The sinus node and the autonomic nervous system in normals and in sick sinus patients.

To determine the evolution with age, of extrinsic and intrinsic sinus node electrophysiological parameters and to assess the role of each component of the autonomic nervous system relative to age in patients with and without sick sinus syndrome, electrophysiological studies of sinus node function were performed in 227 patients subdivided into four groups according to the results of their electrophysiological testings: group I included patients with normal extrinsic and intrinsic sinus node function, group II patients with exclusive extrinsic sinus dysfunction, group III patients with exclusive intrinsic sinus dysfunction and group IV patients with extrinsic and intrinsic sinus node dysfunction. The electrophysiological study was performed 4 times: at basal state, after sympathetic, autonomic and parasympathetic blockades. Whatever the sinus node function (normal or abnormal) the extrinsic sinus node electrophysiological variables did not correlate with age; inversely all the electrophysiological measurements of the intrinsic sinus node (normal or abnormal) lengthened progressively with age, suggesting an ageing phenomenon of the intrinsic sinus node throughout life. Moreover, the study of the percentage of chronotropy of the sinus node electrophysiological variables shows a predominance of vagal tone in young subjects, whereas sympathetic activity is most prominent in elderly patients with and without sick sinus syndrome. Besides, sympathetic activity increases and vagal tone decreases with increasing age in normals whereas the age-related modifications of each component of the autonomic nervous system in sick sinus patients vary according to the type of sinus node dysfunction. The sinus node (normal or pathological) represents an equilibrated system: the age-related modification of the autonomic nervous system counterbalances the senescence of the intrinsic sinus node in such a way that the basal electrophysiological characteristics remain stable throughout life.

The sinus node function: normal and pathological.

To determine the evolution with age, of extrinsic and intrinsic sinus node electrophysiological parameters and to assess the role of each component of the autonomic nervous system relative to age in patients with and without sick sinus syndrome, electrophysiological studies of sinus node function were performed in 223 patients subdivided into four groups according to the results of their electrophysiological testings: group I included patients with normal extrinsic and intrinsic sinus node function, group II patients with exclusive extrinsic sinus dysfunction, group III patients with exclusive intrinsic sinus dysfunction and group IV patients with extrinsic and intrinsic sinus node dysfunction. The electrophysiological study was performed twice: at basal state and after autonomic blockade. Whatever the sinus node function (normal or abnormal) the extrinsic sinus node electrophysiological variables did not correlate with age; inversely all the electrophysiological measurements of the intrinsic sinus node (normal or abnormal) lengthened progressively with age, suggesting an ageing phenomenon of the intrinsic sinus node throughout life. Moreover, the study of the percentage of chronotropy of the sinus node electrophysiological variables shows a predominance of vagal tone in young subjects, whereas sympathetic activity is most prominent in elderly patients with and without sick sinus syndrome. The sinus node (normal or pathological) represents an equilibrated system: the age-related modification of the autonomic nervous system counterbalances the senescence of the intrinsic sinus node in such a way that the basal electrophysiological characteristics remain stable throughout life.

Electrophysiologic effects of intravenous xamoterol in patients with sinus node dysfunction.

The electrophysiologic effects of xamoterol were studied in ten patients with electrophysiologic evidence of sinus node dysfunction. A significant shortening of mean sinus cycle length, maximal corrected sinus-node recovery time, and the mean of the three longest corrected sinus-node recovery times was observed after intravenous administration of 0.1 mg/kg of xamoterol. The atrioventricular (AV) conduction time and the effective and functional refractory periods of the AV node were shortened as the effective refractory period of the atrium. These effects suggest that xamoterol could be tried safely for the treatment of patients with moderate symptoms due to sinus-node disease.

Central inhibition of sympathetic overdrive by clonidine in acute myocardial infarction with systolic hypertension. Haemodynamic study.

