Predictors of pacemaker requirement in patients with implantable loop recorder and unexplained syncope: A systematic review and meta-analysis

Identifying the underlying cause of unexplained syncope is crucial for appropriate management of recurrent syncopal episodes. Implantable loop recorders (ILRs) have emerged as valuable diagnostic tools for monitoring patients with unexplained syncope. However, the predictors of pacemaker requirement in patients with ILR and unexplained syncope remain unclear. In this study, we shed light on these prognostic factors. PubMed/MEDLINE, EMBASE, Web of Science, and Cochrane CENTRAL were systematically searched until May 04, 2023. Studies that evaluated the predictors of pacemaker requirement in patients with implantable loop recorder and unexplained syncope were included. The "Quality In Prognosis Studies" appraisal tool was used for quality assessment. The pooled odds ratio (OR) with 95% confidence intervals (CIs) was calculated. The publication bias was evaluated using Egger's and Begg's tests. Ten studies (n = 4200) were included. Right bundle branch block (OR: 3.264; 95% CI: 1.907-5.588, p < .0001) and bifascicular block (OR: 2.969; 95% CI: 1.859-4.742, p < .0001) were the strongest predictors for pacemaker implantation. Pacemaker requirement was more than two times in patients with atrial fibrillation, sinus bradycardia and first degree AV block. Valvular heart disease, diabetes mellitus, and hypertension were also significantly more in patients with pacemaker implantation. Age (standardized mean difference [SMD]: 0.560; 95% CI: 0.410/0.710, p < .0001) and PR interval (SMD: 0.351; 95% CI: 0.150/0.553, p = .001) were significantly higher in patients with pacemaker requirement. Heart conduction disorders, atrial arrhythmias and underlying medical conditions are main predictors of pacemaker device implantation following loop recorder installation in unexplained syncopal patients.

Twenty-five years of research on syncope

Over the last 25 years, the Europace journal has greatly contributed to dissemination of research and knowledge in the field of syncope. More than 400 manuscripts have been published in the journal. They undoubtedly improved our understanding of syncope. This symptom is now clearly differentiated from other forms of transient loss of consciousness. The critical role of vasodepression and/or cardioinhibition as final mechanisms of reflex syncope is emphasized. Current diagnostic approach sharply separates between cardiac and autonomic pathways. Physiologic insights have been translated, through rigorously designed clinical trials, into non-pharmacological or pharmacological interventions and interventional therapies. The following manuscript is intended to give the reader the current state of the art of knowledge of syncope by highlighting landmark contributions of the Europace journal.

Arrhythmic syncope: From diagnosis to management

Syncope is a concerning symptom that affects a large proportion of patients. It can be related to a heterogeneous group of pathologies ranging from trivial causes to diseases with a high risk of sudden death. However, benign causes are the most frequent, and identifying high-risk patients with potentially severe etiologies is crucial to establish an accurate diagnosis, initiate effective therapy, and alter the prognosis. The term cardiac syncope refers to those episodes where the cause of the cerebral hypoperfusion is directly related to a cardiac disorder, while arrhythmic syncope is cardiac syncope specifically due to rhythm disorders. Indeed, arrhythmias are the most common cause of cardiac syncope. Both bradyarrhythmia and tachyarrhythmia can cause a sudden decrease in cardiac output and produce syncope. In this review, we summarized the main guidelines in the management of patients with syncope of presumed arrhythmic origin. Therefore, we presented a thorough approach to syncope work-up through different tests depending on the clinical characteristics of the patients, risk stratification, and the management of syncope in different scenarios such as structural heart disease and channelopathies.

Five cases of complete atrioventricular block induced by bending forward: unusual but not unique

AIMS

We describe five patients with syncope caused by a complete atrioventricular block (AVB) while they were bending forward, not rising after bending, and aim to describe the occurrence and the association between bending forward and AVB.

METHODS AND RESULTS

In two patients, bending forward was the exclusive trigger for syncope, while in the remaining three, other postural changes (sitting down, standing up, and exertion) could also provoke syncope. Complete AVB as the cause of syncope was documented using ECG monitoring in two cases and an implantable loop recorder in the other three. Ectopic beats without preceding sinus slowing occurred before syncope in four cases. Two cases had a left bundle branch block. All patients responded favourably to cardiac pacing.

CONCLUSION

This is the first case series on complete AVB provoked by bending forward. Syncope during bending forward should suggest a search for an AVB. Arguments in favour of a vagal mechanism were syncope triggered by bending forward, and that other triggers could also evoke syncope. However, the absence of sinus slowing before syncope in some cases and the fact that bending forward did not seem to provoke reflex syncope without AVB, cast doubts on a reflex mechanism. There were also arguments favouring conduction disorder: i.e. ectopic beats before syncope and pre-existing conduction disturbances in two cases. The cases are reminiscent of paroxysmal AVB. Discrimination between paroxysmal AVB and vagal AVB is important because a pacemaker is warranted in arrhythmic complete AVB, while the benefit is limited or absent in reflex AVB.

