Clinical significance of prolonged sinoatrial conduction time

Sinus node dysfunction in 128 patients. A retrospective study with follow-up

A retrospective study covering all admissions during a 6-year period revealed 128 patients with sinus node dysfunction (SND). The patients were grouped according to the ECG criteria chosen: group I 33 patients with sinus bradycardia, group II 37 with sinoatrial block/sinus arrest, group III 58 with brady-tachy syndrome. Additional heart disease, predominantly ischaemic, was found in 56%. The frequency and severity of symptoms increased from group I to group III. Pacemaker treatment was given to 40% of the cases, while medical treatment alone was successful in 17%. A follow-up including 104 patients was carried out after a mean observation period of approximately three years. Sixteen patients had died. The cause of death may have been SND per se in only one case. Five patients died of apoplectic insults or complications to such. In total, nine possible or proven systemic embolic events were found--all occurring in patients with brady-tachy syndrome. A progression of the ECG abnormality from a lower to a higher group took place in nine patients during the observation period. It is concluded that SND is a condition with a broad clinical spectrum and a stationary or slowly progressive course. In general, it carries a good prognosis. A substantial number of deaths of disabilities in patients with brady-tachy syndrome may be ascribed to systemic embolism. Long-term anticoagulant therapy is proposed in this subgroup of patients with SND.

Syncope: current diagnosis and treatment

The patient with syncope often poses a formidable diagnostic challenge. A large number of underlying causes must be considered, ranging in severity from benign to life-threatening. A careful, systematic clinical evaluation beginning with a history, physical examination, and ECG will establish the diagnosis in most patients, and the judicious use of specialized testing will confirm or uncover the cause in many of the remaining cases. Further basic and clinical research into the pathogenesis and treatment of neurocardiogenic syncope, the role of HUT testing in neurally mediated syncope, and the optimal use of EPS in patients with cardiac disease will markedly improve our management of these patients in the future.

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.

Syncope

Syncope is a clinical entity of diverse cause. The historical features surrounding the syncopal event and the presence or absence of heart disease are the most important features in establishing the cause for syncope. Passive head-up tilt study provides a means of identifying many patients with vasodepressor syncope. Electrophysiologic study is important in the elucidation of syncope in patients who have syncope undefined after noninvasive evaluation. With proper use of the modalities available, few patients will have an undefined cause for syncope.

Sinus node pacemaker shift: a phenomenon induced by premature atrial stimulation in man?

The aim of this study was to investigate whether premature atrial stimulation is able to induce a shifting of the sinus node pacemaker. For this purpose we compared, in 18 patients, the curve of sinus node function obtained with Strauss' method with that resulting from the scanning, with premature atrial stimulation, of the first returning cycle following a single premature induced atrial beat. We found that the length of the compensatory phase (zone I) evaluated on the curve resulting from the scanning of the first returning cycle following the single premature induced atrial beat was shorter (15%) than that observed with the original Strauss method. In addition, an inverse relationship between the shortening of the compensatory zone and the estimated sinoatrial conduction time was observed. This result could be accounted for by one of the following explanations: 1) a change in the sinoatrial conduction or in the sinus pacemaker automaticity; 2) sinus node reentry; 3) sinus node pacemaker shift. Even if there is no direct evidence either to prove or to exclude one or more of these explanations, sinus node pacemaker shift seems to be the most convincing explanation.

The role of electrophysiologic studies in the management of patients with unexplained syncope

We evaluated the frequency and type of electrophysiologic abnormalities in an unselected population of consecutive patients with unexplained syncope. Fifty patients were entered in the study; all had 24-hour dynamic electrocardiographic (Holter) recordings and underwent complete electrophysiological studies. An abnormal electrophysiologic study was found in 74% of the patients. Sinus node abnormality was observed in 30%, abnormal AV node function in 14%, long HV in 10%, block distal to H during rapid atrial pacing in 6%, paroxysmal supraventricular tachycardia in 12%, ventricular tachycardia/fibrillation in 8%, and hypersensitive carotid sinus syndrome in 24%. There was no correlation between Holter and electrophysiologic study findings except for the presence of paroxysmal sustained supraventricular tachycardia. Based on clinical, Holter monitoring, and electrophysiologic findings, 38% were treated by antiarrhythmic drugs, 40% received permanent pacemakers, and 22% were not treated at all. During follow-up (23 +/- 13 months), 9 patients (18%) experienced recurrent syncope or death.

