Variability of cardioinhibition in vasovagal syncope: differences between subgroups during cardioinhibition and beyond.

PURPOSE: We compared hemodynamic parameters between subjects with marked, intermediate and minimal cardioinhibition during vasovagal syncope. METHODS: The study included subjects with a decrease in heart rate while experiencing a complete vasovagal syncope during tilt-table testing. The subjects were classified as having marked, intermediate or minimal cardioinhibition, based on tertile values of the decrease in heart rate. Hemodynamic parameters between these groups were compared before tilt in the supine position, shortly after tilt and during cardioinhibition. RESULTS: A total of 149 subjects with a median age of 43 (interquartile range 24-60) years were included in the study. Among the three groups with different levels of cardioinhibition, the highest heart rate was observed in subjects with marked cardioinhibition both before and shortly after tilt and at the start of cardioinhibition. The heart rate decrease in these subjects was both larger and faster compared to subjects with minimal and intermediate cardioinhibition. CONCLUSION: Subjects with marked cardioinhibition have both a larger and faster decrease in heart rate compared to subjects with intermediate and minimal cardioinhibition, as early as from the start of cardioinhibition. Marked cardioinhibition is related to differences in hemodynamic profiles already present well before the start of cardioinhibition.

Novel Methods for Quantification of Vasodepression and Cardioinhibition During Tilt-Induced Vasovagal Syncope.

RATIONALE: Assessing the relative contributions of cardioinhibition and vasodepression to the blood pressure (BP) decrease in tilt-induced vasovagal syncope requires methods that reflect BP physiology accurately. OBJECTIVE: To assess the relative contributions of cardioinhibition and vasodepression to tilt-induced vasovagal syncope using novel methods. METHODS AND RESULTS: We studied the parameters determining BP, that is, stroke volume (SV), heart rate (HR), and total peripheral resistance (TPR), in 163 patients with tilt-induced vasovagal syncope documented by continuous ECG and video EEG monitoring. We defined the beginning of cardioinhibition as the start of an HR decrease (HR) before syncope and used logarithms of SV, HR, and TPR ratios to quantify the multiplicative relation BP=SV·HR·TPR. We defined 3 stages before syncope and 2 after it based on direction changes of these parameters. The earliest BP decrease occurred 9 minutes before syncope. Cardioinhibition was observed in 91% of patients at a median time of 58 seconds before syncope. At that time, SV had a strong negative effect on BP, TPR a lesser negative effect, while HR had increased (all P<0.001). At the onset of cardioinhibition, the median HR was at 98 bpm higher than baseline. Cardioinhibition thus initially only represented a reduction of the corrective HR increase but was nonetheless accompanied by an immediate acceleration of the ongoing BP decrease. At syncope, SV and HR contributed similarly to the BP decrease (P<0.001), while TPR did not affect BP. CONCLUSIONS: The novel methods allowed the relative effects of SV, HR, and TPR on BP to be assessed separately, although all act together. The 2 major factors lowering BP in tilt-induced vasovagal syncope were reduced SV and cardioinhibition. We suggest that the term vasodepression in reflex syncope should not be limited to reduced arterial vasoconstriction, reflected in TPR, but should also encompass venous pooling, reflected in SV.

Inappropriate sinus tachycardia: an examination of existing definitions.

