagnostic performance of duplex and color-guided duplex, defined as the ability to detect a stenosis of 50-99% or an occlusion, was compared using summary ROC curve methodology. This method takes into account heterogeneity across studies attributable to differences in the threshold values used. RESULTS: The summary ROC curves demonstrated a high level of diagnostic performance for both types of duplex imaging, with color-guided duplex scanning being superior (p = .022). For example, at a false-positive rate of .05 (specificity = .95), the analysis predicted a true-positive rate (sensitivity) of .83 for duplex alone and .93 for color guided duplex. Differences in the case mix of the study population and study design did not affect the results. Furthermore, sensitivity analysis did not reveal a strong effect of any single study on the results. CONCLUSION: For aortoiliac and femoropopliteal arteries, the addition of color flow imaging to duplex scanning improves diagnostic performance in evaluating peripheral arterial disease.

[The effect of thymectomy in patients with myasthenia gravis without thymoma; a statistical analysis]. / Het effect van thymectomie bij patiënten met myasthenia gravis zonder thymoom; een statistische analyse.

In order to determine the effect of thymectomy on the prognosis of patients with myasthenia gravis, an analytical-descriptive study was carried out in the Neurological Clinic of the Groningen University Hospital and the Mathematical Institute of Groningen University. In 183 patients with generalized myasthenia gravis without thymoma, with onset between 9 and 46 years of age, the severity of the disease was scored by one neurologist at fixed times (0.5, 1, 2, 3, etcetera up to 15 years) after onset. Thymectomy was performed in 144 patients at different times (0.5, 1, 2, 3, etcetera up to 7 years) after onset. Logistic regression analysis was carried out with, as the criterion for marked improvement, a decrease of the disease score by 50%. Using this criterion, age, sex, duration of the disease and severity of the disease prior to operation played no distinct parts as prognostic factors. At different periods after the onset of the disease, groups of patients operated or not (yet) operated were compared. Patients subjected to thymectomy within 5 years after onset of myasthenia gravis had a better probability of halving of the severity score than patients not subjected to operation. These data render it possible in the individual patient to make an adequate estimate of the probability of marked improvement if thymectomy is performed or postponed.

Results of aortic bifurcation grafts for aortoiliac occlusive disease: a meta-analysis.

PURPOSE: To summarize mortality, morbidity, and long-term patency data of bifurcated aortoiliac or aortofemoral bypass graft procedures in aortoiliac occlusive disease. METHODS: A Medline search was performed of the medical literature published between 1970 and 1996. Studies were included if (1) they reported patency rates based on life tables and the number at risk was provided at yearly intervals; and (2) patient and study characteristics were reported in sufficient detail. Mortality and morbidity risks were pooled using a fixed-effects model. The patency data were combined using a technique that enables adjustment for differences across studies in patient characteristics or reporting methods. In the current analysis, we corrected for the symptomatic status of the patients at the time of surgery (claudication vs ischemia) and the unit of observation used in reporting the patency (limb vs patient). RESULTS: We identified 23 studies that met the inclusion criteria. The aggregated operative mortality risk in the older studies (started before 1975) was 4.6%, as compared with 3.3% in the more recent studies (p = 0.01). The aggregated systemic morbidity risk was 13.1% in the older studies and 8.3% in the more recent studies (p < 0.001). Limb-based patency rates for patients with claudication were 91.0% and 86.8% at 5 and 10 years, respectively, as compared with 87.5% and 81.8% for patients with ischemia. Patency rates reported in the older studies were markedly similar to those of more recent studies (p = 0.58). CONCLUSIONS: Our study suggests that mortality and systemic morbidity rates of aortic bifurcation graft procedures have dropped since 1975, whereas patency rates seem to be fairly constant over the years.

Contralateral symptoms after unilateral intervention for peripheral occlusive disease.

OBJECTIVE: The objectives of this study were (1) to determine the incidence of contralateral symptoms in patients with a unilateral intervention for peripheral arterial occlusive disease and (2) to identify characteristics that predict these symptoms. SUBJECTS AND SETTING: We included patients who had a unilateral surgical or percutaneous intervention for peripheral arterial occlusive disease at the Brigham and Women's Hospital (Boston) between 1990 and 1995 (n = 532). MAIN OUTCOME MEASURE: The main outcome measure was the first occurrence of contralateral critical ischemia or intermittent claudication. RESULTS: The annual incidence rate of contralateral critical ischemia was considerable, ranging from 3.3% to 8.3% during the first 4 years after the initial ipsilateral intervention. The annual incidence rate of contralateral critical ischemia and claudication combined varied from 7.7% to 21.3%. Cox regression analysis indicated that the initial ipsilateral symptoms and the initial contralateral ankle/brachial index can be used to predict the occurrence of contralateral symptoms. After correction was done for these two variables, we found no statistically significant effects for other factors including age, sex, diabetes, smoking, antihypertensive medication, history of coronary artery disease, the type of intervention, and the arterial level of the intervention. CONCLUSIONS: The results of our analysis emphasize that peripheral arterial occlusive disease is essentially a two-limb problem. Especially patients with previous ipsilateral critical ischemia and patients with a poor initial contralateral ankle/brachial index have a high risk for contralateral critical ischemia.

