Pacing Mode and Long-Term Survival in Elderly Patients with Congestive Heart Failure: 1980-1985

Dual-chamber pacing may improve short-term hemodynamics and functional class in some patients with congestive heart failure, even in the absence of conventional indications for pacemaker implantation. However, the impact of different pacing modes on survival of patients with congestive heart failure is controversial. In this retrospective study we analyzed survival data from 546 elderly patients, aged 70 years and older, who underwent implantation of a permanent dual-chamber (DDD, n = 62, DVI, n = 102) or single-chamber (VVI) pacemaker (n = 382) between 1980 and 1985. Survival was further analyzed according to the presence or absence of congestive heart failure, and pacemaker mode (DDD vs. DVI vs. VVI). Overall, dual-chamber pacing (DDD and DVI) was associated with a more favorable long-term outcome when compared with single-chamber ventricular pacing, although differences were only significant for DDD pacing (P = 0.002). When patients with and without preexisting congestive heart failure were analyzed separately, survival following dual-chamber pacing (DDD and DVI) was significantly better than survival following single-chamber pacing in patients without congestive heart failure (P = 0.03), but not in patients with preexisting heart failure (P = 0.139). When patients were analyzed according to the electrophysiological indication for pacemaker implantation, overall survival of patients with AV block (P = 0.0025) but not sinus node dysfunction (P = 0.346) was improved with dual-chamber pacing. This survival advantage in patients with AV block following dual-chamber pacing was lost in the presence of heart failure P = 0.11). These findings suggest that dual-chamber pacing, in particular DDD pacing, improves the survival in elderly patients without preexisting congestive heart failure. In contrast to the short-term hemodynamic improvement observed in selected patients with congestive heart failure, dual-chamber pacing in elderly patients with congestive heart failure, paced for conventional indications, is not associated with improved survival when compared with single-chamber ventricular pacing.     

Natural history of sinus node disease treated with atrial pacing in 213 patients: implications for selection of stimulation mode.

OBJECTIVES. This study was designed to analyze the incidence and determinants of complications and long-term survival in sinus node disease treated with atrial pacing. BACKGROUND. Knowledge of the natural history of sinus node disease treated with different pacing modes is imperfect, and controversy exists regarding the optimal pacemaker therapy. METHODS. A consecutive series of 213 patients with sinus node disease initially treated with atrial pacing was studied for a median follow-up period of 60 months. The end points studied were permanent atrial fibrillation, high grade atrioventricular (AV) block, P wave undersensing, pacing mode change, reoperation and death. Several prognostic factors were evaluated statistically and the survival rate was compared with that of a matched general population. RESULTS. The incidence rate of permanent atrial fibrillation during follow-up was 7% (1.4%/year). The risk of this arrhythmia increased substantially with age greater than or equal to 70 years at pacemaker implantation. Only 2 of the 15 patients who developed permanent atrial fibrillation required ventricular pacing. High grade AV block occurred in 8.5% (1.8%/year) and its incidence was much greater in patients with complete bundle branch block or bifascicular block (35%) than in patients without such conduction disturbances (6%). A change to ventricular or dual-chamber stimulation was necessary in 14% of all patients, primarily because of early lead dislodgment or high grade AV block. Surgical intervention with maintenance of atrial pacing was required in 7% of patients. The survival rates of 97% at 1 year, 89% at 5 years and 72% at 10 years did not differ significantly from those of a matched general population. CONCLUSIONS. In sinus node disease, atrial pacing can be successfully applied during long-term follow-up. Patients with complete bundle branch or bifascicular block in addition to sinus node disease should initially receive a dual-chamber pacemaker, but routine application of dual-chamber stimulation does not appear to be warranted.     

