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Biomedical subjects

S B Olsson

Publications and source records attributed to S B Olsson.

At least 55 records · Page 3Linked to original sources
PubMed1998

Autonomic modulation of the atrial cycle length by the head up tilt test: non-invasive evaluation in patients with chronic atrial fibrillation.

OBJECTIVE: To determine the effects of upright posture compared with supine position on the dominant atrial cycle length (DACL) in patients with chronic atrial fibrillation. DESIGN: The power/frequency spectrum of QRST suppressed lead V1 ECG was studied in 14 patients in the supine position and during the head up tilt table test. The DACL changes were compared with changes in heart rate and blood pressure. RESULTS: Compared with the supine position, the upright position reduced the DACL from 160 to 150 ms (p < 0.01). The DACL was increased after returning to the supine position from the upright position, from 147 to 154 ms (p < 0.01). Heart rate increased from 91 beats/min in the supine position to 106 in the upright position (p < 0.01). There was a decrease in heart rate from 109 beats/min in the upright position to 93 after returning to the supine position (p < 0.01). No significant changes were seen in systolic or diastolic blood pressure. There were indications of an inverse relation between DACL and heart rate when comparing the supine position before and after tilt with the upright position (p < 0.001). CONCLUSIONS: The sympathetic stimulation and vagal withdrawal induced by rising to upright body position are associated with a decrease in DACL during chronic atrial fibrillation. Thus a reflex increase in sympathetic discharge after induction of atrial fibrillation could favour the persistence of the arrhythmia.

Aged↗
PubMed1997

Pregnancy and heart disease: a review.

About one per cent of all pregnancies are affected by maternal heart disease, which may have significant influence on the maternal and foetal outcome. In this context rheumatic heart disease is declining and congenital heart disease is becoming the dominant category. Our experience of pregnancy in the new groups of patients created by paediatric heart surgery is scant and a continuous update is required.

Anticoagulants↗
PubMed1997

Epicardial right atrial free wall mapping in chronic atrial fibrillation. Documentation of repetitive activation with a focal spread--a hitherto unrecognised phenomenon in man.

BACKGROUND: Previous studies have shown that atrial fibrillation of recent onset in man is based on a varying number of simultaneously present activation waves reentering either themselves or each other. In the present study, right atrial activation during chronic atrial fibrillation in man was studied. METHODS AND RESULTS: In 16 patients with chronic atrial fibrillation multiple epicardial recordings of 8 s each were made at the right atrial posterior free wall and at the appendage using a 20 x 35 mm electrode array with 56 bipolar measurement points. The preferable activation pattern of each recording and the propagation direction, cycle length and conduction velocity of individual activation waves within each recording were determined. Activation was characterized by unorganised activation with several simultaneously present activation waves: inconsistent preferable activation pattern (n = 5), predominantly organised activation with either frequent episodes of uniform activation: consistent preferable activation pattern (n = 7) or frequent episodes of activation with focal spread; focal preferable activation pattern (n = 4). Random re-entry was frequently documented in recordings with the inconsistent preferable activation pattern and less frequently in recordings with the consistent and focal preferable activation pattern. Complete re-entry circuits were rarely documented. The median fibrillation cycle length was 146, 159 (P < 0.05) and 165 ms (not significant) and the mean conduction velocity during uniform activation was 64, 67 and 83 cm. s-1 (not significant) in recordings with the inconsistent, consistent and focal preferable activation pattern, respectively. CONCLUSIONS: During chronic atrial fibrillation in man, right atrial free wall activation ranges from disorganised activation with multiple co-existing activation waves to predominantly organised activation characterized by either uniform activation consistent with the presence of large re-entry circuits or repetitive activation of unknown mechanism and focal spread.

Aged↗
PubMed1997

Signed value of monophasic action potential duration difference. A useful measure in evaluation of dispersion of repolarization in patients with ventricular arrhythmias.

