Conventional Dual-chamber Pacing Research Articles

Atrioventricular Synchrony Delivered by a Dual-Chamber Leadless Pacemaker System.

A dual-chamber leadless pacemaker system has been designed for atrioventricular synchronous pacing using wireless, beat-to-beat, implant-to-implant (i2i) communication between distinct atrial and ventricular leadless pacemakers. The atrioventricular synchrony achieved across various ambulatory scenarios has yet to be systematically evaluated. A prospective, single-arm, unblinded, multicenter, international clinical trial of the leadless pacemaker system was conducted in patients with a conventional dual-chamber pacing indication enrolled from February 2022 to March 2023. Leadless pacemaker systems were implanted, and 12-lead Holter electrocardiographic recordings were collected 3 months after implantation over various postures/activities: sitting, supine, left lateral recumbent, right lateral recumbent, standing, normal walk, and fast walk. An independent Holter core laboratory performed a manual adjudication of the percent of atrioventricular synchronous beats using the standard 300-millisecond PR interval limit. Atrium-to-ventricle and ventricle-to-atrium i2i communication success rates were also assessed. Post hoc summary statistics describing the relationships between atrioventricular synchrony and i2i success, posture/activity, implantation indication, atrioventricular event, and heart rate were calculated. In the evaluable population (n=384 of 464 enrolled [83%]; 61% male; age, 70 years; weight, 82 kg; 60% ejection fraction; 95% of beats evaluable), the mean atrioventricular synchrony of 98% of beats observed across all postures using the standard 300-millisecond limit was greater than both atrial-to-ventricular i2i (94%) and ventricular-to-atrial i2i (94%; P<0.001), exceeding both i2i values in 95% of patients. Atrioventricular synchrony was achieved in >95% of evaluable beats across all postures/activities, implantation indications, atrioventricular paced/sensed event combinations, and heart rate ranges (including >100 bpm). This dual-chamber leadless pacemaker system demonstrated atrioventricular synchrony in 98% of evaluable beats at 3 months after implantation. Atrioventricular synchrony was maintained across postures/activities and remained robust for heart rates >100 bpm.

Therapeutic options for neurocardiogenic syncope: a meta-analysis of randomised trials with and without blinding

BackgroundNeurocardiogenic syncope is a common condition with significant associated psychological and physical morbidity. The effectiveness of therapeutic options for neurocardiogenic syncope beyond placebo remains uncertain.MethodsThe primary endpoint was the risk...

Therapeutic options for syncope: a meta-analysis of trials with and without placebo control

Abstract Funding Acknowledgements Type of funding sources: None. Background 8% of the population suffer recurrent episodes of syncope which can cause physical injury and psychological morbidity. The extent to which therapeutic options effectively reduce syncope recurrence beyond placebo remain unclear. Methods We performed a meta-analysis of randomised trials including pharmacological, cardiac pacing and physical interventions for syncope. We assessed the effect of these therapeutic interventions on clinical syncope recurrence. We stratified the trials by use of placebo control. Results There were 50 eligible trials: 22 pacing, 19 pharmacological and 9 of physical interventions including 3,975 patients. Trials assessing syncope recurrence with placebo control were neutral for Beta-Blockers (RR 1.11, 95% CI 0.85 to 1.45, p=0.36), Fludrocortisone, (RR 0.83, 95% CI: 0.63 to 1.11 p=0.83) and conventional dual-chamber pacing (RR 0.81, 95% CI 0.61 to 1.09 p=0.287). However, they were favourable for Selective Serotonin Reuptake Inhibitors [SSRIs] (RR 0.40, 95% CI 0.25 to 0.63 p&amp;lt;0.001), Midodrine (RR 0.70, 95% CI 0.53 to 0.94, p=0.016) and Closed-Loop-Stimulation (CLS) pacing (RR 0.21, 95% CI 0.12 to 0.34, p &amp;lt; 0.001). Non-placebo-controlled trials reported significant benefit for every category of therapy including conventional dual-chamber pacing, medicines (Beta-Blockers, Midodrine and Oral rehydration salts) and physical interventions including tilt-training. Three categories of therapy have been trialled with and without placebo control: the non-placebo-controlled studies showed significantly different results from their placebo-controlled counterparts (beta-blockers p=0.024, midodrine p=0.006, dual-chamber pacing p=0.017) (figure 2). Conclusion Under placebo-controlled conditions, CLS pacing reduces risk of syncope recurrence by ~75%, whereas conventional pacing does not. SSRIs and midodrine also show significant efficacy under placebo-controlled conditions. Without placebo control, trials consistently show artefactually larger benefits. Future non-placebo-controlled trials for syncope should not be conducted.

