The pacemaker syndrome -- a matter of definition

Imaging in patients with cardiovascular implantable electronic devices: part 2-imaging after device implantation. A clinical consensus statement of the European Association of Cardiovascular Imaging (EACVI) and the European Heart Rhythm Association (EHRA) of the ESC

Cardiac implantable electronic devices (CIEDs) improve quality of life and prolong survival, but there are additional considerations for cardiovascular imaging after implantation-both for standard indications and for diagnosing and guiding management of device-related complications. This clinical consensus statement (part 2) from the European Association of Cardiovascular Imaging, in collaboration with the European Heart Rhythm Association, provides comprehensive, up-to-date, and evidence-based guidance to cardiologists, cardiac imagers, and pacing specialists regarding the use of imaging in patients after implantation of conventional pacemakers, cardioverter defibrillators, and cardiac resynchronization therapy (CRT) devices. The document summarizes the existing evidence regarding the role and optimal use of various cardiac imaging modalities in patients with suspected CIED-related complications and also discusses CRT optimization, the safety of magnetic resonance imaging in CIED carriers, and describes the role of chest radiography in assessing CIED type, position, and complications. The role of imaging before and during CIED implantation is discussed in a companion document (part 1).

Dual-Chamber Leadless Pacing: Atrioventricular Synchrony in Preclinical Models of Normal or Blocked Atrioventricular Conduction

BACKGROUND

Dual-chamber leadless pacemakers (LP) require robust communication between distinct right atrial (RA) and right ventricular (RV) LPs to achieve atrioventricular (AV) synchrony.

OBJECTIVE

This preclinical study evaluated a novel, continuous implant-to-implant (i2i™) communication methodology for maintaining AV-synchronous, dual-chamber DDD(R) pacing by the 2 LPs.

METHODS

RA and RV LPs were implanted and paired in 7 ovine subjects, 4 of 7 with induced complete heart block. AV synchrony (% AV intervals <300 ms) and i2i communication success (% successful i2i transmissions between LPs) were evaluated acutely and chronically. During acute testing, 12-lead ECG and LP diagnostic data were collected from 5-minute recordings, in 4 postures and 2 rhythms (AP-VP and AS-VP or AP-VS and AS-VS) per subject. Chronic i2i performance was evaluated through 23 weeks post-implant (final i2i evaluation period: week 16-23).

RESULTS

Acute AV synchrony and i2i communication success across multiple postures and rhythms were 100.0% [100.0-100.0] (median [interquartile range]) and 99.9% [99.9-99.9], respectively. AV synchrony and i2i success rates did not differ across postures (P=0.59, P=0.11) or rhythms (P=1.00, P=0.82). During the final i2i evaluation period, the overall i2i success was 98.9% [98.1-99.0].

CONCLUSION

Successful AV-synchronous, dual-chamber DDD(R) leadless pacing using a novel, continuous, wireless communication modality was demonstrated across variations in posture and rhythm in a preclinical model.

Clinical symptoms of limited exercise capacity linked to AAI-DDD functionality: An in silico and in vivo approach

BACKGROUND

Exercise capacity is an important aspect of quality of life in patients undergoing pacemaker implantation. Device algorithms for ventricular pacing avoidance have been developed to avoid unnecessary and potentially harmful effects of right ventricular pacing. However, little data exists on the immediate response of these algorithms to sudden AV block during exercise.

METHODS

The ventricular pacing avoidance algorithms of four pacemaker manufacturers were tested in an ex-vivo model. The RSIM-1500-USB Device-Interactive Heart Simulator (Rivertek Medical Systems, Inc.) was used to simulate three different scenarios: the first one starting with an initially conducted atrial pacing rate of 60 min^-1 , the second one starting with an atrial rate of 120 min^-1 and finally a scenario starting with an atrial rate of 150 min^-1 . In all three scenarios, the initially conducted atrial rate was followed by a sudden, long lasting episode of third-degree AV-block. The response to those scenarios was recorded for each of the (brand-specific) ventricular pacing avoidance algorithms.