AIMS: Inappropriate sinus tachycardia (IST) is a syndrome characterized by an elevated sinus rate unassociated with known physiological, pathological, or pharmacological causes. Despite published consensus documents, IST definitions appear to vary in the literature. In this study, we reviewed IST publications to evaluate IST definition variability and ascertain the degree to which consensus definitions are being adopted. METHODS AND RESULTS: English-language articles in PubMed, Ovid MEDLINE, Ovid Embase, and Google Scholar published from 1 January 1970 to 1 June 2021 with the title terms 'inappropriate sinus tachycardia,' 'non-paroxysmal sinus tachycardia,' or 'permanent sinus tachycardia' were searched. In each, the IST definition used, qualifying characteristics, and publications cited to support each definition were recorded. We identified 138 publications meeting the search criteria. Inappropriate sinus tachycardia definitions were provided in 114 of 138 articles (83%). A majority of definitions (92/114, 81%) used distinct heart rate (HR) thresholds. Among these, the most common threshold was ≥100 beats per minute (BPM) (75/92, 82%), mainly measured at rest (54/92, 59%). Most definitions (47/92, 51%) included a second criterion to qualify for IST; these were most often an HR threshold of 90 BPM measured over 24 h by ambulatory electrocardiogram (37/47, 79%). Diagnosis of exclusion was a common criterion (75/92, 82%) but symptom status was not (41/92, 45%). The 2015 Heart Rhythm Society IST consensus was commonly cited but adopted in only 37% of definitions published after 2015. CONCLUSIONS: Inappropriate sinus tachycardia definitions in current literature are inconsistent, and professional society consensus IST definitions have, to date, had limited impact.

Tilt testing remains a valuable asset.

Head-up tilt test (TT) has been used for >50 years to study heart rate/blood pressure adaptation to positional changes, to model responses to haemorrhage, to assess orthostatic hypotension, and to evaluate haemodynamic and neuroendocrine responses in congestive heart failure, autonomic dysfunction, and hypertension. During these studies, some subjects experienced syncope due to vasovagal reflex. As a result, tilt testing was incorporated into clinical assessment of syncope when the origin was unknown. Subsequently, clinical experience supports the diagnostic value of TT. This is highlighted in evidence-based professional practice guidelines, which provide advice for TT methodology and interpretation, while concurrently identifying its limitations. Thus, TT remains a valuable clinical asset, one that has added importantly to the appreciation of pathophysiology of syncope/collapse and, thereby, has improved care of syncopal patients.

Timing of syncope in ictal asystole as a guide when considering pacemaker implantation.

INTRODUCTION: In patients with ictal asystole (IA) both cardioinhibition and vasodepression may contribute to syncopal loss of consciousness. We investigated the temporal relationship between onset of asystole and development of syncope in IA, to estimate the frequency with which pacemaker therapy, by preventing severe bradycardia, may diminish syncope risk. METHODS: In this retrospective cohort study, we searched video-EEG databases for individuals with focal seizures and IA (asystole ≥ 3 s preceded by heart rate deceleration) and assessed the durations of asystole and syncope and their temporal relationship. Syncope was evaluated using both video observations (loss of muscle tone) and EEG (generalized slowing/flattening). We assumed that asystole starting ≤3 s before syncope onset, or after syncope began, could not have been the dominant cause. RESULTS: We identified 38 seizures with IA from 29 individuals (17 males; median age: 41 years). Syncope occurred in 22/38 seizures with IA and was more frequent in those with longer IA duration (median duration: 20 [range: 5-32] vs. 5 [range: 3-9] s; p < .001) and those with the patient seated vs. supine (79% vs. 46%; p = .049). IA onset always preceded syncope. In 20/22 seizures (91%), IA preceded syncope by >3 s. Thus, in only two instances was vasodepression rather than cardioinhibition the dominant presumptive syncope triggering mechanism. CONCLUSIONS: In IA, cardioinhibition played an important role in most seizure-induced syncopal events, thereby favoring the potential utility of pacemaker implantation in patients with difficult to suppress IA.

A randomized study of yoga therapy for the prevention of recurrent reflex vasovagal syncope.