Different determination of sinoatrial conduction time (SACT) in man

Using intracardiac recordings of electrical activity and programmed electrical right atrial stimulation of the human heart, the sinoatrial conduction time (SACT) in the method of Strauss et al. 1973 (SACTc) was calculated in 80 patients with and without disturbances of rhythm and compared to the modified measurement of the SACT in the method reported by Narula et al. in 1978 (SACTN). The number of continuously stimuli varied from 4, 8 and 16 stimuli with a frequency of 10% just above the averaged spontaneous frequency. The best correlation was found between the SACTc and the SACTN16 (r = 0.74; p less than 0.001) with a regression line of: SACTN16 = 1.04 SACTc + 28.6. Under these conditions, as opposed to SACTN4 or SACTN8, the most favourable reproducibility and relative coefficient of variation (rVk) could be observed: SACTN16: rVk = 9.5%; r = 0.91; SACTN8: rVK = 12.3%; r = 0.89; SACTN4: rvK = 24.3%; r = 0.53. Higher individual values for SACTN16 were found by continuous atrial stimulation as compared to other methods of determination indicating mainly a higher depression of sinus node automaticity due to overdrive suppression. Under parasympathicolysis (1 mg atropine) the lowest values of SACT were found for SACTN4 (45.9 +/- 20.7 ms) coming closest the "true" SACT, since these conditions neither an increase of the refractory period nor an overdrive suppression exert an influence.

Evaluation of the patient with syncope

The evaluation of the syncopal patient is often expensive and may not yield a specific diagnosis. An understanding of the cardiac and noncardiac causes of syncope can be helpful in making a specific goal-oriented evaluation of these patients.

A second zone of compensation during atrial premature stimulation: evidence for decremental conduction in the sinoatrial junction

125 consecutive patients with premature atrial stimulation were studied. Three demonstrated sinus node return cycles that were fully compensatory following premature atrial stimuli delivered early in diastole. This second zone of compensation was unaccompanied by significant alterations in the post-return cycle lengths or in P-wave morphology of the return cycle. To account for the occurrence of a complete compensatory pause following very early premature atrial depolarizations, we consider the possibility that retrograde conduction of the early atrial premature depolarization (APD) in the sinoatrial junction was delayed for a sufficient length of time to allow the sinus node to depolarize spontaneously on schedule. Collision between the APD and sinus beat would then occur despite the marked prematurity of the APD. Thus, the early APD had encountered the relative refractory period of the sinoatrial junction, suggesting that decremental conduction takes place within the sinoatrial region in man. These findings imply that there is the potential for reentry in the region of the human sinoatrial junction.

Evaluation and outcome of emergency room patients with transient loss of consciousness

We identified 198 patients who presented to our emergency room with transient loss of consciousness. Seizures (29 percent of patients) and vasovagal/psychogenic episodes (40 percent of patients) were the most common presumptive causes of loss of consciousness, but the cause of loss of consciousness remained uncertain even at follow-up in 11 +/- 6 months in 13 percent of the patients. The history and physical examinations were sufficient for diagnosis in 85 percent of the patients in whom a diagnosis could be established. These data guided inpatient and outpatient with potentially dangerous causes of loss of consciousness except for one patient who had pulmonary embolism. In selected patient, diagnostic tests such as blood chemistries (three patients), electrocardiograms (four patients) electroencephalograms (three patients), and Holter monitoring (four patients) provided crucial information, and CT scans identified new brain tumors in four patients with focal neurologic presentations. At the time of follow-up, 7.5 percent of patients had suffered either major morbidity or death related to the cause of the index episode of loss of consciousness. Patients with cardiac causes represented a high risk (33 percent) group for such poor outcome, whereas patients who were under age 30, or who were under age 70 and had loss of consciousness on a vasovagal/psychogenic or unknown basis, constituted a low risk (1 percent) subgroup.