AIMS: To evaluate the usefulness of the signed value of monophasic action potential duration difference in analysing the cause of dispersion of ventricular repolarization. METHODS AND RESULTS: Monophasic action potentials were simultaneously recorded from the right ventricular apex and outflow tract during programmed stimulation in 36 patients with ventricular arrhythmias. The time difference between the ends of repolarization on the two monophasic action potentials was used as a measure of the dispersion of ventricular repolarization, and the signed value of the monophasic action potential duration difference was used to specify the contributions of the activation time difference and the monophasic action potential duration difference to the dispersion of ventricular repolarization. During right ventricular pacing, single and double programmed stimulation and at the induction of ventricular arrhythmias, the dispersion of ventricular repolarization and the signed value of monophasic action potential duration difference were markedly greater in the 11 patients with polymorphic ventricular tachycardia/ventricular fibrillation induced than in the 13 patients with monomorphic ventricular tachycardia induced, and in the 10 patients with clinical polymorphic ventricular tachycardia/ventricular fibrillation/cardiac arrest than in the 12 patients with sustained monomorphic ventricular tachycardia. This disclosed that the increased dispersion of ventricular repolarization was caused by increases in both the activation time difference and the monophasic action potential duration difference in the former, but mainly by an increased activation time difference in the latter groups. CONCLUSION: The signed value of monophasic action potential duration difference can specify whether an increased dispersion of ventricular repolarization is caused by inhomogeneous repolarization, inhomogeneous conduction or both, and thereby it is useful in study of the mechanism of ventricular arrhythmias.

Action Potentials↗
PubMed1996

Dispersion of repolarization following double and triple programmed stimulation. A clinical study using the monophasic action potential recording technique.

To study the dispersion of ventricular repolarization following double and triple programmed stimulation and its correlation with the inducibility of ventricular arrhythmias, monophasic action potentials were simultaneously recorded from the right ventricular apex and outflow tract during programmed stimulation in 12 patients with ventricular arrhythmias and a normal QT interval. The time difference between the ends of the two monophasic action potentials were used as a measure of the dispersion of ventricular repolarization, which consists of the activation time difference and the monophasic action potential duration difference. During double and triple programmed stimulation, the dispersion of ventricular repolarization increased significantly with the shortening of the coupling interval but decreased slightly with the shortening of the preceding interval. The induction of the ventricular arrhythmias in these patients was invariably associated with a marked increase in the dispersion of ventricular repolarization. The maximal dispersion of ventricular repolarization was significantly larger in the seven patients with polymorphic ventricular tachycardia and/or ventricular flutter/fibrillation induced than in the four patients with monomorphic ventricular tachycardia induced. Analysis of the two components of the dispersion of ventricular repolarization revealed that the increased dispersion of ventricular repolarization was mainly caused by an increase in the activation time difference in the monomorphic ventricular tachycardia subgroup, and by increases in both the activation time difference and monophasic action potential duration difference in the polymorphic ventricular tachycardia/fibrillation subgroup. These findings suggest that increased dispersion of ventricular repolarization is one of the underlying mechanisms accounting for the myocardial vulnerability to ventricular arrhythmias and that repolarization disturbance is important for the genesis of polymorphic ventricular tachycardia/fibrillation.

Action Potentials↗
PubMed1996

Potential cardioembolic sources in an elderly population without stroke. A transthoracic and transoesophageal echocardiographic study in randomly selected volunteers.

Transoesophageal echocardiography renders a better image than transthoracic echocardiography of cardiac changes especially at the atrial level, and of atherosclerotic changes in the aorta. Although several studies on stroke patients have included transthoracic and transoesophageal echocardiography, the relevance of the reported findings remains unclear because of limited information on the prevalence of cardiac changes related to cardioembolism in a control population without stroke. In order to define a non-hospitalized group of volunteers without previous stroke or transient ischaemic attack, we randomly selected a group of 68 volunteers (mean age 65.4 years). These volunteers were divided into two groups: the elderly group, 65 years or older (n = 38) and the younger group, younger than 65 years (n = 30). The subjects underwent transthoracic and transoesophageal echocardiography, sonography of the carotid arteries, and magnetic resonance imaging of the brain. The prevalences of atrial septal aneurysm, patent foramen ovale, mitral annulus calcification, and protruding plaque in the aorta were investigated. We found atrial septal aneurysm in 13%, patent foramen ovale in 22%, protruding plaque in the aorta in 7%, and mitral annular calcification in 22% of the 68 subjects. No significant differences were found between the two age groups with the exception of mitral annular calcification, which was seen more often in the older group (P < 0.001). Total cardiac changes related to thromboembolism (including three cases with atrial fibrillation in the older group and other less common cardiac embolic sources) were more common in the older than in the younger group (23/38 vs 9/30; P < 0.05). If mitral annular calcification was excluded, no difference was found between the elderly and the younger group, 14/38 vs 8/30; ns. Even when subjects with a history of heart disease or a pathological ECG were omitted, no differences between the two age groups were found. The causal relationship between a possible embolic source and a clinical embolic event remains unsettled. The high prevalence of cardiac changes in a control population has to be considered when evaluating the significance of similar findings in patients with stroke.