AIMS: Vasovagal syncope (VVS) is a common cardiovascular dysautonomic disorder that significantly impacts health and quality of life (QoL). Yoga has been shown to have a positive influence on cardiovascular autonomics. This study assessed the effectiveness of yoga therapy on the recurrence of VVS and QoL. METHODS AND RESULTS: We randomized subjects with recurrent reflex VVS (>3 episodes in the past 1 year) and positive head-up tilt test to guideline-directed therapy (Group 1) or yoga therapy (Group 2). Patients in Group 1 were advised guideline-directed treatment and Group 2 was taught yoga by a certified instructor. The primary endpoint was VVS recurrences and QoL. Between June 2015 and February 2017, 97 highly symptomatic VVS patients were randomized (Group 1: 47 and Group 2: 50). The mean age was 33.1 ± 16.6 years, male:female of 40:57, symptom duration of 17.1 ± 20.7 months, with a mean of 6.4 ± 6.1 syncope episodes. Over a follow-up of 14.3 ± 2.1 months Group 2 had significantly lower syncope burden compared with Group 1 at 3 (0.8 ± 0.9 vs. 1.8 ± 1.4, P < 0.001), 6 (1.0 ± 1.2 vs. 3.4 ± 3.0, P < 0.001), and at 12 months (1.1 ± 0.8 vs. 3.8 ± 3.2, P < 0.001). The Syncope functional score questionnaire was significantly lower in Group 2 compared with Group 1 at 3 (31.4 ± 7.2 vs. 64.1 ± 11.5, P < 0.001), 6 (26.4 ± 6.3 vs. 61.4 ± 10.7, P < 0.001), and 12 months (22.2 ± 4.7 vs. 68.3 ± 11.4, P < 0.001). CONCLUSION: For patients with recurrent VVS, guided yoga therapy is superior to conventional therapy in reducing symptom burden and improving QoL.

Sinus arrest: A rare observation during radiofrequency ablation along the coronary sinus roof.

Catheter-based radiofrequency (RF) ablation targeting segments of the cardiac conduction system and/or selected regions of myocardium is an accepted treatment for many cardiac arrhythmias. On the other hand, while purposeful extension of RF ablation to include nearby cardiac neural elements, particularly epicardial ganglionated plexi (GP), remains a subject of ongoing study, inadvertent stimulation of such structures may occur during an otherwise conventional RF ablation procedure. Thus, asystolic pauses have been observed during RF ablation of left ventricular free-wall accessory pathways, slow AV node pathways, and the left superior pulmonary vein. In this report, sinus arrest occurred within 3.3 s of RF application (40 W at 50°C) along the coronary sinus roof for treatment of an atypical "slow-slow" atrioventricular nodal reentrant tachycardia. Energy delivery was immediately terminated, but asystole persisted for 4.7 s followed by sinus bradycardia. The procedure was temporarily halted, but later was successfully resumed. Given the latency from terminating RF to return of sinus node function, the sinus arrest was likely a centrally mediated reflex vagal response. Consequently, while parasympathetic ganglia near the CS os are believed to principally innervate the AV node, not the sinus node, our observation highlights the neural cross-communications that likely exist in this region of the heart.

A higher proportion of men than of women fainted in the phase without nitroglycerin in tilt-induced vasovagal syncope.

PURPOSE: Vasovagal syncope (VVS) affects more women than men. We determined whether this sex ratio affects tilt table test (TTT) results. METHODS: We retrospectively studied TTT outcomes in suspected VVS. TTT consisted of supine rest, a maximum 20 min of head-up tilt without and, if nitroglycerin was needed, a further maximum 20 min after nitroglycerin administration. TTT was terminated if VVS occurred. We used binary logistic regression for the entire TTT and for each phase, with VVS as outcome and age and sex as predictors. RESULTS: TTT provoked vasovagal (pre)syncope in 494 out of 766 tests (64%). The proportion of men and women who fainted during the entire TTT did not differ significantly between the sexes (p = 0.13, corrected for age). A lower proportion of women than men had VVS in the phase without nitroglycerin (odds ratio 0.54; 95% confidence interval 0.37-0.79; p = 0.002, corrected for age), whereas a higher proportion of women than men fainted after nitroglycerin (odds ratio 1.58; 95% confidence interval 1.13-2.21; p = 0.008, corrected for age). These sex differences remained significant after correction for a history of orthostatic versus emotional triggers. The effect of sex on TTT outcome was closely associated with differences of blood pressure change upon tilt-up (lower in men in both TTT phases: without nitroglycerin p = 0.003; with nitroglycerin p = 0.05), but not with heart rate changes. CONCLUSION: Men were more susceptible to induction of VVS without nitroglycerin and women after it. The unexpected findings may be due to sex-specific pathophysiological differences.

Abnormal repolarization: A common electrocardiographic finding in patients with epilepsy.

