Biomedical subjects

Roman Trobec

Publications and source records attributed to Roman Trobec.

8 recordsLinked to original sources

PubMed2007

3D heart model for computer simulations in cardiac surgery.

For a satisfactory computer simulation, a model, which imitates a natural situation, is needed. The Human heart is an irregular 3D object and thus difficult to reproduce. Basic data was taken from Visible Human Dataset (VHD), National Library of Medicine. The heart area was cut out of the original cross-sections and different tissues segmented. All the slices also had to be aligned to assure precise overlapping of the structures. A 3D computer heart model with the resolution of 1mm was designed. The heart model was dedicated to simulations of heat transfer during heart surgery however, it is applicable also to other medical simulations.

Cardiac Surgical Procedures↗

PubMed2006

Assessment of cardiac autonomic regulation and ventricular repolarization after off-pump coronary artery bypass grafting.

BACKGROUND: Altered autonomic regulation precipitates cardiac arrhythmias and increases the risk of sudden cardiac death. This risk is further increased by changes in ventricular repolarization. Autonomic regulation is deranged in patients after myocardial on-pump revascularization. We aimed to clarify how off-pump coronary artery bypass grafting (CABG) affects postoperative cardiac autonomic regulation and ventricular repolarization within 4 weeks after CABG. METHODS: Forty-two patients (mean age, 61.9 +/- 9.3 years; mean EURO score 2.6 +/- 1.9) were electively admitted for off-pump CABG. The electrocardiographic and respiratory waveform recordings were performed in the afternoon in the supine position for 10 minutes. Autonomic modulation was assessed using heart rate variability analysis. Power spectra were computed from 5-minute stable RR intervals using Fourier Transform analysis. Total power of spectra was defined in the range of 0.01 to 0.40 Hz, high-frequency power within 0.15 to 0.40 Hz, and low-frequency power within 0.04 to 0.15 Hz. Normalized power was defined as a ratio of power in each band/total power. The high- and low-frequency power as well as their normalized values indicated cardiac vagal and sympathetic modulation, respectively. Ventricular repolarization was assessed using QT interval, QT interval variability, and QT-RR interdependence analysis. QT intervals were determined from the beginning of the 5-minute segments. QT interval variability was evaluated by a T-wave template-matching algorithm. Pearson correlation between length of RR and QT interval was applied to study QT-RR characteristics. The results were tested for significance using the Fisher exact test, nonpaired t test, and analysis of variance; a P <.05 was considered significant. RESULTS: The frequency of arrhythmic events and heart rate increased from the fourth to the seventh postoperative day and returned to preoperative levels 4 weeks after CABG. Heart rate variability measures indicating autonomic modulation remained depressed even 4 weeks after the procedure. QT variability index increased from -1.2 +/- 0.5 to -0.8 +/- 0.4 on the fourth day after the operation (P <.05) and returned to -1.0 +/- 0.5 4 weeks after CABG (P = not significant). QT-RR correlation decreased from 0.41 to 0.23 (P <.05) and remained significantly impaired as long as 4 weeks after CABG. CONCLUSIONS: Observed faster heart rates until 1 week after off-pump CABG imply excessive adrenergic activation, which is comparable to on-pump CABG procedure rates. The results indicate profound autonomic derangement and loss of rate-dependent regulation after off-pump CABG even 4 weeks after operation. Restituted repolarization as assessed by QT variability index 4 weeks postoperatively corresponded with decreased frequency of rhythm disturbances 4 weeks after CABG. The loss of coupling between QT and RR intervals shows increased electrical instability postoperatively, which may serve as an additional promoter for postoperative arrhythmias, especially at higher heart rates.

Aged↗

PubMed2004

Sympathetic reinnervation after heart transplantation, assessed by iodine-123 metaiodobenzylguanidine imaging, and heart rate variability.

OBJECTIVE: Complete allograft denervation occurs during heart transplantation. Partial ventricular sympathetic reinnervation may develop one year or later after transplantation and can be measured with iodine-123-meta-iodobenziylguanidine (MIBG) uptake. Aim of this study was to assess sinus node sympathetic reinnervation measured with heart rate variability and ventricular sympathetic reinnervation evaluated with MIBG. METHODS: Twelve patients and 14 healthy controls were included. In patients, MIBG scintigraphy with early and late imaging was performed. Heart to mediastinum ratio (HMR) was calculated and patients were divided in groups with (HMR>1.3) and without left ventricular reinnervation (HMR<1.3). Bipolar ECG with high sampling rate and resolution was recorded over 8.5 min in supine position and in upright position after 10 min interval. R-R intervals in time domain and heart rate variability in frequency domain through spectral power analysis of R-R intervals were analysed to evaluate sinus node reinnervation. Spectral power in low frequency range (0.04-0.15 Hz) above 4.5 ms(2) was considered as sinus node sympathetic reinnervation. RESULTS: Six (50%) patients had evidence of left ventricular sympathetic reinnervation on scintigraphy. Sinus node sympathetic reinnervation based on heart rate variability was detected in 6 (50%) patients in supine, and in 4 (33%) patients in upright body position. Four patients groups were discerned: (1) with ventricular and sinus node sympathetic reinnervation, (2) with sinus node sympathetic reinnervation, (3) with ventricular sympathetic reinnervation and (4) without atrial or ventricular sympathetic reinnervation. Ventricular reinnervation process was time dependent and sinus node reinnervation was not. CONCLUSIONS: Simultaneous ventricular sympathetic reinnervation assessed by MIBG and sinus node sympathetic reinnervation assessed by heart rate variability in supine as in upright position were detected only in two patients (17%). The results of our study show that eventual sinus node sympathetic reinnervation and left ventricular sympathetic reinnervation do not occur simultaneously.