RESULTS

In the first scenario, the simulation resulted in a ventricular pause of 1333 ms (Boston Scientific), 2000 ms (Medtronic and Microport), and 2340 ms (Biotronik). In the second and third scenario, different results were observed across devices. All simulations of the second and third scenario resulted in repetitive 2:1 block response (during eight cycles) in Boston Scientific and Biotronik devices. These scenarios were confirmed in patient cases.

CONCLUSION

Simulator based observations of unanticipated pacemaker-induced 2:1 block response during exercise may explain clinical symptoms experienced by some patients having a two-chamber pacemaker.

Pacemaker generator replacement as a key to the puzzle of dyspnoea in a community dwelling centenarian

A 104-year-old woman presented with dyspnoea. Workup revealed normal troponins, elevated D-dimer at 2285 with subsequent chest CT angiogram negative for pulmonary embolism. NT-pro BNP elevated to 5208 pg/mL. Chest X-ray revealed mild cardiac enlargement with bilateral pleural effusions. ECG revealed accelerated junctional rhythm. The initial plan was to obtain transthoracic echocardiogram and start diuresis for presumed heart failure. Given her specific cardiac history, pacemaker interrogation was ordered which revealed her pacemaker mode changed from DDDR to VVI. She underwent pacemaker battery exchange with complete resolution in her symptoms and ability to return to prior functional status. Overall, dyspnoea in centenarians could be multifactorial. Pacemaker elective replacement mode secondary to end of life battery can present as non-specific cardio respiratory symptoms. As the pacemaker population ages to the survival beyond the battery life, pacemaker aetiology behind heart failure symptoms needs to be highly considered by medical providers.

Outcomes of single‑lead VDD pacemakers in atrioventricular blocks: The OSCAR study

BACKGROUND

VDD pacemakers are regarded as a second choice in patients with atrio-ventricular blocks mainly due to the potential failure of atrial sensing, leading to a loss of atrio-ventricular synchrony. This single-centre study aimed to evaluate the prevalence of loss of atrial sensing and its potential determinants in patients with VDD pacemakers.

METHOD

142 patients with an implanted VDD device underwent long-term follow-up with clinical evaluation, electrocardiogram, device interrogation and echocardiogram.

RESULTS

Over a long follow-up period [median 110 (68-156) months], 17 patients (12%) in sinus rhythm presented loss of atrial sensing. This was most often intermittent, but three patients required a permanent switch to VVI mode. ECG showed higher prevalence of interatrial blocks (50% vs 26.6%, p = 0.057) and longer P wave duration (116 ± 19 vs 105 ± 15 ms, p = 0.019) in patients with loss of atrial sensing. Echocardiography revealed larger left atrial (LA) volumes (p < 0.05) in patients with loss of atrial sensing, and lower LA ejection fraction (0.40 vs 0.47, p = 0.0037) and expansion index (0.63 ± 0.26 vs 0.90 ± 0.31, p = 0.003). P wave duration on ECG proved to be independently associated with loss of atrial sensing on multivariable analysis (OR 1.062, 95% CI 1.015-1.110; p = 0.008). The prevalence of atrial fibrillation and subsequent switch to VVI mode was high (16%).

CONCLUSIONS

In the long-term follow-up, the loss of atrial sensing is present in 12% of patients with implanted VDD pacemakers. ECG and echocardiographic parameters may serve as screening tools for the detection of atrial myopathy which is associated with the loss of atrial sensing.

Electrocardiographic interpretation of pacemaker algorithms enabling minimal ventricular pacing

Cardiac pacing from the apex of the right ventricle has been shown to result in left ventricular dysfunction, atrial fibrillation, and increased mortality. To counter these effects, one of the strategies developed is avoidance of ventricular pacing when not necessary, using programmable algorithms to minimize ventricular pacing. Seven algorithms are available from 5 manufacturers. Four of the manufacturers have mode conversion algorithms that pace AAI(R) but, in the presence of failed atrioventricular (AV) conduction, demonstrate algorithm-offset and convert to DDD(R) with ventricular pacing. Three manufacturers do not have mode conversion but rather AV extension to encourage AV conduction. Each of these algorithms has a unique design and, when ventricular pacing is present, will regularly schedule conduction testing to encourage AV conduction and hence algorithm-onset. All of these algorithms seem to violate the rule of AV conduction by allowing the AV delay for sensed ventricular events to be longer than for ventricular paced events. The result is frequently bizarre electrocardiographic (ECG) appearances that often are unique to the company's algorithm but also suggest pacemaker malfunction. This review highlights and illustrates the features of these algorithms as they appear on ECG, and discusses other situations that result in unintended ventricular pacing.

