Long-term effect of atrial fibrillation on the evolution of mitral and tricuspid valve regurgitation.

Objective: The present study aims to identify the long-term effects of atrial fibrillation (AF) on atrial remodelling and on the progression of mitral/tricuspid valve regurgitation (MR/TR).Methods: The severity of MR/TR was assessed by the colour jet area and by multi-integrative approach at baseline and after a period of 65 ± 10 months in 37 patients with permanent AF, in 80 patients with non-permanent AF (of whom 43 were treated with ablation) and in 53 control patients with sinus rhythm.Results: At baseline, AF patients had larger MR jet areas than control patients. At follow up, progression of MR, expressed as delta MR jet area, was 0.05 ± 1.3 cm2 in the control group, 0.73 ± 2.1 cm2 in the non-permanent AF group and 1.95 ± 3.6 cm2 in the permanent AF group (p = .001). Severe MR at follow up was observed in 0%, 2.5%, 8%, respectively. There was a significant positive correlation between progression of MR and increase of left atrium volume (r = 0.31, p < .001). After adjustment for baseline clinical and echocardiographic parameters, permanent AF remained independently associated with the progression of MR. Although rhythm control was better with AF ablation than with medical treatment only, the MR evolution was similar. Comparable findings, albeit less pronounced, were observed for the association between of AF and TR progression.Conclusions: The presence of longstanding AF is associated with a significant progression of MR/TR mainly due to atrial remodelling. Our data showed a beneficial effect of sustained rhythm control, either medically or by ablation, on MR/TR progression.

State of play and future direction with NOACs: An expert consensus.

Atrial fibrillation (AF) and venous thromboembolism (VTE) are cardiovascular conditions significant in contemporary practice. In both, the use of anticoagulation with vitamin K antagonists (VKAs) has been traditionally used to prevent adverse events. However, VKA therapy is associated with challenges relating to dose maintenance, the need to monitor anticoagulation, and bleeding risks. The non-vitamin K oral anticoagulants (NOACs) are becoming accepted as a clear alternative to VKA therapy for both AF and VTE management. The aim of this paper was to review contemporary evidence on the safety of NOACs in both conditions. A comprehensive literature review was conducted to explore key safety issues and expert consensus was achieved from eight professionals specialised in AF and VTE care. Consensus-based statements were formulated where available evidence was weak or contradictory. The expert statements in this paper form a key overview of the safety of NOACs compared with VKA therapy, and the comparative safety of different NOACs. It is apparent that a detailed patient work-up is required in order to identify and manage individual risk factors for bleeding and thrombosis prior to NOAC therapy. Additional measures, such as dose reductions, may also be used to maintain the safety of NOACs in practice.

Sudden cardiac arrest in sports - need for uniform registration: A Position Paper from the Sport Cardiology Section of the European Association for Cardiovascular Prevention and Rehabilitation.

There are large variations in the incidence, registration methods and reported causes of sudden cardiac arrest/sudden cardiac death (SCA/SCD) in competitive and recreational athletes. A crucial question is to which degree these variations are genuine or partly due to methodological incongruities. This paper discusses the uncertainties about available data and provides comprehensive suggestions for standard definitions and a guide for uniform registration parameters of SCA/SCD. The parameters include a definition of what constitutes an 'athlete', incidence calculations, enrolment of cases, the importance of gender, ethnicity and age of the athlete, as well as the type and level of sporting activity. A precise instruction for autopsy practice in the case of a SCD of athletes is given, including the role of molecular samples and evaluation of possible doping. Rational decisions about cardiac preparticipation screening and cardiac safety at sport facilities requires increased data quality concerning incidence, aetiology and management of SCA/SCD in sports. Uniform standard registration of SCA/SCD in athletes and leisure sportsmen would be a first step towards this goal.

Edoxaban vs. warfarin in patients with atrial fibrillation on amiodarone: a subgroup analysis of the ENGAGE AF-TIMI 48 trial.

