Nos últimos 15 anos, o uso do propofol vem se popularizando na prática clínica como anestésico intravenoso para indução e manutenção da anestesia em cães e gatos. O objetivo deste estudo foi avaliar os efeitos do propofol na pressão arterial, freqüência e ritmo cardíacos, quando empregado na indução e na manutenção anestésica de cães, verificar a correlação entre os valores de freqüência cardíaca e pressão arterial média, obtidos durante a indução e a manutenção anestésica e avaliar a incidência de efeitos colaterais deste fármaco. Foram utilizados 53 cães, 15 machos e 38 fêmeas, clinicamente sadios, com idades entre 1 e 12 anos, peso entre 2 e 44 kg, de diferentes raças, categoria de risco ASA 1 ? 2. Após avaliação clinica, foi administrada a medicação pré-anestésica (T0) constituída de acepromazina (0,05mg/kg) e meperidina (3mg/kg) pela via intramuscular. A indução da anestesia foi realizada em dois momentos, no primeiro momento infundiu-se metade da dose de propofol calculada (T1), no segundo momento procedeu-se o término da administração da dose total de indução da anestesia (T2), o terceiro momento correspondeu a intubação orotraqueal (T3). Durante a manutenção da anestesia, avaliou-se os momentos após 5 minutos de manutenção (T4), 10 minutos (T5) e 20 minutos (T6), onde o grupo 1 recebeu o agente inalatório isofluorano em O2 a 100% e o grupo 2 infusão contínua de propofol na dose de 0,6mg/kg/min e O2 a 100%, ambos os grupos permanecendo em plano anestésico adequado. Pode-se observar que a freqüência cardíaca foi, em média, superior durante o período de indução anestésica e a pressão arterial média foi, em média inferior, porém, clinicamente, a magnitude destas alterações pode ser considerada de pouca importância clínica. Não existiu correlação estatisticamente significante entre a queda da pressão arterial média e o aumento da freqüência cardíaca em nenhum dos tempos analisados, o que leva a crer que o aumento da freqüência cardíaca se deve provavelmente à diminuição da atividade parassimpática neural cardíaca e prevalência da atividade simpática cardíaca, e a diminuição da pressão arterial encontrada pode ser secundária à diminuição da atividade simpática periferia. A avaliar o ritmo cardíaco notou-se diminuição da incidência de bradiarritmias e arritmia sinusal e um aumento do ritmo sinusal, provavelmente pela diminuição da atividade parassinpática cardíaca. Tais observações sustentam a hipótese de que o propofol pode agir diferentemente na atividade simpática periférica e cardíaca também nos cães. Pode-se ainda levantar a hipótese de que a atividade barorreflexa também pode estar diminuída nos cães já que não houve correlação significante entre a diminuição da pressão arterial e o aumento subseqüente da freqüência cardíaca. Durante a manutenção da anestesia houve uma queda da pressão arterial, sem importância clinica e não houve alteração significante em relação a freqüência cardíaca. Foi possível observar excitação em apenas dois animais no momento T1 e um animal em T2. Apnéia foi observada em apenas oito animais (15,1%) sete no momento T3. Outros trabalhos utilizando-se medidas da atividade barorreceptora, análise espectral da variabilidade da freqüência cardíaca, neuromicrografia ou até mesmo medida do clearence de norepinefrina para melhor avaliação da atividade simpática de cães durante a anestesia ainda devem ser realizados para comprovação destas hipóteses fortemente sugestivas pelos dados encontrados neste estudo. O propofol demonstrou ser um fármaco seguro quando empregado na indução e na manutenção da anestesia em cães, não causando alterações cardiovasculares clinicamente importantes. / In the last 15 years, using propofol has being popular in the