Effectiveness of pacemaker treatment in the bradycardia-tachycardia syndrome

The sick sinus syndrome

Clinical and electrophysiological characteristics have been investigated in a group of 30 patients with a sick sinus syndrome. No predictable response to exercise or drugs was observed, although a poor response of the sinus rate to atropine was present. Distal conduction abnormalities were found in seven of 14 patients, in whom detailed electrophysiological measurements were made, and sinus node recovery time was abnormal in all except one. Treatment with permanent pacing not only relieved syncope and dizziness, but made drug treatment of associated tachyarrhythmias feasible. The elusive and intermittent nature of the syndrome is stressed. The pathological findings in one case are described at length.

Incidence of atrioventricular block and chronic atrial flutter/fibrillation after implantation of atrial pacemakers; follow-up of more than ten years

The incidence of atrioventricular (AV) block and chronic atrial flutter/fibrillation was determined in 41 patients, mean age 62.2 years (22 to 88 years) who received atrial pacemakers before October 1980. The mean follow-up period was 12.3 years, range 11-14.4 years. Twenty-five patients suffered from bradycardia-tachycardia syndrome, 13 symptomatic bradycardia, and 3 bradycardia related ventricular tachycardia. At follow-up: 18 patients (44%) had permanent I-AV block; 11 patients had II-AV block, 9 patients (22%) transient Wenckebach block and 2 patients (5%) transient Mobitz block, all asymptomatic. The cumulative incidence of III-AV block was 1 (2.5%). Chronic atrial flutter/fibrillation occurred in 6 patients (15%), 5 were not pacemaker-dependent; 1 received a ventricular pacemaker. Seventeen patients died after a mean of 7 years (0.6-12.2 years). Cumulative survival rate of 58% for 14.4 years, did not differ from a matched cohort of the normal population. There were no pacemaker related deaths. We conclude that long-term atrial pacing was safe and effective. The incidence of III-AV block and chronic atrial flutter/fibrillation was low.

Incidence and predictors of syncope in paced patients with sick sinus syndrome

In spite of a normal pacemaker function, syncope still occurs in some patients with sick sinus syndrome (SSS). Causes often remain unknown. To identify predictors and etiologies of this bothersome symptom, we studied 507 patients who received atrial, ventricular, and dual-chamber pacemakers for SSS. During a mean follow-up of 62 +/- 38 months, actuarial incidence of syncope was 3% at 1 year, 8% at 5 years, and 13% at 10 years. Causes were vasovagal (18%), orthostatic hypotension (25.5%), rapid atrial tachyarrhythmias (11.5%), ventricular tachycardia (5%), acute myocardial ischemia (2.5%), and pacemaker/lead malfunction (6.5%). In 13 patients (29.5%), syncope remained unexplained. The only preimplant predictor for syncope was syncope as primary indication for pacemaker implant. Electrocardiographic correlation with bradycardia was not a predictor of relief of syncope during the follow-up.

IN CONCLUSION

(1) syncope in paced patients with SSS has multiple etiologies and may be multifactorial; (2) the only predictor of syncope after pacemaker implant is the occurrence of preimplant syncope as the main indication for pacing; (3) extensive Holter monitoring is not useful to document bradycardiac origin of syncope nor to predict its recurrence; (4) SSS probably overlaps with other entities such as autonomic dysfunction, vasovagal syncope, carotid sinus hypersensitivity, and venous pooling, which would provide an explanation for recurrent syncope in patients with normal pacemaker function.

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.