Stability of AV conduction in sick sinus node syndrome patients with implanted atrial pacemakers

Single-chamber atrial pacing is effective in the management of sinus node dysfunction, subject to the uncertainty of long-term atrioventricular conduction. Despite the accepted observation that many patients with sinus node dysfunction also have atrioventricular conduction disease, data do not exist on the development of atrioventricular block in those patients with permanent single-chamber atrial pacing. Of 70 patients who received single-chamber atrial pacing from 1967 to 1982 (mean duration of pacing was 33 months), only two patients of 58 (3.4%) of those with sinus node dysfunction developed atrioventricular (AV) block—after 14 months in one patient and after 23 months of successful atrial pacing in the other. None of the 12 patients paced for tachyarrhythmia management developed AV block. Of the 70 patients, 37 had assessment of AV conduction by incremental atrial pacing at the time of implant and 20 patients underwent atrial pacing on the basis of surface ECG and clinical judgment. Electrophysiologic studies were conducted only in those patients being paced for control of supraventricular arrhythmias. Only 5 of the 70 patients required conversion to ventricular pacing for technical difficulties; three of these conversions occurred in the early 1970's before the advent of atrial tined or J leads; one was for irreparable lead fracture and only one occurred in a patient with a newer design atrial lead. In conclusion, progression to AV block in patients with permanent atrial pacing is uncommon; formal electrophysiologic studies are necessary mainly in patients with supraventricular arrhythmias; and in the majority of patients, AV conduction can be assessed at the time of implant. Continued improvement in atrial leads should make atrial pacing even more successful.     

Cardiac bradyarrhythmia

Permanent cardiac pacing was introduced in 1958 and till the end of 70s this method saved lives in particular of the patients with advanced atrioventricular block. The implantation technique has changed from complicated thoracotomy to endovasal approaches. The introduction of physiological AV sequenced atrioventricular pacing marked a significant progress in this field. Acute haemodynamic studies documented positive effect of the atrial contribution. Numerous studies subsequently analyzed the influence of different pacing regimes on total and specific cardiovascular mortality and morbidity. It can be concluded that on the basis of present evidence-based medicine the use of physiological pacing is clearly indicated in the patients with expressed sinus bradycardia and AV block of a higher degree. Atrial pacing remains an ideal solution for the patients with isolated sinus node dysfunction and sufficient atrioventricular conduction capacity. Research is continued in order to clarify how to influence the occurrence of ventricular fibrillation by permanent cardiac pacing including the use of preventive algorithms. This topic has not yet been reliably and unambiguously concluded. Biventricular pacing is currently established and recognized not only for typical indications in cases of bradyarrhythmias but also to solve primary haemodynamic problems in the patients with advanced heart failure and evidence of ventricular dyssynchrony.     

Bundle branch block and sudden death

It is clear from the available data that the prognosis for patients with chronic BBB depends to a large extent on the presence and etiology, as well as the severity, of the associated heart disease. In most patients, the terminal event is usually one of heart failure or the complication of coronary artery disease. In the absence of clinically detectable heart disease, the long-term prognosis for this group of patients is good.Patients with chronic bundle branch block Have been shown to have an incidence of ventricular arrhythmias greater than that found in a normal population. The mechanism of sudden death in any single unmonitored patient is speculative. Most patients dying suddenly, especially those with coronary artery disease, probably do so from ventricular fibrillation. Patients with documented transient high-degree AV block are at a substantial risk of sudden death.No clinical variable (such as age, syncope, angina, shortness of breath), or physical finding (such as S₃ gallop, cardiomegaly, heart failure), or electrocardiographic finding (such as RBBB with LAD, RBBB with RAD, P-R interval prolongation), or electrophysiologic variable (such as A-H or H-V interval prolongation) is useful in predicting progression to complete heart block. All the above variables occur frequently in patients with BBB and yet the progression to CHB is relatively infrequent. One might single out His-Purkinje block with normal AV nodal conduction during atrial pacing as a possible marker for development of complete heart block. However, the opposite, namely a normal H-V interval, does not rule out progression to complete heart block.The data available on the use of pacing in patients with unexplained recurrent syncope or dizziness suggests that this approach is reasonable provided an effort has been made to exclude noncardiac cause for the symptoms. Some suggest that documentation of bradyarrhythmia or measurement of H-V interval is essential prior to institution of pacing. Further studies are needed to clarify this point.BBB complicating acute myocardial infarction places the individual at significant risk of developing congestive heart failure, with mortality usually secondary to myocardial failure or refractory ventricular arrhythmias. The pressence of high-degree AV block per se does appear to increase the mortality in patients without pump failure. Recent data suggest that immediate survival may be enhanced by prophylactic pacing in patients at high risk for abrupt complete heart block complicating acute myocardial infarction, but who do not manifest evidence of heart failure. The assumption that prophylactic pacing will improve survival of patients with bundle branch block and significant heart failure complicating acute myocardial infarction is purely speculative.Insufficient and conflicting data prevent a definitive statement regarding the usefulness of the P-R and H-V intervals as guidelines for the management of patients with recent-onset bundle branch block and acute myocardial infarction.Permanent pacing appears to benefit survivors of acute myocardial infarction complicated by BBB and transient high-degree AV block. However, the evidence is far from convincing.Little information is available on the influence of antiarrhythmic therapy on sudden death in patients with BBB. All currently used antiarrhythmic agents have a potentially high risk when administered to patients with BBB. Since there is no convincing prospective study as to the efficacy of drugs in preventing sudden death in patients with BBB, drug selection and its use in this group of patients remains at the discretion of the individual physician. It is based on the individual physician's experience with the drug in question and his perception of the benefit-to-risk ratio of the agent to be used.     