The Story of Managed Ventricular Pacing

A significant milestone in cardiac pacing occurred approximately two decades ago, when the primary operating mode was reimagined to more closely mimic normal top-down cardiac activation. When introduced, Managed Ventricular Pacing (MVP™; Medtronic, Minneapolis, MN, USA) was an unprecedented dual-chamber mode as it preferentially paced the right atrium in the AAI/R mode and simultaneously protected against transient heart block, albeit only in the instance of dropped ventricular beats. At the time, dual-chamber DDD/R with atrial-based timing and programmable atrioventricular delay was state of the art. MVP™ “unlocked” conventional dual-chamber pacing by not consistently requiring a 1:1 atrioventricular relationship during its primary operating mode (ie, AAI/R+). Ultimately, MVP™ emerged as a primitive means to promote His–Purkinje activation, and it is not a coincidence that its roots can be traced back to first-in-man permanent His-bundle pacing.

A randomized controlled trial of cardiac resynchronization therapy in patients with prolonged atrioventricular interval: the REAL-CRT pilot study.

A prolonged PR interval is known to be associated with increased mortality and a higher risk of developing atrial fibrillation (AF). We tested the hypothesis that cardiac resynchronization therapy (CRT) is superior to conventional dual-chamber pacing with algorithms for right ventricular pacing avoidance (DDD-VPA) in preserving systolic and diastolic function and in preventing new-onset AF in patients with normal systolic function, indication for pacing and prolonged atrioventricular conduction (PR interval ≥220 ms). We randomly assigned 82 patients with ejection fraction >35%, indication for pacing and PR interval ≥220 ms to CRT or to DDD-VPA. On 12-month follow-up examination, the study and control arms did not differ in terms of left ventricular end-systolic volume (44 ± 17 mL vs. 47 ± 16 mL, P = 0.511) or ejection fraction (55 ± 6% vs. 57 ± 8%, P = 0.291). The E to A mitral wave amplitude ratio was higher in the CRT arm (1.3 ± 1.3 vs. 0.8 ± 0.4, P = 0.046) and the E wave deceleration time was longer (262 ± 83 ms vs. 205 ± 51 ms, P = 0.027). Left atrial volume was smaller in the CRT arm (64 ± 17 mL vs. 84 ± 25 mL, P = 0.035). Moreover, the functional class was lower in CRT patients (1.4 ± 0.6 vs. 1.8 ± 0.5, P = 0.010). During follow-up, CRT was associated with a lower risk of new-onset AF [hazard ratio = 0.37 (0.13-0.98), P = 0.046]. Cardiac resynchronization therapy proved superior to DDD-VPA in terms of better diastolic function, less left atrial enlargement and lower risk of new-onset AF, at 12 months. These data need to be confirmed in a larger trial with longer follow-up. URL: http://clinicaltrials.gov/ Identifier: NCT02150538.

Managed ventricular pacing compared with conventional dual-chamber pacing for elective replacement in chronically paced patients: Results of the Prefer for Elective Replacement Managed Ventricular Pacing randomized study

