The brainstem cardioarrhythmogenic triggers and their possible role in sudden epileptic death.

The cardiovascular effects of simultaneous activation of hypothalamic and mesencephalic cardioarrhythmogenic triggers were studied in hemispherectomized rats. Paroxysmal activity of hypothalamic neurons (HEF), elicited by topical application of penicillin G on the thalamus, triggered short-lasting bradyarrhythmic episodes, up to a maximum of 6 s, and alterations in repolarization. In the hypothalamic neurons, an additional penicillin G epileptic focus at mesencephalic level (MEF) induced the enhancement of paroxysmal activity by a recruitment of new units and potentiation of their background activity. HEF+MEF triggered second-degree 2:1-8:1 atrioventricular (A-V) blocks, impairment of the A-V conduction, alterations in the recovery phase and bundle branch blocks. After HEF, the arterial blood pressure decreased by 4-6%. HEF+MEF induced a further reduction of 17% in systolic pressure only. It is possible that the enhancement of the HEF following MEF could depend on MEF spreading upward. The HEF, in turn, by spreading downward could influence the MEF and so activate, between HEF and MEF, a circuitry with reciprocal co-excitation that could explain the more serious cardiovascular alterations observed during HEF+MEF compared with those observed during HEF only or during MEF only. However, this cardiovascular impairment, which must be neurogenic in origin as it was observed in animals with normal acid-base and blood parameter values, did not induce heart death. Thus, additional concomitances must be considered, such as metabolic derangement which can occur during seizures, to explain sudden death in epileptic patients. Some aspects of metabolic complications in cardiac activity during epilepsy are also discussed.

[Circadian rhythm of spontaneous ventricular arrhythmias in elderly patients with myocardial ischemia at low risk for sudden death]. / Il ritmo circadiano delle aritmie ventricolari spontanee in pazienti anziani con ischemia miocardica a basso rischio di morte improvvisa.

In 26 patients (65-80 yr) with low risk of sudden death, the circadian rhythm of spontaneous ventricular arrhythmias was analyzed, throughout 72 h, by the Holter monitoring method. The prolonged ECG monitoring is indispensable to evaluate the real necessity of an antiarrhythmic therapy and to establish the therapeutic approach. Premature ventricular complexes (PVC): isolated, couplets and runs of ventricular tachycardia have been considered. The isolated PVC showed uniform distribution throughout 24h, with higher frequency/hour ratio (f/h) in females. Couplets and runs showed circadian diurnal distribution with higher f/h ratio in smokers and males. After analysis of the results, the patients were additionally subdivided into smokers and non-smokers. Since smokers showed a diurnal distribution of all kinds of arrhythmias, antiarrhythmic drugs whose pharmacological peak corresponds to the distribution peaks of arrhythmias were proposed. Non-smokers could be divided into two groups: a) patients with isolated extrasystoles which did not show a circadian rhythm of arrhythmias and who must be treated with retard-drugs, which give protection throughout 24h; b) patients with runs or couplets of PVC showing a circadian rhythm of arrhythmias and who must be treated with drugs whose pharmacological peak corresponds to the distribution peaks of arrhythmias.

[Determination of the range of physiologic variation of the electrical axes using P, QRS, and T waves in pregnancy]. / Determinazione del limite di variabilità fisiologica degli assi elettrici medi delle onde P, QRS e T in gravidanza.

Since functional overload in pregnancy frequently induces the appearance of symptoms that could arouse suspicion of myocardiopathy, it is important to analyse and characterize all electrocardiographic modifications during a healthy subject's pregnancy. Variations of the mean electrical axis (A) of P, QRS and T waves were evaluated in 52 healthy volunteers, 17-37 years, during pregnancy. The A values were measured, in the frontal plane, at the end of both I and III quarter of pregnancy, using a method of scalar determination. The As in I and III quarters was compared with those observed in the post-partum (at 5th day) and statistical evaluations were performed (Student t-test for paired observations). In the I quarter the mean A was 40 +/- 3 degrees for P, 40 +/- 16 degrees for QRS and 32.5 +/- 9 degrees for T wave, whereas in the III quarter the mean A changed to 37 +/- 2 degrees for P, 34 +/- 18 degrees for QRS and 31 +/- 9 degrees for T. During pregnancy, all mean As significantly diverted to the left side, AP about 3 degrees, AQRS about 6 degrees and AT about 1.5 degrees. These results were also confirmed by analysis of A frequency distribution histograms. In the post-partum (5th day) the A resumed basal values (I quarter's values). These results show: i) the physiological range of AP, AQRS and AT, during pregnancy; ii) left deviation of all three As at the end of III quarter. It is possible to conclude that variation over this range, particularly for QRS, could give evidence of the onset of cardiopathy.