Biventricular versus right ventricular pacing in patients with AV block (BLOCK HF): clinical study design and rationale

Background: Right ventricular (RV) pacing restores ventricular systole in patients with atrioventricular (AV) block, yet recent studies have suggested that in patients with AV block and left ventricular (LV) dysfunction, RV pacing may exacerbate the progression to heart failure (HF). BLOCK HF is a prospective, multi-center, randomized, double-blind, controlled trial designed to determine whether patients with AV block, LV dysfunction (EF ≤ 50%), and mild to moderate HF (NYHA I-III) who require pacing benefit from biventricular (BiV) pacing, compared with RV pacing alone.
Objective: The primary objective of this trial is to determine whether the time to first event (all-cause mortality, heart failure-related urgent care, or a ≥ 15% increase in left ventricular end systolic volume index [LVESVI]) for patients with BiV pacing is superior to that of patients with RV pacing.
Methods: Patients with AV block and LV dysfunction who require permanent pacing and undergo successful implantation of a commercial Medtronic CRT device, with or without an ICD, will be randomized to BiV or RV pacing. Patients are followed at least every 6 months until study closure. Up to 1,636 patients may be enrolled in 150 centers worldwide.
Conclusion: BLOCK HF is a large, randomized, clinical study in pacing-indicated patients with AV block, mild to moderate HF symptoms, and LV dysfunction to determine whether BiV pacing is superior to RV pacing in slowing the progression of HF.     

Atrial pacing for sick sinus syndrome

Atrial pacing is the most physiological way to pace patients with sinus node disease, as it provides both AV synchrony and a normal ventricular activation pattern. Long-term studies comparing atrial and ventricular pacing imply that atrial pacing results in fewer cardiac complications and, possibly, reduced mortality. Ventricular pacing should thus, if possible, be avoided in patients with sinus node disease. The potential risk of impending high-grade AV block during atrial pacing is low, with an annual incidence around 1% if patients are selected appropriately. Approximately 40-50% of patients with sinus node disease show signs of chronotropic incompetence during physical exercise, and are thus candidates for atrial rate responsive pacing. A preoperative evaluation of candidates for atrial pacing should include long-term Holter/telemetry, exercise test, carotid sinus stimulation, and an electrophysiological study excluding significant AV conduction disturbances.     

His and para-His pacing in AV block: feasibility and electrocardiographic findings

Purpose  

Right ventricular apical pacing induces a dyssynchronous activation of the left ventricle and is associated with adverse clinical outcome. We aimed to establish permanent His-bundle pacing or para-His pacing in patients with high-grade atrioventricular (AV) block.     