BACKGROUND: In the ENGAGE AF-TIMI 48 trial, the higher-dose edoxaban (HDE) regimen had a similar incidence of ischaemic stroke compared with warfarin, whereas a higher incidence was observed with the lower-dose regimen (LDE). Amiodarone increases edoxaban plasma levels via P-glycoprotein inhibition. The current pre-specified exploratory analysis was performed to determine the effect of amiodarone on the relative efficacy and safety profile of edoxaban. METHODS AND RESULTS: At randomization, 2492 patients (11.8%) were receiving amiodarone. The primary efficacy endpoint of stroke or systemic embolic event was significantly lower with LDE compared with warfarin in amiodarone treated patients vs. patients not on amiodarone (hazard ratio [HR] 0.60, 95% confidence intervals [CIs] 0.36-0.99 and HR 1.20, 95% CI 1.03-1.40, respectively; P interaction <0.01). In patients randomized to HDE, no such interaction for efficacy was observed (HR 0.73, 95% CI 0.46-1.17 vs. HR 0.89, 95% CI 0.75-1.05, P interaction = 0.446). Major bleeding was similar in patients on LDE (HR 0.35, 95% CI 0.21-0.59 vs. HR 0.53, 95% CI 0.46-0.61, P interaction = 0.131) and HDE (HR 0.94, 95% CI 0.65-1.38 vs. HR 0.79, 95% CI 0.69-0.90, P interaction = 0.392) when compared with warfarin, independent of amiodarone use. CONCLUSIONS: Patients randomized to the LDE treated with amiodarone at the time of randomization demonstrated a significant reduction in ischaemic events vs. warfarin when compared with those not on amiodarone, while preserving a favourable bleeding profile. In contrast, amiodarone had no effect on the relative efficacy and safety of HDE.

Reduced Penetrance and Variable Expression of SCN5A Mutations and the Importance of Co-inherited Genetic Variants: Case Report and Review of the Literature.

Mutations in the SCN5A gene are responsible for multiple phenotypical presentations including Brugada syndrome, long QT syndrome, progressive familial heart block, sick sinus syndrome, dilated cardiomyopathy, lone atrial fibrillation and multiple overlap syndromes. These different phenotypic expressions of a mutation in a single gene can be explained by variable expression and reduced penetrance. One of the possible explanations of these phenomena is the co-inheritance of genetic variants. We describe a family where the individuals exhibit a compound heterozygosity in the SCN5A gene including a mutation (R1632H) and a new variant (M858L). Individuals with both the mutation and new variant present with a more severe phenotype including spontaneous atrial tachyarrhythmia at young age. We give an overview of the different phenotypes of "SCN5A disease" and discuss the importance of co-inherited genetic variants in the expression of SCN5A disease.

[Rivaroxaban: Xarelto--recommendations for pharmacists]. / Le Rivaroxaban (Xarelto): guide de la pratique officinale.

Rivaroxaban is one of the new oral anticoagulants (NOACs). It has many potential advantages in comparison with Vitamin K Antagonists (VKA). It has a predictable anticoagulant effect and does not theoretically require biological monitoring. It is also characterized by less food and drug interactions. However, due to major risks associated with over- and under-dosage, its optimal use in patients should be carefully followed by health care professionals. The aim of this article is to provide recommendations for pharmacists on the practical use of Xarelto in its different approved indications. This document is adapted from the practical user guide of rivaroxaban which was developed by an independent group of Belgian experts in the field of thrombosis and haemostasis.

Significance of deep T-wave inversions in asymptomatic athletes with normal cardiovascular examinations: practical solutions for managing the diagnostic conundrum.