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.

Permanent Cardiac Pacemaker: an Emergency Perspective

The number of patients with permanent pacemaker are increasing and may present into the emergency department with a variety of complications and malfunctions. The presence of a pacemaker may also affect management of unrelated medical issues. This article review the complications of the implant procedure, the causes, diagnosis and management of pacemaker malfunction, the pacemaker syndrome, Twiddler's syndrome. Interaction of permanent pacemaker with other medical condition and its implication in Emergency Department environment are also discussed.

Heart Rhythm Society: expert consensus statements-part 1

One of the most important roles for professional societies in medicine is assembling multiple stakeholders and experts to develop documents that can help guide and define policies and strategies for best medical care. Each year the Heart Rhythm Society (HRS) develops several consensus documents that address critical clinical subjects that have been identified by input from HRS members and HRS committees. Over the past 5 years, HRS has produced documents with multiple professional societies from around the world, and although the topics chosen for exploration center around arrhythmia management, the reviews and recommendations made in the documents are important for clinical cardiologists and generalists who are not arrhythmia specialists. When an internist or other primary care provider identifies a patient who may be having symptoms from an arrhythmia, the referral first is made to the clinical cardiologist and only later, if necessary, does an arrhythmia specialist become involved. These expert consensus statements are developed for specific clinical questions regarding arrhythmia management where there is controversy or uncertainty, often with less data from randomized controlled trials to help guide recommendations, which must then be made by extrapolation of existing data, observational data, and expert opinion. In this 2-part review, the consensus statements developed by the HRS over the past 5 years that pertain to adults are discussed in part 1; part 2 focuses on consensus statements that HRS has developed in conjunction with the Pediatric and Congenital Electrophysiology Society that address arrhythmia issues in children and adults with congenital heart disease.

Effects of right ventricular pacing sites on blood pressure variation in upright posture: a comparison of septal vs. apical pacing sites

AIMS

Large variations in blood pressure (BP) in the upright position are a major cause of pacemaker syndrome, observed in up to 80% of patients paced non-physiologically at the right ventricular (RV) apex. We hypothesized that the magnitude of BP variations might be influenced by the RV pacing site. To assess this, we compared haemodynamic findings during supine and upright posture with RV apical vs. septal pacing.

METHODS AND RESULTS

The study population comprised a retrospective cohort of 24 dual-chamber pacemaker patients with advanced or complete atrioventricular block, in which 11 were randomly chosen from those with RV apical pacing, and 13 randomly chosen from those with septal pacing. Studies were performed during fixed rate VVI and DDD pacing modes with patients in both supine and passive head-up tilt positions. Continuous BP, stroke volume, cardiac index, and total peripheral resistance index were measured non-invasively. During RV apical pacing, there were significant differences of beat-to-beat BP variation after movement from supine to upright posture for both VVI and DDD pacing modes (P < 0.05); however, this was not the case for either mode during RV septal pacing. Further, comparing RV apical to RV septal pacing in the supine position, there were no BP variation differences for either DDD or VVI modes. Conversely, in the upright position BP variation was significantly greater during RV apical vs. RV septal VVI pacing (P = 0.017) but not during DDD pacing.

CONCLUSION

During VVI pacing, RV septal pacing exhibited lesser BP variation during upright posture compared with RV apical pacing.

Emergency Care of Patients with Pacemakers and Defibrillators

Devices such as pacemakers and implantable cardioverter-defibrillators (ICDs) are commonly inserted to treat unstable cardiac rhythm disturbances. Despite the benefits of these devices on mortality and morbidity rates, patients often present to the emergency department with complaints related to device insertion or malfunction. Emergency physicians must be able to rapidly identify potential life threats caused by pacemaker malfunction, ICD firing, and complications associated with implantation of the devices.