BACKGROUND: Recently, certain forms of early repolarization (ER) on electrocardiograms (ECGs) have been considered a possible marker of increased sudden cardiac death risk. The frequency, characteristics, and clinical follow-up with which these forms of ER are present in epilepsy patients, and whether or not abnormal ER contributes to sudden unexplained death in epilepsy patients (SUDEP) is unknown. METHODS AND RESULTS: The amplitude of J peak and ST-segment morphology after ER on 12-lead ECGs were assessed in 354 epilepsy patients (age, 33 ± 16 years; 54% men) and 140 age- and sex-matched control subjects (age, 31 ± 12 years; 50% men). Abnormal ER prevalence (J-wave amplitude ≥0.1 mV) was greater in epilepsy patients (19.8%) compared with controls (8.6%; P = 0.002) in inferior ECG leads but not in lateral leads ( P = 0.40). ER with a horizontal or descending ST segment was also more prevalent in epilepsy patients ( P < 0.001). After introducing antiepileptic drugs in 36 epilepsy patients, there were no significant ER changes. Similarly, in 64 epilepsy patients with seizure suppression, ER comparison before and after seizure control revealed no significant changes. Male gender was the only significant predictor of abnormal ER in epilepsy patients ( P = 0.03). During a median follow-up of 7 years, SUDEP occurred in two patients, one with abnormal ER. CONCLUSIONS: Abnormal ER may be more prevalent in epilepsy patients than in controls and is not altered by antiepileptic drugs or achievement of epilepsy suppression. The relation of abnormal ER to SUDEP remains in need of further study.

Swallow (deglutition) syncope: An evaluation of swallowing-induced heart rate and hemodynamic changes in affected patients and control subjects.

BACKGROUND: Syncope triggered by swallowing is a well-known but uncommon condition that has been the focus of case reports but is otherwise largely unstudied. To better understand swallow syncope we examined heart rate (HR) and blood pressure (BP) changes during swallowing in clinically suspected swallow syncope patients and asymptomatic control subjects. METHODS: The study population comprised four individuals with a history suggesting swallow syncope (three men, 53 ± 14.9 years) and 15 (nine men, 46 ± 17.1 years, P = NS vs patients) asymptomatic volunteer control subjects. Studies in all individuals comprised noninvasive beat-to-beat HR and BP measurement during swallowing 150 mL of cold liquid while standing. Additional tests in swallow syncope patients included: active standing, Valsalva maneuver, carotid sinus massage (CSM), and head-up tilt (HUT). RESULTS: Swallowing resulted in a greater decrease of both HR (-22 ± 22.1 vs -3 ± 11.7 beats/minute [bpm]; P = 0.045) and BP (-22 ± 17.4 vs - 2 ± 11.8; P = 0.036) in swallow syncope patients than in controls. Further, in swallow syncope patients the time to lowest HR and BP differed (9 ± 5.5 vs 19 ± 7.2 seconds; P = 0.02), suggesting that both cardioinhibitory (CI) and vasodepressor (VD) mechanisms are present but operate independently. Other autonomic studies were normal in swallow syncope patients except for CSM pause more than 3 seconds in two patients. CONCLUSION: Swallow syncope is associated with transient and temporally independent CI and VD features, consistent with reflex syncope. Potentially, a swallowing test during autonomic evaluation may be useful to unmask relative magnitudes of CI and VD responses, thereby facilitating treatment strategy decisions.

Greater early epinephrine rise with head-up posture: A marker of increased syncope susceptibility in vasovagal fainters.

