Propofol has no direct effect on sinoatrial node function or on normal atrioventricular and accessory pathway conduction in Wolff-Parkinson-White syndrome during alfentanil/midazolam anesthesia

Variable effects of adenosine on retrograde conduction in patients with atrioventricular nodal reentry tachycardia

Adenosine has been demonstrated to reliably produce transient block of atrioventricular nodal (AVN) conduction, and has been advocated as a method of differentiating retrograde conduction via the atrioventricular node from accessory pathway conduction. However, the response of retrograde AVN to adenosine in patients with typical atrioventricular nodal reentry tachycardia (AVNRT) remains unclear. We evaluated 13 patients (mean age 45 +/- 20 years) with typical AVNRT prior to AVN modification. During right ventricular pacing, a rapid bolus of adenosine (0.2 mg/kg; maximum 18 mg) was administered. Adenosine sensitivity, defined by transient ventriculoatrial block, was observed in six patients, while in seven patients ventriculoatrial conduction was unaffected. An adenosine bolus administered during sinus rhythm or atrial pacing resulted in antegrade atrioventricular block in all the adenosine resistant patients in whom this was performed (n = 6). Comparisons of AVN electrophysiological characteristics between the adenosine sensitive and adenosine resistant patients were performed. There was no difference with respect to ventriculoatrial effective refractory period, ventriculoatrial Wenckebach, AVNRT cycle length, and His to atrial echo interval in AVNRT. However, there was a trend toward a longer antegrade fast pathway ERP in the adenosine sensitive group (P = 0.07). Electrophysiological properties do not predict retrograde AVN adenosine sensitivity. Adenosine does not cause retrograde AVN block in all patients with AVNRT, and therefore cannot reliably distinguish between retrograde conduction via the AVN or an accessory pathway.

Comparative direct electrophysiological effects of propofol on the conduction system and ionic channels of rabbit hearts

1. Propofol, an intravenous anaesthetic agent, can affect cardiac conduction but the ionic mechanisms have not been well defined. 2. This study measured the direct effects of propofol on the cardiac conduction system by using intracardiac recording/stimulation in Langendorff-perfused rabbit hearts. The underlying ionic mechanism was elucidated by using the whole-cell voltage clamp on rabbit isolated atrial and ventricular myocytes. 3. Propofol prolonged significantly the AV conduction (AH) interval at a clinically relevant concentration (3 microM). This AH interval prolongation was dose-dependent (3 to 100 microM). At higher concentrations, the AV nodal Wenckebach cycle length and its refractory period were also prolonged (10 to 100 microM). In addition, the conduction through the His-Purkinje system (HV interval) and the atrial tissue (SA interval), as well as the spontaneous cycle length, were lengthened dose-dependently (30 to 100 microM). 4. In isolated ventricular myocytes, Na current was decreased dose-dependently by propofol. In part this was due to a negative-shift of the steady-state voltage-dependent inactivation and a slowed rate of recovery from inactivation. The INa suppression by propofol was frequency-dependent. Propofol also blocked the ICa. The ED50 for peak current inhibition was 6.9 +/- 0.9 (n = 6) and 8.3 +/- 1.5 microM (n = 7) for INa and ICa, respectively. 5. The transient outward potassium current (Ito) of atrial myocytes was suppressed with an ED50 of 5.7 +/- 0.8 microM (n = 11), which was only partly caused by a left-shift of the steady-state inactivation. The inward rectifier K current (IK1) of the ventricular cells was reduced somewhat by propofol. 6. In summary, propofol can cause direct dromotropic and chronotropic effects on the cardiac conduction system, especially the atrioventricular node. These changes can be attributed, at least in part, to its direct dose-dependent suppression of the cardiac ICa, INa and Ito. Special concerns in the use of propofol anaesthesia for cardiac patients and the therapeutic antiarrythmic potential of propofol-like compounds are addressed.

Age-related propofol effects on electrophysiological properties of isolated hearts

We compared the direct effects of propofol on the conduction system of neonatal (< 7 days) and adult (> 3 mo) rabbit hearts using intracardiac recording/ stimulation in Langendorff-perfusion and autonomic blockade. At a low concentration (3 microM), propofol caused a slight but significant lengthening of the atrio-ventricular (AV) conduction interval of the adult hearts, but not of neonatal hearts. At a higher concentration (10 microM and above), propofol significantly prolonged the AV conduction interval in a frequency-dependent manner in both neonates and adults. The AV Wenckebach cycle length was also lengthened, with the change more significant in the adults. However, with concentrations of propofol up to 100 microM, the neonatal hearts frequently (9 of 13 experiments) progressed to complete AV block, which was not observed in the adults. Conduction through the atrial tissue (SA interval) and the His-Purkinje system (HV interval), as well as the spontaneous heart rate, were all slowed by propofol at 30 microM or above. However, the lengthening of SA interval was more pronounced in the neonates, and only in the neonate was the atrial refractory period prolonged by propofol at 10 microM and above. We conclude that 3 microM propofol produces no significant direct effects on the neonatal cardiac electrophysiological properties, although AV conduction of the adult heart may be suppressed at this concentration of propofol. At higher concentrations, age-related propofol effects were demonstrated in the AV node and the atrial tissue.