Several studies have shown that unnecessary right ventricular pacing has detrimental effects. To evaluate whether minimization of ventricular pacing as compared with standard dual-chamber pacing (DDD) improves clinical outcomes in patients referred for pacemaker or implantable cardioverter-defibrillator (ICD) replacement. In an international single-blind, multicenter, randomized controlled trial, we compared DDD with managed ventricular pacing (MVP), a pacing mode developed to minimize ventricular pacing by promoting intrinsic atrioventricular conduction. We included patients referred for device replacement with >40% ventricular pacing, no cardiac resynchronization therapy upgrade indication, no permanent atrial fibrillation (AF), and no permanent complete atrioventricular block. Follow-up was for 2 years. The primary end point was cardiovascular hospitalization. The intention-to-treat analysis was performed by using Kaplan-Meier method and the log-rank test. We randomized 605 patients (556 referred for pacemaker and 49 referred for ICD replacement; mean age 75 ± 11 years; 365 [60%] men, at 7.7 ± 3.3 years from first device implantation) to MVP (n = 299) or DDD (n = 306). We found no significant differences in the primary end point cardiovascular hospitalization (MVP: 16.3% vs DDD: 14.5%; P = .72) and the secondary end point persistent AF (MVP: 15.4% vs DDD: 11.2%; P = .08), permanent AF (MVP: 4.1% vs DDD: 3.1%; P = .44), and composite of death and cardiovascular hospitalization (MVP: 23.9% vs DDD: 20.2%; P = .48). MVP reduced right ventricular pacing (median 5% vs 86%; Wilcoxon, P < .0001) as compared with DDD. In patients referred for pacemaker and ICD replacement with clinically well-tolerated long-term exposure to >40% ventricular pacing in the ventricle, a strategy to minimize ventricular pacing is not superior to standard DDD in reducing incidence of cardiovascular hospitalizations.

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.

Closed-loop cardiac pacing vs. conventional dual-chamber pacing with specialized sensing and pacing algorithms for syncope prevention in patients with refractory vasovagal syncope: results of a long-term follow-up

Closed-loop stimulation (CLS) pacing has shown greater efficacy in preventing the recurrence of vasovagal syncope (VVS) in patients with a cardioinhibitory response to head-up tilt test (HUTT) compared with conventional pacing. Moreover, there is no conclusive evidence to support the superiority of CLS over the conventional algorithms for syncope prevention. This study retrospectively evaluated the effectiveness of CLS pacing compared with dual-chamber pacing with conventional specialized sensing and pacing algorithms for syncope prevention in the prevention of syncope recurrence in patients with refractory VVS and a cardioinhibitory response to HUTT during a long-term follow-up. Forty-one patients (44% male, 53 ± 16 years) with recurrent, refractory VVS (26% with trauma) and a cardioinhibitory response to HUTT who had undergone pacemaker implantation were included in the analysis. Twenty-five patients received a dual-chamber CLS pacemaker (CLS group) and 16 patients received a dual-chamber pacemaker with conventional algorithms for syncope prevention (conventional pacing group): 9 patients with Medtronic rate drop response algorithm and 7 patients with Guidant-Boston Scientific sudden brady response algorithm. During the follow-up (mean 4.4 ± 3.0 years, interquartile range 2.2-7.4 years) one patient (4%) in the CLS group and six (38%) in the conventional pacing group had syncope recurrences (P= 0.016). The Kaplan-Meier actuarial estimate of first recurrence of syncope after 8 years was 4% in the CLS group and 40% in the conventional pacing group (P= 0.010). The results of this retrospective analysis show that, in order to prevent a recurrence of VVS in patients with a cardioinhibitory response to HUTT, dual-chamber CLS pacing was more effective than dual-chamber pacing with conventional algorithms for syncope prevention in preventing bradycardia-related syncope.

Outcome of patients aged over 75 years who received a pacemaker to treat sinus node dysfunction

The prognosis for patients aged over 75 years who receive a pacemaker in the context of sinus node dysfunction is unclear. We sought to evaluate the incidences of atrial fibrillation, heart failure and death in such patients, and the role of the pacing mode in their prognosis. This was a retrospective study of 102 patients aged over 75 years (mean 82.2 ± 4.4 years) who received a pacemaker in the context of sinus node dysfunction. During the follow-up period (mean 806 days), 36 patients (35.3%) experienced heart failure, 47 patients (46.1%) had an episode of paroxysmal atrial fibrillation, 19 patients (18.6%) progressed to chronic atrial fibrillation and 29 (28.4%) died, the fatal event being sudden death or of cardiac origin in almost half of these patients (44.8%). Patients assigned to dual-chamber minimal ventricular pacing showed significantly lower rates of heart failure episodes (P=0.023) and all-cause mortality (P<0.001) than those assigned to conventional dual-chamber pacing. In contrast, the two groups did not differ with regard to either paroxysmal or chronic atrial fibrillation. In patients aged over 75 years, the use of dual-chamber pacemakers incorporating an algorithm minimizing ventricular pacing for sinus node dysfunction seems to decrease the number of heart failure episodes and mortality. On the basis of this finding, the implantation of such devices seems justifiable, even in this age group.