Preparticipation screening programmes for underlying cardiac pathologies are now commonplace for many international sporting organisations. However, providing medical clearance for an asymptomatic athlete without a family history of sudden cardiac death (SCD) is especially challenging when the athlete demonstrates particularly abnormal repolarisation patterns, highly suggestive of an inherited cardiomyopathy or channelopathy. Deep T-wave inversions of ≥ 2 contiguous anterior or lateral leads (but not aVR, and III) are of major concern for sports cardiologists who advise referring team physicians, as these ECG alterations are a recognised manifestation of hypertrophic cardiomyopathy (HCM) and arrhythmogenic right ventricular cardiomyopathy (ARVC). Subsequently, inverted T-waves may represent the first and only sign of an inherited heart muscle disease, in the absence of any other features and before structural changes in the heart can be detected. However, to date, there remains little evidence that deep T-wave inversions are always pathognomonic of either a cardiomyopathy or an ion channel disorder in an asymptomatic athlete following long-term follow-up. This paper aims to provide a systematic review of the prevalence of T-wave inversion in athletes and examine T-wave inversion and its relationship to structural heart disease, notably HCM and ARVC with a view to identify young athletes at risk of SCD during sport. Finally, the review proposes clinical management pathways (including genetic testing) for asymptomatic athletes demonstrating significant T-wave inversion with structurally normal hearts.

The right heart in athletes. Evidence for exercise-induced arrhythmogenic right ventricular cardiomyopathy.

Although 'athlete's heart' usually constitutes a balanced dilation and hypertrophy of all four chambers, there is increasing evidence that intense endurance activity may particularly tax the right ventricle (RV), both acutely and chronically. We review the evidence that the high wall stress of the RV during intense sports may explain observed B-type natriuretic peptide (BNP) elevations immediately after a race, may lead to cellular disruption and leaking of cardiac enzymes, and may even result in transient RV dilatation and dysfunction. Over time, this could lead to chronic remodelling and a pro-arrhythmic state resembling arrhythmogenic RV cardiomyopathy (ARVC) in some cases. ARVC in high-endurance athletes most often develops in the absence of underlying desmosomal abnormalities, probably only as a result of excessive RV wall stress during exercise. Therefore, we have labelled this syndrome 'exercise-induced ARVC'. Sports cardiologists should be aware that excessive sports activity can lead to cardiac sports injuries in some individuals, just like orthopaedic specialists are familiar with musculoskeletal sports injuries. This does not negate the fact that moderate exercise has positive cardiovascular effects and should be encouraged.

Importance of characteristics and modalities of physical activity and exercise in the management of cardiovascular health in individuals with cardiovascular risk factors: recommendations from the EACPR. Part II.

In a previous paper, as the first of a series of three on the importance of characteristics and modalities of physical activity (PA) and exercise in the management of cardiovascular health within the general population, we concluded that, in the population at large, PA and aerobic exercise capacity clearly are inversely associated with increased cardiovascular disease risk and all-cause and cardiovascular mortality and that a dose­response curve on cardiovascular outcome has been demonstrated in most studies. More and more evidence is accumulated that engaging in regular PA and exercise interventions are essential components for reducing the severity of cardiovascular risk factors, such as obesity and abdominal fat, high BP, metabolic risk factors, and systemic inflammation. However, it is less clear whether and which type of PA and exercise intervention (aerobic exercise, dynamic resistive exercise, or both) or characteristic of exercise (frequency, intensity, time or duration, and volume) would yield more benefit for each separate risk factor. The present paper, therefore, will review and make recommendations for PA and exercise training in the management of cardiovascular health in individuals with cardiovascular risk factors. The guidance offered in this series of papers is aimed at medical doctors, health practitioners, kinesiologists, physiotherapists and exercise physiologists, politicians, public health policy makers, and individual members of the public. Based on previous and the current literature overviews, recommendations from the European Association on Cardiovascular Prevention and Rehabilitation are formulated regarding type, volume, and intensity of PA and regarding appropriate risk evaluation during exercise in individuals with cardiovascular risk factors.