Complete heart block due to lyme carditis

Lyme carditis is becoming a more frequent complication of Lyme disease, primarily due to the increasing incidence of this disease in the United States. Cardiovascular manifestations of Lyme disease often occur within 21 days of exposure and include fluctuating degrees of atrioventricular (AV) block, acute myopericarditis or mild left ventricular dysfunction and rarely cardiomegaly or fatal pericarditis. AV block can vary from first-, second-, third-degree heart block, to junctional rhythm and asystolic pauses. Patients with suspected or known Lyme disease presenting with cardiac symptoms, or patients in an endemic area presenting with cardiac symptoms with no other cardiac risk factors should have a screening electrocardiogram along with Lyme titers. We present a case of third-degree AV block due to Lyme carditis, illustrating one of the cardiac complications of Lyme disease. This disease is usually self-limiting when treated appropriately with antibiotics, and does not require permanent cardiac pacing.     

Natural history of combined right bundle branch block and left anterior hemiblock (bilateral bundle branch block)

One hundred fifteen patients with combined right bundle branch block (RBBB) and left anterior hemiblock (LAH) were separated into two groups depending upon whether RBBB and LAH was associated with acute myocardial infarction (group I, 32 patients) or was a chance electrocardiographic finding (group II, 83 patients).In 10 patients in group I complete heart block developed and in six patients high grade second degree atrioventricular (A-V) block developed. The incidence of serious arrhythmia was twice and mortality was three times the average for the coronary care unit (CCU).The majority of patients in group II had clinical evidence of advanced myocardial disease as manifested by congestive heart failure, healed myocardial infarction and left ventricular dyskinesia. During a cumulative observation period of 262 patient years, complete heart block developed in only two patients, whereas second-degree A-V block of sufficiently high degree to necessitate permanent cardiac pacing developed in three patients.It is concluded that (1) combined RBBB and LAH usually reflects advanced myocardial disease, (2) the clinical course is determined more by the myocardial disease than by the conduction disorder, (3) prophylactic cardiac pacing is not warranted in chronic RBBB and LAH, and (4) cardiac pacing has little impact on mortality when RBBB and LAH are associated with acute myocardial infarction.     

Bradyarrhythmias: AV conduction disturbances

When conduction block is located in the AV node, the QRS complex is narrow, and the escape rate is near normal. The patient is frequently minimally or not symptomatic. More often, however, the site of block is below the AV node, and the prognosis is much graver. It should be remembered that "high-grade" Type II block is not usually the result of a transient process, but rather of a chronic, progressive infranodal disease. This means that it is more likely to progress to complete heart block and require permanent pacing.     

A complete atrioventricular block during exertion]

Exercise-induced atrioventricular (AV) block in patients with normal electrocardiogram at rest is uncommon. We report the clinical features of two patients with AV block during treadmill test. The first patient was a woman of 54 years of age with presyncope on exercise. She developed complete AV block during exercise testing without evidence of ischemic myocardial disease. Electrophysiologic study documented distal AV block. The second patient was a man 31 years old who developed angina and third-degree AV block with depression of ST segment during treadmill test. Myocardial perfusion study suggested ischemic heart disease. He received anti-ischemic drugs with improvement of symptoms. A control exercise testing demonstrated normal AV conduction and electrophysiologic study was normal. In the first case, exercise AV block was probably due to abnormal His Purkinje conduction system refractoriness to autonomic modulation, while in second case AV block was secondary to ischemic heart disease. Third-degree AV block at exercise can be present in patients without conduction system abnormalities at rest. Exercise-induced infra-Hisian AV block must be treated with pacing until ischemic heart disease has been ruled out.     

