Accessory Atrioventricular Connections Research Articles

A history of collaboration between electrophysiologists and arrhythmia surgeons.

Introduction: The notion that medically‐refractory arrhythmias might one day be amenable to interventional therapy slowly began to appear in the early 1960's. At that time, there were no “interventional electrophysiologists” or “arrhythmia surgeons” and there was little appreciation of the relationship between anatomy and electrophysiology outside the heart's specialized conduction system. Methods: In this review, we describe the evolution of collaboration between electrophysiologists and surgeons. Results: Although accessory atrio‐ventricular (AV) connections were first identified in 1893 and the Wolff‐Parkinson‐White (WPW) syndrome was described 37 years later (1930), it was another 37 years (1967) before those anatomic AV connections were proven to be responsible for the clinical syndrome. The success of the subsequent surgical procedures for the WPW syndrome, AV node reentry tachycardia, automatic atrial tachycardias, ischemic and non‐ischemic ventricular tachycardias and atrial fibrillation over the next two decades depended on a close, sometimes daily, collaboration between electrophysiologists and surgeons. In the past two decades, that tight collaboration was largely abandoned until the recent introduction of “hybrid procedures” for the treatment of atrial fibrillation. Conclusions: A retrospective assessment of the 50 years of interventional therapy for arrhythmias clearly demonstrates the clinical benefits of a close collaboration between electrophysiologists and arrhythmia surgeons, regardless of which one is actually performing the intervention.

Deep Vein Thrombosis is Common After Cardiac Ablation and Pre-Procedural D-Dimer Could Predict Risk

Cardiac catheter ablations are an established treatment for supraventricular tachycardia (SVT) involving prolonged cannulation of the common femoral vein with multiple catheters. This study aimed to identify the risk of deep vein thrombosis (DVT) by studying the frequency of this complication after catheter ablation. This was a prospective multi-centre cohort study of patients undergoing cardiac ablation for atrioventricular nodal re-entry tachycardia or right-sided accessory atrioventricular connection. Those taking anticoagulation or antiplatelet therapy prior to the procedure were excluded. Following the procedure, bilateral venous duplex ultrasonography from the popliteal vein to the inferior vena cava for DVT was undertaken at 24 hours and between 10 to 14 days. Eighty (80) patients (mean age 47.6 yrs [SD 13.4] with 67% female) underwent cardiac ablation (median duration 70 mins). Seven (7) patients developed acute DVT in either the femoral or external iliac vein of the intervention leg, giving a frequency of 8.8% (95% CI 3.6-17.2%). No thrombus was seen in the contralateral leg (p=0.023). An elevated D-dimer prior to the procedure was significantly more frequent in patients developing DVT (42.9% vs 4.1%, p=0.0081; OR 17.0). No other patient or procedural characteristics significantly influenced the risk of DVT. In patients without peri-procedural anticoagulation catheter ablation precipitated DVT in the catheterised femoral or iliac veins in 8.8% of patients. Peri-procedure prophylactic anticoagulation may be considered for all patients undergoing catheter ablation for SVT. https://clinicaltrials.gov/ct2/show/NCT03877770.

