A computer model of the entire human heart has been developed for simulation of the excitation and repolarization process. Spatial distribution of refractory periods and conduction velocities in the different cardiac tissues, the anisotropy of conduction in the ventricles, and the cycle length dependence of refractory periods and conduction velocities are taken into account. The algorithm calculating the activation process is based on a modified version of Huygen's principle for constructing wavefronts. This study presents simulations concerning the gap phenomenon of the conduction system and the initiation of tachycardias in a heart with Wolff-Parkinson-White syndrome. Results are compared for different basic cycle lengths and for normal and prolonged refractory periods in the His-Purkinje system. The gap phenomenon was found to be present only when using the prolonged refractory periods in the His-Purkinje-system at a cycle length of 700 ms. Induction of tachycardia by a single extrastimulus in the high right atrium in a heart with a bidirectionally conducting accessory pathway is possible by properly timed extrastimuli. The coupling interval of the stimulus for initiating a reentrant tachycardia depends on the cycle length, the conduction velocities and the set of refractory periods used. The same parameters determine whether or not a gap phenomenon in atrioventricular conduction occurs. The model may be useful for investigating similar questions concerning the reentry phenomena of tachycardia.

Atrioventricular Node↗

PubMedDate not supplied

A computer model of human ventricular myocardium for simulation of ECG, MCG, and activation sequence including reentry rhythms.

A computer model is presented for simulation of the spread of activation and repolarization in ventricular myocardium. The program calculating the activation sequence is based on an algorithm similar to Huygen's principle of constructing wavefronts. Physiological parameters of the heart, such as areas of early activation on the endocardium, conduction velocity, anisotropy of propagation, duration of action potentials and refractory periods are taken into account. The time-course of ECG and MCG is calculated using the equations of the bidomain model. Simulation of pathologic cases of activation is performed through variation of the physiological heart parameters. The simulations presented here show good agreement of ECG and MCG with measurements in the normal case, the case of bundle branch block and abnormal repolarization. A special feature of the model is the possibility of simulating reentry rhythms following a premature stimulus in ventricular myocardium. Two kinds of reentry are simulated: reentry around an anatomical obstacle and the leading-circle model. The widespread capability for investigating not only ECG but also MCG and various kinds of pathologic activation patterns including reentry rhythms indicates that the model may be useful in studying numerous problems in cardiologic research.

Action Potentials↗

PubMedDate not supplied

[Anesthesia for cardioversion. A comparison of propofol and etomidate].

Anaesthesia for elective direct current cardioversion (DCC) was induced with propofol (Diprivan) 1.2 mg/kg in 28 patients and with 0.2 mg/kg etomidate (Hypnomidate) in 20 patients. These mostly high risk patients (NYHA class II to III) were successfully treated with defibrillation. Blood pressure and heart rate were recorded before and after induction and at 2 minutes intervals up to 20 minutes after DCC. Both anaesthetic agents caused mild hypotension. Heart rate did not change significantly after induction but fell significantly after DCC from the mean value of 124 +/- 26 bpm and 122 +/- 37 bpm to 94 +/- 19 bpm and to 91 +/- 19 bpm in propofol and etomidate treated patients respectively. Four patients became apnoeic necessitating assisted ventilation for approximately four minutes. All propofol treated patients had rapid recovery times and opened eyes on command within 5.6 +/- 1.9 minutes after induction, and were fully orientated about 4 minutes later also. Complete amnesia was observed in all patients in this group. In contrast etomidate induced anaesthesia did not cause respiratory depression, but the recovery time was longer. Four patients of this group complained of recall of DCC. In 7 patients due to involuntary movements or myoclonus, after induction with etomidate reliable EKG monitoring appeared to be difficult.

Adult↗

PubMedDate not supplied

[Blockage of the decrease in eosinophils after adrenaline injection by propranolol].

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Eosinophils↗