Correction of ECG variations caused by body position changes and electrode placement during ST-T monitoring.

BACKGROUND: Electrocardiogram variations (ECG) due to body position changes and electrode placements are common problems of continuous ST-T monitoring. Body position changes may cause QRS and ST-T changes and trigger false alarms. Placement of arm and leg electrodes in a coronary care unit environment is usually near the thorax instead of standard position at the wrists and ankles. This may affect the limb leads and complicate diagnostic interpretation. The purpose of this study was to assess the effects of these sources of ECG variation and to correct for them. Continuous 12-lead ECG recordings were obtained from 160 patients admitted to the coronary care unit. Each patient underwent a body position test (supine, left-lateral, and upright position). Scalar and spatial approaches were investigated for reconstruction of the ECG in supine position. The scalar approach uses linear regression. The spatial approach transforms the ECG into a derived vestorcardiogram. The spatial QRS-loop is then rotated and scaled to match the vector loop in supine position and transformed back to a 12-lead ECG. MATERIALS AND METHODS: To assess the effect of electrode placement, monitoring and standard limb leads were simultaneously recorded in a group of 80 patients. To map the monitoring leads to standard leads, general and patient-specific reconstruction coefficients were derived by linear regression from half of the patients and tested on the other half. Similarity between the reference and reconstructed ECGs was measured by correlation, similarity coefficient [(SC=1-RMS(residual error)/RMS(signal)], and difference in frontal QRS-Axis. RESULTS AND CONCLUSION: Only 14% (23 of 160) of the patients showed marked ECG changes (ST elevations, QRS-axis shifts, T-wave inversions). The scalar method (median correlation > 0.994, SC > 0.902, QRS axis difference 0 degrees) performed better than spatial (median correlation 0.946, SC > 0.792, QRS axis difference 0 degrees). Monitoring leads can be mapped to standard limb leads in good to excellent approximaiton. General reconstruction (median correlation 0.993 and SC 0.764) performed slightly worse than patient-specific reconstruction (median correlation 0.997 and SC 0.908).

Minimal lead sets for reconstruction of 12-lead electrocardiograms.

It may not always be possible to record all precordial leads of the standard 12-lead electrocardiogram (ECG). Especially in monitoring situations, a minimal lead set from which the 12-lead ECG can be reconstructed, would be valuable. This article assesses how well missing precordial leads could be synthesized from the remaining leads of the 12-lead ECG. A total of 2,372 diagnostic 12-lead ECG recordings were obtained from subjects with chest pain suggestive for acute myocardial infarction. Representative average beats were computed from the digital 12-lead ECG recordings with our Modular ECG Analysis System. The recordings were divided into a learning set and a test set. We considered all lead sets with one or more precordial leads removed, but always including limb leads I and II. By using the learning set, general reconstruction coefficients were computed to synthesize the missing precordial leads to each lead set. Performance of the synthesis was assessed by cross correlation between the original and the reconstructed leads. Also, patient-specific reconstruction coefficients were derived for each ECG in the test set and correlations were determined. High correlation coefficients were found with both reconstruction techniques. For different sizes of lead sets, the best patient-specific reconstructions had higher correlation values than the general reconstructions. For example, when 2 precordial leads were excluded, the best patient-specific median correlation was 0.994 compared to 0.963 for the best general reconstruction correlation. General reconstruction allows synthesis of 2 or 3 excluded precordial leads in good approximation. When patient-specific reconstruction can be applied, a minimal lead set including the limb leads and only 2 precordial leads suffices.

Continuous ST-segment monitoring associated with infarct size and left ventricular function in the GUSTO-I trial.

BACKGROUND: The aim of this study was to evaluate whether in patients with myocardial infarction, the intensity and duration of myocardial ischemia as measured by continuous ST monitoring are associated with infarct size and residual left ventricular function. METHODS AND RESULTS: The analyses included patients with myocardial infarction, receiving thrombolytic therapy, who were enrolled in the electrocardiographic substudy of GUSTO-I, monitored by a vector-derived 12-lead electrocardiographic recording system, and in whom either infarct size (defined as cumulative release of alpha-hydroxybutyrate dehydrogenase activity per liter of plasma over a 72-hour period [Q(72)]) or left ventricular ejection fraction (LVEF) was determined. With the use of linear regression analysis, we investigated the association of various ST-trend characteristics with Q(72) (206 patients) and with LVEF (180 patients). A higher area under the ST trend since thrombolysis until 50% ST recovery and a higher area under recurrent ischemic episodes (ST reelevations) were significantly associated with a higher Q(72), whereas only a higher area under recurrent ischemic episodes was significantly associated with a lower LVEF. These associations remained after adjusting for other patient characteristics such as age, sex, infarct location, and time to treatment. CONCLUSIONS: These findings support the physiologic hypothesis that both the intensity and duration of myocardial ischemia (both reflected by the estimated areas under the ST-trend curve) determine myocardial damage and thus are associated with infarct size and ejection fraction in patients with acute myocardial infarction who receive thrombolytic therapy.

Heart rate variability index in congestive heart failure: relation to clinical variables and prognosis.