547 Supernormal conduction of an accessory pathway: the case of a young sportsman

Abstract Aims Ventricular pre-excitation is defined by the presence of all of the following electrocardiographic criteria: PQ interval duration ≤120 ms, QRS duration ≥120 ms, and presence of δ wave (defined as initial ‘slurring’ of the QRS complex). Ventricular pre-excitation together with the presence of symptoms (orthodromic and/or antidromic atrioventricular reentry tachycardia, atrial fibrillation) defines Wolff–Parkinson–White (WPW) syndrome. The anatomical substrate of ventricular pre-excitation consists of an extranodal accessory atrio-ventricular connection: the so-called Kent bundle. Such pathways can have antegrade, retrograde, or mixed conductive properties. Accessory pathways endowed with anterograde conductive capability may be responsible for manifest, intermittent, or non-manifest ventricular pre-excitation depending on whether it is respectively always visible on the ECG, not always visible on the ECG and not visible on the ECG even though the pathway has the ability to antegrade conduction. The rare phenomenon of supernormal conduction of anomalous pathways is part of the manifest pre-excitation, which represents the topic of the case reported below. Methods and results We report the clinical case of a young not agonist sportsman undergoing an electrophysiological study (SEF) because of he is suffering from ventricular pre-excitation. The SEF did not showed the inducibility of arrhythmias and, at the same time, apparently it showed low risk characteristics of the pathway even during adrenergic stimulus. However, a careful study, performed with atrial stimulation with couplings up to refractoriness of the atrioventricular node revealed supernormal conduction properties of the Kent bundle which proved to have high risk characteristics according to current guidelines and, therefore, was effectively treated with catheter ablation. Conclusions This case invites us to careful studying of accessory pathways properties, especially since, although rare, they may possess supernormal conduction characteristics capable of determining high ventricular rates in the case of sustained atrial tachyarrhythmias, especially in conditions of adrenergic hyperactivity.

Apoptosis and epicardial contributions act as complementary factors in remodeling of the atrioventricular canal myocardium and atrioventricular conduction patterns in the embryonic chick heart.

During heart development, it has been hypothesized that apoptosis of atrioventricular canal myocardium and replacement by fibrous tissue derived from the epicardium are imperative to develop a mature atrioventricular conduction. To test this, apoptosis was blocked using an established caspase inhibitor and epicardial growth was delayed using the experimental epicardial inhibition model, both in chick embryonic hearts. Chicken embryonic hearts were either treated with the peptide caspase inhibitor zVAD-fmk by intrapericardial injection in ovo (ED4) or underwent epicardial inhibition (ED2.5). Spontaneously beating embryonic hearts isolated (ED7-ED8) were then stained with voltage-sensitive dye Di-4-ANEPPS and imaged at 0.5-1 kHz. Apoptotic cells were quantified (ED5-ED7) by whole-mount LysoTracker Red and anti-active caspase 3 staining. zVAD-treated hearts showed a significantly increased proportion of immature (base to apex) activation patterns at ED8, including ventricular activation originating from the right atrioventricular junction, a pattern never observed in control hearts. zVAD-treated hearts showed decreased numbers of apoptotic cells in the atrioventricular canal myocardium at ED7. Hearts with delayed epicardial outgrowth showed also increased immature activation patterns at ED7.5 and ED8.5. However, the ventricular activation always originated from the left atrioventricular junction. Histological examination showed no changes in apoptosis rates, but a diminished presence of atrioventricular sulcus tissue compared with controls. Apoptosis in the atrioventricular canal myocardium and controlled replacement of this myocardium by epicardially derived HCN4-/Trop1- sulcus tissue are essential determinants of mature ventricular activation pattern. Disruption can lead to persistence of accessory atrioventricular connections, forming a morphological substrate for ventricular pre-excitation. Developmental Dynamics 247:1033-1042, 2018. © 2018 Wiley Periodicals, Inc.

Confirmation of Novel Noninvasive High-Density Electrocardiographic Mapping With Electrophysiology Study

Background— Twelve lead ECGs have limited value in precisely identifying atrial and ventricular activation during arrhythmias, including accessory atrioventricular conduction activation. The aim of this study was to report a single center’s clinical experience validating a novel, noninvasive, whole heart, beat-by-beat, 3-dimensional mapping technology with invasive electrophysiological studies, including ablation, where applicable. Methods and Results— Using an electrocardiographic mapping (ECM) system in 27 patients, 3-dimensional epicardial activation maps were generated from >250 body surface ECGs using heart–torso geometry obtained from computed tomographic images. ECM activation maps were compared with clinical diagnoses, and confirmed with standard invasive electrophysiological studies mapping. (1) In 6 cases of Wolff–Parkinson–White syndrome, ECM accurately identified the ventricular insertion site of an accessory atrioventricular connection. (2) In 10 patients with premature ventricular complexes, ECM accurately identified their ventricular site of origin in 8 patients. In 2 of 10 patients transient premature ventricular complex suppression was observed during ablation at the site predicted by ECM as the earliest. (3) In 10 cases of atrial tachycardia/atrial flutter, ECM accurately identified the chamber of origin in all 10, and distinguished isthmus from nonisthmus dependent atrial flutter. (4) In 1 patient with sustained exercise induced ventricular tachycardia, ECM accurately identified the focal origin in the left ventricular outflow tract. Conclusions— ECM successfully provided valid activation sequence maps obtained noninvasively in a variety of rhythm disorders that correlated well with invasive electrophysiological studies.