Intermittent claudication: symptom severity versus health values.

OBJECTIVE: The objective of this study was to obtain health values from patients with intermittent claudication with five different instruments and to study the construct validity of these measures of health-related quality of life by examining their relation with symptom severity. METHODS: We included all patients with intermittent claudication who participated in an exercise program of the Department of Internal Medicine at our university hospital (n = 92). Health value instruments included the verbal rating scale, time trade-off, standard gamble, EuroQol, and the Health Utilities Index (Mark III). Symptom-free walking distance was used as a measure of symptom severity. RESULTS: For all instruments the average health values in groups of patients with a symptom-free walking distance < or = 150 m were lower than the average values in patients with a greater walk distance, but the differences for the time trade-off and the standard gamble were small, and only the differences for the verbal rating scale and the EuroQol were statistically significant. At the individual patient level considerable heterogeneity was seen, and the statistical association of the symptom-free walking distance with health values varied from poor to moderate (Spearman rank correlations, 0.03 to 0.48; p values, 0.003 to 0.78). CONCLUSION: At least for the verbal rating scale and the EuroQol, the results of our study provide evidence of the validity of the various health value instruments in a population of patients with peripheral arterial occlusive disease.

Cost-identification analysis of revascularization procedures on patients with peripheral arterial occlusive disease.

OBJECTIVE: To determine average total in-hospital costs of various revascularization procedures for peripheral arterial occlusive disease; to examine the effect of procedure-related complications and patient characteristics on these costs; and to examine whether costs have changed over time. METHODS: We collected cost data on all admissions involving one revascularization procedure for peripheral arterial occlusive disease at the Brigham and Women's hospital from 1990 through 1995 (n = 583). The main outcome measures were total costs per admission in 1995 US dollars and length of stay in days. RESULTS: For each of 12 different procedures identified, total costs per admission varied considerably. Multiple linear regression analysis was performed to determine the effect of local and systemic complications and of patient characteristics on total in-hospital costs per admission. The additional cost incurred for fatal systemic complications was $11,675 (P = .004) and for nonfatal systemic complications was $9345 (P < .001). The results demonstrated significant additional costs with management of critical ischemia versus intermittent claudication ($4478, P < .001), presence of coronary artery disease ($1287, P = .05), female sex ($1461, P = .03), and advanced age ($1345, P = .02). No statistically significant changes over time were demonstrated. CONCLUSION: Total in-hospital costs per admission for peripheral revascularization procedures are highly variable and significantly increased by procedure-related complications, advanced age, female sex, management of critical ischemia, and presence of coronary artery disease.

Cost-effectiveness of diagnostic imaging work-up and treatment for patients with intermittent claudication in The Netherlands.

OBJECTIVE: to determine the societal cost-effectiveness of various management strategies, including both the diagnostic imaging work-up and treatment, for patients with intermittent claudication in The Netherlands. METHODS: a decision-analytic model was used and included probability and quality of life data available from the literature. A cost-analysis was performed in a university setting in The Netherlands. Imaging work-up options included magnetic resonance angiography (MRA), color-guided duplex ultrasound, or intraarterial digital subtraction angiography (DSA) and treatment options were percutaneous transluminal angioplasty with selective stent placement if feasible or bypass surgery. Management strategies were defined as combinations of imaging work-up and treatment options. A conservative strategy with no imaging work-up and walking exercises was considered as reference. Main outcome measures were quality-adjusted life years (QALYs), lifetime costs (euro), and incremental cost-effectiveness (CE) ratios. The base-case analysis evaluated 60-year-old men with severe unilateral intermittent claudication of at least one year duration. RESULTS: the range in QALYs and costs across management strategies that considered angioplasty as only treatment option was small (maximum difference: 0.0033 QALYs and 451 euros). Similarly, the range was small across management strategies that considered angioplasty if feasible otherwise bypass surgery (maximum difference: 0.0033 QALYs and 280 euros). MRA in combination with angioplasty (6.1487 QALYs and 8556 euros) had a CE ratio of 20,000 euros/QALY relative to the conservative strategy. The most effective strategy was DSA in combination with angioplasty if feasible otherwise bypass surgery (6.2254 QALYs and 18,583 euros) which had a CE ratio of 131,000 euros/QALY relative to MRA in combination with angioplasty. CONCLUSION: the results suggest that the imaging work-up with non-invasive imaging modalities can replace DSA for the work-up of patients with intermittent claudication without a substantial loss in effectiveness and a minimal cost-reduction. Management strategies including angioplasty are cost-effective in the Netherlands but although strategies including bypass surgery are more effective, their incremental costs are very high.