Sinus node recovery time related to paced cycle length in normals and patients with sinoatrial dysfunction

Pacing-induced chronic atrial fibrillation impairs sinus node function in dogs. Electrophysiological remodeling

BACKGROUND

We assessed the effects of pacing-induced chronic atrial fibrillation (AF) on sinus node function, intra-atrial conduction, and atrial refractoriness.

METHODS AND RESULTS

In 15 mongrel dogs (20 to 30 kg), AV nodal block was produced by radiofrequency catheter ablation, and a ventricular-inhibited (VVI) pacemaker (Minix 8330, Medtronic) was implanted and programmed to pace at 80 pulses per minute. In 11 of these dogs, right atrial endocardial pacing leads were connected to a pulse generator (Itrel 7432, Medtronic) and set at a rate of 20 Hz to induce AF. Corrected sinus node recovery time, P-wave duration, 24-hour Holter ECG to assess AF duration, maximal heart rate in response to isoproterenol (10 micrograms/min), intrinsic heart rate after administration of atropine (0.04 mg/kg) and propranolol (0.1 mg/kg), and atrial effective refractory periods (ERPs) were obtained at baseline (EPS-1) and after 2 to 6 weeks (EPS-2) of VVI pacing alone (n = 4) or VVI pacing and rapid atrial pacing (n = 11). At EPS-2, corrected sinus node recovery time and P-wave duration were prolonged, maximal heart rate and intrinsic heart rate were decreased, atrial ERPs were shortened, and the duration of AF was increased significantly compared with EPS-1. These changes partially reversed toward baseline 1 week after conversion to sinus rhythm. Sinus node function and AF inducibility observed in the control dogs that underwent ventricular pacing alone (n = 4) did not change.

CONCLUSIONS

Pacing-induced chronic AF induces sinus node dysfunction, prolongs intra-atrial conduction time, shortens atrial refractoriness, and perpetuates AF, changes that reverse gradually after termination of AF.

Sinus node recovery time assessment revisited: role of pharmacologic blockade of the autonomic nervous system

Sinus node recovery time assessment is used to diagnose clinically significant sinus node dysfunction (SND) when Holter has failed to prove a relationship between sinus bradyarrhythmias and symptoms, but consensus has not been reached as to the value of including assessment after pharmacologic blockade of the autonomic nervous system. This issue was addressed in the present study performed on 52 patients with syncope or presyncope/dizziness (n = 48), sinus bradyarrhythmias (n = 45), or both (n = 41). Group 1 consisted of 13 patients with a proven relationship between symptoms and sinus bradyarrhythmias. Group 2 consisted of 39 patients with suspected SND. The protocol included three pacing periods at two pacing rates and was performed at baseline (n = 52), after single doses of atropine and propranolol (0.02 mg/kg and 0.1 mg/kg, respectively) (n = 41), and again after a second dose (n = 29). The sensitivity of prolonged recovery times was 77% in group 1. Among group 2 patients, 56% had prolonged recovery times at baseline (79% when including the results after the first dose of drugs). The second dose did not contribute diagnostic information, but it caused significant adverse reactions in 7 of 29 patients (P < 0.001). These 7 patients were all older than 60 years. Assessment of sinus node recovery time after pharmacologic blockade of the autonomic nervous system thus increases the sensitivity of the method in patients with suspected SND and normal baseline results. However, only 50% of the initially suggested doses of atropine and propranolol is sufficient and eliminates the risk for significant adverse reactions.

Electrophysiological testing of sinus node function: diagnostic and prognostic application-including updated information from sinus node electrograms

Sinus node function, including automaticity, conduction, and refractoriness, can be studied in the human electrophysiology laboratory. This review details the current methods used for such studies and discusses their clinical value. Of special emphasis in this article is the role of sinus node electrography in the clinical laboratory. Included also is an update of the data relating the duration of sinus node depolarization as measure on sinus node electrograms to other parameters that assess sinus node function as well as data supporting the direct relationship between the duration of the sinus node depolarization as the severity of sinus node dysfunction.

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.