practical clinic as intravenous anesthetic for induction and maintenance of the anesthesia in dogs and cats. The aim of this study was to evaluate the effect of propofol in arterial pressure, cardiac frequency and rhythm, when used in the induction and in the anesthetical maintenance of dogs, to verify the correlation between values of cardiac frequency and average arterial pressure, taken during the induction and the anesthetical maintenance and to evaluate the incidence of side effects of this drug. Had been used 53 dogs, 15 males and 38 females, clinically healthy, with ages between 1 and 12 years, weight between 2 and 44 kg, from different breeds, ASA classification 1 - 2. After clinical evaluation, the anesthetical drug was administered (T0) consisting of acepromazine (0,05mg/kg) and meperidine (3mg/kg) through intramuscular injection. The induction of the anesthesia was carried through at two moments: at the first moment was administered half of the dose of propofol calculated (T1), at second moment was proceeded the ending of the administration of the total dose of induction of the anesthesia (T2); the third moment corresponded the orotracheal intubation (T3). During the maintenance of the anesthesia, were evaluated the moments after 5 minutes of maintenance (T4), 10 minutes (T5) and 20 minutes (T6), when group 1 received isofluorane inhalatory agent in 100% O2 and group 2 continuous infusion of propofol in the dose of 0,6mg/kg/min and 100% O2, both groups remaining in adequate anaesthetic stage. It can be observed that the cardiac frequency was, in average, superior during anesthetical induction period and the average arterial pressure was often inferior, however, clinically the magnitude of these alterations can be considered of little clinical importance. Statiscally significant correlation did not exist between the fall of the average arterial pressure and the increase of the cardiac frequency in none of the analyzed periods, leading to believe that the increase of the cardiac frequency is must probably due to the reduction of the cardiac parasympathetic neural activity and prevalence of the cardiac sympathetic activity, and the reduction of arterial pressure can be secondary to the reduction of the periphery sympathetic activity. Evaluating the cardiac rhythm noticed reduction of the incidence of low cardiac frequency and sinusal arrhythmia and an increase of the sinusal rhythm, probably due to the reduction of the cardiac parasympathetic activity. Such comments support the hypothesis that propofol can act differently in the peripheral and cardiac sympathetic activity also in dogs. The hypothesis that pressure-induced activity could be also decreased in dogs can be raised, since there was not significant correlation between the reduction of arterial pressure and the subsequent increase of cardiac frequency. During the maintenance of the anesthesia there was a fall of the arterial pressure, of no clinical importance and there was no cardiac frequency significant change. It was possible to observe excitement in only two animals at moment T1 and one animal in T2. Apnea was observed in only eight animals (15.1%) seven at moment T3. Other studies using measurement of the pressure-induced activity, spectral analysis of the variability of cardiac frequency, neuromicrography or even though norepinephrine clearance measurement for better evaluation of the sympathetic activity of dogs during the anesthesia still must be done to prove these strong suggestive hypotheses for the data found in this study. Propofol demonstrated to be a safe drug when used in the induction and the maintenance of the anesthesia in dogs, not causing important cardiovascular clinical changes.