Morbidity and mortality of patients with sinus node disease: comparative effects of atrial and ventricular pacing

In patients with sinus node disease (SND), VVI pacing seems an inappropriate method of cardiac stimulation because of its potential adverse hemodynamic and arrhythmic effects. AAI-DDD pacing, preferred because of lower morbidity, may also determine a higher survival rate. We examined retrospectively two groups of patients with SND. Stimulated respectively with VVI pacing (group 1 = 57 patients) and AAI pacing (group 2 = 53 patients). The mean duration of the follow-up interval was 40.1 months for group 1 and 45 months for group 2. Ten patients (17.5%) in the VVI group and five (9.4%) in the AAI died. During the follow-up, in the VVI group three patients developed congestive heart failure and ten developed chronic atrial fibrillation, whereas only one case of heart failure and two with atrial fibrillation have been recorded in the AAI group. Moreover, four patients had embolic complications in group 1. Five patients (9.4%) with AAI pacing were converted to sequential pacing due to the occurrence of second-degree heart block. The statistical analysis was developed by the X2 test for the comparison of the proportion of the events (atrial fibrillation, congestive heart failure, embolic accidents) in the two groups: a significantly higher morbidity (P less than 0.01) was recorded in the AAI group. Survival is also higher in AAI patients, but the survival rate difference, calculated using the Mantel-Cox method, is not statistically significant. The findings of our study show that in SND the superiority of AAI pacing over VVI is statistically significant as far as morbidity is concerned, and we have also noticed an evident but not statistically significant superiority regarding mortality.

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.

Permanent cardiac pacing for brady-arrhythmia

The indications for and technology associated with permanent cardiac pacing have undergone major changes during the past decade. In contrast to the 1970s, most patients now receive cardiac pacing devices subsequent to the diagnosis of sick sinus syndrome. However, since this condition is prevalent in elderly patients, it is crucial that indications for pacing be critically evaluated and pacing recommended only for those with documented symptoms or marked abnormalities indicative of high risk for a subsequent cardiac event. This is particularly important because pacing has not been shown to influence survival in these patients. The technological advances in pacing devices during the last ten years now provide many desirable options. As a result, available pacemakers range from very simple to highly complex; accordingly, they have a wide range of prices. It is more important than ever to carefully select the appropriate pacing device for a given patient, since its cost, longevity, and required follow-up may differ greatly.

Chronic sinoatrial disorder (sick sinus syndrome): a possible result of cardiac ischaemia

Postmortem angiography was used to examine the blood vessels supplying the sinoatrial node in 25 subjects with chronic sinoatrial disorder (group 1). The results were compared with similar studies in 54 subjects who died of heart block and in whom sinus node function was normal (group 2). Although no significant lesion obstructing the blood flow to the sinus node was seen in the majority of those in group 1, there were abnormalities in seven cases, with reduced filling of the sinus node artery in five. In group 2 the sinus node artery filled normally in all cases despite major disease of the parent vessel in three. The combination of contralateral coronary artery disease with extensive atrial anastomoses was actively sought because this arrangement might predispose to a steal phenomenon. Such conditions were fully met in three cases in group 1 and two cases in group 2, and were found to a lesser extent in a further two cases in group 1 and three in group 2. Although coronary artery disease was unlikely to be the principal cause of sinus node dysfunction in most of the cases studied it was relatively common and may have been a factor in about one third. Improved survival after myocardial infarction may increase the number of patients with chronic sinoatrial disorder of ischaemic origin.

Comparative survival following permanent ventricular and dual-chamber pacing for patients with chronic symptomatic sinus node dysfunction with and without congestive heart failure

To determine whether survival following permanent ventricular demand pacing differs from survival following permanent dual-chamber pacing in patients with symptomatic sinus node dysfunction (unexplained sinus bradycardia, subsidiary rhythms, sinus arrest, sinoatrial block, or the bradycardia/tachycardia syndrome), we followed 79 patients who received a VVI pacemaker (group 1) and 49 patients who received a DVI or DDD pacemaker (group 2) for 1 to 5 years. There was no significant difference in sex distribution, mean age, or the incidence of coronary heart disease, hypertension, valvular heart disease, diabetes mellitus, stroke, or renal failure between groups 1 and 2. Overall, the predicted cumulative survival rates at 1, 3, and 5 years were 89%, 82%, and 74%, respectively, for group 1 and 94%, 86%, and 78%, respectively, for group 2. In patients with preexistent congestive heart failure (CHF), predicted cumulative survival rates at 1, 3, and 5 years were 78%, 69%, and 57%, respectively, for group 1 (n = 23) and 90%, 83%, and 75%, respectively, for group 2 (n = 16). Five-year predicted cumulative survival was significantly lower in group 1 patients with CHF than in group 2 patients with CHF (p less than 0.03). There was no significant difference in 5-year cumulative survival rates between groups 1 and 2 in patients without CHF. The results suggest that permanent dual-chamber pacing enhances survival to a greater extent than permanent ventricular demand pacing in patients with chronic symptomatic sinus node dysfunction and CHF.