Causes of syncopal recurrences in patients treated with permanent pacing for bradyarrhythmic syncope: Findings from the SYNCOPACED registry

BACKGROUND

Few studies have examined the causes of syncope/collapse recurrences in patients with a previously implanted pacemaker for bradyarrhythmic syncope.

OBJECTIVE

The purpose of this study was to assess the causes of syncope/collapse recurrences after pacemaker implantation for bradyarrhythmic syncope in a large patient population.

METHODS

The SYNCOpal recurrences in patients treated with permanent PACing for bradyarrhythmic syncope (SYNCOPACED) registry was a prospective multicenter observational registry enrolling 1364 consecutive patients undergoing pacemaker implantation for bradyarrhythmic syncope. During follow-up, the time to the first syncope/collapse recurrence was recorded. Patients with syncope/collapse recurrences underwent a predefined diagnostic workup aimed at establishing the mechanism of syncope/collapse.

RESULTS

During a median follow-up of 50 months, 213 patients (15.6%) reported at least 1 syncope/collapse recurrence. The risk of syncope/collapse recurrence was highest in patients who underwent implantation for cardioinhibitory vasovagal syncope (26.4%), followed by unexplained syncope and chronic bifascicular block (21.5%), cardioinhibitory carotid sinus syndrome (17.2%), atrial fibrillation needing pacing (15.5%), atrioventricular block (13.6%), and sinus node disease (12.5%) (P = .017). The most frequent cause of syncope/collapse recurrence was reflex syncope (27.7%), followed by orthostatic hypotension (26.3%), pacemaker or lead malfunction (5.6%), structural cardiac disease (5.2%), and atrial and ventricular tachyarrhythmias (4.7% and 3.8%, respectively). In 26.8% of cases, the mechanism of syncope/collapse remained unexplained.

CONCLUSION

In patients receiving a pacemaker for bradyarrhythmic syncope, reflex syncope and orthostatic hypotension are the most frequent mechanisms of syncope/collapse recurrence after implantation. Pacing system malfunction, structural cardiac diseases, and tachyarrhythmias are rare mechanisms. The mechanism remains unexplained in >25% of patients.

Risk of syncopal recurrences in patients treated with permanent pacing for bradyarrhythmic syncope: role of correlation between symptoms and electrocardiogram findings

Aims 

To evaluate the risk of syncopal recurrences after pacemaker implantation in a population of patients with syncope of suspected bradyarrhythmic aetiology.

Methods and results 

Prospective, multicentre, observational registry enrolling 1364 consecutive patients undergoing pacemaker implantation for syncope of bradyarrhythmic aetiology (proven or presumed). Before pacemaker implantation, all patients underwent a cardiac work-up in order to establish the bradyarrhythmic aetiology of syncope. According to the results of the diagnostic work-up, patients were divided into three groups: Group A, patients in whom a syncope-electrocardiogram (ECG) correlation was established (n = 329, 24.1%); Group B, those in whom clinically significant bradyarrhythmias were detected without a documented syncope-ECG correlation (n = 877, 64.3%); and Group C, those in whom bradyarrhythmias were not detected and the bradyarrhythmic origin of syncope remained presumptive (n = 158, 11.6%). During a median follow-up of 50 months, 213 patients (15.6%) reported at least one syncopal recurrence. Patients in Groups B and C showed a significantly higher risk of syncopal recurrences than those in Group A [hazard ratios (HRs): 1.60 and 2.66, respectively, P &lt; 0.05]. Failure to establish a syncope-ECG correlation during diagnostic work-up before pacemaker implantation was an independent predictor of syncopal recurrence on multivariate analysis (HR: 1.90; P = 0.002).

Conclusion

In selecting patients with syncope of suspected bradyarrhythmic aetiology for pacemaker implantation, establishing a correlation between syncope and bradyarrhythmias maximizes the efficacy of pacing and reduces the risk of syncopal recurrences.

Etiology of syncope in patients with preexisting atrioventricular conduction disorders

BACKGROUND

The discussion about the feasibility of empiric pacemaker implantation in patients with preexisting atrioventricular (AV) conduction disorders continues. The aim of the study was to determine the etiology of syncope and the need for pacemaker insertion in patients with AV conduction impairment using implantable loop recorder (ILR).