Hypothesis: Low frequency heart rate variability (LF-HRV) is an input for undisclosed yet biological adaptive control, governing the cardiovascular regulations to assure optimal functioning

Cardiovascular regulation is considered today as having three levels: autoregulations, neural regulations and hormonal regulations. We hypothesize that the cardiovascular regulation has an additional (fourth) control level which is outer, hierarchical (adaptive) loop where LF-HRV amplitude serves as a reference input which the neural cardiovascular center detects and responses in order to maintain LF-HRV around some prescribed level. Supporting evidences: LF-HRV absence during artificial cardiac pacing may be associated with "pacemaker syndrome" which had not been sufficiently understood regardless of apparently unimpaired cardiovascular performance. The hypothesis may provide an essential basis for understanding several cardiovascular morbidities and insight toward diagnostic measures and treatments (including but not limited to adding variability to the pulse generator of artificial pacemakers to eliminate "pace maker syndrome").

Dizzy spells in a patient with hypertrophic obstructive cardiomyopathy and a pacemaker

Pacemaker syndrome represents the clinical consequences of the haemodynamic adverse effects of atrioventricular asynchrony during pacing. Patients suffering from hypertrophic cardiomyopathy may be particularly sensitive to these effects because of the importance of atrial systolic contribution to left ventricular diastolic filling. In this case report, we describe the symptoms and cause of pacemaker syndrome in a patient with hypertrophic obstructive cardiomyopathy.

Importance of electrocardiography in the assessment and management of heart failure: a case report

Restoring and maintaining optimal electrical activation of the cardiac chambers as well as atrioventricular synchrony are important aspects of heart failure management. The 12-lead electrocardiogram remains a simple and cost-effective diagnostic tool that can provide important clues in achieving this goal. We report a case where careful interpretation of the 12-lead electrocardiogram led to the diagnosis of pacemaker syndrome. This recognition led to a therapeutic intervention that resulted in the resolution of the patient's heart failure symptoms. The importance of electrocardiography and atrioventricular synchrony in the management of heart failure will also be discussed.

First-degree atrioventricular block

Marked first-degree AV block (PR> or =0.30 s) can produce a clinical condition similar to that of the pacemaker syndrome. Clinical evaluation often requires a treadmill stress test because patients are more likely to become symptomatic with mild or moderate exercise when the PR interval cannot adapt appropriately. Uncontrolled studies have shown that many such symptomatic patients with normal left ventricular (LV) function improve with conventional dual chamber pacing (Class IIa indication). In contrast, marked first-degree AV block with LV systolic dysfunction and heart failure is still a Class IIb indication, a recommendation that is now questionable because a conventional DDD(R) pacemaker would be committed to right ventricular pacing (and its attendant risks) virtually 100% of the time. It would seem prudent at this juncture to consider a biventricular DDD device in this situation. Patients with suboptimally programmed pacemakers may develop functional atrial undersensing because the P wave tends to migrate easily into the postventricular atrial refractory period (PVARP). Retrograde vetriculoatrial conduction block is uncommon in marked first-degree AV block so a relatively short PVARP can often be used at rest with little risk of endless loop tachycardia. The usefulness of a short PVARP may be negated by special PVARP functions in some pulse generators designed to time out a long PVARP at rest and a gradually shorter one with activity. First-degree AV block during cardiac resynchronization therapy (CRT) predisposes to loss of ventricular resynchronization during biventricular pacing because it favors the initiation of electrical "desynchronization" especially in association with a relatively fast atrial rate and a relatively slow programmed upper rate. Patients with first-degree AV block have a poorer outcome with CRT than patients with a normal PR interval, a response that may involve several mechanisms. (1) The long PR interval may be a marker of more advanced heart disease. (2) Patients with first-degree AV block may experience more episodes of undetected "electrical desynchronization". (3) "Concealed resynchronization" whereupon ventricular activation in patients with a normal PR interval may result from fusion of electrical wavefronts coming from the right bundle branch and the impulse from the LV electrode. The resultant hemodynamic response may be superior because the detrimental effects of right ventricular stimulation (required in the setting of a longer PR interval) are avoided.