Myocardial infarction in an individual with Wolff-Parkinson-White syndrome

A case of recent myocardial infarction in a 24-year-old man with no known history of Wolff—Parkinson— White syndrome is reported. The patient developed during sport training an exercise tachycardia associated with palpitation and syncope. The electrocardiogram, performed by rescue team, was suggestive of Wolff-Parkinson-White syndrome. He was admitted to Cardiovascular Diseases Institute for this first attack of rapid heart beating which did not readily subside. He died suddenly after admission, with no response to resuscitation maneuvers and before other investigations were performed. Autopsy examination of the heart revealed no accessory atrioventricular connection, but revealed a recent myocardial infarction. The case underlines the potential danger of the Wolff—Parkinson—White syndrome in patients with no or minimal clinical manifestations. The rapid unexpected death can be attributed to atrial fibrillation with rapid ventricular response via the anomalous connection. A meticulous histological study of the atrioventricular function in hearts of young athletes with unexplained death is a necessity.

Can We Do a Prospective Trial for Fetal Tachycardia?

Jaeggi and colleagues1 have added to the literature with their extensive assessment of 159 fetal tachyarrhythmia cases collected from 3 institutions over a 10-year period. However, before we comment on their study, it is worth reviewing some of the relevant issues for management of fetal arrhythmias. An estimated 0.4% to 0.6% of pregnancies have a fetal arrhythmia at some point during the pregnancy.2,3 Although the vast majority are not of clinical significance and require no treatment, a much smaller percentage have a sustained tachyarrhythmia that can be life-threatening to the fetus. The most frequent serious arrhythmias in the fetus are supraventricular, most commonly from atrioventricular reentry tachycardia involving an accessory atrioventricular connection (supraventricular tachycardia [SVT]) or atrial flutter, but occasionally from atrioventricular node reentry (also SVT) or ectopic atrial tachycardia.2,3 Here, we refer to all these mechanisms together as supraventricular a rrhythmias (SVAs) and the subgroups of interest as SVT or atrial flutter. Importantly, SVAs can lead to tachycardia-induced cardiomyopathy because of prolonged decreased cardiac output and myocardial fatigue, which can lead to hydrops fetalis and rare fetal death,2,3 as reviewed by Jaeggi et al.1 Treatment options include careful observation, maternal drug therapy, or delivery of the fetus. Article see p 1747 More than 20 studies have looked at outcomes of drug therapy for fetal SVA, some of which are reviewed by Jaeggi et al.1 The most commonly used antiarrhythmics are digoxin, flecainide, sotalol, and amiodarone, but many drugs have been used less frequently, and results vary widely. In the studies using digoxin as first-line therapy, successful conversion has been reported in 50% to 100% of fetuses without hydrops, but only 0% to 20% of patients with hydrops.4–9 Flecainide has resulted in sinus rhythm in …

Unusual Response of an Accessory Atrioventricular Connection to Adenosine

Unusual Response of an Accessory Atrioventricular Connection to Adenosine

P117. Cell death in the atrioventricular canal myocardium determines ventricular activation patterns