AIM: To evaluate the clinical and prognostic value of the heart rate variability index in patients with congestive heart failure. METHODS: Sixty-four patients with chronic congestive heart failure and sinus rhythm underwent clinical assessment, 24-h ambulatory electrocardiography and echocardiography. Patients were followed for 6 to 30 months. Cardiac death or heart transplantation constituted the primary end-point of the study. RESULTS: The heart rate variability index was related to left ventricular ejection fraction (r=0.29, P=0.02) and New York Heart Association class (P=0.01). Patients with a restrictive left ventricular filling pattern had a lower heart rate variability index compared to patients with a non-restrictive pattern (26+/-11 vs 33+/-9 units, P=0.01). Patients who died (n=11) or underwent heart transplantation (n=4) had a lower heart rate variability index compared to survivors (21+/-10 vs 33+/-9 units, P<0.0001). In multivariate survival analysis, a reduced heart rate variability index was related to survival independent of parameters of left ventricular function. CONCLUSION: The heart rate variability index provides independent information on clinical status and prognosis in patients with chronic congestive heart failure.

Assessment of the bradycardic and inotropic properties of ST 567 using a new scheme of administration.

In 10 patients undergoing diagnostic cardiac catheterisation a bolus of 15 mg ST 567 was administered intravenously in 1.5 min followed by a 30 min infusion of 7.5 mg. The maximal plasma level was 343 +/- 131 ng ml-1 (mean +/- s.d.) 1 min after bolus injection and stabilised around 179 ng ml-1 thereafter. Heart rate decreased from 71 +/- 10 beats min-1 at baseline to 66 +/- 10 beats min-1 at the end of the bolus injection (-7%). This decrease in heart rate persisted during the whole observation period. Also there was an 8% reduction in peak positive first derivative of LV pressure. Cardiac output measured by thermodilution during atrial pacing decreased from 5.9 +/- 1.1 l min-1 to 5.3 +/- 0.7 l min-1 (P less than 0.02). In 3 patients with the largest decrease in cardiac output, the end diastolic LV pressure at the end of the observation period decreased, which may reflect a decrease in pre-load. Only in 1 patient the decrease in end diastolic LV pressure exceeded twice the standard deviation of the random error component of duplicate measurements. Thus, although normal therapeutic plasma levels were achieved, ST 567 demonstrated negative inotropic properties independent of changes in heart rate with this scheme of administration.

Oxygen consumption and blood gas exchange during controlled and intermittent mandatory ventilation after cardiac surgery.

The purpose of this study was to determine the consequence of intermittent mandatory ventilation (IMV) on gas exchange, cardiac function, and blood oxygenation immediately after cardiopulmonary bypass grafting. The results showed a marked increase in oxygen uptake, cardiac index, and pulmonary artery pressure, and a decrease in mixed venous oxygen saturation of 20 adult patients recovering from surgery. These effects may have been associated with the presence of an endotracheal tube, because 2 h after removal of this tube there were significant decreases in elevated cardiac function and blood oxygenation variables, while mixed venous oxygen saturation increased from 64% to 75% (p less than .001). These results suggest that IMV can dramatically increase oxygen uptake, cardiac index, and pulmonary artery pressure in awake and intubated patients.

A microcomputer based charting system for documentation of circulatory, respiratory and pharmacological data during anesthesia.

A system for the on-line production of anaesthetic records with a microcomputer is described. The requirements of the system are a keyboard, a video display unit and a colour plotter. The system requires no programming expertise from anaesthetists and nurses. The records have improved information display, patient care and reduced time spent in administration effort. Disadvantages are the relatively high cost and requirement of preprocessing of haemodynamic and respiratory parameters.

Haemodynamic and biochemical variables after induction of anaesthesia with fentanyl and nitrous oxide in patients undergoing coronary artery by-pass surgery.

The effects on the haemodynamic and biochemical parameters of three different anaesthetic induction regimes, namely fentanyl (4.1 micrograms.kg-1 or 15 micrograms.kg-1) plus 60 per cent nitrous oxide with oxygen and fentanyl 15 micrograms.kg-1 plus 60 per cent nitrogen with oxygen, were studied in patients undergoing coronary artery surgery. Fentanyl 15 micrograms.kg-1 with nitrous oxide and oxygen produced simultaneous reductions in oxygen uptake, cardiac index and left ventricular stroke work with an unaltered oxygen extraction. Diastolic blood pressure (an index of coronary artery perfusion) was only slightly reduced, and there were no changes in arterial lactate, glucose and free fatty acids. The lower dose of fentanyl (4.1 micrograms.kg-1) with nitrous oxide produced no haemodynamic changes but decreased the oxygen uptake and extraction. The patients receiving fentanyl 15 micrograms.kg-1 with nitrogen and oxygen showed increases in heart rate, blood pressure, cardiac index and left ventricular stroke work, together with a significant fall in oxygen extraction. Moreover, in the patients who received fentanyl 4.1 micrograms.kg-1 with nitrous oxide and oxygen and fentanyl 15 micrograms.kg-1 with nitrogen and oxygen there were significant increases in blood lactate, glucose and free fatty acids, indicating increased sympathetic activity. We conclude that fentanyl 15 micrograms.kg-1, together with 60 per cent nitrous oxide with oxygen provides a satisfactory haemodynamic and biochemical state during induction of anaesthesia in patients with myocardial function prejudiced by coronary artery insufficiency.

Cardiovascular monitoring with special emphasis on mixed venous oxygen measurements.

With the advent of complicated surgical procedures the need for invasive hemodynamic monitoring has taken a prominent place in the management of patients. This has resulted in improved morbidity and mortality in overall patient care. Along with conventional monitoring of heart rate, arterial pressure and central venous pressure, the information about the function of the left heart is essential. This paper describes the usefulness of Swan-Ganz catheter (SG catheter) during intensive care. The purposes of the study is to determine the relationship between mixed venous oxygen saturation measurement, peripheral skin temperature and volume replacement in the immediate postoperative period, as well as the need for prolonged mechanical ventilation in shocked patients.