Electronic pacemakers

The number of patients who have cardiac pacemakers has increased markedly over the past few decades since the technology was first introduced in the 1950s. Advances in technology, expanding indications, and the aging of the population ensure that clinicians will encounter patients with cardiac pacemakers on a regular basis. This article summarizes the electrocardiographic manifestations of the normally functioning permanent cardiac pacemaker and abnormalities associated with pacemaker malfunction.

Pacemaker-Like Syndrome Complicating Slow Pathway Ablation for AV Nodal Reentrant Tachycardia

This case report describes pacemaker-like syndrome after successful slow pathway ablation for atrioventricular (AV) nodal reentrant tachycardia due to recurrence of single AV nodal echo beats during sinus rhythm. The resultant AV dyssynchrony was responsible for the symptom complex. Following ablation of retrograde ventriculoatrial conduction, the AV nodal echo beats were eliminated and the pacemaker-like syndrome resolved.

Phase I and Phase II Oxygen Uptake Kinetics During Atrioventricular Dyssynchrony in Chronotropically Competent Pacemaker Patients

OBJECTIVE

To elucidate the effects of atrioventricular (AV) dyssynchrony on phase I and phase II oxygen uptake (V(O2)) kinetics in chronotropically competent pacemaker patients during exercise of an intensity comparable to activities of daily living.

DESIGN

Blinded patients completed sub-ventilatory threshold (VT) work rate (WR) cycle ergometry exercise in random order during asynchronous AV pacing (AV OFF) and synchronous AV pacing.

SETTING

Tertiary care hospital in a major city.

SUBJECTS

Six chronotropically competent male pacemaker patients (mean [+/- SD] age, 68 +/- 10 years) with high-degree AV block and varying cardiac histories.

RESULTS

The phase I and phase II V(O2) amplitude response and gain (deltaV(O2)/WR ratio) were lower (p < 0.05) and the time course of phase II was slower (p < 0.05) during AV OFF; however, the O2 deficit was similar (p > 0.05) across pacing modes. The stroke volume index (SVI) was consistently lower (p < 0.05) during AV OFF pacing and was significantly correlated with the time course of phase II V(O2). A significant compensatory amplitude response in heart rate (HR) was observed in addition to a higher (p < 0.05) deltaHR/V(O2) ratio during AV OFF. Ventilatory responses were consistent with ventilatory-perfusion mismatching and perceived exertion was higher during asynchronous pacing.

CONCLUSION

This study demonstrated that the contribution of SVI affects V(O2) kinetics and underscores the importance of the atrial contribution to ventricular filling and, consequently, to metabolic and hemodynamic responses. This study supports the theory of an O2 transport limitation and further implicates SV as a potential limiting factor during sub-VT exercise intensities that are comparable to those encountered in activities of daily living.

Permanent Transvenous Cardiac Pacing

Transvenous cardiac pacing is a commonly employed treatment for symptomatic bradyarrhythmias in dogs. Medical management of these conditions has not proven to be successful leaving pacing as the only viable alternative. The technique of pacemaker implantation is not difficult, but successful pacemaker therapy requires an understanding of electrophysiology, cardiac fluoroscopic anatomy, pacemaker instrumentation, and programming. Proper patient selection and identification of the underlying rhythm disturbance is essential to a successful clinical outcome. This article discusses the indications, equipment, techniques, complications, and outcome of permanent transvenous cardiac pacing.

Electrocardiographic characteristics in low atrial septum pacing

AIM

The aim of the study was to compare P-wave morphology and duration in pacing from the low right atrial septal wall and the high right atrial appendage (RAA).

METHODS

The electrocardiogram (ECG) of 50 patients with low atrial septum (LAS) pacing and that of 50 patients with RAA pacing were compared with their electrocardiogram during sinus rhythm.