The spectrum of cardiac rate and rhythm in normal newborns

The distribution and variation of cardiac rate and rhythm in normal neonates has previously received little attention. This has made clinical assessment of dysrhythmia in newborns difficult. We therefore performed continuous 24-hour electrocardiography in 29 normal newborn subjects (age range, 1 to 6 days; mean, 3.5 days). The ECG tapes were then analysed in detail to define the normal range of cardiac rate, conduction intervals, and rhythm during waking and sleeping periods. Maximum sinus rate (awake) ranged from 150 to 222 beats per minute (mean, 192 +/- 16 [SD]), and minimum rate (awake) from 78 to 140 beats per minute (mean, 107 +/- 15). During sleep, the maximum rate ranged from 125 to 210 (mean, 168 +/- 23) and the minimum from 72 to 120 beats per minute (mean, 92 +/- 11). The maximum variation in rate for any individual during the 24-hour period ranged from 73 to 134 beats per minute (mean, 100 +/- 17). Sinus rhythm predominated with mild irregularity occurring episodically in 24 and moderate irregularity in 4 infants. An isolated atrial premature beat was present in 2 subjects, and an atrioventricular (AV) junctional escape rhythm occurred in one other after a sinus pause of 840 msec. Ventricular premature beats or AV conduction abnormalities were not observed. The corrected QT interval (QTc) ranged from 0.298 to 0.514 sec (mean, 0.390 +/- 0.026). The maximum variation in QTc over 24 hours ranged from 0.052 to 0.160 sec (mean, 0.097 +/- 0.028). We conclude that cardiac rhythm and conduction appear more stable in normal newborns than in older normal subjects and that bradycardia, conduction defects, and ventricular ectopy of the type recently reported in young normal adults seem to be more uncommon in the neonatal period.

Assessment of oral quinidine effects on sinus node function in sick sinus syndrome patients

The effects of therapeutic doses of orally administered quinidine sulfate on sinus rhythmicity and automaticity were observed in 11 patients with sick sinus syndrome (SSS). Evaluation of sinus node (SN) function was undertaken by assessing sinus nodal recovery time (SNRT), treadmill exercise testing, and 24-hour ambulatory ECG monitoring before and after quinidine administration (25 mg/kg) (range 800 to 1600 mg daily). Corrected SNRT ranged from 100 to 1320 msec (average 551) before quinidine and was not significantly (p greater than 0.05) altered after quinidine to 346 to 660 msec (average 481). Further, quinidine did not induce accelerated infrasinus pacemaker activity. Spontaneous sinus rate evaluated with ambulatory monitoring revealed average rate of 57 bpm (range 53 to 63) before quinidine without significant increase to average 59 bpm (range 52 to 80) after quinidine therapy. Similarly, the maximal SN response to exercise was not significantly affected by quinidine (average 129 bpm before and 129 bpm after drug therapy). It is concluded that therapeutic doses of quinidine do not exert adverse effects on SN function in SSS patients. Chronic oral quinidine therapy can therefore be used safely with caution in patients with chronic SN disease when indicated for control of tachyarrhythmias.

Atrial bigeminy with block associated with bradycardia and paroxysmal atrial fibrillation -- an important variant of the tachycardia-bradycardia syndrome

Serial 2-channel 24 h dynamic ECGs in 7 patients who were referred with the "tachy-brady" syndrome for consideration for permanent cardiac pacing revealed: 1. atrial premature beats (APBs) which were conducted to the ventricles normally or aberrantly; 2. intermittent atrial bigeminy with block towards the ventricles (this rhythm mimicked sinus bradycardia with ventricular rates of 38-45 beats/min and the ectopic P waves were visible on only one of the ECG channels); 3. paroxysms of atrial fibrillation initiated by closely coupled APBs. These findings suggested that both the ventricular bradycardia and the atrial fibrillation were caused by frequent APBs and that pacing therapy was unnecessary. Disopyramide was given to 5 patients resulting in suppression of the arrhythmia and relief of symptoms. In one patient there was spontaneous resolution and one patient refused treatment. This variant of the "tachy-brady" syndrome can be successfully treated by suppression of abnormal atrial impulse formation without recourse to pacemaker implantation.