O traçado eletrocardiográfico, observado durante a anestesia geral, pode diferir morfologicamente do traçado pré-anestésico. O que não se conhece é o grau de influência que os fármacos anestésicos exercem sobre o registro eletrocardiográfico de um cão geriátrico submetido à anestesia geral e a que ponto estas alterações eletrocardiográficas interferem em sua hemodinâmica. Avaliou-se oitenta e dois cães geriátricos (categoria de risco I ou II) foram distribuídos em três grupos: grupo I, cães de pequeno porte (até 10 kg, n=36); grupo II, cães de médio porte (11 a 25 kg, n=27), e grupo III, cães de grande porte (26 a 45 kg, n=19). Além da avaliação eletrocardiográfica, os exames pré-anestésicos constaram de hemograma completo, mensuração sérica de uréia, creatinina, proteína total e albumina; foram feitas mensurações séricas de potássio, cálcio, sódio e magnésio. A medicação pré-anestésica constou de acepromazina associada à morfina ou a meperidina ou somente morfina. A indução foi feita com propofol ou propofol associado ao midazolam, e a manutenção da anestesia realizada com isofluorano em oxigênio a 100%. Durante a anestesia, os cães foram monitorados continuamente com auxílio de um eletrocardiógrafo computadorizado que avaliou o ritmo cardíaco, a freqüência cardíaca, o intervalo PR, a largura e a morfologia do complexo QRS, o segmento ST, a morfologia, a amplitude e a polaridade da onda T. Avaliou-se também a pressão arterial sistólica, média e diastólica; a freqüência respiratória; a ventilação avaliada através da observação da concentração de dióxido de carbono expirado e dos valores de pressão parcial de dióxido de carbono no sangue arterial; a oxigenação, avaliada através da oximetria de pulso, da pressão parcial de oxigênio no sangue arterial e da saturação da oxi-hemoglobina arterial. Os animais foram submetidos à ventilação assistida ou à controlada quando observou-se hipoventilação e hipercapnia. Nos três grupos, o ritmo cardíaco mais freqüente foi o sinusal normal (88%). Observou-se taquicardia sinusal em alguns momentos do trans-operatório em 9% dos animais. Pouco freqüente, mas com importância hemodinâmica, observou-se bradicardia sinusal (3%) associada à hipotensão. Assim, neste estudo o isofluorano não proporcionou o aparecimento de arritmias e promoveu estabilização hemodinâmica dos animais. Observou-se aumento não significante do intervalo PR que do ponto de vista biológico deve ser considerado importante, visto que aproximadamente 11% dos animais que apresentavam intervalo PR normal com ritmo sinusal , evoluíram para bloqueio atrioventricular de primeiro grau. Observou-se bloqueio atrioventricular de primeiro grau em 2% dos animais no eletrocardiograma pré-anestésico, e 1% evoluiu com bloqueio atrioventricular de 2o grau Mobitz tipo I. As alterações no segmento ST e onda T durante o período trans-anestésico, foram muito freqüentes e relacionadas principalmente a hipoventilação. / The electrocardiogram observed during the general anesthesia, can differ from the morfology of the preanesthetic record. It is unknown the influence of the anesthetic drugs in the electrocardiographic record of a elderly dog during general anesthesia, and if electrocardiographic disturbances interfere in their hemodynamic. Eighty two geriatrics dogs (risk category I or II) were evaluated and distributed in three groups: group I, small-size breeds (less than 10 kg, n=36); group II, medium-size breeds (11 to 25 kg, n=27), and group III, large-size breeds (26 to 45 kg, n=19). Beyond electrocardiographic evaluation, the preanesthetic profile consisted in packed cell volume, seric measurement of urea, creatinine, total protein and albumin; the eletrolytes (potassium, calcium, sodium and magnesium). The preanesthetic medication consisted in acepromazine with morphine or meperidine or only morphine. Anesthesia was induced with propofol or propofol with midazolam and maintained with isoflurane in 100% oxygen. During the anesthesia, the animals were monitoried with a continued computadorized electrocardiogram, recording rhythm, heart rate, P-R interval, QRS complex, ST segment and T wave. The systemic blood pressure (systolic, mean and dyastolic), the respiratory rate, the end-tidal carbon dioxide, partial pressure of arterial CO2, the arterial oxygen saturation, the partial pressure of arterial oxygen and oxygen saturation of hemoglobin were evaluated continuously. The animals were submitted to assisted or controled ventilation when hypoventilation and hypercapnia were observed. In the three groups, the normal sinus rhythm was more common (88%). Sinus tachycardia was observed in 9% of the animals. Sinus bradycardia and a decrease in the systemic blood pressure was observed in 3% of the animals. In view of the results obtained it is possible to conclude that, the isoflurane didn\'t provide the observation of arrhythmias and it gave hemodynamic stability. The prolonged P-R interval was observed although of no statistical significance. However it is important, because 11% of the animals that have prolonged P-R interval, developed first degree atrioventricularricular block. First degree AV block was observed in 2% of the animals in the preanesthetic electocardiogram, and 1% developed second degree AV block Mobitz I during the anesthesia. The changes of ST segment and T wave during the anesthetic proceeding was too common and it was related to hipoventilation.

