Sinuatrial Conduction Time Research Articles

Parasympathetic overactivity and its evaluation in patients with sinus nodal dysfunction

In 17 controls, and 17 patients with sinus nodal dysfunction, an electrophysiologic study was made of sinus nodal function and atrioventricular nodal conduction in the basal state. The study was then repeated in all patients after atropine. The heart rate, mean sinus cycle length, variations of sinus cycle length, sinus node recovery times, sinuatrial conduction time, AH interval, and atrioventricular nodal Wenckebach threshold were significantly different in patients from those of controls. All these parameters changed significantly in patients after atropine, and were comparable to those of controls except for the atrioventricular nodal Wenckebach threshold. Atropine failed to increase the heart rate beyond 90 beats per minute in 10 of 17 patients (sensitivity of 59%) or by at least 30% above the resting heart rate only in 4 of them (sensitivity of 24%). The variations of sinus cycle length, and their standardized value, could detect sinus nodal dysfunction with sensitivities of 59 and 47%, respectively. From our results, we conclude that there is parasympathetic overactivity in patients with sinus nodal dysfunction. Because of their very low sensitivities, the atropine test and variations of sinus cycle length were not useful in identifying sinus nodal dysfunction noninvasively. The normal response of the heart rate to atropine does not exclude sinus nodal dysfunction, but atropine may help to differentiate abnormalities intrinsic and extrinsic to the sinus node during the electrophysiologic study.

Electrophysiologic evaluation of intravenous L-propionylcarnitine in man

L-propionylcarnitine, a short-chain acylcarnitine, has been shown in experimental studies to induce, during acidic and hypoxic conditions, some electrophysiological changes such as an increase of duration of the action potential and of the effective refractory period. In this study, the acute electrophysiological effects of intravenous L-propionylcarnitine (30 mg/kg in 3 min) were studied in 12 subjects with estimated normal function of the sinus node and normal parameters for atrioventricular conduction. Statistically significant changes were observed 2 min after infusion. The sinus cycle length shortened (866 ± 138 vs 818 ± 124 msec, P < 0.05) while refractory periods of the atrioventricular node increased (effective by 30–50 msec in four cases; functional from 425 ± 52 to 436 ± 55 msec, P < 0.05). Sinuatrial conduction time, atrial refractory periods, infranodal conduction, bundle branch, His-Purkinje system and ventricular refractoriness were unchanged. Systolic and diastolic blood pressure were also unchanged. Because of the limited effects on electrophysiological parameters, L-propionylcarnitine should be used as a metabolic drug even in patients with mild disturbances of conduction.

Cardiac electrophysiologic effects of adaprolol maleate, a new β-blocker, in closed chest dogs

Adaprolol maleate (adaprolol) is a new β-adrenergic receptor blocker. The cardiac electrophysiologic characteristics and the duration of action of adaprolol were studied in intact anesthetized dogs. The electrophysiologic parameters were evaluated before drug administration and 10 min after the administration of maintenance infusion of adaprolol (N=5). The duration of action was measured during constant infusion of isoproterenol, giving the adaprolol as a single i.v. bolus in different concentrations (N=5). Results of this study showed that adaprolol has marked electrophysiologic effects. Its major action was on sinus mode; it prolonged the basic sinus cycle length and had significant effect on intrinsic automaticity as reflected by the prolonged corrected sinus node recovery time and sinuatrial conduction time. There was, also, direct effect on atrial function and AV nodal function. Adaprolol prolonged the effective refractory period of the His-Purkinje system and the ventricle. The onset of action was very rapid (within seconds) and the duration of action was relatively prolonged (3 hrs). The potency of adaprolol's electrophysiologic effects are higher compared to other widely used β-blockers. Adaprolol appears to be a potent β-blocker with particularly strong antiarrhythmic effect and it would be very useful in the treatment of both supraventricular and ventricular tachyarrhythmias and ectopic beats.

Electrophysiological studies after the Mustard and Senning operations for complete transposition. Do they have prognostic value?