BACKGROUND: Head-up tilt (HUT) is widely used for diagnostic evaluation of patients with suspected vasovagal syncope (VVS), but also offers an opportunity to study VVS pathophysiology. In this regard, it is known that plasma epinephrine (Epi) levels and Epi/norepinephrine (NE) ratio are markedly increased from baseline at the time of HUT-induced VVS. However, whether these changes contribute to VVS susceptibility remains uncertain. OBJECTIVE: We hypothesized that if catecholamines contributed to VVS directly, then a greater increase of plasma Epi and Epi/NE ratio early during HUT would be associated with shorter time to syncope. METHODS: The patient population comprised 33 individuals (14 men, 43 ± 2 years) with suspected VVS in whom 70° HUT reproduced symptoms. Arterial Epi and NE concentrations were collected at baseline (supine) and 2 minutes of HUT. Linear, exponential, and multiple regression were used to access the association between changing catecholamine levels and time to syncope. RESULTS: Mean ± SD time to positive HUT was 11 (7.6) minutes. Higher plasma Epi levels (pg/mL) both at baseline and at 2 minutes upright correlated with shorter time to syncope (baseline, R = -0.35, P = 0.048; and 2 minutes, R = -0.58, P = 0.001). Similarly, a greater Epi/NE ratio at 2 minutes head-up correlated with earlier time to syncope (R = -0.49, P = 0.007). These relationships remained significant after adjusting for age and sex (P = 0.006 and 0.02, respectively). CONCLUSION: Greater Epi levels and Epi/NE ratio early during HUT were associated with shorter time to VVS, suggesting a possible contribution to VVS susceptibility.

Outcomes following persistent atrial fibrillation ablation using localized sources identified with Ripple map.

BACKGROUND: Ablation of persistent atrial fibrillation (AF) remains challenging. Identification and ablation of localized AF drivers may offer the possibility for improved outcomes. Ripple map is a novel software algorithm that may allow improved localization of possible AF drivers through the whole chamber graphical display of continuously recorded bipolar electrograms. The objective of this study was to determine whether regions of high-frequency Ripple activation (HFRA) observed on Ripple map provide useful ablation targets in patients with persistent AF. METHODS AND RESULTS: Consecutive patients underwent the first-time ablation of persistent AF (n = 162) using a standard stepwise (n = 105) or a Ripple map guided approach (n = 57). Ripple map guided patients underwent pulmonary vein antral isolation followed by ablation of HFRA sites. Acute termination of AF was observed in 91.2% of the Ripple-guided patients vs 52.4% in the stepwise approach, P < .0001. Following a single ablation procedure, after 18 months 98.2% of Ripple map guided patients were free of AF, compared with 81.4% of standard stepwise ablation (P = .005). Freedom from atrial tachycardia (54.4% Ripple map vs 52.4% standard, P = .9) or any atrial arrhythmia (52.6% Ripple map vs 39.0% standard, P = .10) did not differ between the two strategies. In a subset analysis (n = 30 of 56), Ripple map regions corresponded to sites with spatiotemporal dispersion in all atrial locations. No differences were observed in the rate of procedural complications. CONCLUSIONS: Ablation of HFRA sites identified with Ripple map resulted in a higher rate of acute termination and improved freedom from AF compared to a standard stepwise approach.

A feasibility study of noninvasive ablation of ventricular tachycardia using high-intensity focused ultrasound.

BACKGROUND: Current transcatheter ablation of ventricular tachycardia (VT) techniques is limited in part by its invasive nature and superficial depth of ablation lesions. OBJECTIVES: This study was aimed at evaluating the feasibility of targeted ablation of cardiac tissues using high-intensity focused ultrasound (HIFU) as a potential means for noninvasive ablation of VT. METHODS: Ablation of ventricular myocardium was performed in anesthetized closed-chest dogs using a HIFU therapeutic system that is currently used clinically for ablation of human solid tumors. Ventricular pacing using a bipolar catheter was performed at a rate slightly higher than intrinsic sinus rate to mimic VT. The myocardium at the tip of the pacing catheter was targeted for ablation. Ablation endpoint was loss of ventricular capture first and confirmed by electrical nonexcitation with 10-mA, 2-ms pulse-width unipolar stimulation. RESULTS: Optimal ablation energy was identified at 400 W for 2-4 seconds. In five separate experimental preparations, pacing could be terminated successfully during HIFU energy delivery, which was further confirmed by electrical nonexcitation. However, capture could be obtained at other nonablated locations using the same pacing catheter. Both transmural and localized lesions could be created in a controlled fashion without apparent injury to skin, lung, or pericardium on postmortem examination. CONCLUSION: This pilot study suggests that HIFU is potentially useful for noninvasive ablation of targeted, localized myocardial tissues, and it may be potentially applicable for VT ablation, particularly for those with intramyocardial/epicardial origins.