Thesis. 1976. M.S.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / Microfiche copy available in Archives and Barker. / Includes bibliographical references. / M.S.

O traçado eletrocardiográfico, observado durante a anestesia geral, pode diferir morfologicamente do traçado pré-anestésico. O que não se conhece é o grau de influência que os fármacos anestésicos exercem sobre o registro eletrocardiográfico de um cão geriátrico submetido à anestesia geral e a que ponto estas alterações eletrocardiográficas interferem em sua hemodinâmica. Avaliou-se oitenta e dois cães geriátricos (categoria de risco I ou II) foram distribuídos em três grupos: grupo I, cães de pequeno porte (até 10 kg, n=36); grupo II, cães de médio porte (11 a 25 kg, n=27), e grupo III, cães de grande porte (26 a 45 kg, n=19). Além da avaliação eletrocardiográfica, os exames pré-anestésicos constaram de hemograma completo, mensuração sérica de uréia, creatinina, proteína total e albumina; foram feitas mensurações séricas de potássio, cálcio, sódio e magnésio. A medicação pré-anestésica constou de acepromazina associada à morfina ou a meperidina ou somente morfina. A indução foi feita com propofol ou propofol associado ao midazolam, e a manutenção da anestesia realizada com isofluorano em oxigênio a 100%. Durante a anestesia, os cães foram monitorados continuamente com auxílio de um eletrocardiógrafo computadorizado que avaliou o ritmo cardíaco, a freqüência cardíaca, o intervalo PR, a largura e a morfologia do complexo QRS, o segmento ST, a morfologia, a amplitude e a polaridade da onda T. Avaliou-se também a pressão arterial sistólica, média e diastólica; a freqüência respiratória; a ventilação avaliada através da observação da concentração de dióxido de carbono expirado e dos valores de pressão parcial de dióxido de carbono no sangue arterial; a oxigenação, avaliada através da oximetria de pulso, da pressão parcial de oxigênio no sangue arterial e da saturação da oxi-hemoglobina arterial. Os animais foram submetidos à ventilação assistida ou à controlada quando observou-se hipoventilação e hipercapnia. Nos três grupos, o ritmo cardíaco mais freqüente foi o sinusal normal (88%). Observou-se taquicardia sinusal em alguns momentos do trans-operatório em 9% dos animais. Pouco freqüente, mas com importância hemodinâmica, observou-se bradicardia sinusal (3%) associada à hipotensão. Assim, neste estudo o isofluorano não proporcionou o aparecimento de arritmias e promoveu estabilização hemodinâmica dos animais. Observou-se aumento não significante do intervalo PR que do ponto de vista biológico deve ser considerado importante, visto que aproximadamente 11% dos animais que apresentavam intervalo PR normal com ritmo sinusal , evoluíram para bloqueio atrioventricular de primeiro grau. Observou-se bloqueio atrioventricular de primeiro grau em 2% dos animais no eletrocardiograma pré-anestésico, e 1% evoluiu com bloqueio atrioventricular de 2o grau Mobitz tipo I. As alterações no segmento ST e onda T durante o período trans-anestésico, foram muito freqüentes e relacionadas principalmente a hipoventilação. / The electrocardiogram observed during the general anesthesia, can differ from the morfology of the preanesthetic record. It is unknown the influence of the anesthetic drugs in the electrocardiographic record of a elderly dog during general anesthesia, and if electrocardiographic disturbances interfere in their hemodynamic. Eighty two geriatrics dogs (risk category I or II) were evaluated and distributed in three groups: group I, small-size breeds (less than 10 kg, n=36); group II, medium-size breeds (11 to 25 kg, n=27), and group III, large-size breeds (26 to 45 kg, n=19). Beyond electrocardiographic evaluation, the preanesthetic profile consisted