Sinus bradycardia in the aged

In the aged, sinus bradycardia represents the sinus-node-dysfunction component of diffuse conduction system disease associated with coronary and cerebral arteriosclerosis. Findings are presented on 15 patients whose ages ranged from 69 to 93 years at the time of admission to a home for the aged. They remained under observation (with electrocardiographic data) for from less than 1 year up to 18 years. The findings illustrate the evolution of conduction system abnormalities, including sinus node dysfunction, occurring either as an initial or an interval event. These abnormalities represent positive indications for pacemaker insertion in the aged.

Sinus node dysfunction. An overview with emphasis on autonomic and pharmacologic consideration

Sinus node dysfunction is a disorder of impulse generation and impulse conduction. Previous works have emphasized that the dysfunction occurs not only within the sinus node but also within the escape pacemaker. Adrenergic and cholinergic mechanisms, as well as pulsations and pressure within the sinus node artery, play an important role in normal sinus node activity. Although perinodal fibers act as a buffer zone for sinoatrial conduction, their role in man is yet to be clarified. During normal sinus node activity, pacemaker shifts from the sinus node to the crista terminalis have been shown to occur. Following sinus node destruction, similar shifts do occur. Clinical methods of determining sinus node function, such as the sinus node recovery time and sinus atrial conduction time, are useful but have limitations. Dynamic electrocardiographic monitoring provides the best clinical method available for detecting sinus node dysfunction. Digitalis appears to improve the parameters of sinus node function by increasing the automaticity of latent atrial pacemakers. The atrial arrhythmia of sinus node dysfunction appears to be related to the characteristics of latent atrial pacemaker and "enhanced" cholinergic tone.

Effects of digitalis on sinus nodal function in patients with sick sinus syndrome

The effect on sinus rhythmicity and automaticity of complete digitalization in a 24 hour period was observed in 14 patients with sick sinus syndrome. Sinus nodal function was evaluated in these patients by assessing sinus nodal recovery time and by treadmill exercise testing and 24 hour Holter monitoring, before and after digoxin administration. Corrected sinus nodal recovery times ranged from 240 to 2,065 msec (average 714) before digoxin and were shortened to 250 to 1,260 msec (average 565) after the glycoside. Further, digoxin induced accelerated infra sinus escape pacemaker activity in five patients: junctional and ventricular in one and atrial in four. Spontaneous sinus rate evaluated with Holter monitoring revealed an average of 56 beats/min (range 43 to 69) before digitalis that was unchanged (average 58 beats/min; range 48 to 74) after digoxin therapy. Similarly, the sinus nodal response to exercise was unaffected after digitalization (average 118 beats/min both before and during digitalis therapy). It is concluded that digoxin does not exert adverse effects on sinus nodal function in patients with sick sinus syndrome. The glycoside can be used safely in these patients when indicated for cardiac pump dysfunction or for control of tachyarrhythmia.

Obscure syncope and the sick sinus syndrome

This report describes a 25-year-old vigorous young man who had a history of eight years of near syncope and syncope of unknown etiology. Repeat in-hospital observation and laboratory electrophysiologic functional testing did not elucidate the origin of the symptoms. Prolonged Holter monitoring finally showed that the syncopal attacks were caused by a sick sinus syndrome (SSS). On electrophysiologic study, a concealed rate-dependent unidirectional antegrade accessory A-V pathway (AP) was found to be present. The AP was an incidental finding and was unrelated to the patient's symptoms. The symptomatic SSS may occur in the young as well as in the elderly. Sinoatrial dysfunction may be intermittent and difficult to detect, may cause severe symptoms, and may even be life-threatening. Prior to definitive therapy (such as the permanent implantation of a pacemaker), the importance of relating symptoms to a rhythm disturbance has been stressed. In cases where the cause of the symptoms is not obvious, this is best accomplished by continuous Holter monitoring.