Associated conduction disturbances in patients with symptomatic sinus node disease

Indications for permanent pacing in dogs and cats

Pacemaker implantation is considered as a standard procedure for treatment of symptomatic bradycardia in both dogs and cats. Advanced second-degree and third-degree atrioventricular blocks, sick sinus syndrome, persistent atrial standstill, and vasovagal syncope are the most common rhythm disturbances that require pacing to either alleviate clinical signs or prolong survival. Most pacemakers are implanted transvenously, using endocardial leads, but rarely epicardial leads may be necessary. To decide whether a patient is a candidate for pacing, as well as which pacing modality should be used, the clinician must have a clear understanding of the etiology, the pathophysiology, and the natural history of the most common bradyarrhythmias, as well as what result can be achieved by pacing patients with different rhythm disturbances. The goal of this review was, therefore, to describe the indications for pacing by evaluating the available evidence in both human and veterinary medicine. We described the etiology of bradyarrhythmias, clinical signs and electrocardiographic abnormalities, and the choice of pacing modality, taking into account how different choices may have different physiological consequences to selected patients. It is expected that this review will assist veterinarians in recognizing arrhythmias that may require permanent pacing and the risk-benefit of each pacing modality and its impact on outcome.

Atrial septal pacing in small dogs: a pilot study

OBJECTIVE

To determine the feasibility of atrial septal pacing via a delivery catheter-guided small non-retracting helix pacing lead.

ANIMALS

Six healthy beagles (8.3-12.9 kg).

METHODS

Using single plane fluoroscopic guidance, Medtronic(®) 3830 SelectSecure leads were connected to the atrial septum via Medtronic® Attain Select® II standard 90 Left Heart delivery catheter. Pacing threshold and lead impedance were measured at implantation. The Wenckebach point was tested via atrial pacing up to 220 paced pulses per minute (ppm). Thoracic radiographs were performed following implantation to identify the lead position, and repeated at 24 h, 1 month, and 3 months post-operatively.

RESULTS

Macro-lead dislodgement occurred in two dogs at 24 h and in three dogs at one-month post-implantation. Lead impedance, measured at the time of implantation, ranged from 583 to 1421 Ω. The Wenckebach point was >220 ppm in four of the six dogs. The remaining two dogs had Wenckebach points of 120 and 190 ppm.

CONCLUSIONS

This pilot study suggests the selected implantation technique and lead system were inadequate for secure placement in the atrial septum of these dogs. The possible reasons for inadequate stability include unsuitable lead design for this location, inadequate lead slack at the time of implantation and inadequate seating of the lead as evidenced by low impedance at the time of implantation. Other implantation techniques and/or pacing leads should be investigated to determine the optimal way of pacing the atria in small breed dogs that are prone to sinus node dysfunction.

The impact of NICE (UK) recommendations on outcomes of cardiac pacemaker implantations--a single-centre, district hospital experience

AIMS

The National Institute for Health and Clinical Excellence (NICE) recommends the use of dual-chamber pacemakers for all patients with bradycardia with a few exceptions. We aimed to evaluate our compliance to the guidelines and the implications of different pacing modalities on follow-up outcomes.

METHODS

We conducted two retrospective studies involving a total of 316 patients. The first study conducted over a 36-month period examined our performance prior to the introduction of the NICE guidance. The more recent second study conducted over a 12-month period examined our compliance to the NICE guidance upon its introduction and adoption. Data were analysed in separate groups according to pacemaker types. Symptom control and mortality were measures on follow-up outcomes.

RESULTS

Our compliance to the guidance increased from 72% in the former study to 78% in the latter study (P = 0.17). Symptom control and mortality were not significantly different between the two studies. Combining both studies, fewer NICE-compliant patients complained of persisting symptoms after 1 year (P = 0.36). Although fewer deaths were observed in the compliant group, this again was not statistically significant (P = 0.10). Although age was not a criteria in selecting a device, younger patients were more likely to receive a pacemaker according to NICE recommendations (P = 0.001).

CONCLUSIONS

We achieved a near 80% level of compliance to NICE guidance. Our non-NICE-compliant patients did not have a poorer outcome than those who were compliant. The decision to insert single- or dual-chamber pacemakers is often multifactorial and individual doctors may have different practices.