in packed cell volume, seric measurement of urea, creatinine, total protein and albumin; the eletrolytes (potassium, calcium, sodium and magnesium). The preanesthetic medication consisted in acepromazine with morphine or meperidine or only morphine. Anesthesia was induced with propofol or propofol with midazolam and maintained with isoflurane in 100% oxygen. During the anesthesia, the animals were monitoried with a continued computadorized electrocardiogram, recording rhythm, heart rate, P-R interval, QRS complex, ST segment and T wave. The systemic blood pressure (systolic, mean and dyastolic), the respiratory rate, the end-tidal carbon dioxide, partial pressure of arterial CO2, the arterial oxygen saturation, the partial pressure of arterial oxygen and oxygen saturation of hemoglobin were evaluated continuously. The animals were submitted to assisted or controled ventilation when hypoventilation and hypercapnia were observed. In the three groups, the normal sinus rhythm was more common (88%). Sinus tachycardia was observed in 9% of the animals. Sinus bradycardia and a decrease in the systemic blood pressure was observed in 3% of the animals. In view of the results obtained it is possible to conclude that, the isoflurane didn\'t provide the observation of arrhythmias and it gave hemodynamic stability. The prolonged P-R interval was observed although of no statistical significance. However it is important, because 11% of the animals that have prolonged P-R interval, developed first degree atrioventricularricular block. First degree AV block was observed in 2% of the animals in the preanesthetic electocardiogram, and 1% developed second degree AV block Mobitz I during the anesthesia. The changes of ST segment and T wave during the anesthetic proceeding was too common and it was related to hipoventilation.

University of Macau / Faculty of Science and Technology / Department of Electrical and Computer Engineering

Understanding heart&rsquo / s electrical activity is very important because coronary problems -such as heart attacks, arrhythmia and stroke- are the leading cause of death in the world. Forward and inverse problems of electrocardiography (ECG) are methods that provide detailed information about the electrical activity of the heart. Forward problem of electrocardiography is the estimation of body surface potentials from equivalent cardiac sources. Inverse problem of electrocardiography can be described as estimation of the electrical sources in the heart using the potential measurements obtained from the body surface. Due to spatial smoothing and attenuation that occur within the thorax, inverse ECG problem is ill-posed and the transfer matrix is ill-conditioned. Thus, regularization is needed to find a stable and accurate solution. In this thesis, epicardial potentials used as equivalent cardiac sources to represent electrical activity of the heart and performances of five different regularization methods are compared. These regularization methods are Tikhonov regularization, truncated singular value decomposition, least squares QR factorization, truncated total least squares, and Lanczos truncated total least squares. Results are assessed qualitatively using correlation coefficient (CC) and relative difference measurement star (RDMS) measures. In addition, real and reconstructed surface potential distributions are compared qualitatively. Body surface potential measurements are simulated with different levels of measurement noise. Geometric errors are also included by changing the size and the location of the heart in the mathematical torso model. According to our test results, the performances of the regularization methods in solving the inverse ECG problem depend on the form and amount of the noise.