Based on our previous study showing accelerated conversion of ventricular activation sequence during hypoxic incubation correlating with increased apoptosis in the atrioventricular canal, we hypothesized that this slight increase in apoptosis could lead to an accelerated pruning of myocardial atrioventricular connections, which would manifest as earlier appearance of mature apex-to-base activation patterns. To test this hypothesis, we blocked apoptosis using an established caspase inhibitor in chick embryonic heart and analyzed the effects of this treatment on cell death and ventricular activation patterns. ED4 chick embryonic hearts were treated with the peptide Caspase inhibitors zVAD-fmk by intrapericardial injection in ovo. Spontaneously beating embryonic hearts isolated at ED8 were stained with voltage-sensitive dye Di-4-ANEPPS and imaged at 37 °C with Ultima L high-speed camera at 1 kHz. Amount of apoptotic cells was analyzed at ED 7 by whole mount LysoTracker Red staining and confocal microscopy. Hearts of embryos treated with zVAD showed a significantly increased proportion of immature (base to apex) activation patterns at ED8, including ventricular activation originating from right atrioventricular junction, a pattern never observed in control hearts. The number of apoptotic cells in atrioventricular canal myocardium was decreased at ED7 in the treated hearts. Apoptosis in the atrioventricular canal myocardium is thus an important contributor to ventricular activation pattern. Its inhibition at critical stages can lead to persistence of accessory atrioventricular connections, which form a morphological substrate for ventricular pre-excitation. Supported by project of MSMT VZ 0021620806, LC 06061, and by grant of AS CR AV0Z50450515.

Preexcitation unmasked after successful accessory atrioventricular connection ablation: What is the mechanism?

Case presentation A 19-year-old man with a history of palpitations and no underlying structural heart disease underwent electrophysiologic diagnostic evaluation for possible catheter ablation of the arrhythmogenic substrate responsible for the palpitations. Twelve-lead ECG showed ventricular preexcitation consistent with a left free-wall accessory atrioventricular (AV) connection (Figure 1A). Electrophysiologic study was performed using standard methodology with catheters in the right ventricular apex (RVA), high right atrium (HRA), His bundle, and coronary sinus. Basic intervals during sinus rhythm were as follows: PR interval 110 ms, AH interval 40 ms, HV interval 0 ms, and QRS duration 110 ms. Ventricular preexcitation was maximal during incremental atrial pacing (Figure 1B). Ventricular pacing showed nondecremental and eccentric retrograde ventriculoatrial (VA) conduction. HRA programmed stimulation induced a minimally preexcited AV reciprocating tachycardia with eccentric VA conduction (Figures 1B and 2A). Measurements of the tachycardia were as follows: AH interval 238 ms, HV interval 16 ms, and VA interval 151 ms. Retrograde conduction was due to a left free-wall accessory AV connection. However, during tachycardia, the HV interval was shorter than expected (Figure 2A). We performed radiofrequency catheter ablation of the left freewall accessory AV connection with subsequent VA dissociation during RVA pacing. After the successful ablation, a short HV interval and ventricular preexcitation of possible septal origin were apparent (Figures 1C and 2B). Atrial pacing showed rateependent prolongation of the AH interval with fixed HV nterval. Intravenous adenosine bolus showed blocked P aves with no change in degree of ventricular preexcitation.

Trpm4-Linked Isolated Cardiac Conduction Defects

Cardiac conduction system disease (CCD) is a common medical problem, with about 3 million people worldwide with pacemakers and 600 000 implanted each year.1 Despite its prevalence, there is little known about the molecular pathogenesis of CCD in the general population. Therefore, investigators have turned to cases of familial conduction system disease to gain insights. Article see p 374 This approach has led to the discovery of several genes involved in syndromic CCD (reviewed by Wolf and Berul).2 Mutations in the transcription factor NKX2.5 cause atrial septal defects and progressive atrioventricular block (AVB). Defects in another transcription factor, Tbx5, cause Holt-Oram syndrome, characterized by atrial septal defects, progressive AVB, and radial limb deformities. Muscular dystrophies can be associated with AVB as well. Emery-Dreifuss muscular dystrophy, whether caused by defects in Emerin or Lamin A/C, is associated with AVB, and myotonic dystrophy, caused by expansion of a trinucleotide repeat downstream of the DMPK gene, is also associated with progressive AVB. Atrioventricular block is a frequent finding in patients with PRKAG2 mutations who also have accessory atrioventricular connections and glycogen storage cardiomyopathy. Finally, AVB can be seen as part of the Andersen-Tawil syndrome of prolonged QT interval, potassium-sensitive periodic paralysis, ventricular arrhythmias, and dysmorphic features. What about isolated atrioventricular conduction disease? Until recently, the only gene implicated in human-isolated progressive CCD was the cardiac voltage-gated sodium channel, SCN5a.3 Thus, there is great interest in the causative gene recently identified in a large South African family with autosomal dominant progressive familial heart block, type I.4 …