The natural history of sick sinus syndrome

A literature review has addressed the two major factors in disease progression in sick sinus syndrome: atrioventricular block and atrial fibrillation. An incidence of atrioventricular block of 8.4 percent in a follow-up period of 34.2 months is considered clinically significant and sufficient to justify use of a ventricular lead in pacemaker management. Atrial fibrillation occurs much more commonly (22.3%) in ventricular pacing than with atrial demand pacing (3.9%) in a 2 1/2 year observation period. Coincident with the reduction in arrhythmia achieved by atrial demand pacing is a significant reduction in systemic embolism (1.6% vs. 13%). This is considered largely to be due to the improved rhythm control with AAI pacing but also possibly to the avoidance of retrograde atrioventricular conduction. The benefits of AAI pacing in terms of mortality in sick sinus syndrome have not yet been fully assessed. In the future, DDI pacing is recommended with, in some patients, the addition of another sensor to provide rate responsiveness on exercise.

Atrial versus ventricular pacing in sinus node disease: a treatment comparison study

Treatment with conventional ventricular pacing does not seem to influence the natural course in patients with sinus node disease (SND). In the present study the natural course of SND was compared in patients treated with ventricular (VVI) and those treated with atrial (AAI) pacing. The study population comprised 168 patients, 89 with atrial and 79 with ventricular pacing. The two groups were comparable with respect to clinical characteristics, degree of severity of SND, and length of follow-up period (average 2 years). Development of chronic atrial fibrillation and congestive heart failure was significantly more common in patients with ventricular than in those with atrial pacing (30% vs 4%, p less than 0.001; 23% vs 7%, p less than 0.01). Second-degree atrioventricular block developed in 4% of the atrially paced patients. Thus, atrial pacing is apparently superior to ventricular pacing in patients with SND.

Reappearance of persistent normal sinus rhythm in a patient with the sick sinus syndrome following cardiac pacing for 10.5 years

A patient with symptomatic sick sinus syndrome which manifested as a brady-tachy syndrome, was admitted to our institute in 1969. Following cardiac pacing for 10.5 years, the brady-tachy syndrome disappeared and normal sinus rhythm was restored. Her stable normal sinus rate has persisted up to the present, 2.5 years after termination of pacing.

Tracking of atrial flutter during DDD pacing: another form of pacemaker-mediated tachycardia

Two patients who had DDD pacemakers inserted for symptomatic sick sinus syndrome developed sustained upper-rate limit pacing. It was demonstrated in these two patients that pacemaker-mediated tachycardia was due to tracking of atrial flutter. DDD pacemakers should be used with caution in patients with the sick sinus syndrome and associated atrial tachyarrhythmias. Medical treatment of recurrent atrial tachyarrhythmias may allow patients to remain in the DDD mode.