The relationship between right ventricular pacing and atrial fibrillation burden and disease progression in patients with paroxysmal atrial fibrillation: the long-MinVPACE study

In patients requiring permanent pacemaker implantation for sinus node disease (SND) or atrioventricular (AV) block, right ventricular (RV) pacing has been demonstrated to increase the risk of developing atrial fibrillation (AF). The effects of RV pacing in patients with paroxysmal AF are less well defined. Short- and medium-term studies have suggested no significant correlation between RV pacing and atrial fibrillation burden (AFB) measurement; we sought to assess for an effect in the long-term. Sixty-six patients were randomized to receive either conventional dual chamber pacing (DDDR, n = 33), or dual chamber minimal ventricular pacing (MinVP, n = 33), for a period of at least 1 year. Patients were reviewed every 6 months and all pacemaker data were downloaded. The primary outcome measures were device-derived AFB and progression to persistent AF. The mean duration of study follow-up was 1.4 ± 0.6 years. Mean ventricular pacing was less in the MinVP cohort compared with the DDDR cohort (5.8 vs. 74.0%, P < 0.001). At follow-up, the device-derived AFB was significantly lower in the MinVP cohort when compared with the DDDR cohort (12.8 ± 15.3% vs. DDDR 47.6 ± 42.2%, P < 0.001). Kaplan-Meier estimates of time to onset of persistent AF showed significant reductions in the rates of persistent AF for MinVP pacing (9%) when compared with conventional DDDR pacing (42%), P = 0.004. Right ventricular pacing induces increased AFB in patients with paroxysmal AF in the long term. Dual chamber MinVP algorithms result in reduced AFB and reduced disease progression from paroxysmal to persistent AF in the long term.

186 Outcome of patients over 75 years old receiving a pacemaker to treat sinus-node dysfunction

The prognosis of patients over 75 years old receiving a pacemaker in the context of sinus-node dysfunction is unclear. This study sought to evaluate the incidences of atrial fibrillation (AF), heart failure (HF) and death in this population and the role of the pacing mode in their prognosis. This was a retrospective study on 102 patients over 75 years old (mean 82.2 ± 8.6 years) who received a pacemaker in the context of sinus-node dysfunction. During the follow-up period (mean: 806 days), 36 patients (35.3%) experienced HF and 47 patients (46.1%) an episode of paroxysmal AF, 19 patients (18.6%) progressed to chronic AF, and 29 (28.4%) died, the fatal event being sudden death or of cardiac origin in almost half these patients (44.8%). Patients assigned to dual-chamber minimal ventricular pacing showed a significantly lower rate of HF episodes (p = 0.023), and a lower all-cause mortality (p<0.001) than those assigned to conventional dual-chamber pacing. In contrast, the two groups did not differ with regard to either paroxysmal or chronic AF, regardless of whether or not the algorithms designed to prevent AF were activated. In patients with a high risk of mortality and morbidity, the use of dual-chamber pacemakers incorporating an algorithm minimizing ventricular pacing seems to decrease the number of HF episodes and mortality. On the basis of this finding, the implantation of such devices even in this age group seems justifiable.

Effect of Pacing for Soft Indications on Mortality and Heart Failure in the Dual Chamber and VVI Implantable Defibrillator (DAVID) Trial

The dual chamber and VVI implantable defibrillator (DAVID) trial demonstrated that dual chamber (DDDR) pacing in defibrillator candidates with impaired ventricular function and no established indication for pacing resulted in worsened congestive heart failure (CHF) or death. Many patients had abnormalities for which pacing is often advocated to improve the management of ventricular dysfunction. Evaluate the impact and interaction of nonessential but potentially justifiable reasons to pace ("soft indications"), together with pacing mode, on outcome. DAVID patients were stratified by those with and without "soft indications" for pacing (rate < 60 beats/min or first-degree atrioventricular block) (n = 169; n = 335, respectively). This analysis also stratified patients by normal and abnormal QRS conduction (QRS >or= 110 ms), who were previously found to be affected differently by DDDR pacing. Groups were analyzed according to the combined endpoint of mortality or CHF hospitalization. When assigned to treatment that promoted pacing (DDDR), the incidence of death or CHF tended to be higher in patient subgroups with and without "soft indications," consistent with results from DAVID. Patients with, compared to those without, these abnormalities neither benefited nor were less adversely affected when actively paced. The presence or absence of "soft indications" also provided no additional explanation for the differing outcomes in patient cohorts with and without abnormal QRS conduction. Sinus bradycardia or first-degree atrioventricular block did not ameliorate the poor outcomes associated with dual-chamber compared with VVI pacing, and do not justify conventional dual-chamber pacing in defibrillator recipients with ventricular dysfunction.