Measure twice, cut once: pitfalls in the diagnosis of supraventricular tachycardia.

In atrioventricular nodal and atrioventricular reentrant tachycardia, the relative timing of atrial and ventricular activation may sometimes be very similar, even during electrophysiological studies, and this may lead to an erroneous diagnosis and inappropriate treatment. As examples, we describe two cases that were recently referred to our hospital for a second opinion and treatment of paroxysmal supraventricular tachycardia. In both, the original diagnosis of the referring centres was commontype atrioventricular nodal reentrant tachycardia. Catheter ablation in those centres was unsuccessful. During our electrophysiological studies, however, an atrioventricular reentrant tachycardia was demonstrated, using a concealed accessory pathway for retrograde conduction in both patients. The accessory atrioventricular connection was successfully ablated and on follow-up both patients remained free of symptoms without medication. These findings illustrate the importance of complete electrophysiological analysis even for apparently simple supraventricular arrhythmias. (Neth Heart J 2010;18:78-84.).

Supraventricular tachyarrhythmias: drug therapy versus catheter ablation.

Until recently, the only options available for treatment of supraventricular arrhythmias involved the use of drug therapy or cardiac surgery. However, over the past several years with the introduction of radiofrequency energy sources as well as steerable catheters, the clinician has a variety of additional nonpharmacologic options. This article reviews the use of pharmacologic therapy versus catheter ablation for the treatment of reentrant supraventricular arrhythmias, involving the atrioventricular junction and/or accessory atrioventricular connection, as well as arrhythmias emanating from the atria such as atrial fibrillation, atrial flutter, and atrial tachycardia.

Molecular analysis of PRKAG2, LAMP2, and NKX2‐5 genes in a cohort of 125 patients with accessory atrioventricular connection

Molecular analysis of <i>PRKAG2</i>, <i>LAMP2</i>, and <i>NKX2‐5</i> genes in a cohort of 125 patients with accessory atrioventricular connection

Accessory Atrioventricular Myocardial Connections in the Developing Human Heart

Fetal and neonatal atrioventricular (AV) reentrant tachycardias can be life-threatening but resolve in most cases during the first year of life. The transient presence of accessory AV myocardial connections during annulus fibrosus development may explain this phenomenon. A total of 45 human embryonic, fetal, and neonatal sectioned hearts (4 to 36 weeks of development) were studied immunohistochemically. Accessory myocardial AV connections were quantified and categorized according to their specific location, and 3D reconstructions were made. Between 4 and 6 weeks of development, the atrial and ventricular myocardium was continuous at the primitive AV canal. At 6 to 10 weeks, numerous accessory myocardial AV connections were identified in the left (45%), right (35%), and septal (20%) regions of the AV junction. Most right-sided accessory connections comprised distinct myocardial strands, whereas left-sided connections consisted of larger myocardial continuities. At 10 to 20 weeks, all accessory AV connections comprised discrete myocardial strands and gradually decreased in number. The majority of accessory connections were located in the right AV junction (67%), predominantly in the lateral aspect (45%). Seventeen percent of the accessory connections were observed in the left AV junction, and 16% were observed in the septal region. 3D reconstructions of the developing AV nodal area at these stages demonstrated multiple AV node-related accessory connections. From 20 weeks until birth, and in neonatal hearts, no further accessory myocardial AV connections were observed. Isolation of the AV junction is a gradual and ongoing process, and right lateral accessory myocardial AV connections in particular are commonly found at later stages of normal human cardiac development. These transitory accessory connections may act as substrate for AV reentrant tachycardias in fetuses or neonates.