Overall, long-term survival after the Mustard or Senning operation is good, but late arrhythmias remain a concern. Whether postoperative electrophysiological investigations can identify patients at risk of developing serious arrhythmias is unknown. In this study, 16 children who underwent electrophysiological study after the Mustard or Senning operation for complete transposition (the combination of a concordant atrioventricular and a discordant ventriculo-arterial connexion) were followed up for one month to 9 years (mean 4.33 years) after this investigation. At the electrophysiological study, sinus nodal dysfunction was diagnosed in 9 16 patients, and abnormalities of atrial conduction and refractoriness in 7 13 . During follow-up, 7 children developed clinical evidence of the sick sinus syndrome. When considering corrected sinus node recovery time as the only electrophysiological parameter, the sensitivity of predicting sick sinus syndrome from the electrophysiological study was 42%, and specificity 66%. The sensitivity increased to 71% if additional electrophysiological criteria of sinus node dysfunction were included, such as sinuatrial conduction time or sinus node entrance block, but specificity dropped to 55%. Atrioventricular conduction disturbances were rare. Thus, abnormalities at electrophysiological studies after the Mustard or Senning operations are frequent, but identification of patients at risk of developing sick sinus syndrome remains difficult.

Electrophysiologic effects of intravenous dipyridamole

We evaluated the electrophysiologic effects of dipyridamole given intravenously to 24 patients during intracardiac electrophysiologic study. Electrophysiologic parameters were measured before and 5 minutes following infusion of 0.5 mg/kg of dipyridamole. The drug significantly shortened the sinus cycle length by 26 per cent ( P < 0.001), sinuatrial conduction time by 15 per cent ( P < 0.01), maximal sinus node recovery time by 21 per cent ( P < 0.001), atrial and atrioventricular nodal effective refractory period by 8 and by 11 per cent, respectively (both P < 0.01), ventricular effective refractory period by 4 per cent ( P < 0.001), paced cycle length to atrioventricular nodal Mobitz type II block by 5 per cent ( P = 0.046), and QT interval during sinus rhythm by 10 per cent ( P < 0.01). After dipyridamole, the PA interval increased by 16 per cent ( P < 0.001), the AH interval by 11 per cent ( P < 0.01), and the corrected QT interval by 5 per cent ( P < 0.01). During retrograde conduction we observed a shortening of the ventriculoatrial interval by 6 per cent ( P = 0.036), retrograde atrioventricular nodal effective refractory period by 5 per cent ( P < 0.001), paced cycle length to atrioventricular nodal Wenckebach and atrioventricular nodal Mobitz type II block both by 8 per cent ( P < 0.01). We conclude that intravenous dipyridamole increases sinus node automaticity and reduces atrial, atrioventricular nodal and ventricular refractory periods, prolongs intra-atrial and atrioventricular nodal conduction, but does not produce any changes in His-Purkinje system conduction times. Paced cycle length to atrioventricular nodal Wenckebach and Mobitz type II block decreased after dipyridamole during antegrade as well as retrograde conduction.

Recording of the electrocardiogram from the sinus node and direct measurement of the sinuatrial conduction time in children

Using a simple technique, the electrocardiogram from the sinus node, which had been previously recorded in adults, was for the first time derived successfully in 27 of 31 children (87%). The values of the sinuatrial conduction time were then precisely measured directly according to the electrocardiogram from the sinus node. The sinuatrial conduction time measured directly was significantly longer in 6 children with sick sinus syndrome (138.3 ± 10.3 msec, mean ± standard deviation) than in 21 normal children (66.9 ± 14.4 msec, mean ± standard deviation). No overlap was found between them. Furthermore, comparison was made between the children and the adults (7 cases with sick sinus syndrome, 32 cases with normal sinus nodal function). The results suggested that the electrocardiogram recorded from the sinus node may be a valuable and promising technique for the evaluation of sinus nodal function and in the accurate diagnosis of the sick sinus syndrome in children.