Clinical and Electrophysiological Characteristics of Binodal Disease

BACKGROUND

Although coexistence of atrioventricular conduction disturbances with sick sinus syndrome (SSS), so-called binodal disease (BND), is a frequently encountered disorder, its clinical significance and electrophysiological characteristics remain unknown.

METHODS AND RESULTS

One hundred and seven patients with SSS were divided into BND (n=30) and N-BND groups (n=77). Sinus cycle length, sinus node recovery time (SRT), sino-atrial conduction time (SACT), the number of isolated sinus node electrograms, atrio-His (AH) interval, His-ventricular (HV) interval, intra-atrial conduction time (PA intervals) and QRS width were measured. In addition, the prevalence of bundle-branch block was obtained. The parameters of sino-atrial and intra-atrial conduction were significantly longer in the BND group: SRT (5,070+/-2,628 vs 3,122+/-1,856 ms, p<0.05), SACT (115+/-30 vs 87+/-21 ms, p<0.05), PA intervals (56+/-13 vs 41+/-8 ms, p<0.05). The BND group was more likely to have atrial fibrillation than the N-BND group (83.3% vs 53.2%, p<0.01). HV interval, QRS width and the prevalence of associated bundle-branch block did not differ between the 2 groups.

CONCLUSION

BND patients not only had sino-atrial and atrioventricular node dysfunction, but also widespread atrial conduction disturbances. Thus, in the clinical setting BND should be categorized as severe SSS.

Implications of marked fatty infiltration around and in the atrophic atrioventricular node in elderly patients with permanent pacemaker implantation for symptomatic sick sinus syndrome

The present study undertook an extensive analysis of the histopathological findings of the atrioventricular conduction system in 14 elderly patients treated with permanent pacemakers for sick sinus syndrome (SSS). Special attention was given to the lowest Wenckebach block points of atrioventricular conduction during rapid atrial pacing, and ventricular rate or duration of ventricular pause during chronic atrial fibrillation. An electrophysiological study (EPS) was conducted under sinus rhythm in 13 patients and under junctional escape rhythm in 1 patient. Three of the 14 cases showed a lower Wenckebach block point of 130 beats/min or less. Two of these 3 cases showed excessive fatty infiltration around the atrionodal junction area and into the atrophic atrioventricular node (AVN) itself. Of the 6 patients who had chronic atrial fibrillation after pacemaker implantation, 2 cases showed a slow ventricular response of less than 60 beats/min and/or a long ventricular pause of 3.3 s. One of the 2 cases showed a lower Wenckebach block point of 130 beats/min at the time of EPS. The other, who later progressed to idiopathic atriomegaly, also showed marked fatty infiltration around the AVN. This fatty lesion was closely associated with diffuse disruption of the muscular fibers connecting the atrophic AVN with the atrium. In addition, most of the remaining cases also had an atrophic AVN. In conclusion, a sparse or absent atrionodal connection and an atrophic AVN due to excessive fatty infiltration in the atrionodal transitional area should be investigated in atrioventricular conduction disturbances in the elderly with SSS.

Rate adaptive atrial pacing in the bradycardia tachycardia syndrome

In 42 patients (26 men, 16 women; mean age 69 +/- 10 years), who were paced and medicated with antiarrhythmic drugs for the bradycardia tachycardia syndrome, chronotropic response and AV conduction with rapid atrial pacing during exercise were studied. Patients were included if they had no second- or third-degree AV block, no complete bundle branch or bifascicular block, and a PQ interval < or = 240 ms during sinus rhythm at rest. The interval between the atrial spike and the following Q wave (SQ) was measured in the supine position at rest with an AAI pacing rate of 5 beats/min above the sinus rate (SQ-R + 5), and at the end of exercise with 110 beats/min (SQ-E110). Bicycle ergometry was performed using the Chronotropic Assessment Exercise Protocol with the pacemakers being programmed to AAI with a fixed rate of 60 beats/min. Chronotropic incompetence was defined as peak exercise heart rate: (1) < 100 beats/min; (2) < 75% of the maximum predicted heart rate; or (3) the heart rate at half the maximum workload < 60 + 2 beats/min per mL O2/kg per minute (calculated O2 consumption). During exercise, one patient developed atrial fibrillation. Chronotropic incompetence was present in 71% (29/41) of the patients according to definition 2, and in 76% (31/41) according to definition 1 or 3. Ten out of 41 patients (24%) exhibited a second-degree AV block with atrial pacing at 110 beats/min at the end of exercise. Only 9 out of the remaining 31 patients (29%) showed a physiological adaptation of the SQ-E110, and 21 patients (68%) exhibited a paradoxical increase of the SQ interval with rapid atrial pacing at the end of exercise as compared to the SQ-R + 5. These observations indicate that the pacing system to be used in most patients paced and medicated for the bradycardia tachycardia syndrome should be dual chamber, and the option of rate adaptation should be considered.