RESULTS

In the frontal plane, patients with LAS pacing showed a superior P-wave axis between -60 degrees and -90 degrees . In all patients with RAA pacing, a P-wave axis between 0 degrees and +90 degrees was observed as in sinus rhythm. In the horizontal plane, all patients with LAS pacing had an anterior P-wave axis between +90 degrees and +210 degrees , whereas all patients with RAA pacing had a posterior P-wave axis between -30 degrees and -90 degrees . The terminal part of biphasic P waves in lead V 1 in LAS pacing was always positive, a pattern that was never observed in P waves of sinus origin or in RAA pacing. P-wave duration was longer with RAA pacing compared with LAS pacing (115 +/- 19 vs 80 +/- 14 milliseconds [ P < .01]).

CONCLUSION

The total atrial activation time during LAS pacing is shorter than that during RAA pacing. The electrical atrial activation sequences in LAS pacing and RAA pacing are significantly different. The morphology of biphasic P waves in lead V1 during LAS pacing suggests that the initial part of activation occurs in the left atrium and the terminal part in the right atrium.

High incidence of pacemaker syndrome in patients with sinus node dysfunction treated with ventricular-based pacing in the Mode Selection Trial (MOST)

OBJECTIVES

We evaluated the incidence, predictors, and treatment of pacemaker syndrome in patients with sinus node dysfunction treated with ventricular-based (VVIR) pacing in the Mode Selection Trial (MOST).

BACKGROUND

Pacemaker syndrome, or intolerance to VVIR pacing, consists of cardiovascular signs and symptoms induced by VVIR pacing.

METHODS

The definition of pacemaker syndrome required that a patient with single-chamber VVIR pacing develop either congestive signs and symptoms associated with retrograde conduction during VVIR pacing or a >or=20 mm Hg reduction of systolic blood pressure during VVIR pacing, associated with reproducible symptoms of weakness, lightheadedness, or syncope.

RESULTS

Of 996 patients randomized to VVIR pacing, 182 (18.3%) met criteria for pacemaker syndrome in follow-up. Pacemaker syndrome occurred early in most patients (13.8% at 6 months, 16.0% at 1 year, increasing to 19.7% at 4 years). Baseline univariate predictors of pacemaker syndrome included a lower sinus rate and higher programmed pacemaker rate. Previous heart failure, ejection fraction, and drop in systolic blood pressure with VVIR pacing at implantation did not predict the development of pacemaker syndrome. Post-implantation predictors of pacemaker syndrome were a higher percentage of paced beats, higher programmed low rate, and slower underlying spontaneous sinus rate. Quality of life decreased at the time of diagnosis of pacemaker syndrome and improved with reprogramming to atrial-based pacing.

CONCLUSIONS

Severe pacemaker syndrome developed in nearly 20% of VVIR-paced patients and improved with reprogramming to the dual-chamber pacing mode. Because prediction of pacemaker syndrome is difficult, the only way to prevent pacemaker syndrome is to implant atrial-based pacemakers in all patients.

Pacemaker Syndrome in the Young:. Do Children Need Dual Chamber as the Initial Pacing Mode?

The aim of this study was to determine if single chamber rate responsive ventricular pacing (VVIR) predisposes growing children to develop pacemaker syndrome (PS), and if so, what are determining factors and/or clinically useful predictors. PS is a constellation of symptoms that result from the lack of consistent AV sequential filling due to atrial contraction against closed AV valves. PS has not been commonly reported in the young. Data from all patients with pacemakers with congenital complete atrioventricular block (CAVB) with normal anatomy, and those with congenital heart disease (CHD), and surgically acquired CAVB were reviewed. Inclusion criteria were normal ventricular function by cardiac ultrasound and 100% VVIR pacing. Of 89 patients with VVIR pacemaker implants, 33 met these criteria. Of these, 19 developed PS. For statistical analysis, chi-square and independent samples t-test was used with significance defined at P < or = 0.05. No consistent association was found between cardiac anatomy, type of CAVB, or age at implant with development of PS. However, PS did correlate with duration of pacing (P = 0.02). The exercise stress test showed significant differences between 100% VVIR-paced patients with and without PS, in terms of work rate (P = 0.002) and measured oxygen consumption (P = 0.01). This study shows that PS appears to be a time related event in younger children with normal ventricular function who are 100% ventricular paced. Thus, this supports VVIR pacing as an adequate and cost-effective initial therapy for symptomatic bradycardia due to CAVB.