Long-term follow-up of pacemaker therapy

The use of pacemakers has been a major advance in the treatment of different forms of bradycardias and tachyarrhythmias. The main objectives for cardiac pacing in heart block are to improve the chances of survival and to prevent disabling symptoms, especially Stokes-Adams attacks. The long-term follow-up results of cardiac pacing are affected by different factors, in particular age and underlying heart disease; major technical aspects include pulse generator, lead and electrode longevity, and the pacing mode (VVI, atrioventricular sequential pacing, rate response stimulation, etc.). - Sinoatrial dysfunction is a relatively benign condition. Hence, pacing should probably not be adopted as a routine measure but should be reserved for patients with clinical (troublesome) symptoms. Based on earlier studies it can be concluded that patients with complete heart block and second degree atrioventricular block (Mobitz Type II) should be treated with pacemakers from the prognostic point of view. During chronic rate-responsive pacing improvement of exercise capacity can be expected in patients with sinus node disease and after His-bundle ablation. In patients with complete AV-block or bradycardia rate-responsive pacing can increase exercise tolerance and improve clinical symptoms as well. The automatic implantable cardioverter/defibrillator prevents sudden death over a long-term follow-up period in a high risk group of patients suffering from life-threatening ventricular tachyarrhythmias.     

Ventrikuläre Stimulationsvermeidung bei Patienten mit Sinusknotenerkrankung oder intermittierendem AV-Block

In patients with frequent right ventricular stimulation, worsening of heart failure and atrial fibrillation may occur. Avoidance of unnecessary right ventricular pacing is a major requirement for pacemaker selection and programming in patients with sinus node disease or intermittent AV block. In dual chamber pacemakers this goal can be achieved by programming a long AV delay or an AV delay hysteresis. Algorithms that allow AAI pacing in a dual chamber pacing mode and change to DDD mode in case of high degree AV block are a new attempt to avoid unnecessary right ventricular pacing. The article describes various strategies to avoid unnecessary ventricular pacing and discusses their advantages and disadvantages.     

Pacemaker hemodynamics: Clinical implications

Our review of the current literature and experience in caring for pacemaker patients suggests that a consideration of hemodynamics is a logical way to approach pacemaker selection and programming. Multiple clinical factors enter into the selection of a pacemaker or pacemaker programming settings in each case. It appears that in patients with sinus node disease, atrial-inhibited or dual-chamber pacing provides the best chance for preventing the development of chronic atrial fibrillation with its attendant risks of embolism and stroke. It is clear that AV synchrony has beneficial hemodynamic effects at rest in most patients. The results of Labovitz would suggest that in patients with marked left atrial enlargement, this may be less so. The results of Stewart et al would further suggest that in patients with retrograde VA conduction, dual-chamber pacing is preferable. Retrograde VA conduction can be intermittent and this makes it difficult to use its absence on a single test to decide on the type of pacemaker to use. It appears that baseline left ventricular function does not determine the relative improvement in cardiac output observed with AV synchrony or rate-adaptive pacing. However, in patients with severe congestive heart failure even a small improvement in cardiac output may result in significant clinical improvement. Studies have shown that in any given patient, there may be an optimal AV interval at rest. In general, this ranges from 100 to 150 milliseconds. In normal individuals the optimal AV interval shortens with increased heart rate during exercise in a predictable and linear fashion. The hemodynamic benefits of a shortened AV interval with faster heart rates in pacemaker patients have not yet been shown. Intuitively, however, this would appear to be a desirable approach and will probably be added to the design of future generations of dual-chamber pacemakers. Studies of the effect of different pacing modes on secretion of atrial natriuretic factor are intriguing and may contribute more to our understanding of pacing hemodynamics in the future. During exercise, heart rate increase is more important than AV synchrony and this has been shown by several studies. Thus, in active patients with chronotropic incompetence due to sick sinus syndrome, the addition of rate-adaptive pacing is important. Because single-chamber rate-adaptive atrial pacing leaves the patient exposed to the risk of future development of AV block and DDD pacing does not provide chronotropic support, it is likely that the new rate-adaptive dual-chamber (DDDR) devices will be used in a significant number of these patients.(ABSTRACT TRUNCATED AT 250 WORDS)     

Permanent pacing of the bundle of His after radiofrequency atrioventricular node ablation in patients with suprahisian conduction disturbances]

