Mitigation of the clinical significance of spurious elevations of cardiac troponin I in settings of coronary ischemia using serial testing of multiple cardiac markers.

The ability to differentiate between true positives, false positives, and sporadically elevated cardiac troponin levels has grown in importance as cardiac troponins assume an increasingly dominant role in the diagnosis of coronary syndromes. In a population sample of 1,000 patients who presented consecutively to a large urban hospital emergency room, 50 of 112 patients who had elevated troponin levels (> 0.6 ng/ml) during evaluation for myocardial injury were subsequently found to have had an isolated, spurious elevation of cardiac troponin, and not a diagnosed myocardial infarction. Logistic regression analysis shows that by hierarchically analyzing electrocardiographic changes with concurrent creating kinase-MB and myoglobin levels at the time of the troponin elevation, one may predict with 91% accuracy whether the troponin elevation is actually indicative of a myocardial infarction in a patient. Spurious troponin elevations may be a common occurrence, and if not detected, may result in an increased number of falsely diagnosed myocardial infarctions.

Utility of B-natriuretic peptide as a rapid, point-of-care test for screening patients undergoing echocardiography to determine left ventricular dysfunction.

BACKGROUND: Although echocardiography is an important tool for making the diagnosis of left ventricular (LV) dysfunction, the cost of this procedure limits its use as a routine screening tool for this purpose. Brain natriuretic peptide (BNP) accurately reflects ventricular pressure, and preliminary studies have found it to be highly sensitive and highly specific in diagnosing congestive heart failure in the emergency department. We hypothesized that BNP might therefore be useful as a screening tool before echocardiography in patients with suspected LV dysfunction. METHODS: Subjects included patients referred for echocardiography to evaluate the presence or absence of LV dysfunction. Patients with known LV dysfunction were excluded from analysis. BNP was measured by a point-of-care immunoassay (Biosite Diagnostics, San Diego, Calif). The results of BNP levels were blinded from cardiologists making the assessment of LV function. Patients were divided into those with normal ventricular function, abnormal systolic ventricular function, abnormal diastolic function, and evidence of both systolic and diastolic dysfunction. RESULTS: Two hundred patients in whom LV function was unknown were studied. In the 105 patients (53%) whose ventricular function was subsequently determined to be normal by echocardiography, BNP levels averaged 37 +/- 6 pg/mL. This was significantly less than in those patients with either ultimate diastolic dysfunction (BNP 391 +/- 89 pg/mL (P <.001) or systolic dysfunction (BNP 572 +/- 115 pg/mL (P <.001). A receiver-operator characteristic curve showing the sensitivity and specificity of BNP against the echocardiography diagnosis revealed the area under the curve (accuracy) was 0.95. At a BNP level of 75 pg/mL was 98% specific for detecting the presence or absence of LV dysfunction by echocardiography. CONCLUSIONS: A simple, rapid test for BNP, which can be performed at the bedside or in the clinic, can reliably predict the presence or absence of LV dysfunction on echocardiogram. The data indicate that BNP may be an excellent screening tool for LV dysfunction and may, in fact, preclude the need for echocardiography in many patients.

Usefulness of cardiac troponin I in patients undergoing open heart surgery.

BACKGROUND: Significant myocardial injury during cardiac surgery is associated with a 10-fold increase in 2-year complication rates, yet there remains no clinical gold standard for diagnosis. Troponin I has complete cardiospecificity and is clinically used for diagnosis of myocardial infarction in other settings. METHODS AND RESULTS: One hundred consecutive patients undergoing open heart surgery (71 coronary artery bypass grafts and 29 aortic valve replacements) were enrolled and blood samples were drawn preoperatively, at 5 AM and 5 PM on days 1 and 2 after surgery, and at 5 AM for 3 more days. Twelve-lead electrocardiograms were performed daily and echocardiographic studies were performed on patients with either; electrocardiographic changes signifying likely myocardial damage, intraoperative complications, or elevated creatine kinase subfraction MB or troponin values. Seventeen patients had either new wall motion abnormalities or new Q waves all with peak cardiac troponin I >40 ng/mL. Stratification of patients by peak troponin values <40 and >60 ng/mL was highly predictive (P <.001) of days in intensive care unit, days on ventilator, development of new arrhythmia, and especially cardiac events. These postoperative variables also showed a stronger correlation with peak cardiac troponin I than did peak creatine kinase subfraction MB. CONCLUSION: Peak troponin I values detect myocardial infarction the day after heart surgery and predicts patient outcome.

A comparison of the brain weights of normal, untreated hydrocephalic and treated hydrocephalic rat pups.

The dry brain weights of normal, untreated and treated hydrocephalic pups of Texas, Lewis and Texas/Lewis cross rats aged from 2 to 60 days were compared using the technique of generalised linear modelling. It was found that with increasing age there is a steadily progressive increase in the weight of the brains of the normal animals. The brains of the untreated hydrocephalics showed a normal increase in weight up to about the 25th day but after that whilst the weight continued to increase, it was significantly less than normal. On the other hand the weight gain of the brains of the treated hydrocephalic pups resembled that of the normals and steadily increase in weight throughout the period of observation.

The effect of interscapular brown adipose tissue removal on body-weight and cold response in the mouse.

1. The removal of the interscapular brown adipose tissue (IBAT) led to an increase in body-weight of normal, lean mice as compared to anaesthetized controls. 2. No significant difference in food consumption could be detected between the two groups of mice over the period of the experiment. 3. Fat extraction of the whole carcasses with chloroform:methanol showed a statistically significant increase in fat content in the animals without IBAT. 4. There was no apparent failure in the operated animals to sustain core temperature when exposed to a cold stress situation (4 degrees for 24 h). 5. There was no difference in the wet weight, protein content or cytochrome oxidase content of the dorso-cervical brown adipose tissue (DCBAT) between operated and control mice. This is indicative of a lack of proliferation of other brown adipose tissue sites in the operated mice in response to the removal of the IBAT. 6. It is suggested that brown adipose tissue is implicated in dietary thermogenesis in the mouse.