Managed ventricular pacing vs. conventional dual-chamber pacing for elective replacements: the PreFER MVP study: clinical background, rationale, and design

Several clinical studies have shown that, in patients with intact atrioventricular (AV) conduction, unnecessary chronic right ventricular (RV) pacing can be detrimental. The managed ventricular pacing (MVP) algorithm is designed to give preference to spontaneous AV conduction, thus minimizing RV pacing. The clinical outcomes of MVP are being studied in several ongoing trials in patients undergoing a first device implantation, but it is unknown to what extent MVP is beneficial in patients with a history of ventricular pacing. The purpose of the Prefer for Elective Replacement MVP (PreFER MVP) study is to assess the superiority of the MVP algorithm to conventional pacemaker and implantable cardioverter-defibrillator programming in terms of freedom from hospitalization for cardiovascular causes in a population of patients exposed to long periods of ventricular pacing. PreFER MVP is a prospective, 1:1 parallel, randomized (MVP ON/MVP OFF), single-blinded multi-centre trial. The study population consists of patients with more than 40% ventricular pacing documented with their previous device. Approximately, 600 patients will be randomized and followed for at least 24 months. The primary endpoint comprises cardiovascular hospitalization. The PreFER MVP trial is the first large prospective randomized clinical trial evaluating the effect of MVP in patients with a history of RV pacing.

Minimizing Ventricular Pacing to Reduce Atrial Fibrillation in Sinus-Node Disease

Conventional dual-chamber pacing maintains atrioventricular synchrony but results in high percentages of ventricular pacing, which causes ventricular desynchronization and has been linked to an increased risk of atrial fibrillation in patients with sinus-node disease. We randomly assigned 1065 patients with sinus-node disease, intact atrioventricular conduction, and a normal QRS interval to receive conventional dual-chamber pacing (535 patients) or dual-chamber minimal ventricular pacing with the use of new pacemaker features designed to promote atrioventricular conduction, preserve ventricular conduction, and prevent ventricular desynchronization (530 patients). The primary end point was time to persistent atrial fibrillation. The mean (+/-SD) follow-up period was 1.7+/-1.0 years when the trial was stopped because it had met the primary end point. The median percentage of ventricular beats that were paced was lower in dual-chamber minimal ventricular pacing than in conventional dual-chamber pacing (9.1% vs. 99.0%, P<0.001), whereas the percentage of atrial beats that were paced was similar in the two groups (71.4% vs. 70.4%, P=0.96). Persistent atrial fibrillation developed in 110 patients, 68 (12.7%) in the group assigned to conventional dual-chamber pacing and 42 (7.9%) in the group assigned to dual-chamber minimal ventricular pacing. The hazard ratio for development of persistent atrial fibrillation in patients with dual-chamber minimal ventricular pacing as compared with those with conventional dual-chamber pacing was 0.60 (95% confidence interval, 0.41 to 0.88; P=0.009), indicating a 40% reduction in relative risk. The absolute reduction in risk was 4.8%. The mortality rate was similar in the two groups (4.9% in the group receiving dual-chamber minimal ventricular pacing vs. 5.4% in the group receiving conventional dual-chamber pacing, P=0.54). Dual-chamber minimal ventricular pacing, as compared with conventional dual-chamber pacing, prevents ventricular desynchronization and moderately reduces the risk of persistent atrial fibrillation in patients with sinus-node disease. (ClinicalTrials.gov number, NCT00284830 [ClinicalTrials.gov].).

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.