ECG electrode reversals: An opportunity to learn from mistakes.

An ECG with an "odd" appearance may raise the suspicion that ECG recording electrodes may have been reversed. Odd appearances include unexpected Q-waves or R-waves, markedly isoelectric leads, and abrupt changes from previous ECGs. A few examples of ECG electrode reversal provide the opportunity to review some fundamental principles of ECG recording. Some ECG electrode reversals will invert the QRS complex recorded in a lead. Other ECG leads may be affected in a manner that initially may seem unexpected. These patterns may be understood upon reviewing the genesis of the "unipolar" leads, particularly the "augmented" leads. Recording an ECG between electrodes placed on the two legs will produce a nearly isoelectric tracing. Elucidation of electrode reversals is often less difficult than it seems, may present an enjoyable intellectual challenge, and provides insight into the process of ECG recording.

Trends of hospitalizations for syncope/collapse in the United States from 2004 to 2013-An analysis of national inpatient sample.

INTRODUCTION: Syncope/collapse is a common reason for emergency department visits, and approximately 30-40% of these individuals are hospitalized. We examined changes in hospitalization rates, in-hospital mortality, and cost of syncope/collapse-related hospital care in the United States from 2004 to 2013. METHODS: We used the US Nationwide Inpatient Sample (NIS) from 2004 to 2013 to identify syncope/collapse-related hospitalizations using ICD-9, code 780.2, as the principal discharge diagnosis. Data are presented as mean ± SEM. RESULTS: From 2004 to 2013, there was a 42% reduction in hospitalizations with a principal discharge diagnosis of syncope/collapse from 54,259 (national estimate 253,591) in 2004 to 31,427 (national estimate 156,820) in 2013 (P < 0.0001). The mean length of hospital stays decreased (2.88 ± 0.04 days in 2004 vs. 2.54 ± 0.02 in 2013; P < 0.0001), while in-hospital mortality did not change (0.28% in 2004 vs. 0.18% in 2013; P  =  0.12). However, mean charges (inflation adjusted) for syncope/collapse-related hospitalization increased by 43.6% from $17,514 in 2004 to $25,160 in 2013 (P < 0.0001). The rates of implantation of permanent pacemakers and implantable cardioverter defibrillator remained low during these hospitalizations, and decreased over time (P for both < 0.0001). CONCLUSIONS: Hospitalization rates for syncope/collapse have decreased significantly in the US from 2004 to 2013. Despite a modest reduction in length of stay, the cost of syncope/collapse-related hospital care has increased.

Ambulatory diagnostic ECG monitoring for syncope and collapse: An assessment of clinical practice in the United States.

INTRODUCTION: Diagnostic ambulatory electrocardiogram (AECG) monitoring is widely used for evaluating syncope and collapse, and practice guidelines provide recommendations regarding optimal AECG device selection. However, whether physicians utilize AECGs in accordance with the pertinent guidelines is unclear. This study assessed utilization of AECG monitoring systems for syncope and collapse diagnosis by physicians in the United States. METHODS AND RESULTS: A quantitative survey was undertaken of physicians comprising multiple specialties (emergency department, n = 35; primary care, n = 35; hospitalists, n = 30; neurologists, n = 30; nonimplanting, n = 34, and implanting-cardiologists, n = 35). Depending on specialty, respondents reported that neural-reflex and orthostatic causes accounted for 17-23%, cardiac causes for 12-20%, and "neurological causes" (specifically psychogenic pseudo-syncope/pseudo-seizures and acute cerebrovascular conditions) for 7-12% of their syncope/collapse cases. The choice of AECG technology varied by specialty. Thus, despite patients having daily symptoms, 25% of respondents chose an AECG technology other than a Holter-type monitor. Conversely, when monitoring for infrequent events (e.g., less than monthly), 12-18% indicated that they would choose a 24- to 48-hour Holter, 20-34% would choose either a conventional event recorder or a mobile cardiac telemetry system, and only 53-65% would select an insertable cardiac monitor. CONCLUSIONS: In evaluation of syncope/collapse, most U.S. clinicians across specialties use AECGs appropriately, but in a substantial minority there remains discordance between choice of AECG technology and guideline-based recommendations.