Electrophysiological evaluation of the sinus node in patients with atrioventricular and/or intraventricular conduction defects

The authors evaluated retrospectively sinoatrial conduction time (SACT), sinus node recovery time (SNRT), and corrected sinus node recovery time (CSNRT) in 272 patients with atrioventricular and/or intraventricular conduction defects without evidence of overt sinus node dysfunction. The study was designed to determine the prevalence of electrophysiologic sinus node abnormalities in patients with overt atrioventricular and/or intraventricular conduction defects. One or more sinus node electrophysiological abnormalities were observed in 133 cases (48.9%). There was a significant prevalence of electrophysiologic sinus node abnormalities only in patients older than 71 years of age. The data suggest that the involvement of the specialized conduction system is much more diffuse than one might expect simply observing the single recorded ECG defect and that the prevalence of associated defects of the conduction system increases with increasing age of patients.

Atrial pacing: efficacy and safety

Atrial pacing has the advantages of simplicity, maintenance of AV synchrony, and economy. The major detraction has been the potential for deterioration of atrioventricular conduction. In this study, we followed 43 patients with sick sinus syndrome treated with atrial (AAI) pacing. Excellent initial implant parameters were obtained in all. Three early lead repositionings were required. Minor sensing and pacing problems could all otherwise be handled by reprogramming. Follow-up for a mean of 25 +/- 20 months demonstrated excellent performance of the pacing systems. Pacing and sensing thresholds and lead impedance indicated excellent lead performance. There were no late lead failures. Nine patients have had mild deterioration in atrioventricular conduction and one of these had a change to DDD pacing at the time of elective battery change. All patients are asymptomatic. Thus, chronic atrial pacing in selected patients is safe and reliable with good chronic lead performance and low risk of subsequent conduction system disease.

The atrial pacemaker: retrospective analysis of complications and life expectancy in patients with sinus node dysfunction

The safety of atrial pacemakers is still a remaining cause of controversy. Since 1972, we have implanted 111 atrial pacemakers and we were able to follow-up 100 patients continuously. Mean follow-up time was 47 +/- 36 months (maximum 154 months) with a total population time of 391 patient years. Over a period of 10 years, the cumulative incidence of complete atrioventricular block was 4% (2 patients). The cumulative incidence of atrial fibrillation was 11% (5 patients). Lead-related complications were strongly dependent on the type of the lead and the mode of fixation. The cumulative incidence of all lead-related problems was 19% over a period of 5 years and 33% over a period of 10 years. The cumulative survival rate was 85% for 5 years and 61% for 10 years. These survival rates were not different from the survival rate of a matched cohort of the normal population. We conclude that atrial pacing could be done in patients with sick sinus syndrome. The risk of developing a complete atrioventricular block seems to be rather low. The main problem of the atrial pacemaker is the fixation of the lead which could be reduced by using screw-in-type leads.

Atrial pacing and the risk for AV block: is there a time for change in attitude?

A literature survey was performed to establish the prevalence of second and third degree AV block among patients with permanent atrial pacemakers because of sinus node disease. This study reviews data from 28 different studies on atrial pacing with a median follow-up of 36 months. The collected data shows a median annual incidence of second and third degree AV block of 0.6%, range 0%-4.5% with a total prevalence of 2.1%, range 0%-11.9%. There was no significant difference in follow-up time between studies that showed a low, compared with a high incidence of AV-block. Patients with sinus node disease treated with atrial pacing have a low risk of developing clinically important conduction disturbances.