Reproducibility of electrophysiologic parameters of extrinsic sinus node function in patients with and without sick sinus syndrome

In a group of 50 patients we investigated the daily reproducibility of the resting heart rate (RHR), the maximal corrected sinus node recovery time (CSNRTM), the pacing rate at which the CSNRTM occurred (OP), and the sinoatrial conduction time (SACT) during basal state. The study population was divided into two groups according to the presence or absence (as evidenced during the initial electrophysiologic study) of sinus node disease: group I included 35 patients with normal sinus node function, and group II included 15 patients with sick sinus syndrome. The electrophysiologic study was repeated approximately at the same hour and under similar conditions after an interval of at least two days (mean: 3.2 days for group I and 4.7 days for group II). The results showed good reproducibility with the exception of RHR in group I which slightly but significantly decreased in the second electrophysiologic study. The daily variations of the sinus node parameters appeared to be of similar levels in the two groups except for the CSNRTM; this parameter showed wide variations in single values in both groups, more marked in group II than in group I. Furthermore, if the CSNRTM and/or SACT were normal, it was likely that they would remain normal whatever the electrophysiologic status of the patient. Inversely, the change of status from abnormal to normal CSNRTM or SACT was not uncommon in patients with electrophysiologic signs of sinus node disease.

Electrophysiologic testing in patients with recurrent syncope: are results predicted by prior ambulatory monitoring?

Syncope is a common medical problem which can result from many etiologies, including cardiac dysrhythmias. Because ambulatory monitoring usually fails to capture a syncopal episode, electrophysiologic testing has been used to elucidate dysrhythmic mechanisms in patients with recurrent syncope. To assess whether findings on ambulatory monitoring not obtained during syncope can be used to indicate the results which are found on electrophysiologic testing in patients with recurrent syncope, we reviewed the ambulatory monitoring records of 59 such patients referred for electrophysiologic testing. Although 29 patients had abnormalities on electrophysiologic testing, 13 of which were severe, in only six were the findings suggested by the abnormalities recorded during ambulatory monitoring. Twenty-one patients actually had concordance between electrophysiologic testing and ambulatory monitoring results, but in 15 of the 21 results of both tests were normal. Severe abnormalities were more frequently detected in our patient population by electrophysiologic testing than by ambulatory monitoring, especially if patients had organic heart disease.

The values and limitations of deductive analysis and electrophysiological testing in patients with sinoatrial arrhythmias

We reviewed the values and the limitations of deductive analysis and electrophysiological testing of sinoatrial arrhythmias (SAA). Both methods have a place in the evaluation of SAA and are complementary. Careful analysis of the surface ECG and the response of the sinus node to various tachyarrhythmias and to atrial premature beats can provide important information about the automaticity of the sinus node and sinoatrial and atriosinus conduction. Because of the sporadic nature of some SAA, the surface ECG sometimes must be supplemented by ambulatory ECG recording. This approach improves one's ability to analyze the underlying mechanism and it can also clarify the relation between the SAA and the patient's symptoms. Electrophysiological testing can be employed to reproduce certain SAA and to assess the effects of various drugs on sinus node function. This approach is superior to deductive analysis in the identification of some sinoatrial conduction abnormalities and sinus node reentry. Among the disadvantages of electrophysiological testing are its invasive character and the fact that normal electrophysiological results do not exclude sinus node dysfunction. A definitive clarification of the underlying mechanism of SAA requires direct recording of the sinus node electrogram.

Sinus node recovery times following the spontaneous termination of supraventricular tachycardia and following atrial overdrive pacing: a comparison

We compared the pauses that followed the spontaneous termination of supraventricular tachyarrhythmias with the pauses that followed the cessation of atrial overdrive pacing in 21 patients. In 10 patients with abnormal sinus node function and in 11 patients with normal sinus node function we recorded the spontaneous termination of supraventricular tachyarrhythmia in the clinical electrophysiology laboratory; a strong correlation (r = 0.94) was found between the maximal spontaneous sinus node recovery time and the maximal paced sinus node recovery time. A weaker correlation was found between the paced and spontaneous sinus node recovery times (r = 0.57) when the spontaneous termination of supraventricular tachyarrhythmia was recorded during ambulatory electrocardiographic recording in seven patients. Spontaneous sinus node recovery times were significantly shorter than maximal paced sinus node recovery times (p less than 0.001). However, no significant difference was detected between the paced and spontaneous sinus node recovery times when atrial pacing was performed at the rate of the tachycardia. We conclude that spontaneous and postpacing sinus node recovery times are closely correlated. The paced sinus node recovery time is, however, frequently more prolonged than spontaneous sinus node recovery time because of probable atriosinus entrance block during rapid supraventricular tachycardia.