Electrophysiologic evaluation of intravenous nicardipine in man

The acute electrophysiological effects of intravenous nicardipine (0.014 mg/kg per min for 5 minutes) were studied in 12 subjects with estimated normal sinus node functions and atrioventricular conduction parameters. The most important effects were sinus cycle length shortening, increase of corrected sinus node recovery time and reduction of effective and functional refractory period of the atrioventricular node. Sinuatrial conduction time, atrial refractory periods, intranodal conduction, bundle branch refractoriness and ventricular refractoriness were unchanged. Systolic and diastolic blood pressure was reduced. The clinical implications of these properties of the drug are discussed and compared with those of verapamil, diltiazem and nifedipine.

Comparison of indirect and direct sinuatrial conduction time by synchronous sinus node electrogram

In order to determine whether or not the estimated indirect sinuatrial conduction time represented the real sinuatrial conduction time, we recorded the synchronous sinus node electrogram, on which direct sinuatrial conduction time could be measured during constant atrial pacing, in 21 cases with normal sinus node function. The results show first that the difference between direct and indirect sinuatrial conduction time is statistically significant ( P < 0.05); the correlation of the two is poor ( r = 0.29). Second, the direct sinuatrial conduction time after constant atrial pacing is significantly longer than that before constant atrial pacing, which means constant atrial pacing has resulted in obvious depression of conduction through the sinus node. Our conclusion is that estimated indirect sinuatrial conduction time does not represent real sinuatrial conduction time. The calculation formula using constant atrial pacing has been based on a major unproven assumption.

Functional abnormalities of the conduction system in children with an atrial septal defect

We performed an electrophysiologic study in 40 children with an atrial septal defect and analyzed their pre- and postoperative electrocardiograms and 24-hour Holter recordings. The electrophysiologic study showed a prolonged corrected sinus node recovery time in 83% and an abnormal sinuatrial conduction time in 25% of the children. An early Wenckebach response to atrial pacing was seen in 18%. Sixteen percent had a prolonged atrial conduction time. The atrial functional refractory period was abnormal in 35%. Two children developed nonsustained supraventricular tachycardia during the electrophysiologic study. The preoperative electrocardiogram showed first-degree atrioventricular block in 15% of the children; prolonged periods of accelerated atrial rhythm were found in 35% of the preoperative 24-hour Holter recordings. The incidence of first-degree atrioventricular block and accelerated atrial rhythm decreased postoperatively. We could not find a significant correlation between age or shunt size and the presence of electrophysiologic abnormalities or arrhythmias. These results indicate that the sinus node, atrioventricular node and atrial myocardium show some degree of dysfunction in patients with an atrial septal defect. An early operation may prevent further progression of electrophysiologic abnormalities and the development of symptomatic arrhythmias.

Electrophysiological effects of intravenous MDL 17.043

MDL 17.043, a nonglycoside, noncatecholamine imidazolone derivative with phosphodiesterase inhibiting activity, has been shown to possess both positive inotropic and vasodilator properties. In the present study, the electrophysiological effects of intravenous MDL 17.043 were assessed in 10 patients undergoing programmed right atrial stimulation for diagnostic purposes. MDL 17.043 was administered as a single intravenous bolus injection of 1.5 mg/kg body weight over 4 min followed by an intravenous infusion of 0.75 mg/kg body weight over 20 min. With the dosage schedule used, the MDL 17.043 plasma levels achieved were similar to those previously reported to be associated with significant hemodynamic improvement of congestive heart failure. Electrophysiological measurements were performed before and during MDL 17.043 administration. MDL 17.043 consistently shortened basic sinus cycle length, sinus node recovery time and sinuatrial conduction time and decreased Wenckebach cycle length, atrioventricular and atrial refractoriness leading to positive chronotropic and dromotropic effects.