Lower than expected desmosomal gene mutation prevalence in endurance athletes with complex ventricular arrhythmias of right ventricular origin.

OBJECTIVE: To determine the prevalence of desmosomal gene mutations in athletes with complex arrhythmias (VA) of right ventricular (RV) origin and structural RV abnormalities to evaluate whether there is sufficient genetic overlap with arrhythmogenic right ventricular cardiomyopathy (ARVC) to consider them the same or different entities. DESIGN: Observational cohort SETTING: Tertiary hospital referrals PATIENTS: Forty-seven consecutive athletes (age 42 (11) years) with complex VA of RV morphology (excluding idiopathic right ventricular outflow tract ventricular tachycardia), who performed 14 (9) h/week of moderate to intense sport practise for 19 (9) years. INTERVENTIONS: Clinical evaluation (detailed sports history, multi-modality imaging, electrophysiological study) and sequencing of five candidate desmosomal genes. RESULTS: A clinical diagnosis of definite or suspected ARVC by task force criteria (TFC) was met in 24 (51%) and 17 (36%), respectively. ARVC classification was not related to the rate of major arrhythmic events (p=0.28). Pathogenic mutations (four novel) were identified in six athletes (12.8%), which is below published rates for familial ARVC (27-52%). Moreover, only two athletes had a suggestive family history. Severe RV dysfunction was more frequent in mutation carriers (33% vs 2%, p=0.04), but otherwise TFC features were similar to those without mutations. No mutations were found in the 20 athletes performing more than average weekly exercise, yet all met the criteria for definite or suspected ARVC. CONCLUSIONS: In this athletic cohort, we found lower than expected rates of desmosomal gene mutations, particularly among those performing the most exercise. This adds further weight to the hypothesis that an ARVC-like phenotype may be acquired through intense exercise without an identifiable genetic predisposition.

Effective dose analysis of three-dimensional rotational angiography during catheter ablation procedures.

There is increasing use of three-dimensional rotational angiography (3DRA) during cardiac ablation procedures. As compared with 2D angiography, a large series of images are acquired, creating the potential for high radiation doses. The aim of the present study was to quantify patient-specific effective doses. In this study, we developed a computer model to accurately calculate organ doses and the effective dose incurred during 3DRA image acquisition. The computer model simulates the exposure geometry and uses the actual exposure parameters, including the variation in tube voltage and current that is realized through the automatic exposure control (AEC). We performed 3DRA dose calculations in 42 patients referred for ablation on the Siemens Axiom Artis DynaCT system (Erlangen, Germany). Organ doses and effective dose were calculated separately for all projections in the course of the C-arm rotation. The influence of patient body mass index (BMI), dose-area product (DAP), collimation and dose per frame (DPF) rate setting on the calculated doses was also analysed. The effective dose was found to be 5.5 +/- 1.4 mSv according to ICRP 60 and 6.6 +/- 1.8 mSv according to ICRP 103. Effective dose showed an inversely proportional relationship to BMI, while DAP was nearly BMI independent. No simple conversion coefficient between DAP and effective dose could be derived. DPF reduction did not result in a proportional effective dose decrease. These paradoxical findings were explained by the settings of the AEC and the limitations of the x-ray tube. Collimation reduced the effective dose by more than 20%. Three-dimensional rotational angiography is associated with a definite but acceptable radiation dose that can be calculated for all patients separately. Their BMI is a predictor of the effective dose. The dose reduction achieved with collimation suggests that its use is imperative during the 3DRA procedure.

Transapical left ventricular access for difficult to reach interventional targets in the left heart.