A case of pacemaker and pacemaker-like syndrome

This report describes the occurrence of both pacemaker syndrome and a pacemaker-like syndrome (so-called "pseudopacemaker syndrome") in a patient who exhibited an atrioventricular junctional rhythm probably on the basis of sick sinus syndrome. The clinical and hemodynamic manifestations of the two clinical situations were similar and associated with regular retrograde ventriculoatrial conduction. The abnormalities during the junctional rhythm were reproduced during ventricular pacing. Surprisingly, the occurrence of the pacemaker-like syndrome during junctional rhythm in patients with normal left ventricular function has rarely been described.

Ventricular pacing or dual-chamber pacing for sinus-node dysfunction

BACKGROUND

Dual-chamber (atrioventricular) and single-chamber (ventricular) pacing are alternative treatment approaches for sinus-node dysfunction that causes clinically significant bradycardia. However, it is unknown which type of pacing results in the better outcome.

METHODS

We randomly assigned a total of 2010 patients with sinus-node dysfunction to dual-chamber pacing (1014 patients) or ventricular pacing (996 patients) and followed them for a median of 33.1 months. The primary end point was death from any cause or nonfatal stroke. Secondary end points included the composite of death, stroke, or hospitalization for heart failure; atrial fibrillation; heart-failure score; the pacemaker syndrome; and the quality of life.

RESULTS

The incidence of the primary end point did not differ significantly between the dual-chamber group (21.5 percent) and the ventricular-paced group (23.0 percent, P=0.48). In patients assigned to dual-chamber pacing, the risk of atrial fibrillation was lower (hazard ratio, 0.79; 95 percent confidence interval, 0.66 to 0.94; P=0.008), and heart-failure scores were better (P<0.001). The differences in the rates of hospitalization for heart failure and of death, stroke, or hospitalization for heart failure were not significant in unadjusted analyses but became marginally significant in adjusted analyses. Dual-chamber pacing resulted in a small but measurable increase in the quality of life, as compared with ventricular pacing.

CONCLUSIONS

In sinus-node dysfunction, dual-chamber pacing does not improve stroke-free survival, as compared with ventricular pacing. However, dual-chamber pacing reduces the risk of atrial fibrillation, reduces signs and symptoms of heart failure, and slightly improves the quality of life. Overall, dual-chamber pacing offers significant improvement as compared with ventricular pacing.

Atrioventricular block and problems with atrioventricular conduction

This chapter has summarized briefly the current state of our knowledge on the incidence, etiology, presentation, investigation, and management of patients with AV block. The scope of the material covered has been widened intentionally to include a plethora of AV-conduction abnormalities because of the increases in the understanding of their clinical importance and contribution to left ventricular dysfunction. Under this heading, the critical importance of heart rate, maintenance of AV synchrony, and the sequence of ventricular activation and relaxation have been introduced and summarized briefly. The authors make a strong plea that, in the future, the reader consider AV-conduction abnormalities to be the parent topic, with the more-traditional, narrower subject of AV block forming a subunit thereof.

Clinical characteristics of patients intolerant to VVIR pacing

The incidence and clinical predictors of the development of intolerance to VVIR pacing have not been extensively studied in prospective long-term randomized trials comparing different pacing modes. The frequency and clinical factors predicting intolerance to ventricular pacing are controversial. The Pacemaker Selection in the Elderly (PASE) Trial enrolled 407 patients aged >/=65 years in a 30-month, single-blind, randomized, controlled comparison of quality of life and clinical outcomes with ventricular pacing and dual-chamber pacing in patients undergoing dual-chamber pacemaker implantation for standard clinically accepted indications. We reviewed the clinical, hemodynamic, and electrophysiologic variables at the time of pacemaker implantation in 204 patients enrolled in the PASE trial and randomized to the VVIR mode, some of whom subsequently required crossover (reprogramming) to DDDR pacing. During a median follow-up of 555 days, 53 patients (26%) crossed over from VVIR to DDDR pacing. A decrease in systolic blood pressure during ventricular pacing at the time of pacemaker implantation (p = 0.001), use of beta blockers at the time of randomization (p = 0.01), and nonischemic cardiomyopathy (p = 0.04) were the only variables that predicted crossover in the Cox multivariate regression model. After reprogramming to the dual-chamber mode, patients showed improvement in all aspects of quality of life, with significant improvements in physical and emotional role. The high incidence of crossover from VVIR to DDDR pacing along with significant improvements in quality of life after crossover to DDDR pacing strongly favors dual-chamber pacing compared with single-chamber ventricular pacing in elderly patients requiring permanent pacing.

