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Biomedical subjects

L Sörnmo

Publications and source records attributed to L Sörnmo.

7 recordsLinked to original sources
PubMed1992

Reconstruction of the electrocardiogram during heart surgery.

Electrocardiograms (ECG) recorded during arrhythmia surgery are used for identification of arrhythmias of different morphology. However, the interpretation of an intraoperative ECG is difficult because some leads cannot be recorded and the signals of the remaining leads often differ from those of a preoperative recording because of the sternotomy. Therefore, a method for reconstruction of a complete intraoperative ECG, which resembles a preoperatively recorded ECG, was studied in 24 patients undergoing heart surgery. The reconstruction method involves calculating coefficients for a transformation matrix, using a preoperative ECG recording and a first intraoperative ECG recording. Once this matrix has been established, further intraoperative recordings can be transformed into an ECG which strongly resembles a preoperative ECG. The correlation between reconstructed intraoperative leads and the corresponding preoperative leads was high in the leads Vx and Vy (median correlation coefficient 0.98 and 0.97) and slightly smaller in lead Vz (0.94). Further studies will prove if the method can be useful in arrhythmia surgery.

Aged↗
PubMed1990

ST changes in relation to heart rate during bicycle exercise in patients with coronary artery disease.

Exercise test on cycle ergometer and coronary angiography were performed on 190 patients with chest pain. Volunteers with a normal thallium scintigraphy (n = 47) served as controls. The load started at 20 W and increased at a rate of 10 W min-1 until exhaustion or symptoms. Conventional 12-lead ECGs were recorded by means of computer before, during and after exercise. Minimum ST amplitude 60 ms after the STJ point (ST60) at end of work with a cut-off level of -1.10 mm had a sensitivity of 69% (52/75) and a specificity of 89% (37/42) when individuals with a normal resting ECG were considered. ST80 and sum of ST60 in left ventricular leads had slightly lower values of sensitivity and specificity. Changes in ST60 during exercise discriminated less well between the groups. Final heart rate during exercise (less than 148 min-1) had a sensitivity of 88% (53/60) and a specificity of 89% (42/47). The change in heart rate during exercise (less than 66 min-1) had a sensitivity of 50/60 (only patients without beta-blockers were considered). The best discrimination was obtained by defining a test score (TS) according to the linear equation TS = 2.95-0.23 x HRE-0.301 X ST60 where a positive value indicates a positive test and a negative value a negative test. Sensitivity and specificity were 21/23 (91%) and 40/42 (95%), respectively. The test score was also calculated in those patients having significant coronary disease and an abnormal resting ECG (no bundle branch block, no beta-blockers) and this yielded a sensitivity of 30/34.

Adult↗
PubMed1989

An accurate exercise lead system for bicycle ergometer tests.

In order to minimize muscle noise in the exercise electrocardiogram, Mason and Likar proposed a new lead system where the limb electrodes are instead placed on the trunk. The Mason-Likar system is widely used for both the resting ECG before exercise and recordings during exercise. Several studies have, however, reported great differences between this lead system and the standard lead system. This study shows greater R wave amplitudes in leads II, aVF and III, smaller R wave amplitudes in leads aVL and I and thus a vertical shift of the frontal plane QRS axis for the Mason-Likar system compared with the standard system. For many years another lead system for exercise tests with the bicycle ergometer has been used in our laboratory. The limb electrodes are placed at the proximal part of the arms and the left iliac crest. This lead system yields ECG signals with a low level of muscle noise. The differences between this lead system and the standard ECG are much less pronounced than the differences between the Mason-Likar ECG and standard ECG. We propose our lead system for exercise tests with the bicycle ergometer.

Ankle↗
PubMed1987

A model-based approach to QRS delineation.

QRS delineation is considered to be a problem of finding changes in the spectral behavior of an ECG. Based on statistical models for the "low-frequency" and "high-frequency" segments of the ECG, the points for QRS onset and end are obtained from a maximum-likelihood procedure. This procedure is based on the properties of the prediction errors obtained from two different Kalman filters. The accuracy of the delineation scheme is studied on a QRS complex material in terms of agreement with manually obtained delineations. The material was independently delineated by three different readers. The sensitivity to noise is studied by adding white noise to the QRS complexes. The performance is compared to those of envelope-based delineation and template waveform delineation.

Electrocardiography↗