OBJECTIVE: Interventional targets may be virtually "excluded" due to vascular access problems or complex previous surgical procedures. This study reviews our experience using transapical ventricular puncture to gain direct access to the systemic ventricle. PATIENTS: Patient 1 (74 years, 2 previous sternotomies), patient 2 (66 years, 5 previous sternotomies), and patient 5 (69 years, 3 previous sternotomies) with prosthetic valves had paravalvular mitral valve leaks. Patient 3 (6.3 years, 2 previous sternotomies) with an extracardiac Fontan conduit, had a significant residual leak after two previous surgical attempts of patch closure of a severely regurgitant right atrioventricular valve. Patient 4 (10 months) had failure of standard ablation of the posteroseptal region of the mitral valve with persistent life-threatening episodes of ventricular tachycardia. METHODS: Procedures were performed under general anesthesia. Entry site was percutaneous in three patients and in two (and one conversion) a mini-thoracotomy was used. Sheaths were placed (6 F) using standard Seldinger technique, followed by the procedure as required. Direct surgical closure of the puncture site was done in 4 patients and in patient 3, a percutaneous vascular occlusion device was used. RESULTS: Easy and immediate access was obtained in all patients. The paravalvular leaks were crossed within seconds and completely closed with Amplatzer occluders. In patient 3 the valve was crossed using a Brokenbrough needle and a 12-mm Amplatzer device was placed in the patch leak. Patient 4 was successfully ablated using a 7-F irrigated catheter endo- and epicardially. Complications were in the percutaneous puncture group: in one patient a coronary artery was punctured and in one a hemothorax developed. CONCLUSION: Direct left ventricular puncture offers a very useful alternative access site in selected patients to reach "inaccessible" targets for certain percutaneous interventions in patients where standard approaches may be impossible or difficult.

Unconventional intronic splice site mutation in SCN5A associates with cardiac sodium channelopathy.

BACKGROUND: Mutations in the cardiac sodium channel, SCN5A, have been associated with one type of long-QT syndrome, with isolated cardiac conduction defects and Brugada syndrome. The sodium channelopathies exhibit marked variation in clinical phenotypes. The mechanisms underlying the phenotypical diversity, however, remain unknown. Exonic SCN5A mutations can be detected in 20% of Brugada syndrome patients. RESULTS: An intronic mutation (c.4810+3_4810+6dupGGGT) in the SCN5A gene, located outside the consensus splice site, was detected in this study in a family with a highly variable clinical phenotype of Brugada syndrome and/or conduction disease and in a patient with Brugada syndrome. The mutation was not found in a control panel of 100 (200 alleles) ethnically matched normal control subjects. We provide in vivo and in vitro evidence that the mutation can disrupt the splice donor site, activate a cryptic splice site, and create a novel splice site. Notably, our data show that normal transcripts can be also derived from the mutant allele. CONCLUSIONS: This is the first report of an unconventional intronic splice site mutation in the SCN5A gene leading to cardiac sodium channelopathy. We speculate that its phenotypical diversity might be determined by the ratio of normal/abnormal transcripts derived from the mutant allele.

Radiation dose levels during interventional cardiology procedures in a tertiary care hospital.

The aim of our investigation was to prospectively measure the patient radiation exposure from different cardiological procedures performed in the Catheterisation laboratory of the University Hospital Gasthuisberg in Leuven. The following local reference values were proposed: 40, 47 and 80 Gycm2 for coronary angiography (CA) or angioplasty (PTCA and stent implantation for elective patients), radio frequency ablation with angiographic images and CA plus ad hoc PTCA, respectively.

Atrial fibrillation after radiofrequency ablation of atrial flutter: preventive effect of angiotensin converting enzyme inhibitors, angiotensin II receptor blockers, and diuretics.