Inhibition of ventricular stimulation in patients with dual chamber pacemakers and prolonged AV conduction

Episodes of repetitive P wave undersensing have been described in dual chamber pacemakers due to automatic extension of the postventricular atrial refractory period (PVARP). Pacemaker stimulation was completely inhibited despite the presence of adequate P waves. This study sought to determine whether cycles of repetitive P wave undersensing occur even in the absence of PVARP extension. Two-hundred fifty-five patients were investigated after DDD or VDD pacemaker implantation for intermittent atrioventricular (AV) block. Forty-six episodes of repetitive atrial undersensing were found during 24-hour Holter ECG in nine patients. Pacemaker syndrome-like symptoms occurred. Episodes were elicited by atrial or ventricular premature contractions when (1) native AV conduction was present but considerably prolonged, (2) intrinsic sinus rate exceeded pacemaker intervention rate, and (3) native AV interval plus PVARP exceeded sinus cycle length. Programming of a particularly short AV interval and PVARP helped to reduce the incidence of repetitive P wave undersensing. Patients with dual chamber devices and prolonged native AV conduction are prone to develop episodes of output inhibition. Standard timing cycles may be inappropriate in these patients.

Permanent cardiac pacemakers: issues relevant to the emergency physician, part II

Many people benefit from the implantation of cardiac pacemakers for management of certain cardiac dysrhythmias. These patients are seen regularly in the Emergency Department with a variety of pacemaker complications and malfunctions. The presence of a pacemaker may also affect management of unrelated medical problems. This, the second of a two-part series, covers the causes, diagnosis, and management of pacemaker malfunction; the pacemaker syndrome; the pacemaker Twiddler's syndrome; and other considerations in the paced patient including diagnosis of acute myocardial infarction, ACLS protocols, trauma, and sources of interference.

Quality of life and clinical outcomes in elderly patients treated with ventricular pacing as compared with dual-chamber pacing. Pacemaker Selection in the Elderly Investigators

BACKGROUND

Standard clinical practice permits the use of either single-chamber ventricular pacemakers or dual-chamber pacemakers for most patients who require cardiac pacing. Ventricular pacemakers are less expensive, but dual-chamber pacemakers are believed to be more physiologic. However, it is not known whether either type of pacemaker results in superior clinical outcomes.

METHODS

The Pacemaker Selection in the Elderly study was a 30-month, single-blind, randomized, controlled comparison of ventricular pacing and dual-chamber pacing in 407 patients 65 years of age or older in 29 centers. Patients received a dual-chamber pacemaker that had been randomly programmed to either ventricular pacing or dual-chamber pacing. The primary end point was health-related quality of life as measured by the 36-item Medical Outcomes Study Short-Form General Health Survey.

RESULT

The average age of the patients was 76 years (range, 65 to 96), and 60 percent were men. Quality of life improved significantly after pacemaker implantation (P<0.001), but there were no differences between the two pacing modes in either the quality of life or prespecified clinical outcomes (including cardiovascular events or death). However, 53 patients assigned to ventricular pacing (26 percent) were crossed over to dual-chamber pacing because of symptoms related to the pacemaker syndrome. Patients with sinus-node dysfunction, but not those with atrioventricular block, had moderately better quality of life and cardiovascular functional status with dual-chamber pacing than with ventricular pacing. Trends of borderline statistical significance in clinical end points favoring dual-chamber pacing were observed in patients with sinus-node dysfunction, but not in those with atrioventricular block.

CONCLUSION

The implantation of a permanent pacemaker improves health-related quality of life. However, the quality-of-life benefits associated with dual-chamber pacing as compared with ventricular pacing are observed principally in the subgroup of patients with sinus-node dysfunction.