Η διπλωματική εργασία μου ασχολείται με την αφαίρεση θορύβου από Ηλεκτροκαρδιογράφημα(ΗΚΓ), με σκοπό τη καθαρότερη λήψη του σήματος για διαγνωστικούς σκοπούς. Ο θόρυβος στο ΗΚΓ προέρχεται από διάφορες πηγές, είτε τεχνικές, είτε φυσιολογικές. Η αφαίρεσή του είναι ουσιαστικής σημασίας. Στόχος της εργασίας αυτής είναι η παράθεση των κυρίων μεθόδων αφαίρεσης θορύβου από ΗΚΓ και του τρόπου λειτουργίας τους, καθώς και η παράθεση παραδειγμάτων από την πρόσφατη βιβλιογραφία. / --

Pagrindinis širdies ir kraujagyslių sistemos uždavinys – deguonies ir maisto medžiagų tiekimas. Deguonimi ir maisto medžiagomis kraujas aprūpina dirbančius raumenis ir kitus organus. Darbo tikslas – palyginti ištvermę lavinančių sportininkų ir nesportuojančiųjų širdies funkcinį parengtumo ypatybes taikant elektrokardiografijos metodą ir skirtingo kryptingumo fizinio krūvio mėginius. Uždaviniai: 1 - palyginti nesportuojančiųjų ir ištvermę lavinančių sportininkų ŠSD kaitos ypatybes atliekant pakopomis didėjantį krūvį veloergometru; 2 - palyginti nesportuojančiųjų ir ištvermę lavinančių sportininkų ŠSD kaitos ypatybes atliekant dozuoto krūvio mėginį; 3 - palyginti nesportuojančiųjų ir ištvermę lavinančių sportininkų ŠSD kaitos ypatybes atliekant maksimalaus anaerobinio krūvio mėginį; 4 – palyginti trijų skirtingų fizinio krūvio mėginių informacinės dimensijos reikšmes, kai elektrokardiografijos metodu vertinama funkcinio parengtumo ypatybės. Metodika. Buvo tirta 7 ištvermės rungčių atstovai lengvaatlečiai ir 16 nesportuojančių asmenų. Tiriamieji atliko tris fizinio krūvio mėginius: pakopomis didėjantį krūvį veloergometru; Rufje fizinio krūvio mėginį ir 30 - s vertikalaus šuoliavimo testą. Kompiuterine EKG registravimo ir analizės sistema „Kaunas-krūvis“ buvo registruojama EKG ir vertinama ŠŠD, JT intervalo, ST-segmento depresijos kaita atliekant krūvius ir pirmąsias tris atsigavimo minutes. Rezultatai ir išvados. Pakopomis didėjančio krūvio metu registruojant... [toliau žr. visą tekstą] / Cardiovascular system is the main physiological system determining physical working capasity or endurance. The main task of cardiovascular system to deliver the oxygen anf energy substrates to tisues and muscles as well. The purpors of this study was to compare functional peculiarities of cardiovascular system in endurance and non-sportsmans cohorts while performing various exercise tests. Objectives: 1 - to compare the cardiovascular reactions in endurance and non-sportsmans cohorts while performing graded exercise stress (bycycle ergometry); 2 – to compare the cardiovascular reactions in endurance and non-sportsmans cohorts while performing dosed aerobic exercise test; 3 – to compare the cardiovascular reactions in endurance and non-sportsmans cohorts while performing maximal anaerobic workload (30-s vertical jumps test); 4 – to compare the informativeness of aplyed exercise protocols for assessment of cardiovascular reactions in endurance and non-sportsmans cohorts. Methods. The participant fo this study was 7 endurance athletes and 16 non-sportsman. Subjects performed three exercise tests: graded exercise stress (bycycle ergometry); dosed aerobic exercise test (Roufier Test) maximal anaerobic workload (30-s vertical jumps test). A computerized ECG analysis system "Kaunas-load" was recorded ECG and assessed FCU, JT interval, ST-segment depression changes in workloads and the first three minutes of recovery. Results and Conclusions. The registration of ECG during the... [to full text]

Non-invasive electrical imaging of the heart aims to quantitatively reconstruct information about the electrical activity of the heart from multiple thoracic ECG signals. The computational framework required to produce such electrical images of the heart from non-invasive torso surface signals is presented. It is shown reliable electrical images of the heart can be obtained under a controlled environment. This has been demonstrated using an anatomically realistic boundary element porcine torso model. The procedures required to create a subject specific model using a small number of control points and to create a specific heart model from three-dimensional ultrasound images using a linear fitting procedure are presented. From discrete ECG electrodes a continuous representation of the potential field over the entire torso surface can also be produced using this linear fitting procedure. The construction of the transfer matrices for the two predominant electrocardiographic sources (epicardial potentials and myocardial activation times) are described in detail. The transfer matrices are used to compute activation times within the heart and epicardial potentials on the heart surface. Myocardial activation times are computed using an algorithm based on the Critical Point Theorem while epicardial potentials are computed using standard Tikhonov and Truncated SVD spatially regularised methods as well as Greensite's spatial and temporal regularisation method. The regularisation parameters for the epicardial potentials are determined using a variety of methods (e.g., CRESO criterion, L-curve, zero-crossing). The