Persisting symptoms despite permanent pacing. Incidence, causes, and follow-up

Persisting symptoms, consisting of palpitations, dizziness, or syncope, were found in 49 of 570 consecutively followed patients (8.6 percent) with permanent pacemakers (PM). Among 540 patients with ventricular PM, 19 had syncope and 24 dizziness; among 30 patients with dual-chamber PM, five had palpitations and one dizziness. Symptoms were PM-related in 17, caused by tachyarrhythmias in 12, of noncardiac origin in 16, and of unknown origin in four patients. Holter monitoring was necessary for evaluating the persisting symptoms in 36 patients and helpful in 32 studies (89 percent). Symptoms were relieved in all patients with PM-related causes but only in 6/16 patients (38 percent) with syncope or dizziness of noncardiac origin despite various therapeutic measures. In patients with either documented tachyarrhythmias or unknown cause of syncope or dizziness, antiarrhythmic drugs led to symptomatic improvement in 11 of 12 treated patients during an average follow-up of 15 months. We concluded that: (1) persistent syncope, dizziness, or palpitations occurred in 8.6 percent of 570 patients after PM-implantation; (2) symptoms were more frequent but less severe in patients with dual-chamber PM than in those with ventricular PM; (3) tachyarrhythmias as a possible cause of symptoms were found in 25 percent of patients; (4) symptomatic improvement was noted in 28 of 29 patients when a PM-related cause or tachyarrhythmias were treated.

Comparative evaluation of depressed automaticity in sick sinus syndrome by Holter monitoring and overdrive suppression test

To ascertain whether the long cardiac pauses on the Holter ECGs of patients with the sick sinus syndrome were related to the spontaneously occurring overdrive suppression, the heart rates for the 12 seconds preceding the cardiac pauses longer than 5 seconds were compared with that averaged for 24 hours. Even in six out of seven patients with bradycardia-tachycardia syndrome the former rate was not significantly greater than the latter, indicating that episodes of such long cardiac pauses may not result from spontaneously occurring overdrive suppression. This observation was also consistent with the result that no statistically significant correlation was obtained between the maximum pauses measured from Holter ECGs of sick sinus syndrome and those obtained by the overdrive suppression test. In conclusion, many episodes of long life-threatening cardiac pauses observed in sick sinus syndrome may be attributed to accidental depression of the sinus nodal and subsidiary pacemaker activity rather than to spontaneously occurring overdrive suppression; therefore, Holter monitoring may be useful as an additional tool for diagnosis of sick sinus syndrome.

Interactions between a rapid atrial stimulator and a multiprogrammable ventricular demand pacemaker

A patient with drug-resistant supraventricular tachycardia was well controlled for 8 years with a patient-activated rapid atrial pacemaker until she developed symptomatic bradycardic episodes. A multiprogrammable ventricular pacemaker was implanted. Assessment of the interactions between the two pacemakers demonstrated inhibition of VVI pacing by the atrial stimulator initially. Two months after implant no interaction was seen. At no time was VVT pacing affected by the atrial stimulator. Thus, interactions between these two units can occur and a multiprogrammable pacemaker should be used in this situation as it offers the flexibility to minimize any interaction that might be present.

Long-term follow-up after pacemaker implantation in sick sinus syndrome

In 74 symptomatic patients suffering from sick sinus syndrome, survival after pacemaker implantation and additional drug therapy was determined. The 5-year survival was poor (47.2%). Evidence of other cardiac disease (present in 44.6%) influenced the prognosis unfavorably, especially in combination with continuing symptoms. As yet the phase of SSS in which chronic cardiac pacing is required, should be considered as a critical stage.

Dispersion of atrial refractoriness in patients with sinus node dysfunction

Abnormal atrial refractoriness was examined as a cause of atrial fibrillation/flutter (AFF) in patients with bradycardia. Refractory periods at three disparate right atrial sites were compared in 17 patients with sinus node dysfunction (SND) and 16 controls. Atrial pacing shortened refractory periods, but failed to decrease dispersion of refractoriness significantly. During sinus rhythm, duration and dispersion of refractoriness were greater in SND patients than in controls. These differences persisted with atrial pacing. For example, at the paced rate, dispersion of effective refractory periods in SND patients was greater than in controls (62.9 +/- 34 vs 36.6 +/- 21 msec, p less than 0.01). Six SND patients had AFF, but they did not have greater dispersion than other SND patients, or unusually short or long refractory periods. Thus, prolonged and nonuniform refractoriness were features of SND. Abnormal refractoriness in SND reflected atrial disease and persisted with pacing. These abnormalities were not unique to patients with AFF.