METHODS

ILR was implanted after negative diagnostic workup in 37 patients with syncope (24 men, 13 women, age 72 ± 10 years) and preexisting impairment of AV conduction. First-degree AV block (AVB I) was present in 26 patients, and bundle branch block (BBB) in 17 patients.

RESULTS

ILR-based diagnosis was made in 28 patients (75%)-sinus arrest in 13 patients, complete AVB in 10 patients, and vasodepressor syncope in five patients. In patients with preexisting BBB, sinus arrest occurred during ILR monitoring significantly more frequently than in patients without BBB (53% vs 20%, P = .03). Complete AVB was significantly less common in patients with preexisting BBB than in patients without BBB (12% vs 40%, P = .04). On multivariate regression analysis, the only independent predictor of AVB occurrence during ILR monitoring was preexisting AVB I (P = .03). The only independent predictor of sinus arrest during ILR monitoring was preexisting BBB (P = .03).

CONCLUSIONS

In patients with preexisting AV conduction disorders, prevailing syncopal mechanism during ILR monitoring was asystole. However, sinus arrest occurred more often than complete AVB and was predicted by preexisting BBB. Preexisting AVB was a predictor of complete AVB during ILR monitoring.

Pacing in vasovagal syncope: Physiology, pacemaker sensors, and recent clinical trials-Precise patient selection and measurable benefit

The role of pacing in vasovagal syncope (VVS) is considered from a physiological basis. Most VVS patients lose consciousness due to hypotension before severe bradycardia/asystole occurs. Patients who benefit from dual-chamber pacing typically are older with highly symptomatic, late-onset, frequent and severe syncope with short/no prodrome and documented severe cardioinhibition. Tilt testing is of value in patients with recurrent unexplained syncope to identify important hypotensive susceptibility stemming from reduced venous return and stroke volume (SV). A negative tilt test in vasovagal patients with spontaneous asystole documented by an implantable/insertable loop recorder is associated with lower syncope recurrence rates after pacemaker implantation. Pacing may be more effective if triggered by sensor detection of a parameter changing earlier in the reflex than bradycardia when SV may still be relatively preserved. In this regard, detection of right ventricular impedance offers promise. Conservatism is recommended, limiting pacing in VVS to a small subset of symptomatic older patients with clearly documented cardioinhibition and paying particular attention to the timing of loss of consciousness in relation to asystole/bradycardia. Understanding VVS physiology permits application of well-timed, appropriate pacing that yields benefit for highly symptomatic patients.

Cardiovascular Autonomic Dysfunction Is the Most Common Cause of Syncope in Paced Patients

Introduction: Syncope and orthostatic intolerance in paced patients constitute a common clinical dilemma. We, thus, aimed to determine the etiology of syncope and/or symptoms of orthostatic intolerance in paced patients.

Methods: Among 1,705 patients with unexplained syncope and/or orthostatic intolerance that were investigated by cardiovascular autonomic tests, including Valsalva maneuver, active standing, carotid sinus massage, and tilt-testing, 39 patients (2.3%; age 65.6 years; 39% women) had a cardiac implantable electronic device (CIED). We explored past medical history, diagnoses found during cardiovascular autonomic tests, and the further clinical workup, in case of negative initial evaluation.

Results: An etiology was identified during cardiovascular autonomic tests in 36 of the 39 patients. Orthostatic hypotension (n = 16; 41%) and vasovagal syncope (n = 12; 31%) were the most common diagnoses. There were no cases of pacemaker dysfunction. The original pacing indications followed guidelines (sick-sinus-syndrome in 16, atrioventricular block in 16, atrial fibrillation with bradycardia in five). Twenty-two of the 39 patients (56%) had experienced syncope prior to the original CIED implantation. Orthostatic hypotension was diagnosed in seven (32%) and vasovagal syncope in nine (41%) of these patients. Of the 17 patients that had not experienced syncope prior to the original CIED implantation, nine patients (53%) were diagnosed with orthostatic hypotension and vasovagal syncope was diagnosed in three (18%). Of the 39 patients, two had implantable cardioverter-defibrillators to treat malignant ventricular arrhythmias diagnosed after syncopal episodes.

Conclusion: Cardiovascular autonomic tests reveal the etiology of syncope and/or orthostatic intolerance in the majority of paced patients. The most common diagnosis was orthostatic hypotension (40%) followed by vasovagal syncope (30%), whereas there were no cases of pacemaker dysfunction. Our results emphasize the importance of a complete diagnostic work-up, including cardiovascular autonomic tests, in paced patients that present with syncope and/or orthostatic intolerance.

