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Pacemaker Inverse Problem--Computer Supported Diagnosis of Electrocardiograms of Paced Patients. M. Malik, A. J. Camm. D e p a r t m e n t of Computer Science, Charles University, Prague, Czechoslovakia.

Similarly to the Electrocardiographic Inverse Prob- lem, the objective of which is the algorithmical analysis and diagnosis of the electrocardiographic record (ECG), the Pacemaker Inverse Problem means the computerized analysis of the ECG in order to establish exact details of the heart-pacemaker interaction and to diagnose the pacemaker failures. The solution of this problem is of great practical importance, since it is often extremely difficult to evaluate the paced ECG records clinically. The ECG pat terns of natural extra-systolic heart depolari- zations and paced events are often hardly distinguish- able and very many combinations of pacemaker state changes have to be taken into consideration.

A computer system providing the automatic analysis of the heart-pacemaker interface has been developed and implemented on an IBM PC AT computer. The system is based on the ECG data elaboration and uses a com- plex algorithm which enables the evaluation for all pos- sible combinations of the heart and pacemaker events. For each of these combinations, the system establishes its correspondence to the specified pacemaker algorithm and parameters. The system is written in Turbo Pascal and its source text ha~ approximately 11000 lines.

The first version of the system has been tested with algorithms of the dual chamber cardiac pulse generator AUTIMA-I I (Telectronics). The interactive input of the system consists of pacemaker algorithm specification and of the analysed ECG in the form of t iming of 'defi- nite' and possible' sensing events and pacemaker pulses. The performed analysis establishes whether the device operates correctly within its permitted error. Should one or more explanations of the elaborated case be found, the system prints simplified pat tern of the elaborated ECG accompanied by simulated marker channel.

Improved Diagnosis of Cardiac Dysrhythmias During Stress Tests Using Bipolar Esophageal ECG. H. Schwela, G. Oltmanns, M. Knorre, H. C. Reissmann, K. H. Bischoff, T. Franke. Medical Academy, Erfurt, GDR.

The evaluation of heart rhythm response is an impor- tant aspect of exercise ECG. Improved diagnosis of heart rhythm in stress-testing can be obtained from bipolar esophageal ECG simultaneously recorded with conven- tional surface ECG. The advantages are:

1. clear-cut identification of P-wave incidence 2. determination of irregular P-waves 3. improved statement of the atrioventricular sequence This contributes to a bet ter differentiating between

supra-ventricular or ventricular origin of cardiac activa- tion, especially in cases of stress-induced aberrancies or bundle branch block. With suitable application the method can be applied in clinical routine.

With regard to the good quality of documentation and the diagnostic improvement which can be obtained, the additional technical efforts and the moderate dis- comfort for the patient are justifiable. Moreover this method offers further possibilities for automatic analy- sis of heart rhythm.

Dynamic Anisotropy of Atrioventricular Nodal Conduction?--Computer Experiments. M. Malik, D. Ward, A.J. Camm. Department of Cardio- logical Sciences, St. George's Hospital, London England.

The atrioventricular (AV) node is one of the most com- plicated cardiac structures and the complexity of its function is very important from the clinical point of view. Several different physiological and pathophysio- logical hypotheses have been suggested in order to ex- plain the AV nodal complex behaviour which is known from laboratory measurements and clinical observations. Most of these hypotheses explain the complexity of the nodal function as an integration result of complex be- haviour of individual nodal cells and conduction fibres.

Special mathematical theory describing the function of conduction element networks and a complex computer model simulating the transmission of excitation within the cardiac tissues, have been employed to test the hypothesis that the complexity of the nodal structure itself may be responsible for its behaviour and that separated nodal cells and fibres may be considered to operate in a rather simple way.

Different network structures have been created using conduction elements which instantaneously change their state from resting to depolarized and vice vers& The com- puter simulation technique enables the functions of these networks to be evaluated. When considering a structure with different refractory periods of its elements and with anisotropic conduction, we were. able to model much com- plicated phenomena of AV nodal function as: the Wencke- bach periodicity, dependence of AV conduction delay on the prematurity of atrial depolarizations, Rosenblueth's hypothesis of the AV nodal delay mechanism, etc.

The results of our mathematical considerations and computer analysis suggest that the complex AV nodal function may be due to the complexity of its structure. The experiments also suggest that dynamic anisotropy of intra AV nodal conduction should be examined since it may explain even more complicated phenomena such as the rhythm oscillations of reentry tachycardia, etc.

How to Translate Magnetocardiographical Localization Data to the Physician? L. Schmitz, R. Schneider, M. Oeff, G. Bein, S. N. Ern~. Children's Hospital of the Free University, Berlin-West.

Magnetocardiography (MCG) has gained an accuracy level of mm in the localization of arrhythmogenic loci within the heart. Consequently, there is a demand for a suitable method describing MCG coordinate positions in anatomically comprehensible terms.

Applying ECG-triggered nuclear magnetic resonance tomography, calculated sources of ventr icular extra- systoles could be projected into distinct structures of the heart. This correlated well with the morphology of the VE S and with the locsllzation during invasive endo- cardial mapping.

Nuclear magnetic tomography in conjunction with the MCG localization procedure offers a suitable means for the anatomical demonstration of originating areas of ventricular arrhythmogenic foci.

JOURNAL OF ELECTROCARDIOLOGY 21 (1), 1988