Accessory Atrioventricular Pathways

By definition, accessory atrioventricular pathways are aberrant muscle bundles that connect the atrium to a ventricle outside of the regular atrioventricular conduction system. Clinically, they may manifest as substrates for ventricular preexcitation. The first accessory pathway in a patient who suffered from Wolff-Parkinson-White syndrome was described in 1943 by Wood, Wolferth, and Geckler.1 Shortly after, Ohnell created a reconstruction of an accessory pathway that very elegantly showed the close proximity of the pathway to the fibrous attachment of the mitral valve and its relationship with the sulcus coronarius (Figure, A).2 Subsequent histological studies have demonstrated unequivocally that these pathways are the anatomic substrates for the classical Wolff-Parkinson-White variety of preexcitation. Figure. A, Ohnell’s depiction of an accessory bundle in the left atrioventricular groove.2 Reprinted with permission from Blackwell Publishing. B, Histological section stained with Masson’s trichrome (fibrous tissue in green and myocardium in red) to show an accessory left-sided pathway (arrow) skirting the mitral annulus. C, Histological section showing a broad right-sided accessory pathway (arrow) that is formed by a myocardial pouch extending from the right atrial appendage to the ventricle and ultimately traced to a small right ventricular vein. This pathway is some distance from the fibrous annulus of the tricuspid valve. *Valvar annulus. Article p 1508 Accessory atrioventricular pathways are found most often in the parietal atrioventricular junctional areas, including the paraseptal areas. They breach the insulation provided by the fibrofatty tissues of the atrioventricular groove (sulcus tissue) and the hingelines (fibrous annulus) of the valves. They are rarely found in the area of fibrous continuity between the aortic and mitral valves because in this area, there is usually a wide gap between the atrial myocardium and ventricular myocardium to accommodate the aortic outflow tract. On the left parietal side, the accessory pathways tend …

AMP-Activated Protein Kinase in the Heart

AMP-activated protein kinase (AMPK) is a heterotrimeric enzyme that is expressed in most mammalian tissues including cardiac muscle. Among the multiple biological processes influenced by AMPK, regulation of fuel supply and energy-generating pathways in response to the metabolic needs of the organism is fundamental and likely accounts for the remarkable evolutionary conservation of this enzyme complex. By regulating the activity of acetyl-coenzyme A carboxylase, AMPK affects levels of malonyl-coenzyme A, a key energy regulator in the cell. AMPK is generally quiescent under normal conditions but is activated in response to hormonal signals and stresses sufficient to produce an increase in AMP/ATP ratio, such as hypoglycemia, strenuous exercise, anoxia, and ischemia. Once active, muscle AMPK enhances uptake and oxidative metabolism of fatty acids as well as increases glucose transport and glycolysis. Data from AMPK deficiency models suggest that AMPK activity might influence the pathophysiology and therapy of diabetes and increase heart tolerance to ischemia. Effects that are not as well understood include AMPK regulation of transcription. Different AMPK isoforms are found in distinct locations within the cell and have distinct functions in different tissues. A principal mode of AMPK activation is phosphorylation by upstream kinases (eg, LKB1). These kinases have a fundamental role in cell-cycle regulation and protein synthesis, suggesting involvement in a number of human disorders including cardiac hypertrophy, apoptosis, cancer, and atherosclerosis. The physiological role played by AMPK during health and disease is far from being clearly defined. Naturally occurring mutations affecting the nucleotide-sensing modules in the regulatory gamma subunit of AMPK lead to enzyme dysregulation and inappropriate activation under resting conditions. Glycogen accumulation ensues, leading to human disease manifesting as cardiac hypertrophy, accessory atrioventricular connections, and degeneration of the physiological conduction system. Whether AMPK is a key participant or bystander in other disease states and whether its selective manipulation may significantly benefit these conditions remain important questions.

