Statistical methodology: VI. Mathematical modeling of the electrocardiogram using factor analysis.

UNLABELLED: The ECG is a 12-lead-vector system and is known to contain redundant information. Factor analysis (FA) is a statistical technique that improves measured data and eliminates redundancy by identifying a minimum number of factors accounting for variance in the data set. OBJECTIVE: To identify the minimum number of lead-vectors required to predict the 12-lead ECG. METHODS: A total of 104 ECGs were obtained from 24 normal men, 22 normal women, and 28 men and 30 women with variable pathologies. Each ECG lead was simultaneously acquired and digitized, resulting in a voltage-time data array stored for mathematical analysis. Each array was factor-analyzed to identify the minimum number of lead-vectors spanning the ECG data space. The 12-lead ECG was then predicted from this minimum lead-vector set. ANOVA was used to test for statistical significance between normal and pathologic data groups. RESULTS: FA revealed that 3 lead-vectors accounted for 99.12%+/-0.92% (95% CI+/-0.18%) of the variance contained in the 12-lead ECG voltage-time data for all 104 cases. There were no statistically significant differences between men and women (99.25%+/-0.66% vs 98.98+/-1.11%; p=0.139). Statistically significant differences were noted between normal and acute myocardial infarction ECGs (99.5%+/-0.27% vs 98.66+/-1.25%; p=0.00003). The measured and predicted leads were almost identical. A 3-dimensional spatial ECG derived from the 3-lead-vector set resulted in variable curved surfaces that differed by pathology. CONCLUSIONS: The 12-lead ECG can be derived from only 3 measured leads and graphed as a 3-D spatial ECG. This type of data processing may lead to instantaneous acquisition and may enhance the diagnostic capability of the ECG from routine bedside telemetry equipment.

Incidence of deep venous thrombosis associated with femoral venous catheterization.

OBJECTIVE: To determine in adult medical patients the incidence of deep venous thrombosis (DVT) resulting from femoral venous catheterization (FVC). METHODS: A prospective, observational study was performed at a 420-bed community teaching hospital. Heparin-coated 7-FR cm femoral venous catheters were inserted unilaterally into a femoral vein. Each contralateral leg served as a control site. Age, gender, number of FVC days, DVT risk factors, administration of DVT prophylaxis, and DVT formation and site were tabulated for each patient. Venous duplex sonography was performed bilaterally on each patient within 7 days of femoral venous catheter removal. RESULTS: Catheters were placed in 29 men and 13 women. Femoral DVT was identified by venous duplex sonography in 11 (26.2%) of the FVC legs and none (0%) in the control legs. Posterior tibial and popliteal DVT was identified in both the FVC and control legs of 1 patient. DVT formation at the site of FVC insertion was highly significant (p = 0.005). There were no statistically significant associations with age (p = 0.42), gender (p = 0.73), number of DVT risk factors (p = 0.17), number of FVC days (p = 0.89), or DVT prophylaxis (p = 0.99). CONCLUSION: Placement of femoral catheters for central venous access is associated with a significant incidence of femoral DVT as detected by venous duplex sonography criteria at the site of femoral venous catheter placement. Physicians must be aware of this risk when choosing this vascular access route for adult medical patients. Further studies to assess the relative risk for DVT anf its clinical sequelae when using the femoral vs other central venous catheter routes are indicated.

Emergency management of atrial fibrillation and flutter: intravenous diltiazem versus intravenous digoxin.