Adult↗
PubMed1996

A new method for analysis of atrial activation during chronic atrial fibrillation in man.

To further clarify the mechanisms maintaining chronic atrial fibrillation (CAF), a method identifying preferable activation patterns of the atria during fibrillation, by time averaging of multiple discrete excitation vectors, was developed. Repeated recordings, each of 56 atrial bipolar electrograms simultaneously acquired during 8 s, were made at multiple sites in the right atrial free wall and the left atrial appendage in 16 patients with CAF using a 2.17 x 3.54 cm electrode array. The local activation times (LAT's) in each recording were estimated as the median activation time at the respective measurement point. By calculating the time difference between the LAT's at adjacent measurement points in two spatial dimensions, a direction vector was created for each activation wave passing each set of measurement points, a total of 42 sets. By time averaging of the individual direction vectors (typically n = 55) at each set of measurement points, preferable activation patterns were determined. Three types of activation patterns were found: 1) inconsistent activation (n = 5), 2) consistent activation with preferential propagation directions (n = 7) and 3) consistent activation with impulses originating from a localizable site within the recording area (n = 4). All activation patterns were reproducible and the two latter patterns were proven significant using statistical tests. We conclude that this new method is useful in further clarification of the mechanisms involved in the maintenance of atrial fibrillation.

Aged↗
PubMed1996

Clinical application of a microcomputer system for analysis of monophasic action potentials.

UNLABELLED: Computerized analysis of monophasic action potentials (MAPs) has rarely been reported in clinical setting. We developed a computer system featuring on-line acquisition and user-monitored automatic measurement of multichannel MAPs with the capability of manual corrections. This system has been used in 34 patients in whom two-channel MAPs and 1-lead ECG were digitized during sinus rhythm, pacing, and programmed stimulation (PS). In total, 41, 413 MAPs in 212 data files were measured. The correct determination rate was 100% for MAP onset and plateau, 99.78% (95.76% during PS) for MAP baseline, and 99.96% (54.29% during PS) for QRS onset. The comparison between the computerized and manual measurements in 292 MAPs showed that the former highly agreed with the latter, with the limits of agreement, defined as mean difference +/- 2 SD, being from -4.8-4.9 ms for activation time and from -4.1-6.0 ms for MAP duration measurements. Using this system, two-channel MAPs of more than 300 consecutive beats can be measured in a few minutes, which made it possible to determine the steady state of MAP duration individually, and evaluate the MAP changes during intervention in detail. The clinical routine procedure for testing the effective refractory period and several new MAP parameters were also evaluated using this system. CONCLUSION: The MAP measurement using this computer system is reliable, rapid and accurate; it can therefore replace the manual method and provide more useful information for clinical research.

Action Potentials↗
PubMed1996

Atrial fibrillation--new aspects on mechanism and treatment.

