Veterinary/zoology session

Electrocardiography is a common method for detecting the extreme alterations in the physiologic state of the heart. Heart rate variance (HRV) analysis, however, is a new method mainly used in the human medicine, and it is based on the alterations of RR-intervals in time, which method ignores extreme alterations and focuses rather on systematical tendencies. There is much more information hidden in this series of signals– regarding both the heart and the organism as a whole – than medical and veterinary sciences currently use. A number of time- and frequency-domain analyses are available to examine HRV, although their biological background is not fully elucidated yet.

HRV is a physiologic process showing fractal dynamics, i.e. the heart rate signal series are comprised of statistically self-similar subunits and sub-subunits. The degradation of this complexity – shifting either towards periodicity or uncorrelated randomness – is a sign of aging or some pathological process.

In the experiments the effects of lidocaine – a well-known antiarrhythmic drug – on HRV were investigated, administering doses of 3, 9, 30 and 60-75 mg/kg (groups 1-4) to 10 BALB-C mice per group – except for group 4, where only 6 mice were used. The animals were kept in sexually separated groups of five.

For each animal the values measured prior to lidocaine treatment were matched with the values after the administration of the antiarrhythmic. We used the heart rate value, the standard deviation of RR-intervals and the triangular index, calculated on the basis of the recorded ECG-signals. These signals were processed by the Poincaré plot and the fast Fourier transformation (FFT) as well. The statistical analysis of the values obtained was also carried out. According to our results, calculated on the basis of the Poincaré plot, one of the two standard deviation parameters, SD1 (reflecting short-term variance) increased in groups 1 and 2, while in group 4 it decreased. On the contrary, SD2 (reflecting long-term variance) decreased in groups 2 and 4, while increased in group 3. The FFT produced LF/HF ratio, which describes the sympatho-parasympathetic balance, increased in groups 2 and 3, but decreases in group 4. The standard deviation of RR-intervals and the triangular index, which reflects the distribution of the length of RR-intervals and thus the rate of variance, showed a steady increase in group 1, but in group 4 it tended to decrease. Our recorded data show that lidocaine induced a drop in the heart rate of the first three groups.

Summing up our results it can be concluded that lidocaine in lower doses increase short-time variability and decrease heart rate (antiarrhythmic effect), whereas high dose diminish these phenomena. Besides, low doses of lidocaine proved to induce a shift in autonomic balance towards sympathicotony, while a high dose resulted in an inverse tendency.