INTRODUCTION AND OBJECTIVES: The asynchronic contraction of the left ventricle due to left bundle branch block or right ventricular pacing is inferior from a hemodynamic point of view to the synchronic contraction through the conduction system. Several authors have reported some cases of pump failure and deterioration of mitral regurgitation after AV nodal ablation. Alternative sites of pacing such as the right ventricular outflow tract pacing have been proposed in order to avoid these complications. Direct His bundle pacing might be a new alternative for permanent pacing, however, it has not been extensively evaluated in humans yet. Our aim is to prove the feasibility of permanent His pacing in terms of stability, thresholds and pump function. PATIENTS AND METHOD: Population: patients without structural heart disease, selected for AV nodal ablation due to uncontrolled paroxysmal atrial fibrillation, or for pacemaker implantation due to supraHis conduction disturbance, with normal conduction system. An active fixation permanent lead was placed in His position using an steering guidewire and a diagnostic catheter as an anatomical reference. We also implanted a lead in the right atrial appendage and both were connected to a DDDR generator. Pacing thresholds and ecocardiographic ventricular function parameters were evaluated (ejection fraction, cavity size, mitral regurgitation). RESULTS: 12 patients met the inclusion criteria. Successful His pacing was achieved in 8 out of 12 cases (66%) with acceptable thresholds at implantation (1.24 +/- 0.13 volts at 0.5 ms) and during follow up at 3 months (1.31 +/- 0.20 volts at 0.5 ms). Neither a significant change in the ecocardiographic parameters not a deterioration in the clinical status caused by ablation or stimulation was evidenced. CONCLUSION: The His bundle may be the site of choice for long term pacing in patients with AV block and normal infraHis conduction system.     

Multisite stimulation in refractory heart failure.

Since the early nineties, the employment of DDD pacing from a right ventricular site with a short AV delay in patients with severe heart failure has led to considerable conflicting results, so that the real benefit of this method remains to be defined even in selected patients, such as those with first-degree AV block, QRS duration > 140 ms due to left bundle branch block (LBBB), mitral regurgitation time > or = 450 ms and diastolic filling time < or = 200 ms. Indeed, the asynchronous activation induced by pacing the right apex is the most important limitation to the technique, particularly in patients without an LBBB pattern or in those with an incomplete LBBB pattern. Recent studies have also shown that pacing of the right interventricular septum provides no better results than pacing of the right apex, at least in selected patients with no LBBB pattern and no significant mitral regurgitation. Today, it has been suggested that permanent biventricular pacing could be proposed as a feasible and reliable approach to improving ventricular function through the synchronization of the septum and the apex of the left ventricle, particularly in patients with a marked delay in ventricular activation sequence. This technique may be performed by means of transvenous leads inserted through the coronary sinus into the cardiac veins to stimulate both ventricles simultaneously, starting from the right apex and left lateral wall. Consequently, this approach supplies a strong basis for initiating further studies to examine the chronic effects of left ventricular pacing in patients with severe heart failure. We also suggest that the new tissue Doppler imaging techniques could usefully be applied to accurately select candidates to biventricular pacing.     

First‐Degree AV Block—An Entirely Benign Finding or a Potentially Curable Cause of Cardiac Disease?

First‐degree atrioventricular (AV) block is a delay within the AV conduction system and is defined as a prolongation of the PR interval beyond the upper limit of what is considered normal (generally 0.20 s). Up until recently, first‐degree AV block was considered an entirely benign condition. In fact, some complain that it is a misnomer since there is only delay and no actual block in the AV conduction system (usually within the AV node). However, it has long been acknowledged that extreme forms of first‐degree AV block (typically a PR interval exceeding 0.30 s) can cause symptoms due to inadequate timing of atrial and ventricular contractions, similar to the so‐called pacemaker syndrome. Consequently, the current guidelines state that permanent pacemaker implantation is reasonable for first‐degree AV block with symptoms similar to those of pacemaker syndrome or with hemodynamic compromise, but also stresses that there is little evidence to suggest that pacemakers improve survival in patients with isolated first‐degree AV block. Recent reports suggest that it may be time to revisit the impact of first‐degree AV block. Also, several findings in post hoc analyses of randomized device trials give important insights in possible treatment options. The present review aims to provide an update on the current knowledge concerning the impact of first‐degree AV block and also to address the issue of pacing in patients with this condition.     