Symptomatic sinus node disease: natural history after permanent ventricular pacing

Fifty-nine patients between the ages of 13 and 88 with sinus node disease, who received a permanent ventricular pacemaker between 1965 and 1976 at one institution, were followed to determine the natural history of the disorder after permanent pacing. Nineteen had ischemic heart disease, six had primary myocardial disease, and eight valvular heart disease. In 26, no etiology for the arrhythmia was apparent. The one- and five-year survival was 85.5% and 73.1%, respectively. Patients with underlying heart disease had a significantly poorer survival when compared to those without (58% versus 94% at 36 months) and all but 3 of 13 deaths in the first 36 months were in those with ischemic heart disease. There was a distinct trend toward poor survival in those with heart failure prior to pacemaker implant and those over age 65. Patients with sinus bradycardia alone did best (91% survival three years after implant), while those with bradycardia-tachycardia syndrome and those with sinoatrial arrest alone did distinctly worse (76% and 65% survival at three years, respectively). Twelve of 18 deaths were due to progression of underlying heart disease. The long-term prognosis with symptomatic sinus node disease can be predicted in part by (1) etiology of the underlying heart disease, (2) pre-implant arrhythmia, and (3) ventricular function prior to implant.

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.

The sick sinus syndrome. A study of 50 cases

The long term prognosis was studied in 50 patients treated for the sick sinus syndrome with pacemaker insertion. The mean age of the patients was 71 years. There were 31 females and 19 males in the series. Nine patients (18%) died during the average follow-up period of 19 months. Dizzy and syncopal episodes were abolished in most patients with pacemaker therapy. However only two of the nine patients in congestive heart failure improved with the pacemaker. Thus the long term prognosis of patients with the sick sinus syndrome is poor despite pacemaker therapy. This is particularly true for the patient in chronic congestive heart failure who does not respond to the pacemaker treatment.

Pathological studies in sinoatrial disorder (sick sinus syndrome)

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Recurrent paroxysmal supraventricular tachycardia: a complication of ventricular pacing in a patient with occult Wolff-Parkinson-White syndrome

A 60 year old man suffering from syncope believed to be due to the sick sinus syndrome was treated with a permanent demand ventricular pacemaker. This led to almost continous bouts of paroxysmal supraventricular tachycardia (SVT) over the ensuing two years, mistakenly believed to be part of the sick sinus syndrome. Careful study showed that this man had a type A Wolff-Parkinson-White accessory atrioventricular connection which consistently conducted retrogradely, but only rarely antegradely, during applications of carotid sinus massage. Episodes of SVT were repeatedly induced whenever ventricular-paced impulses captured the atria retrogradely. All episodes of SVT stopped when the ventricular pacemaker was removed. Following insertion of an atrial pacemaker, the patient had no episodes of SVT or syncope over a nineteen month follow-up period. This case illustrates the care required in selecting a proper site for protective pacing in patients who suffer from paroxysmal SVT.

Atrial pacing in patients with sinus node dysfunction

Sinus nod recovery time (SNRT) at paced atrial rates of 100 (SNRT100) and 120 (SNRT120) beats/min, atrial effective refractory periods at spontaneous heart rates (AERP) and at paced rates of 100 (AERP100) and 120 (AERP120) beats/min, and premature atrial stimulation were among the studies in evaluating 33 patients with symptomatic sinus node disease and 42 normal subjects. Although mean SNRT100 and SNRT120 were statistically significantly greater in patients than in control subjects, there was a significant overlap between patient and control groups, and SNRT100 or SNRT120 was associated with a 30.3 per cent false-negative and 5 per cent false-positive incidence. Correction for heart rate (SNRT-spontaneous cycle length) failed to improve the sensitivity or specificity of this test. There was no significant difference in mean AERP, AERP100 or AERP120, or in sinoatrial conduction time in patients compared with control subjects. Analyses of curves derived from plots of test and return cycles showed abnormal curves in only five of the 24 patients studied by progressively premature atrial stimulation. Two of these five patients showed normal zone I and II phenomena followed by a progressive linear increase in the return cycle that was thought to be due to abnormal refractoriness of the perinodal fibers.