Stimulation cardiaque et insuffisance cardiaque

Cardiac activation and heart failure. Dilated cardiomyopathies are frequently associated with atrioventricular and intra ventricular conduction disorders. Such conduction disorders modify the cardiac activation sequence and impair left ventricular systolic and diastolic function. The aim of pacing in dilated cardiomyopathy is to restore a cardiac activation sequence as normal as possible. Conventional dual-chamber pacing was first proposed to treat drug-refractory heart failure but was soon replaced by multisite biventricular pacing. The aim of biventricular pacing is to correct intraventricular asynchrony by pacing the two ventricles simultaneously. Acute studies have shown that biventricular pacing could improve hemodynamic parameters in patients with dilated cardiomyopathy and severe intraventricular conduction disorders. More recently, chronic studies demonstrated a significant improvement in exercise tolerance and quality of life with biventricular pacing in patients with drug-refractory heart failure and with intraventricular conduction disorders. To safely pace the left ventricle specific materials and tools had to be developed. With those developments, biventricular pacing is now a feasible and safe technique. Regarding the results of several clinical studies, biventricular pacing could now be proposed to treat patients with drug-refractory heart failure in the setting of chronic left ventricular systolic dysfunction and with major intraventricular conduction disorders.

Methods other than tilt testing for diagnosing neurocardiogenic (neurally mediated) syncope.

The recording of spontaneous episodes of bradycardiac neurocardiogenic syncope (NCS) has shown that: a prolonged ventricular asystole seems necessary to cause syncope; asystole is preceded by other bradyarrhythmias in the vast majority of cases; some warning symptoms precede the loss of consciousness in most cases; conventional dual-chamber pacing is efficacious both in patients with a positive response to carotid sinus massage (CSM) and eyeball compression test (EBC) and in those with a positive response to tilt-testing (TT). CSM, EBC, and TT are established tools for diagnosing NCS, when the recording of spontaneous syncope is lacking. When combined together, they are probably able to correctly identify most patients affected by NCS. Nevertheless, whether the type of reflex induced by the cardiovascular reflexivity maneuvers correlates with that of the spontaneous syncope is largely unknown. Our knowledge suggests that the correlation may be unsatisfactory, owing to the following: the variability of the mechanism of spontaneous syncope from patient to patient and also, in the same patient, from one episode to another; the discordance of the type of response when 2 or 3 tests are positive in the same patient, the response being more frequently asystolic with CSM and EBC and more frequently vasodepressor with TT: the different timing between hypotension induced by CSM (in which it follows the bradycardia) and that induced by TT (in which it usually precedes the bradycardia) and the uncertainty about the timing of hypotension during the spontaneous syncope; the good reproducibility of the spontaneous event by CSM and EBC, but not by TT, when cardiac asystole is the manifestation of NCS; and the fairly high rate of false-positive results of cardiovascular reflexivity maneuvers. Hypotension is the main reason for the failure of pacemaker therapy in all the forms of neurocardiogenic syncope (NCS), whether diagnosed by CSM, EBC, or TT. Thus, the need arises to correctly identify the magnitude of the hypotensive reflexes of spontaneous events.

Atrial sensing performance of the single-lead VDD pacemaker during exercise

Objectives. The purpose of this study was to examine the atrial sensing performance of the single-lead VDD pacing system during exercise and concomitant changes in the amplitude of the atrial electrogram.Background. Studies of conventional dual-Chamber pacing have demonstrated an overall reduction in the atrial signal amplitude and a variable incidence of atrial undersensing during vigorous exercise.Methods. Tht telemetered atrial electrogram and simultaneous surface electrocardiogram (ECG) were continuously recorded in 12 patients (mean age 70.8 years) with an implanted single-lead VDD pacing system during treadmill stress testing, The atrial signal amplitude was measured at peak exercise, and the patients were monitored for maintained atrial synchronized ventricular pacing during the entire exercise and recovery period.Results. The atrial electrographic voltage decreased an average of 19.5% (p < 0.05) during peak exercise, and the reduced P wave amplitude ranged from 6.9% to 59.4% of the preexercise values in 8 of 12 patients. Three patients showed a modest increase in atrial signal amplitude, and one pateint had no change. The telemetered electrogram displayed persistent and intact atrial synchronous ventricular pacing throughout the study period.Conclusions. Despite relatively low atrial signal amplitudes at rest and further decreases during exercise, the single-lead VDD pacemaker maintains reliable atrial tracking and ventricular pacing during vigorous exercise.