During recent years, the exploration of different aspects of atrial fibrillation (AF) has become increasingly interesting. Thus, knowledge about basic underlying mechanisms, consequences and different modes of treatment has rapidly expanded. At a meeting in Lund, Sweden, in 1993, scientists within different fields of AF research gathered for the exchange of information. This paper is a short summary of some topics discussed at the Lund meeting and some suggestions as to how further research in this field may help to improve our understanding of this arrhythmia and the treatment of patients suffering from it. Underlying pathoelectrophysiological mechanisms in AF have been explored in experimental models in animals and by direct recordings of different atrial myocardial electrophysiological variables both in the catheter laboratory and during open heart surgery in man. Some findings illustrate possible generalized atrial myocardial mechanisms, whilst other findings clearly indicate the possibility of localized pathoelectrophysiological mechanisms. The generally accepted hypothesis that AF is perpetuated by multiple re-entry mechanisms is, thus, both verified and modified by recent studies. In addition to subjective symptoms and well identified thromboembolic consequences, accumulating evidence tells us that AF may precipitate a myocardial dysfunction which may be misinterpreted as an underlying factor initiating the arrhythmia. Today's treatment of AF includes several newer antiarrhythmic drugs, different ablation techniques, the application of different electrical devices as well as different surgical methods. New, improved and simplified methods are expected. Atrial fibrillation is the single most important supraventricular arrhythmia needing substantial further exploration of mechanisms, consequences and treatment. The Lund symposium contributed to this process by defining the state of knowledge in 1993 and outlining the need for the years to come.

Animals↗
PubMed1995

Pro- and antifibrinolytic effects of ultrasound on streptokinase-induced thrombolysis.

We have earlier documented that ultrasound can enhance the fibrinolytic effect of streptokinase and shorten the reperfusion time under experimental conditions. The present study concerns the magnitude of the effect in relation to ultrasound frequency, intensity and exposure time. The effect of ultrasound on the structural properties of the fibrin network was evaluated by scanning electron microscopy. Whole blood clots were created and exposed to streptokinase (5000 U/mL). In paired experiments, one clot was also exposed to pulsed ultrasound. Lysis is expressed as the percentage decrease in clot weight. Clot lysis was equally affected by ultrasound in the range of 0.5 to 2.3 MHz. Below 0.5 W/cm2 no enhancing effect was observed, while intensities between 0.5 and 1.5 W/cm2 resulted in a significant enhancement of clot lysis. Intensities above 4 W/cm2 inhibited the fibrinolytic effect of streptokinase but not of rt-PA. From scanning electron microscopy there was no evidence that ultrasound disrupted the clot surface or damaged the fibrin structure.

Analysis of Variance↗
PubMed1995

The dispersion of repolarization in patients with ventricular tachycardia. A study using simultaneous monophasic action potential recordings from two sites in the right ventricle.

The role of increased dispersion of repolarization in the genesis of torsade de pointes and ventricular fibrillation has been well recognized generally, but not in the genesis of monomorphic ventricular tachycardia (VT). Monophasic action potentials (MAP) were therefore recorded simultaneously from the right ventricular (RV) apex (RVA) and outflow tract (RVOT) during sinus rhythm, RV pacing and programmed extra stimulation (PES) in 24 patients with VT. The activation time (AT), MAP duration at 90% repolarization (MAPd), and repolarization time (RT) were measured and their dispersions, defined as the differences in these parameters between RVA and RVOT, were calculated. During sinus rhythm and RV pacing, the dispersions of AT, MAPd and RT (dispersions) were significantly larger in the 17 patients with a VT induced than in those without. During PES, the dispersions were further augmented in the S2 beats in the seven patients with a sustained VT induced, the maximal dispersion of RT being 85 +/- 22 ms. Both the dispersion of AT and that of MAPd contributed to the dispersion of RT. In both of our two patients with a sustained VT induced during MAP recording, a marked increase in dispersions of RT (140 and 190 ms, respectively) was observed immediately before the initiation of the VT. A link between the dispersions and the inducibility of a monomorphic VT was found in our patients, which suggests that the increased dispersions play an important role in the genesis of a monomorphic VT.

Action Potentials↗
PubMed1994

Enhancement of thrombolysis by ultrasound.