Sick sinus syndrome requiring permanent pacemaker implantation in a patient with mirror-image dextrocardia

A patient with the sick sinus syndrome accompanying mirror-image dextrocardia which was associated with double superior venae cavae and an absent inferior vena cava is presented. A permanent transvenous demand pacemaker was inserted because of repeated episodes of dizziness and a documented 31/2-second period of asystole. Precise knowledge of the venous system and the location of the apex of the right ventricle was necessary prior to permanent pacemaker implantation.

Long-term survival of elderly patients after pacemaker implatation

The follow-up of 80 patients above the age of 70 years with implanted pacemakers is described. These patients were the most advanced in age from a total group of 150 with implanted pacemakers. Their ages ranged from 70 to 87 years, with an average of 75.4 years; 50 were male and 30 were female. An epicardial electrode was implanted in 13 patients and an endocardial electrode in 67. The pacemaker was implanted in 76 patients for symptomatic atrioventricular block and in four patients for sick-sinus syndrome. Two patients (2.5 per cent) died during the postoperative period and 19 patients within a period of 3 months to 6 years after the implantation. The survival rates were: 1 year, 90.0 per cent; 2 years, 82.1 per cent; 3 years, 74.1 per cent; 4 years, 67.2 per cent; 5 years, 58.3 percent. These survival rates were surprisingly similar, for the first 3 years of follow-up, to those of our and others' previous studies, which included all age groups. The survival rates in the most advanced age groups decreased in comparison only in fourth and fifth years after the implantation. There was no evidence of new episodes of myocardial infarction among this group of patients during the follow-up period. We conclude that even in patients of the most advanced age groups the implantation of an endocardial pacemaker significantly prolongs life, improves its quality, and this at a low operative risk.

Tachycardias and electrical pacing

Techniques of electrical pacing for the treatment of tachycardias are multiple. The choice of a suitable method for a particular tachycardia depends upon understanding the mechanism of the tachycardia and the pacing characteristics that will lead to interruption or suppression of the tachycardia, or to ventricular slowing. Electrical pacing is indicated for tachycardias when drug therapy alone has failed or cannot be initiated or continued, and only for those tachycardias that are likely to respond to this type of electrical stimulation. In either the circus movement type or the ectopic pacemaker type an ectopic tachycardia is more likely to be suppressed if the pacing site is near the site of origin of the tachycardia. Pacing more rapidly than the basic rate in order to prevent or abolish tachycardias is termed overdrive suppression. The mechanisms responsible for this phenomenon may be associated with release of acetylcholine, release of potassium, activation of an electrogenic sodium pump, increase in cardiac output and coronary flow, decrease in size of the heart with a consequent decrease in wall tension, and decrease in the inhomogeneity of recovery of excitability that occurs at more rapid rates in the non-ischemic heart. All of these effects of pacing suppress accelerated pacemaker activity or prevent emergence of conditions favorable for development of circus movement tachycardias. Paired, coupled, or rapid atrial pacing may improve ventricular performance or slow ventricular rate, or both, without abolishing the ectopic pacemaker activity. Atrial pacing with pacing sites located at endocardial, epicardial, coronary sinus, trans-septal, or esophageal locations may interrupt or prevent rapid supraventricular or ventricular arrhythmias. Similarly, ventricular pacing at endocardial, epicardial, myocardial, or transthoracic sites may be equally effective. Artificial pacing has abolished almost every type of tachycardia. Ventricular fibrillation always, and atrial fibrillation usually, require countershock if electrical treatment is to be employed, although defibrillation of the atria by rapid pacing has been reported once. Unipolar or bipolar pacemakers may be used temporarily, or permanently after implantation. Pacing rates used to abolish supraventricular tachycardias range from single premature beats to alternating current atrial pacing at 3600 cycles per minute. Artificial electrical stimulation of the heart may be on demand, or may be competitive (fixed rate). External magnets, induction coil coupling, and radio frequency signals allow competitive pacing to be used intermittently, with permanently implanted pacemakers. Thus, electrical pacing of the heart is a technique of major importance for the control of rapid heart rates.