Experiences with atrial pacing

The records of 187 patients with permanent atrial pacemakers implanted between 1970 and 1980 were studied retrospectively to define the indications, outcome and short- and long-term complications of single-chamber atrial pacing. Pacemakers were implanted in 145 (77%) patients with tachybrady syndrome, 35 (19%) with sinus bradycardia and 7 (4%) with ventricular arrhythmia. Intact atrioventricular (AV) conduction was defined as absence of second- or third-degree heart block with incremental atrial pacing to a heart rate of 120 beats/min before implantation. The average follow-up was 30 months, including 87 patients (46%) who were followed an average of 48 months. Four patients developed significant conduction disease requiring placement of a ventricular lead. Complications included 4 lead fractures (all coronary sinus leads), 10 dislodgments (9 coronary sinus, 1 tined atrial "J") and 6 threshold rises requiring repositioning of the lead. Eight dislodgments occurred within an average of 5.6 days. The average increase in threshold that required repositioning occurred at 14 days. The average lead fracture occurred at 25 months. Atrial pacing is safe and effective for patients with sinoatrial node disorder (sick sinus syndrome) and intact AV conduction. Progression to clinically significant AV block is uncommon. Complications occur early with coronary sinus leads and are less common with newer leads.

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.

Clinical and electrophysiologic course of sinus node disease: five-year follow-up study

Thirty patients with symptomatic sinus node disease (SND) who 5 years previously had undergone a clinical investigation including intracardiac electrophysiologic studies with pharmacologic inhibition of autonomic tone were followed up with respect to development of arrhythmias and cardiac conduction abnormalities. In 17 of these patients a reinvestigation, including a second intracardiac study, was performed. Stable atrial fibrillation developed in five patients, paroxysmal supraventricular tachycardia occurred in one patient, and complete heart block appeared in another patient. Paroxysmal atrial arrhythmias and radiographic atrial enlargement were more common at the initial investigation in patients who during follow-up developed either stable atrial fibrillation or paroxysmal supraventricular tachycardia. Development of complete heart block was associated with signs of severe conduction defects at the initial study. General progression of conduction dysfunction as evaluated by intracardiac techniques was not a finding in this study. Conduction abnormalities limited to the atrioventricular (AV) node did not in this context predict a clinically important progression. The results indicate that those patients with SND who are predisposed to develop high-grade AV block and atrial arrhythmias can be identified by Holter monitoring, chest x-ray examination, and an intracardiac electrophysiologic study. These possibilities improve the selection of patients suitable for pacing modes preserving atrial transport.

Rate hysteresis pacing: how valuable is it? A comparison of the stimulation rates of 70 and 50 beats per minute and rate hysteresis in patients with sinus node disease

The main disadvantages of VVI pacing are absence of acceleration of the heart rate and loss of atrial synchronization. The alternatives to AAI and DDD pacing are stimulation at a low rate or hysteresis in order to decrease pacing time and thus reduce AV asynchrony. Nine patients who suffered from sinus node disease and who had been given a multiprogrammable pacemaker were monitored at each of three stimulation rates: 70, 50, and 70 bpm with an inhibition rate of 50 bpm (hysteresis). The total pacing time was shortest (p less than 0.05) for the stimulation rate of 50 bpm as compared to 70 bpm and hysteresis. It was also shorter for the hysteresis mode than for the 70 bpm mode (p less than 0.05). Only for hysteresis pacing was there a significant reduction in the number of changes from conducted cardiac rhythm to pacemaker-induced rhythm. Most patients found the 50 bpm mode preferable. None favored the hysteresis mode. In patients with sinus node disease and intermittent bradycardia being permanently paced, the periods of AV-conducted rhythm may be lengthened by reducing the stimulation rate from 70 bpm, with or without hysteresis pacing, to 50 bpm. In paced patients with sinus node disease and symptoms due to AV asynchrony, it might be worth trying a decrease in the stimulation rate before resorting to other pacemaker systems.