Plasma lipids in beta-thalassemia minor.

Because total cholesterol levels have been found to be lower in patients affected by thalassemia major and intermedia, we examined the plasma lipid pattern of 628 beta-thalassemia trait carriers and 4552 controls in order to evaluate whether the plasma lipid impairment is also present in the heterozygous state. Total cholesterol and low density lipoprotein (LDL)-cholesterol levels were significantly lower in beta-thalassemia trait carriers when compared to controls, whereas plasma triglycerides and high density lipoprotein (HDL)-cholesterol levels did not differ between the two groups. We suggest that accelerated erythropoiesis and increased uptake of LDL by macrophages and histiocytes of the reticuloendothelial system are the main determinants of low plasma cholesterol levels in heterozygous thalassemia.

Neurogenic myocardial arrhythmias in experimental focal epilepsy.

The potential for cardiac arrhythmia was studied in an experimental focal epilepsy induced in hemispherectomized rats by topical application of buffered penicillin G onto the thalamus. The epileptic burst triggered cardiac and hemodynamic responses, as simultaneously monitored by arterial pressure, and hypothalamic and heart activity. During interictal epileptic activity, the single burst triggered a short-latency cardiac arrhythmia, characterized by sinus bradyarrhythmia and junctional rhythm, and lengthening of intervals between sphygmic waves with significant reduction of diastolic pressure. When the epileptic burst stopped, the cardiac activity resumed normal rhythm, and diastolic pressure returned to basal value. During ictal epileptic activity, the sinus and junctional bradyarrhythmic episodes lasted longer, and supraventricular extrasystoles, sinus arrest, and bigeminal ventricular extrasystoles were observed. Both systolic and diastolic pressures decreased from 120/85 to 100/65 mm Hg. The end of the ictal episode always marked resumption of normal cardiac rhythm and systemic pressure. Considering the absence of metabolic complications (blood-gas analytic parameters and acid-base balance being controlled) and the short latency of the cardiac and hemodynamic responses, it is suggested that during paroxysmal hypothalamic activity the observed cardiac arrhythmias and the hemodynamic modifications were neurogenic in origin. A role for cardiovascular alterations in sudden unexplained epileptic death is postulated.

Detection of sinusoidally amplitude modulated noise by the chinchilla.

Amplitude modulation thresholds for sinusoidally amplitude modulated noise were obtained from four monaural chinchillas using shock-avoidance conditioning procedures. The noise was band limited at either 10 or 20 kHz, amplitude modulated at frequencies between 2 and 4096 Hz and presented at levels between 52 and 73 dB SPL. The modulation thresholds of the chinchilla were approximately 9% (-- 2 dB) at modulation frequencies below 32 Hz. At higher modulation frequencies, thresholds increased at the rate of 1.9 dB/octave. Modulation thresholds were also measured in human listeners using the same experimental apparatus. Amplitude modulation functions for both subject groups exhibited low-pass characteristics; however, the thresholds for humans were better than those of the chinchilla at modulation frequencies below 64 Hz.

Systolic time intervals in hyperthyroidism.

PEPI (pre-ejection period index), QS2I (total electromechanical systolic index), LVETI (left ventricular ejection time index), and PEP/LVET ratio were measured in 35 thyrotoxic patients. None of the patients had clinical evidence of heart disease nor received drugs which might have affected the systolic time intervals. the hyperthyroid subjects showed significant shortening of PEPI and significant reduction of PEP/LVET, which returned within normal limits when the patients became euthyroid during treatment. No correlation could be found between T3, T4, FTI and PEPI or PEP/LVET. However, serial measurements indicated that the fall toward the normal range of PEPI parallelled that of T3; the latter is considered the most important index of thyroid function. Our study suggests that PEPI and PEP/LVET ratio may be of great usefulness in detecting hemodynamic alterations in subjects with uncomplicated hyperthyroidism. Moreover, these methods may facilitate the diagnosis in unusual types of hyperthyroidism occurring in the absence of clinical signs of toxicosis. In addition, PEPI and PEP/LVET appear to be useful in detecting T3 toxicosis. Finally, serial controls of PEPI could represent a useful index to monitor the response to therapy.

Gap detection by the chinchilla.

Five monaural chinchillas were trained with a method of shock-avoidance conditioning to respond to silent intervals, or gaps, in an otherwise noise. The noise was low-pass filtered at either 10 or 6 kHz and presented at six intensities ranging between 23- and 77- dB sound-pressure level (SPL). Gap detection thresholds were determined according to the method of constant stimuli. For both noise bands, gap thresholds were approximately 3 ms at the highest intensity levels and increased to approximately 6 ms at the lowest level. The results obtained from the chinchilla are in general agreement with those obtained from man.