Value of Holter monitoring in assessing cardiac arrhythmias in symptomatic patients

Holter electrocardiographic monitoring in 55 symptomatic patients with syncope, palpitations or dizziness uncovered significant arrhythmias in 30 patients (55 percent). By providing an observation period of at least 24 hours including a period of sleep, the procedure aided detection and diagnosis in both symptomatic and asymptomatic patients of transient arrhythmias or conduction abnormalities not documented by routine electrocardiograms. Bradyarrhythmias accounted for the majority of arrhythmias recorded in 21 or 30 symptomatic patients (70 percent); 15 had sinus bradycardia (35 to 55 beats/min) alone and 6 also had long episodes of sinus arrest of up to 5 seconds. Two had sinus bradycardia with periods of atrioventricular block with Wenckebach phenomenon. Five patients had a tachycardia-bradycardia syndrome; three had other episodic arrhythmias and one had pacemaker failure. In 15 (60 percent) of the 25 patients without arrhythmias, monitoring did not document the cause of symptoms. Holter monitoring is of considerable value in assessing the efficacy and adequacy of drug treatment, especially in patients with known heart disease, and in detecting pacemaker malfunction. However, very long periods of monitoring may be needed to make a diagnosis in those with only sporadic symptoms.

The tachycardia-bradycardia syndrome

The tachycardia-bradycardia syndrome (paroxysmal atrial fibrillation, flutter, or tachycardia followed by sinoatrial block or sinus arrest resulting in Stokes-Adams attacks) is an important clinical entity that requires familiarity by the clinician. Pathologic studies and physiologic mechanisms as revealed in the electrocardiogram indicate multiple disturbances in the conduction system of the heart (sinus node, atria, and atrioventricular junctional tissues). The electrocardiogram establishes the diagnosis. Pacemaker implantation with supplementary drugs has provided a satisfactory means of therapy. With proper treatment the prognosis of patients with the tachycardia-bradycardia syndrome has improved to the extent that the primary determinant of mortality is no longer the arrhythmia, but the underlying cardiac and/or systemic pathology.

Treatment of sinoatrial syndrome with permanent cardiac pacing in 90 patients

Out of a pacemaker population of 392 patients, 90 (23%) have been found to have sinoatrial syndrome. Their ages ranged from 22 to 86 years, and averaged 66 for men and 70 for women. The male-to-female ratio was 1:1.6. Before pacemaker implantation, syncopal attacks had occurred in 54%, dizziness without syncope in 31% and tachyarrhythmias in 57%. Atrial or paroxysmal supraventricular tachycardia had been recorded in 33%, atrial fibrillation or flutter in 28%, and ventricular tachycardia in 11%. First and/or second degree AV block was found in 36%. Coronary heart disease was present in 61% and 20% had had myocardial infarction. Cardiomyopathy and previous carditis were other associated heart diseases. Sinoatrial syndrome was the only manifestation of heart disease in 20%. Follow-up time after pacemaker implantation ranged from 3 months to 7 years, mean 23 months. Syncopal attacks were stopped in 48 of 49 patients, dizziness was relieved in all 28 patients and tachyarrhythmias were controlled by combined drug treatment in 43 of 51 patients. Nineteen patients died during the follow-up, most of them of cerebrovascular events or myocardial infarction. Associated coronary heart disease was especially frequent in this group. The death of one patient was caused by a run-away pacemaker. Other pacing failures were due to electrode movement or premature battery exhaustion. There was no mortality associated with pacemaker implantations or replacements. These results strongly support the view that pacemaker treatment most effectively controls symptoms of sinoatrial syndrome when drug treatment fails.

