["Critical interval of the dispersion of refractoriness" in the pathogenesis of ventricular extrasystole in the long QT syndrome]. / L'"intervallo critico della dispersione della refrattarietà" nella patogenesi delle extrasistoli ventricolari nella sindrome del QT lungo.

The reentry mechanism (R.M.) has been demonstrated to be relevant in the genesis of experimental extrasystoles. The extrapolation of these observations to the ventricular extrasystoles (V.E.) observed in clinical situations is still debated. However, the V.E. related to the long QT syndromes have been commonly considered to be caused by R.M. In fact an abnormal prolongation of the repolarization time favors the dispersion of the myocardial recovery time. A critical lengthening of the QT interval has been observed by several Authors to underlie the appearance of V.E. That after a further critical prolongation of the QT the V.E. disappear, has not been so far described. We report a patient with long QT syndrome in whom the ECG demonstrated an extreme variability of the QT interval. The V.E. appeared only when the QT interval was greater than 580 msec, whereas they disappeared when the QT interval was greater than 660 msec. Thus, a critical interval of refractoriness dispersion (C.I.R.D.) between 580 and 660 msec was established. We suggest that in our case the V.E. were probably due to R.M., caused by regional lengthening of the repolarization; a further prolongation of repolarization time probably induced either an antegrade block in both limbs of the circuit or a retrograde block in the reentry pathway and consequently the abolition of R.M. The identification of a C.I.R.D. suggest a possible R.M. in the pathogenesis of clinical ventricular extrasystoles.

[The hemodynamic effects of nifedipine in congestive cardiomyopathy (author's transl)]. / Effetti emodinamici della nifedipina nella cardiomiopatia congestizia.

The Authors present the haemodynamic effects of nifedipina (Adalat-Bayer) in nine patients with congestive cardiomyopathy. Heart rate (HR), systemic vascular resistances (SVR) and mean aortic blood pressure (MABP) were significantly modified in all nine patients following the administration of the drug. Six of them showed an increase of cardiac index (CI) and a decrease of myocardial oxygen consumption (MVO2); three of them presented a decrease of CI and an increase of MVO2. This discrepancy can be due to the different percentage of increase and to the maximal of valves of HR in the two groups. Nifedipina can be useful in the treatment of congestive cardiomyopathy with elevated STR (afterload) and peripheral hypoperfusion (more than pulmonary congestion).

[Chronobiological pattern size of cardiac rhythm (author's transl)]. / La dimensione cronobiologica del ritmo cardiaco.

The basic knowledge of statistical methods in chronobiology are exposed, for the analysis of chronobiological features of cardiac rhythm. The cosinor's method, with definition of chronobiological parameters (acrophase, mesor and amplitude) allows a microscopic approach to study of biological rhythms. The AA. relate some chronobiological studies: a) on heart rate in normal subjects and in patients with myocardial infarction (MI); b) on premature ventricular beats in MI; c) on atrial and ventricular rates in complete AV block. These results demonstrate that there is an evident circadian rhythmicity for all analyzed parameters. The AA. analyse the physiological and clinical meaning of the chronobiological approach to cardiac rhythm for the chronopharmacological and pathophysiological studies and suggests the implications in pathology of adaptation to shift work.

[Effect of potassium chloride on myocardial stimulation threshold and correlated electrophysiologic parameters (author's transl)]. / Effetti del cloruro di potassio sulla soglia di stimolazione miocardica e sui parametri elettrofisiologici correlati. Studio diretto nell'uomo.

The influence of KCl on different electrophysiologic parameters and myocardial stimulation threshold (MST) are considered in 9 patients with cardiac pacemaker. Reduction of MST during the diastolic period and the supernormal phase of excitability (SNP), depression of automaticity and slight bradycardia have been observed. The Authors, on the basis of kaliemia values and electrophysiologic parameters, emphasize the improvement of myocardial responsiveness when kaliemia does not exceed 6.5 mEq/l. The electrophysiologic effects of KCl are compared with those obtained in vitro on the transmembrane potential. Therapeutic effects for the treatment of arrhythmias and exit block in patients with cardiac pacemakers are considered.

[Psychological problems of pacemaker carriers (author's transl)]. / Problemi psicologici della vita col pacemaker.

The Authors examine the peculiar psychological problems of pacemaker carriers. According to the degree of adjustment to the new clinical condition, it is possible to distinguish patients who react developing an anxious-depressive status (10-20%), those who realistically adjust to the new functional condition allowed by the pacemaker (70-80%) and those who, denying their disease, tend to overdo in their physical performance (10-20%). These characteristic psychological behaviors are examined with their family social, and physical implications. On the basis of these observations the importance of psychological support of nurses and physicians is emphasized.