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.

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.