Anterograde sinuatrial conduction evaluated by sinus node electrogram in atropine blocked retrograde atrial conduction

Two cases are described where atropine induced the disappearance of reset zone as response to premature atrial stimulation for blocked retrograde atrial conduction. Because of this, sinuatrial conduction time could not be estimated. The sinus node electrogram allowed the direct measurement of sinuatrial conduction and showed a facilitated anterograde conduction through the perinodal fibers after administration of the drug.

A method for evaluating different modes of action of an antiarrhythmic drug in man. The effects of propafenone on sinus nodal functions

In vitro experiments have shown that the antiarrhythmic effects of propafenone are due to a direct depressant action and to a beta-blocking activity. In this study a method was used to evaluate the direct effect and the autonomically mediated actions of an antiarrhythmic agent in a clinical setting. An electrophysiological study was performed twice, at an interval of 24 hr, in 17 patients (age: 52±17 years) with normal resting and intrinsic heart rate. In the first study the overall effect of intravenous propafenone (1.5–2 mg/kg) was evaluated by comparing the sinus node parameters obtained during the basal state and after drug administration. In the second study the direct depressant effect of the drug was evaluated by comparing the electrophysiological variables obtained following autonomic blockade (propranolol 0.2 mg/kg and atropine 0.04 mg/kg) and after propafenone. In the first study there was no significant change in the sinus cycle length and corrected sinus node recovery time and only a small (9.1%) increase in sinuatrial conduction time, whereas in the second study these variables increased significantly. The degree of increase in sinus cycle length and corrected sinus node recovery time was significantly higher in the second study than in the first one. These data suggest that: (1) propafenone has direct depressant effect on sinus automaticity but this effect is counteracted by autonomically mediated actions (most likely of vagolytic type); (2) the beta-blocking effect of the drug demonstrated in isolated atria is not seen in a clinical setting.

Electrophysiological factors of left bundle-branch block.

Left bundle-branch block is rarely an isolated disorder of conduction, additional disorders being found in 29 of 30 patients studied by intracardiac stimulation techniques. These included disorders of sinus node function (prolonged maximum sinus node recovery time (corrected) in 23%, prolonged sinuatrial conduction time in three of eight patients), atrioventricular node function (prolonged AH interval in 33%, prolonged effective and functional refractory periods in 37% and 74%, respectively), "His bundle to right bundle branch" conduction (prolonged HV interval in 53%), and ventriculoatrial conduction (absent in 62%). It is postulated that at least half of the cases of left bundle-branch block were incomplete, even though the duration of the QRS complex exceeded 120 ms, because of (further) leftward deviation of the mean frontal QRS axis with sufficiently premature atrial extrastimuli. Block may be complete or incomplete in left bundle-branch block with left axis deviation of -30 degrees or more on the standard electrocardiogram.

Effects of amiodarone on sinus node in man.

The effects of amiodarone on the sinuatrial node were studied in 24 patients after an intravenous injection of the drug (5 mg/kg). Sinuatrial function was assessed by rapid atrial pacing and premature atrial stimulation. Sinus cycle length did not change significantly, but the corrected sinus node recovery time was prolonged. While there was no significant change in sinuatrial conduction time, prolongation of the non-reset zone in 14 cases, as well as the abolition of the platesu in 2/24 patients, suggested that conduction of the atrial responses to the sinus node might have been depressed.

Clinical electrophysiological effects of propranolol on normal sinus node function.

In 35 patients aged 18 to 69 years (mean 48) with clinical, electrocardiographic, or electrophysiological evidence of normal sinus node function, the effect of intravenous propranolol (0.1 mg/kg) was assessed on 3 indices of sinus node function. The drug significantly prolonged sinus node cycle length (12%), slightly prolonged the corrected sinus node recovery time (15%), and slightly but insignificantly lengthened sinuatrial conduction time. Propranolol may be administered safely in patients with normal sinus node function without the fear of producing severe sinus bradycardia, sinuatrial block, sinuatrial pauses, or prolonged sinus asystole, after spontaneous or stimulation-induced conversion of a tachycardia.