potential and activation based formulations are compared in a comprehensive inverse simulation study. To try and capture the dynamic and variable nature of cardiac electrical activity, the study is performed with three different types of cardiac sources with a realistic porcine model. These simulations investigate the effect on the computed solutions of individual and combinations of modelling errors. These errors include corruption in the torso surface signals, changes in material properties and geometric distortion. In general, the activation based formulation is preferred over the epicardial potential formulations, with Greensite's method found to be the best method for reconstructing epicardial potentials. Under optimal conditions, the activation approach could reconstruct the activation times to within RMS. Both potential and activation based formulations were found to be relatively insensitive to changes in material properties such as lung conductivities and activation function shapes. When examining individual errors, the geometry and positions of the torso and heart had the greatest effects on the inverse solutions. The relative heart position needed to be determined to within to obtain results within of the solutions obtained under control conditions. When the modelling errors are combined to produce errors which can be expected in a clinical or experimental situation the activation based solutions were consistently more accurate than potential based solutions. The next necessary step in this project is the detailed validation of the results against in-vivo data. This step is necessary before such algorithms can be reliably used to aid in the assessment of heart function in a clinical environment.

Non-invasive electrical imaging of the heart aims to quantitatively reconstruct information about the electrical activity of the heart from multiple thoracic ECG signals. The computational framework required to produce such electrical images of the heart from non-invasive torso surface signals is presented. It is shown reliable electrical images of the heart can be obtained under a controlled environment. This has been demonstrated using an anatomically realistic boundary element porcine torso model. The procedures required to create a subject specific model using a small number of control points and to create a specific heart model from three-dimensional ultrasound images using a linear fitting procedure are presented. From discrete ECG electrodes a continuous representation of the potential field over the entire torso surface can also be produced using this linear fitting procedure. The construction of the transfer matrices for the two predominant electrocardiographic sources (epicardial potentials and myocardial activation times) are described in detail. The transfer matrices are used to compute activation times within the heart and epicardial potentials on the heart surface. Myocardial activation times are computed using an algorithm based on the Critical Point Theorem while epicardial potentials are computed using standard Tikhonov and Truncated SVD spatially regularised methods as well as Greensite's spatial and temporal regularisation method. The regularisation parameters for the epicardial potentials are determined using a variety of methods (e.g., CRESO criterion, L-curve, zero-crossing). The potential and activation based formulations are compared in a comprehensive inverse simulation study. To try and capture the dynamic and variable nature of cardiac electrical activity, the study is performed with three different types of cardiac sources with a realistic porcine model. These simulations investigate the effect on the computed solutions of individual and combinations of modelling errors. These errors include corruption in the torso surface signals, changes in material properties and geometric distortion. In general, the activation based formulation is preferred over the epicardial potential formulations, with Greensite's method found to be the best method for reconstructing epicardial potentials. Under optimal conditions, the activation approach could reconstruct the activation times to within RMS. Both potential and activation based formulations were found to be relatively insensitive to changes in material properties such as lung conductivities and activation function shapes. When examining individual errors, the geometry and positions of the torso and heart had the greatest effects on the inverse solutions. The relative heart position needed to be determined to within to obtain results within of the solutions obtained under control conditions. When the modelling errors are combined to produce errors which can be expected in a clinical or experimental situation the activation based solutions were consistently more accurate than potential based solutions. The next necessary step in this project is the detailed validation of the results against in-vivo data. This step is necessary before such algorithms can be reliably used to aid in the assessment of heart function in a clinical environment.