Pacing therapy in the management of unexplained syncope: a tertiary care centre prospective study

Objective

Pacemaker (PM) therapy is effective when syncope is associated with bradycardia, but syncope recurrences and fall injuries after PM implantation may occur. We aimed to survey indications and outcomes of PM implantation, following evaluation of unexplained syncope.

Methods

Among 1666 consecutive unpaced patients investigated in a tertiary syncope unit by carotid-sinus massage (CSM), head-up tilt test (HUT) and ECG monitoring, 106 (6.4%; age, 65 ± 17 years) received a PM. We assessed bradycardia detection methods, PM implantation indications, and explored incidence of recurrent syncope, fall-related fractures and mortality.

Results

Indications for PM therapy were met in 32/106 patients (30%) by CSM, in 41/106 (39%) by HUT, in 14/106 patients (13%) by implantable loop-recorder (ILR) and in 19/106 (18%) by standard ECG. Sinus arrest with asystole was the predominant PM indication during CSM/HUT and external ECG monitoring, whereas ILR detected proportionally the same numbers o f asystole due to sinus arrest and atrioventricular block. During follow-up (median, 4.3 years), 15 patients (14%) had syncope recurrence, 15 suffered fall-related fractures and 9 died. Neither syncope recurrence nor fall-related fractures were dependent on initial PM indication. The composite endpoint of recurrent syncope/fall-related fracture was associated with treated hypertension (OR 2.45; 95% CI 1.00 to 6.0), reduced glomerular filtration rate (OR 1.63 per 10 mL/min↓; 95% CI 1.22 to 2.19) and atrial fibrillation (OR 3.98; 95% CI 1.11 to 14.3). Recurrent syncope predicted increased mortality (OR 9.20; 95% CI 1.89 to 44.8).

Conclusions

Cardiovascular autonomic testing and ECG monitoring effectively identify pacing indications in patients with unexplained syncope. After PM implantation, treated hypertension, renal failure and atrial fibrillation predict syncope recurrence and fall-related injury. Recurrent syncope predicts increased mortality.

Potential usage of cardioneuroablation in vagally mediated functional atrioventricular block

An increase in parasympathetic tone may be the main cause of some transient or permanent atrioventricular block cases. Some of these patients, defined as vagally mediated functional atrioventricular block, may be severely symptomatic and refractory to conventional therapies and may necessitate cardiac pacing. Cardioneuroablation is a relatively new strategy for management of patients with excessive vagal activation based on radiofrequency catheter ablation of main ganglionated plexi around the heart. Present review was dedicated to discuss potential usage of cardioneuroablation in patients with vagally mediated functional atrioventricular block.

Pacing in neurocardiogenic/vasovagal syncope

Pacing for neurocardiogenic or vasovagal syncope (VVS) has been practised for five decades, but the 1986 advent of tilt testing provided a means of diagnosis frequently revealing, in the early days, asystole caused by VVS. This was the basis for pacing these patients and the first studies created enthusiasm followed by randomised controlled trials, which were imperfectly designed, "confirming" benefit. When better trial design was employed, there was no obvious benefit. However, some cardiologists had seen patients experience a huge positive difference with pacing, so they set out to identify them. Two studies using ECG loop recorders to document heart rhythm during spontaneous attacks allowed better patient selection for pacing and appeared to achieve the aim. Further, it was noted in the second study, a randomised controlled trial (RCT) with good design, that tilt testing added a further dimension to the identification of the patient who would benefit. Thus, loop recorders are used to show asystole in spontaneous attacks and when tilt testing is negative, implying a lesser vasodepressor component, the patient will have the best outcome. From the available evidence, pacing should be dual-chamber in older patients (>40 years) with severe symptoms and in whom standard measures have demonstrably failed. The method of triggering pacing and its timing of introduction have not yet been resolved. Today's method is rate-hysteresis but there is another sensed event as an alternative: right ventricular impedance, which is now in RCT with substantial pilot evidence in its favour.

Syncope and paroxysmal atrioventricular block

Current literature reveals three types of paroxysmal atrioventricular block (AVB) that can cause syncope: Intrinsic paroxysmal atrioventricular block is due to an intrinsic disease of the AV conduction system; this type of "cardiac syncope" is also called Stokes-Adams attack; Extrinsic vagal paroxysmal atrioventricular block is linked to the effect of the parasympathetic nervous system on cardiac conduction and is one of the mechanisms involved in "reflex syncope." Extrinsic idiopathic paroxysmal atrioventricular block is associated with low levels of endogenous adenosine and is supposed to be one of the mechanisms involved in "low-adenosine syncope." These three types of paroxysmal AVB present different clinical and electrocardiographic features. Additionally, the efficacy of cardiac pacing and theophylline therapy to prevent syncopal recurrences is also different for these three types of AVB.