Pacing techniques in the management of supraventricular tachycardias. Part 1. The use of high frequency stimulation (HFS) in the management of paroxysmal supraventricular tachycardia

Using techniques for programmed electrical stimulation of the heart, seven patients with paroxysmal supraventricular tachycardia have been studied and shown to have a reciprocal mechanism as the most likely basis for the tachycardia. In four patients it was found that the tachycardia could be terminated by single right atrial premature beats and in three patients two right atrial premature beats were required. A variable zone for tachycardia termination was found when single or double stimuli were used and so a system for introducing high frequency stimuli at 100 or 1000 stimuli/sec for a given duration is described. Using this system a wider range of the cardiac cycle could be covered, thereby increasing the likelihood of producing correctly timed premature beats. The results of using this system are presented and its practical usage discussed.

Overdrive suppression in diagnosis of sick sinus syndrome

A criterion to determine the indication for pacemaker implantation in the sick sinus syndrome by overdrive suppression is proposed. Overdrive suppression was performed in 10 patients with the sick sinus syndrome (SSS) and another 10 patients with normal sinus rhythm (NSR) who served as controls. In the SSS group, 9 patients had complained of such severe symptoms as Adams-Stokes attack and/or congestive failure and were referred to our laboratory for pacemaker implantation. One other patient, an apparently robust young man (20 years old) referred for detailed cardiac examination, had no remarkable symptoms except for arrhythmias, but was found dead two months later. Atrial pacing for overdrive suppression was carried out at first at various rates ranging from 60 to 180 beats/min for 15 sec, and then at a rate of 100 beats/min for various durations ranging from 5 to 180 sec. After cessation of the atrial pacing, asystolic pauses were measured and the maximum (maximum pause) among the pauses obtained was used as a parameter indicating depression of cardiac automaticity. The maximum pause in the SSS group ranged from 5.6 to 9.0 sec (mean +/- SD = 7.0 +/- 1.2), WHILE THOSE IN THE NSR group ranged from 0.7 to 1.5 sec (mean +/- SD = 1.2 +/- 0.14). Therefore, the maximum pause was considered not only to reflect the severity of the symptoms necessitating pacemaker implantation in the 9 patients of the SSS group but to have warned us of sudder death in another patient. We concluded that overdrive suppression is useful as a supplementary challenge to determine indications for pacemaker implantation for the sick sinus syndrome, and that prolongation of the maximum pause beyond 5.0 sec is the critical level for pacemaker implantation.

Sinus node recovery time in the elderly

Measurement of the sinus node recovery time has been proposed as a diagnostic tool for recognition of the sick sinus syndrome. The latter is most frequently encountered in elderly patients with hypertension, coronary heart disease, and atherosclerosis. In order to provide normal values for the sinus node recovery time in this particular population group, atrial pacing studies were carried out in 30 subjects over 50 years of age, all with peripheral vascular disease and some with angina pectoris (10), residua of infarction (6), or hypertension (7). On stimulation, 7 patients maintained a I:I atrioventricular conduction up to the rate of 180/min. Second degree atrioventricular block developed in all other cases. On six occasions, Wenckebach's periods appeared at the relatively slow pacing rate of 120/min. The maximum postoverdrive pause ranged from 680 to 1600 ms with an average of 1100 ms plus or minus 190 (10). For each pacing speed, a correlation was found between the duration of the pause and the control intrinsic cardiac rate, longer pauses being associated with longer resting PP intervals. Beyond 120/min, the duration of the pause was seen to shorten progressively as the driving rate was increased. Finally, the behavior of the sinus node pacemaker following interruption of pacing showed individual variations. After pacing at relatively slow rates, a prompt return to near control values was consistently observed, whereas, after fast rates of driving, a phase of secondary depression developed in about one-half of the studied cases.