A single center experience on the clinical utility evaluation of an insertable cardiac monitor.

BACKGROUND: The evaluation of insertable cardiac monitor (ICM) has been largely on the device performance and safety with only limited studies on the clinical utility. The aim of this study was to evaluate the clinical utility of ICM in patients with a variety of clinical presentations. METHODS: A single-center retrospective study on the clinical utility, as measured by both expected and unexpected clinical useful ICM findings and the initiation of therapeutic interventions, was conducted. RESULTS: Ninety-five consecutive patients (median age 68 years) received ICM Reveal LINQ™ for clinical indications of unexplained syncope (53), cryptogenic stroke (19), unexplained infrequent palpitations (14) and AF management (9). During a median follow-up of 414 days, the causes for unexplained syncope were arrhythmia-related (11.3%), arrhythmia-unrelated (32%) and undetermined (56.6%). Atrial fibrillation in patients with cryptogenic stroke was detected in 31.6% (6/19). The clinical utility occurrence was 48.4% with the expected and incidental (unexpected) clinical utility of 41% and 7.4% patients respectively. Of these, therapeutic interventions based on ICM diagnoses were initiated in 18.9% (18/95) of patients. CONCLUSIONS: ICM (Reveal LINQ™) offers substantial expected and unexpected clinical utility in patients with a variety of clinical presentations. The causes of nearly one third of patients receiving ICM for unexplained syncope were unrelated to cardiac arrhythmia. Nearly one fifth of patients with newly diagnosed arrhythmia from ICM received therapeutic interventions.

Clinical Implications of Brief Device-Detected Atrial Tachyarrhythmias in a Cardiac Rhythm Management Device Population: Results from the Registry of Atrial Tachycardia and Atrial Fibrillation Episodes.

BACKGROUND: The RATE Registry (Registry of Atrial Tachycardia and Atrial Fibrillation Episodes) is a prospective, outcomes-oriented registry designed to document the prevalence of atrial tachycardia and/or fibrillation (AT/AF) of any duration in patients with pacemakers and implantable cardioverter defibrillators (ICDs) and evaluate associations between rigorously adjudicated AT/AF and predefined clinical events, including stroke. The appropriate clinical response to brief episodes of AT/AF remains unclear. METHODS: Rigorously adjudicated electrogram (EGM) data were correlated with adjudicated clinical events with logistic regression and Cox models. Long episodes of AT/AF were defined as episodes in which the onset and/or offset of AT/AF was not present within a single EGM recording. Short episodes of AT/AF were defined as episodes in which both the onset and offset of AT/AF were present within a single EGM recording. RESULTS: We enrolled 5379 patients with pacemakers (N=3141) or ICDs (N=2238) at 225 US sites (median follow-up 22.9 months). There were 359 deaths. There were 478 hospitalizations among 342 patients for clinical events. We adjudicated 37 531 EGMs; 50% of patients had at least one episode of AT/AF. Patients with clinical events were more likely than those without to have long AT/AF (31.9% vs. 22.1% for pacemaker patients and 28.7% vs. 20.2% for ICD patients; P<0.05 for both groups). Only short episodes of AT/AF were documented in 9% of pacemaker patients and 16% of ICD patients. Patients with clinical events were no more likely than those without to have short AT/AF (5.1% vs. 7.9% for pacemaker patients and 11.5% vs. 10.4% for ICD patients; P=0.21 and 0.66, respectively). CONCLUSIONS: In the RATE Registry, rigorously adjudicated short episodes of AT/AF, as defined, were not associated with increased risk of clinical events compared with patients without documented AT/AF. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00837798.

Pathophysiology of reflex syncope: A review.

In this correspondence, the pathophysiology of reflex syncope (vasovagal syncope, carotid sinus syndrome, and situational syncope) is reviewed, including clarification of the nomenclature.