Intravenous clonidine was used to treat systolic hypertension (systolic blood pressure greater than 160 mm Hg) in 15 patients with acute myocardial infarction and documented sympathetic overactivity (high plasma norepinephrine). Its effects on haemodynamics and blood gases were studied. After one hour, clonidine significantly reduced the systolic (195 +/- 7 to 137 +/- 7 mm Hg, p less than 0.01) and diastolic (81 +/- 4 to 60 +/- 3 mm Hg, p less than 0.01) blood pressures as well as the systemic vascular resistance (26 +/- 2 to 20 +/- 1 IU, p less than 0.01). The cardiac index was reduced from 2.8 +/- 0.2 to 2.4 +/- 0.2 l/min X m2, p less than 0.01. This change was related to a reduction of the heart rate (92 +/- 4 to 81 +/- 4 beats/min, p less than 0.01) as the stroke index was unchanged. Pulmonary wedge pressure (15 +/- 3 to 10 +/- 2 mm Hg, p less than 0.01) and rate pressure product (18.034 +/- 1.159 to 11.274 +/- 917 mm Hg, beats/min, p less than 0.01) were also significantly decreased. The arterial oxygen tension did not change significantly but there was a significant drop in the mixed venous oxygen saturation (63 +/- 2 to 61 +/- 2%, p less than 0.02) and oxygen transport (433 +/- 41 to 409 +/- 36, p less than 0.01). Clonidine is thus able to normalize blood pressure in acute myocardial infarction; this is accompanied by a reduction in myocardial oxygen requirements and pulmonary wedge pressure. Oxygen transport to the tissues, however, may be decreased.

[Hemodynamic repercussions and clinical tolerance of 6 class I anti-arrhythmia agents in acute myocardial infarction]. / Répercussions hémodynamiques et tolérance clinique de six agents antiarythmiques de la classe I dans l'infarctus aigu du myocarde.

Clinical safety and hemodynamic repercussions were studied after administration of six class I antiarrhythmics (xylocaine, ajmaline, mexiletine, lorcainide, indecainide and tocainide) to patients presenting acute myocardial infarction without complications. The hemodynamic parameters monitored generally followed the same trends. A significant decrease of more than 10 per cent of the initial value was seen in systolic blood flow after injection of lorcainide, indecainide and tocainide. Peripheral vascular resistance increased moderately. Pulmonary capillary pressure increased by more than 40 per cent of the starting value after administration of mexiletine, indecainide and tocainide (significant increase in case of mexiletine). These changes in patients presenting infarction without complications are not of clinical importance. There were, however, two very severe cases of hemodynamic reaction after administration of mexiletine. Other signs of intolerance were seen, but they were of minor importance and administration of the drugs was not interrupted. Xylocaine and ajmaline produced the smallest depression of left ventricular functional activity in these patients.

Effects of obstructive sleep apneas on transcutaneous oxygen pressure in control infants, siblings of sudden infant death syndrome victims, and near miss infants: comparison with the effects of central sleep apneas.

In order to investigate the effects of obstructive sleep apneas upon transcutaneous PO2 75 polysomnograms, recorded during night sessions in 25 control infants, 25 siblings, and 25 near miss for sudden infant death syndrome (SIDS) infants were studied. These observations were compared with the decreases in transcutaneous PO2 measured during central sleep apneas in the same infants. During a total of 707.6 hours of sleep, 33 obstructive apneas and 1,650 central apneas were recorded. Obstructive apneas were seen in three control infants (three episodes), one sibling (five episodes), and six near miss for SIDS infants (25 episodes). The obstructive apneas tended to be short (less than 10 seconds). Comparatively, the central apneas were equally distributed in the three groups of infants, and only the near miss children presented apneas that lasted as long as 19 seconds. The decrease in transcutaneous PO2 was proportional to the duration of both types of apnea, but for a given duration the decrease in transcutaneous PO2 was significantly greater for the obstructive apneas than for the central apneas (with a mean difference of 7.59 +/- 0.53% PO2. It is concluded that the hypoxic effects of the obstructive apneas might have important clinical implications in infants, such as the near miss for SIDS.

Effects of central apneas on transcutaneous PO2 in control subjects, siblings of victims of sudden infant death syndrome, and near miss infants.

A total of 75 polysomnograms recorded during night sessions in 25 control subjects, 25 siblings of sudden infant death syndrome victims, and 25 near miss infants were studied in order to correlate the duration of central apnea to the decrease in transcutaneous oxygen pressure (tcPO2). A total of 1,650 central apneas were recorded. The three groups of infants presented the same tendency for a lower tcPO2 in indeterminate and active sleep as in quiet sleep (P greater than .10). The apneas were not preceded by a decrease in tcPO2, but were followed by a decrease in tcPO2, directly proportional to the duration of apnea. The correlation was measured in each infant individually, and proved to be significant in all cases, and comparable in the three groups. The longest apneas (greater than ten seconds) were followed by the greatest decrease in tcPO2, and were restricted to the near miss group. Apart from this observation, the near miss and sibling infants did not show lower tcPO2 than the control subjects, at any time, during sleep.