Drug-induced early reperfusion in acute myocardial infarction reduces myocardial damage and decreases mortality. A further beneficial effect may be achieved if the time from start of thrombolytic treatment to reperfusion, on average 45 min, can be shortened. With this purpose in mind, we have analysed the effect of ultrasound on the reperfusion time in an experimental model in vitro. A cylindrical fibrin thrombus with a 2 mm diameter and a 20 microL volume was made by thrombin activation of a pure 0.5% fibrinogen solution in a soft silicone tube. The tube was placed in a low pressure perfusion system and maintained at 37 degrees C. The thrombi were then exposed to hydrostatic loading with a streptokinase concentration of 5000 units/mL. Reperfusion times (RT) were measured from time of Streptokinase exposure to fluid passage, identified by the photoelectric technique. RT increased significantly with increasing thrombus age (r = 0.92, p < 0.05) and was 34-45 min (95% confidence limits) at a thrombus age of 1 h and 102-122 min at a thrombus age of 2 h. RT was unaffected by temperatures between 33 and 45 degrees C but increased with higher temperatures. All investigations of ultrasound effects were performed with 1 h old thrombi and at 37 degrees C. RT decreased by 49% (p < 0.01) as an effect of exposure to 1 MHz ultrasound at 1 W/cm2 SATA. Intermittent ultrasound exposure for 10 microseconds/ms with the same intensity and frequency shortened RT by 54% (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Circulation↗
PubMed1994

Monophasic action potentials: concepts to practical applications.

Monophasic action potential (MAP) recordings reproduce the repolarization time course of intracellular action potentials with high accuracy and provide precise information on the local activation time. With the advantage of in vivo application and the development of the safer and simpler contact catheter technique, MAP recording has become the method of choice for evaluating myocardial repolarization changes. This review aims to provide information on practical application of MAP recording in the clinical setting. MAPs can easily be recorded from the endocardium with the contact catheter technique in the electrophysiology laboratory and from the epicardium with electrode probes during open heart surgery. The technical aspects are described in detail. The rate dependence of myocardial excitability and repolarization and the effect of antiarrhythmic drugs on MAP duration and effective refractory period are thoroughly reviewed. The use of MAPs in detecting myocardial ischemia, in studying early afterdepolarization and triggered arrhythmias, in measuring dispersion of repolarization, in identifying intracardiac conduction and the development of the T wave, and in verifying the arrhythmogenic effect of mechanoelectric feedback are presented. Computerized automatic analysis of MAPs and the limitations of the MAP technique are also discussed.

Action Potentials↗
PubMed1993

Arrhythmia during extracorporeal shock wave lithotripsy.

A prospective study of arrhythmia during extracorporeal shock wave lithotripsy (ESWL) was performed in 50 patients, using an EDAP LT01 piezoelectric lithotriptor. The 12-lead standard ECG was recorded continuously for 10 min before and during treatment. One or more atrial and/or ventricular ectopic beats occurred during ESWL in 15 cases (30%). The occurrence of arrhythmia was similar during right-sided and left-sided treatment. One patient developed multifocal ventricular premature beats and ventricular bigeminy; another had cardiac arrest for 13.5 s. It was found that various irregularities of the heart rhythm can be caused even by treatment with a lithotriptor using piezoelectric energy to create the shock wave. No evidence was found, however, that the shock wave itself rather than vagal activation and the action of sedo-analgesia was the cause of the arrhythmia. For patients with severe underlying heart disease and a history of complex arrhythmia, we suggest that the ECG be monitored during treatment. In other cases, we have found continuous monitoring of oxygen saturation and pulse rate with a pulse oximeter to be perfectly reliable for raising the alarm when depression of respiration and vaso-vagal reactions occur.

Adult↗
PubMed1992

Effects of diltiazem, propranolol, and their combination in the control of atrial fibrillation.

The effect of the combined treatment with propranolol 20 mg tid and diltiazem 60 mg tid in patients with chronic atrial fibrillation treated with digoxin was evaluated. Thirteen patients entered a double-blind, three-phase crossover study. Heart rate was significantly reduced during rest and at maximal exercise (p less than 0.05) during combined treatment compared with treatment with any single drug. No significant changes in maximal work load, exercise time, systolic blood pressure at maximal work load, or subjective sensation of well-being could be demonstrated during combined drug treatment. The RR distribution pattern was unaffected by the addition of propranolol, diltiazem, or their combination to the chronic digoxin treatment. It is concluded that the combination of diltiazem and propranolol has no advantages over any of these drugs singly, in the moderation of heart rate in patients with atrial fibrillation even combined with basic digitalis treatment, and that the intrinsic AV nodal function is unaffected by these drugs or their combination.

Atrial Fibrillation↗