STUDY OBJECTIVE: To compare the effects of i.v. diltiazem and i.v. digoxin on ventricular rate control in the emergency treatment of acute atrial fibrillation and flutter (AFF). METHODS: This prospective, randomized, open-label trial involved 30 consecutive patients who presented with acute AFF to the emergency department of an urban, 420-bed community teaching hospital from April 1993 through March 1994. Exclusion criteria included systolic blood pressure lower than 100 mm Hg, treatment with calcium-channel blockers other than diltiazem, lack of informed consent, and objection of the private physician. Patients were randomly assigned to receive either i.v. diltiazem alone, i.v. digoxin alone, or both. Heart rate control was defined as a ventricular rate of less than 100 beats/minute. I.v. digoxin, 25 mg, was given as a bolus at time 0 and at time 30 minutes. An initial dose of .25 mg/kg diltiazem was given intravenously over the first 2 minutes, followed by a dose of .35 mg/kg at time 15 minutes and then a titratable i.v. infusion at a rate of 10 to 20 mg/hour to maintain heart rate control. The dosing regimens were the same whether the drugs were given alone or in combination. Heart rhythm, heart rate, and blood pressure were measured at time 0, 5, 10, 15, 30, 60, 120, and 180 minutes. Statistical significance was assessed with the use of Student's t test and ANOVA methodology. RESULTS: At time 0, the heart rate (mean +/- SD) was 150 +/- 19 beats/minute in the diltiazem group and 144 +/- 12 in the digoxin group (difference not significant, P = .432). The decrease in heart rate from time 0 reached statistical significance at time 5 minutes in the diltiazem group (P = .0006); the mean rates at time 5 minutes were 111 +/- 26 beats/minute for diltiazem and 144 +/- 13 for digoxin. The decrease in heart rate achieved with digoxin did not reach statistical significance until time 180 minutes (P = .0099), at which time the rates were 90 +/- 13 for diltiazem and 117 +/- 22 for digoxin. CONCLUSION: Treatment of acute AFF with i.v. diltiazem decreases ventricular heart rate significantly within 5 minutes, compared with 3 hours for treatment with i.v. digoxin. No advantage was noted within 3 hours for i.v. treatment with a combination of diltiazem and digoxin. I.v. diltiazem is superior to i.v. digoxin in the emergency control of ventricular rate in acute AFF and should be considered as a drug of choice for this condition. This study was not large enough to adequately assess adverse effects, and further studies may be warranted for clinical validation.

A prospective evaluation of glucose reagent teststrips in the prehospital setting.

Reagent teststrip determination of blood glucose has been shown to be accurate for hospital and home testing and is commonly used in prehospital care despite the lack of studies in this arena. This prospective, multicenter study examines the ability of glucose reagent teststrips to detect hypoglycemia when used under field conditions compared with simultaneously drawn control samples for laboratory glucose determination. Also examined was the accuracy of the teststrips in the laboratory glucose range less than or equal to 200 mg/dL. One hundred eighty-one pairs of data were analyzed. Hypoglycemia was defined as laboratory glucose less than or equal to 60 mg/dL. The teststrips correctly identified 31 of 33 patients in this range (sensitivity = 94%), and 125 of 148 patients without hypoglycemia (specificity = 85%). The two false negative readings were 70 and 90 mg/dL. Reagent teststrips were within +/- 40 mg/dL of the laboratory value in 70% of cases. The correlation coefficient (Spearman r) between teststrip and laboratory glucose in the range less than or equal to 200 mg/dL was .80. Using teststrip readings of 90 mg/dL or less as a measure of hypoglycemia yields 100% sensitivity with a specificity of 57%. We conclude glucose reagent teststrips are a useful adjunct for use in the prehospital setting and may be valuable for the detection of hypoglycemia.

Correlation of nonlinear mathematical transformation of the normal electrocardiogram with the severity of coronary artery disease.

Signal processing was applied to normal ECGs to study whether the results could predict coronary artery disease (CAD) on angiography. ECGs determined to be normal by conventional criteria for 116 white males and 84 white females were subjected to signal processing. The technique applied nonlinear mathematical transformation to a segment of seven ECG leads which were photographically imaged, automatically digitized, normalized for time, and had topographical coordinate transformation using an IBM-XT microcomputer. The resulting curvilinear display on the computer monitor was termed a biopotential coordinate transformation (BCT). Successive superimposition of BCTs from normal ECGs of patients with normal angiograms developed boundaries of a normal template for each lead. Study BCTs were then compared to the normal templates to predict the presence or absence of CAD. Correlation of the BCT results with the severity of CAD for the males resulted in average sensitivities of 80%, 84.4%, and 91.7% for single, double, and triple-vessel CAD, respectively. Similarly, for the females average sensitivities were 59.1%, 73.9%, and 88.9%, respectively. In past studies on the same population, the BCT process detected CAD with average sensitivity of 85.1% and specificity of 81.8% for white males and average sensitivity of 73% and specificity 81% for white females. As such, computerized signal processing of ECGs may provide a noninvasive method for detection of CAD in patients with seemingly normal resting ECGs. The results of this study indicate that the sensitivity of the process increases in direct proportion to the severity of CAD. Further investigation is warranted for process refinement and verification.