OBJECTIVES: To determine risk factors for the development of atrial fibrillation (AF) after atrial flutter (AFL) ablation; and to study the relation between AF development and periprocedural drug use. METHODS: AFL ablation was performed in 196 patients. The relation between AF occurrence and clinical, echocardiographic, and procedural factors and periprocedural drug use was analysed retrospectively by a Cox proportional hazard method. RESULTS: After a median follow up of 2.2 years, 114 patients (58%) developed at least one AF episode. Factors associated with AF development were the presence of preprocedural AF, a history of cardioversion, and the number of antiarrhythmic drugs used before the procedure. Use of angiotensin converting enzyme (ACE) inhibitors/angiotensin II receptor blockers and diuretics was significantly associated by univariate and multivariate analyses with less development of AF. CONCLUSIONS: A high proportion of patients develop AF after AFL ablation. The incidence of AF is related to pre-ablation AF and its persistence. ACE inhibitors/angiotensin II receptor blockers and diuretics seem to protect against AF.

Relation between different methods for analysing ST segment deviation and infarct size as assessed by positron emission tomography.

OBJECTIVE: To study the relation between resolution of ST segment deviation and infarct size using positron emission tomography. METHODS: 45 patients with ST segment elevation acute myocardial infarction treated with thrombolysis or percutaneous coronary intervention were studied prospectively. An ECG was taken before and at (mean (SD)) 100 (45) min after reperfusion therapy. ECGs were analysed by three methods. Residual ST segment deviation, obtained from the ECG immediately after completion of reperfusion therapy, was defined by summation for each of the three methods. Relative resolution of ST segment deviation was defined as the absolute resolution divided by the ST segment deviation score at baseline x 100 (%). After 29 (14) hours, myocardial blood flow was measured with 13NH3. For each patient, the regions with a myocardial blood flow < 80% of normally perfused myocardium ( = hypoperfusion) and < 50% ( = no reflow) were automatically delineated. RESULTS: Substantial differences were found between different ECG analysis methods. There were moderate correlations between the area with myocardial hypoperfusion and ST segment deviation scores at baseline and after reperfusion therapy. After reperfusion therapy, residual ST segment deviation in the single lead with maximum ST segment deviation was as good at discriminating between tertiles of myocardial damage as summed ST segment elevation. Relative ST segment resolution did not discriminate between different degrees of myocardial damage. CONCLUSIONS: In the individual patient, residual ST segment deviation after reperfusion in the single lead with maximum ST segment deviation is at least as good as summed ST elevation in predicting final myocardial damage.

Pericardial effusion and right-sided pneumothorax resulting from an atrial active-fixation lead.

We report on a patient in whom an active-fixation pre-shaped atrial lead caused perforation of the right atrial wall, pericardium and pleura, resulting in pericardial effusion and right-sided pneumothorax. Chest X-ray did not demonstrate protrusion of the atrial lead outside the cardiac silhouette but computed tomography visualized the tip of the helix of the atrial screw-in electrode outside the contours of the right atrial appendage touching the right upper lobe of the lung. The lead was repositioned with resolution of pericardial effusion and pneumothorax. Due to their proximity to the right lung, high anterolaterally positioned atrial screw-in leads carry a small but definite risk for right-sided pneumothorax.

Ablation of post-surgical intra-atrial reentrant tachycardia. Predilection target sites and mapping approach.

BACKGROUND: Atrial arrhythmias are a frequent complication of atrial surgery. The location of these tachycardias is very diverse due to the individual difference in the original anatomy, surgical corrections, and effects of atrial fibrosis. Nevertheless some recurrent patterns are emerging. METHODS AND RESULTS: Forty-five patients underwent 51 ablation procedures between September 1995 and March 2001 using conventional mapping and temperature-controlled ablation. A duadecapolar catheter was swept from anterior to posterior in the right (and/or left) atrium, allowing for rapid mapping followed by entrainment confirmation. Twenty-eight patients had corrected congenital heart disease, 17 surgery for acquired heart disease. One hundred and sixteen arrhythmias were found, 86 circuits were targeted, 81 with success (94%). Despite the heterogeneous anatomy, the same targets were often encountered: the posterior isthmus between the inferior vena cava and the tricuspid ring (62%), the gap between the inferior vena cava and the atriotomy scar (49%), and the region around the atriopulmonary connection in Fontans (two out of four patients). After a mean follow-up of 24 months, 13 patients had a recurrent arrhythmia (29%) after their last procedure. There was a significant association between the number of circuits found during the initial procedure and the likelihood of recurrent arrhythmias. CONCLUSION: Knowledge of anatomical predilection sites and mapping the right (and/or left) atrium with a 'sweeping Halo technique' allow for effective ablation of most post-surgical atrial tachycardias. Severely damaged atria with multiple arrhythmias may require 'preventive' ablation of all recognizable channels.