3-Iodobenzylguanidine↗

PubMed2003

Topical cardiac cooling--computer simulation of myocardial temperature changes.

Topical cardiac cooling (TC) is often used in cardiac surgery. We used a computer simulation to study temperature changes in the heart, especially in the right ventricular wall. A three-dimensional computer heart model, derived from Visible Human Data set, National Library of Medicine was used. The model is made from cubes, with spatial resolution of 1mm. Explicit Finite Different method and temperature diffusion equation were used to calculate new temperatures. Three different simulations were performed and simulated temperatures were drawn on a cross-section of heart model in different colors. The results show that areas not immersed into TC solution are less protected against ischemia. It is important not to rely solely on topical cooling but use appropriate method of myocardial protection technique.

Anatomy, Cross-Sectional↗

PubMed2003

Computer analysis of multichannel ECG.

Multichannel electrocardiography (MECG) is an extension of the conventional electrocardiography that is aimed at refining the non-invasive characterisation of cardiac activity. Body surface mapping is a graphical presentation of cardiac activity as measured from the body surface. Body surface maps can show the distribution of the potential at a selected moment in time or over a specified time interval. A new family of maps, based on the characteristics derived from the complete analysed beat, is described. Some new computer supported methods, which are able to calculate automatically different temporal maps, are proposed. MECG measurements can be seen in this context as a powerful research and clinical tool for improving the resolution of cardiac measurements.

Body Surface Potential Mapping↗

PubMed2003

Breathing rates and heart rate spectrograms regarding body position in normal subjects.

The right lateral body position has been proposed as an effective vagal enhancer. However, the possibility of breathing affecting heart rate power spectra in different body positions has not been assessed. The level of vagal modulation in various body positions in normal subjects was estimated by calculating heart rate power spectra. The results suggest that the levels of vagal modulation do not necessarily reflect a change due to assuming different body position, but might be the consequence of changed breathing patterns. Before adopting the right lateral body position as vagal enhancing, the contribution of varying breathing pattern should be eliminated.

Adult↗

PubMed2002

Body surface mapping after partial left ventriculotomy.

OBJECTIVE: To demonstrate cardiac electrophysiological changes in patients where partial left ventriculotomy was performed and multichannel electrocardiographical measurements and body surface potential mapping were used. METHODS: Body surface ECG signals were recorded during sinus rhythm for one minute. Six patients were operated on with partial left ventriculotomy were monitored. All patients had normal coronary angiography data. The data were acquired prior to the partial left ventriculotomy, and on the second, third, fourth, and fifth postoperative day using 32-body surface leads. The recorded data were analysed by determining ST-40 and QRS integral maps. The analysis was done on a set of selected beats during the sinus rhythm and on the averaged beats. RESULTS: Before the operation, ST-40 maps typically showed an area of strong positive potentials (elevation) over the anterior aspect of the torso and a region of strong negative potentials (depression) over the lateral, and posterior aspects of the torso. After the operation, the ST elevation over the anterior, lateral and posterior aspects of the torso was reduced. An area of marked positive potentials remained in the precordial area (overlying the excised area of the heart), even during the postoperative monitoring interval (day two through day five). We also noticed that the amplitude of cardiac signals decreased by approximately 30% after the partial left ventriculotomy. Qualitative map changes were substantiated by statistical parameters. CONCLUSIONS: Results of our study demonstrate that noninvasive acquisition of body-surface electrocardiographs may detect changes in the cardiac activity of patients undergoing partial left ventriculotomy. This finding suggests that body surface mapping may also be useful in assessing the arrhythmia vulnerability.

Adult↗

PubMedDate not supplied

Biomedical simulation of heat transfer in a human heart.

Theory and practical experiences from numerical simulations of heat transfer in the field of medicine are presented in this paper. The cooling of a human heart during surgery was taken as an illustrative example. All phases of the simulation process are described starting with the construction of an irregularly shaped 3-dimensional model. The mathematical model is based on diffusion and Navier-Stokes equations. The system of partial differential equations is solved by finite difference approximation using an explicit time-stepping scheme to obtain the time evolution of the solution for the complete simulated interval, which is typically 1 h. A typical domain is composed of several million voxels; therefore, the program was parallelized to speed up the simulation. A speed-up of 8.2 was obtained on 16 processors in a Linux cluster.

Algorithms↗