Unterstützung der spontanen atrioventrukulären Überleitung bei Patienten mit DDD(R)-Schrittmachern Effektivität und Sicherheit

AIM: In a prospective and randomized multicenter study using a cross-over protocol we compared the efficacy and the safety of the ELA medical mode-switch algorithm (DDD/AMC = DDD to AAI) to conventional DDD stimulation in patients with spontaneous AV conduction. PATIENTS AND METHOD: Forty-eight patients with a mean age of 67 +/- 13 years were included. Underlying heart disease was present in 54%. Pacemaker indications were paroxysmal AV block (21%), sick-sinus syndrome (46%), paroxysmal AV block + sick-sinus syndrome (31%) and tachycardia-bradycardia syndrome (8%). Patients were excluded from the study in case of a permanent 1st to 3rd degree AV block, a right bundle-branch block with QRS > 120 ms, severe coronary heart disease or idiopathic cardiomyopathy. The programming of the pacemaker was randomized to either DDD/AMC or DDD and was crossed over after 1 month. The AV interval (AVI) which was programmed in conventional DDD pacing was calculated as AVI = PR (or AR) + 30 ms at rest or as AVI = PR (or AR) - 50 ms during exercise. When the DDD/AMC mode was programmed, the AV interval was calculated automatically. We analyzed the AV interval, the frequency of ventricular pacing, the number of pacemaker-induced tachycardias, the number of atrial tachyarrhythmias, and the final programming which was left to the physician's choice. RESULTS: The AV interval after conventional DDD stimulation was 201 +/- 38 ms vs 195 +/- 28 ms with DDD/AMC (p = ns). Ventricular stimulation was significantly less often in the DDD/AMC mode than in the DDD mode (15 +/- 17% vs 48 +/- 37%, p < 0.001). Thereby the DDD/AMC algorithm led to a 69% reduction of ventricular pacing which means an approximately 5.5 months prolongation of the battery lifetime. There was no significant difference in the incidence of pacemaker-induced tachycardias. At the end of the study 77% of the physicians programmed the DDD/AMC mode. CONCLUSION: The analyzed DDD/AMC mode-switch algorithm leads to a significant reduction of ventricular pacing in patients with spontaneous AV conduction or with only paroxysmal AV block. Thereby the battery lifetime is prolonged and the incidence of complications due to ventricular pacing can be reduced.     

Conventional and biventricular pacing in patients with first-degree atrioventricular block

Recent reports suggest that first-degree atrioventricular block is not benign. However, there is no evidence that shortening of the PR interval can improve outcome except for symptomatic patients with a very long PR interval ≥0.3 s. Because these patients require continual forced pacing, biventricular pacing should be used according to accepted guidelines for third-degree AV block. Functional atrial undersensing may occur in patients with conventional dual-chamber pacing and first-degree AV block because the sinus P-wave tends to be displaced into the post-ventricular atrial refractory period (PVARP) an arrangement that may cause a pacemaker syndrome. Prevention requires programming a shorter AV and PVARP that is feasible because retrograde conduction is rare in first-degree AV block patients. A relatively new pacing mode to minimize right ventricular stimulation has been designed by eliminating the traditional AV interval but with dual-chamber backup. This pacing mode permits the establishment of very long AV intervals that may cause pacemaker syndrome. About 50% of patients undergoing cardiac resynchronization therapy (CRT) have a PR interval ≥200 ms. The CRT patients with first-degree AV block are prone to develop electrical desynchronization more easily than those with a normal PR interval. The duration of desynchronization after exceeding the upper rate on exercise is also more pronounced. AV junctional ablation is rarely necessary in patients with first-degree AV block but should be considered for symptomatic functional atrial undersensing or when the disturbances caused by first-degree AV block during CRT cannot be managed by programming.