Effect of different pacing protocols on the induction of atrial fibrillation in a transvenously paced sheep model.

In different animal models rapid atrial stimulation led to a shortening and maladaptation to rate of the atrial effective refractory period (AERP). This atrial electrical remodeling resulted in an increased vulnerability to atrial fibrillation (AF). These experimental findings formed the rationale for a stringent pursuit of sinus rhythm in patients with AF, since this would prevent or reverse atrial remodeling. This study tested the hypothesis that a reduction of arrhythmia burden would lead to a decreased vulnerability for AF. Different rapid atrial pacing protocols in a sheep model were used. During 15 weeks, 13 animals were continuously rapid paced and 7 animals were intermittently burst-paced, resulting in rapid atrial activation during 100% versus 33 +/- 4% of the time, respectively. In the continuously paced group, 77% of the animals developed sustained AF (i.e., > 1 hour) versus only 29% in the burst-paced group (P < 0.05). However, there was no difference in mean AERP shortening over time, nor maximal AERP shortening per animal, between both protocols. Minimal AERP was 103 +/- 5 ms in the continuously paced group and 107 +/- 5 in the burst-paced group (P = NS). Significant changes could be identified in effect on P wave duration, AVN function, and atrial dilation. Conduction slowing was more pronounced in the continuously paced group with a maximal P wave duration of 136 +/- 4 ms in this group versus 116 +/- 5 in the burst-paced group (P < 0.05). In the continuously paced group, the right atrial area significantly increased from 2.5 +/- 0.1 cm2 at baseline to 4.2 +/- 0.2 cm2. In the burst-paced group there was no significant atrial dilatation (from 2.6 +/- 0.1 to 2.8 +/- 0.1 cm2). In conclusion, limiting atrial arrhythmia burden slowed the development of sustained AF in this sheep model. This was not mediated by a decreased influence on atrial refractoriness but seemed to be dependent on smaller changes in atrial conduction and dimensions.

Paradoxical undersensing at a high sensitivity in dual chamber pacemakers.

In view of the evolving indications for device therapy in atrial arrhythmia the accurate detection of high rate atrial events is a necessity. In a sheep model of atrial fibrillation (AF) we observed a contradictory behavior of the Thera DR pacemaker. The pacemakers were programmed to deliver burst pacing on detection of sinus rhythm (SR). Paradoxically, progressively more inappropriate bursts were delivered during AF, at a higher sensitivity. This implied that the pacemaker interpreted AF as SR. We assessed the atrial detection of the Thera DR, Diamond, Saphir, and Marathon pacemakers during AF, in a sheep model and in vitro using a waveform generator. By counting the annotated atrial-sensed events reported by the pacemaker we charted the behavior of the pacemakers at different sensitivities. At a higher sensitivity both the Thera DR and the Diamond paradoxically reported fewer atrial events during AF. This behavior led to inappropriate mode switching and incorrect diagnostic data collection. It could be reproduced in vitro. The Marathon did not show this paradoxical undersensing in vivo or in vitro. This paradoxical undersensing at a high sensitivity is dependent on the amplitude of the input signal and could not be explained by an overlap of programmable timing parameters. It is caused by ringing of the atrial sensing amplifier. At high atrial rates and a high sensitivity the ringing of the repetitive atrial signal input results in blanking of the atrial amplifier. This observation may be relevant in the device management of patients with paroxysmal AF.