Simultaneous dorsal dislocation of the proximal and distal interphalangeal joints in one digit.

Dorsal dislocation of a proximal and distal interphalangeal joint is a common clinical problem. However, simultaneous dorsal dislocation of both interphalangeal joints in a single digit is rare. We describe the first case of an open, simultaneous proximal and distal interphalangeal dislocation. Patient outcome following vigorous wound care, closed reduction, and four weeks of immobilization was excellent. Review of reported cases revealed that these injuries occur most commonly in men, on the dominant hand, and in association with sporting injuries or falls, and typically have a good outcome following closed reduction and splinting.

Detection of coronary artery disease from the normal resting ECG using nonlinear mathematical transformation.

In order to enhance subtle changes not apparent in resting ECGs by conventional criteria, a computerized signal processing technique, biopotential coordinate transformation (BCT), has been developed to increase the physician's perceptibility of CAD in seemingly "normal" resting ECGs. ECGs initially read as normal then can be tested with this process to predict the presence or absence of CAD. A blinded, retrospective study of 93 Caucasian patients with normal ECGs was performed using coronary angiography as the test standard. The BCT process identified the presence or absence of CAD with an 84.3% sensitivity and 81.8% specificity in 62 men. Similarly, a 76.2% sensitivity and 80% specificity was obtained for 31 women. These results suggest that the BCT process may provide the emergency physician with a noninvasive screening test for the detection of CAD in patients with apparently normal resting ECGs. Further studies are necessary for process refinement and verification.

Nonlinear transformation of the resting electrocardiogram in the diagnosis of coronary artery disease.

Despite the common use of the standard 12-lead ECG, its reliability as an indicator of coronary artery disease (CAD) is poor. The normal ECG is falsely negative in more than 50% of angiographically proven CAD. The waveform of the standard ECG, however, can be transformed mathematically by nonlinear signal transformation to enhance its interpretation by computer. Using such a process it is possible that abnormalities can be identified in "normal" ECGs that can be correlated with CAD, thus identifying high-risk patients. A computer template that represents grouped data of normal ECGs for patients who also have normal coronary angiography was developed. Unblinded, preliminary testing of the template on normal ECGs of 107 white patients who had normal or abnormal coronary angiograms was performed. The process identified presence or absence of CAD with 82% specificity and 71% sensitivity for 53 women, and with 82% specificity and 86% sensitivity for 54 men. These preliminary results are promising, but further refinement of the templates is required and blinded studies with larger numbers and varieties of patients are needed.

Diagnosis of complex acid-base disorders: physician performance versus the microcomputer.

Patients with acid-base disturbances that are often complex frequently present to the emergency department. The sometimes hectic nature of the ED can preclude the appropriate quantitative analysis required by these disorders, especially when mixed disturbances are present. A computer program using generally accepted acid-base and electrolyte formulae was developed for use on the Apple II+ or IBM-PC microcomputer. Each of a series of 35 acid-base disturbances incorporating single, double, and triple disorders was correctly identified by the computer in less than 45 seconds. Problem sets based on the same 35 disturbances were presented to 21 physician-subjects at various levels of training from the emergency medicine, internal medicine, pediatrics, surgery, and family practice specialties. Although the physicians were given unlimited time and the necessary formulae to reach a diagnosis, they were requested to perform their analyses in the same fashion used in the ED. Although times varied widely, no physician spent more than five minutes on any problem. The physician correct response rates were 86%, 49%, and 17% for single, double, and triple disorders, respectively. The primary disorder correct response rate was 89% for double disorders and 94% for triple disorders. The primary and secondary disorder correct response rate was 58% for triple disorders. The data suggest that the microcomputer may be beneficial in the rapid assessment of complex disorders.