Arrhythmias in Adult Patients With Congenital Heart Disease

By the time patients with congenital heart disease (CHD) reach adolescence and early adulthood, rhythm status has often become an active issue, if not the central issue, in their cardiac management. For some, arrhythmias are intrinsic to the structural malformation itself, as is the case with Wolff-Parkinson-White syndrome in the setting of Ebstein’s anomaly, or atrioventricular (AV) block in the setting of “congenitally corrected” transposition of the great arteries (L-TGA). For most other CHD patients, arrhythmias represent an acquired condition related to the unique myocardial substrate created by surgical scars in conjunction with cyanosis and abnormal pressure/volume loads of long duration. This review will attempt to address the major rhythm difficulties faced by adults with CHD, concentrating on electrophysiological features that distinguish CHD from more conventional forms of adult heart disease. A listing of specific arrhythmias and commonly associated congenital defects is provided in Table 1 to serve as an outline for the discussion. View this table: TABLE 1. Specific Arrhythmias and Associated Defects in Adults With Congenital Heart Disease As of 2001, there were estimated to be 800 000 adults with CHD living in the United States,1 a number that has grown steadily as more survivors of childhood surgery reach maturity. Of these, roughly 45% are considered to have mild forms of CHD (eg, atrial septal defect, valvar pulmonary stenosis), 40% are classified as having moderate disease (eg, tetralogy of Fallot, Ebstein’s anomaly), and 15% are considered to have complex disease (eg, single ventricle, transposition of the great arteries). Although arrhythmias can develop within any of the 3 subgroups, the incidence is highest for patients in the moderate and severe categories. Tetralogy of Fallot is an instructive example of moderate CHD with a large arrhythmia burden. As many as one third of patients with repaired tetralogy develop symptomatic atrial tachycardias by …

Persistence of Functional Atrioventricular Accessory Pathways in Postseptated Embryonic Avian Hearts

During heart development, the ventricular activation sequence changes from a base-to-apex to an apex-to-base pattern. We investigated the possibility of impulse propagation through remnants of atrioventricular (AV) connections in quail hearts. In 86 hearts (group A, HH30-34, n=15; group B, HH35-44, n=65; group C, 5 to 6 months, n=6) electrodes were positioned at the left atrium, right ventricular base, left ventricular (LV) base, and LV apex. In group A, LV base activation preceded LV apex activation in the majority of cases (60%; 9 of 15), whereas hearts in group B primarily demonstrated an LV apex-to-base activation pattern (72%; 47 of 65). Interestingly, in group B, the right ventricular base (17%; 11 of 65) or LV base (8%; 5 of 65) exhibited premature activation in 25% (16 of 65) of cases, whereas in 26% (17 of 65), the right ventricular base or LV base was activated simultaneously with the LV apex. Morphological analysis confirmed functional data by showing persistent muscular AV connections in embryonic hearts. Interestingly, all myocardial AV connections stained positive for periostin, a nonmyocardial marker. Longitudinal analysis (HH35-44) demonstrated a decrease in both the number of hearts that exhibited premature base activation (P=0.015) and the number (P=0.004) and width (P=0.179) of accessory AV pathways with developmental stage in a similar time course. In the adult quail hearts, accessory myocardial AV pathways were functionally and morphologically absent. Thus, impulse propagation through persistent accessory AV connections remains possible at near-hatching stages (HH44) of development, which may provide a substrate for AV reentrant arrhythmias in perinatal life. Periostin positivity and absence of AV pathways in the adult heart suggest that these connections eventually lose their myocardial phenotype, which implicates ongoing AV ring isolation perinatally and postnatally.

Intermittent Noninfarction Q Waves: A Finding Suggestive of Latent Preexcitation

To describe 3 patients who presented with chest pain and intermittent Q waves on the electrocardiogram (ECG) and were subsequently found to have latent preexcitation. During a span of 8 years, 3 patients were evaluated because of atypical chest pain and pathologic Q waves in the inferior leads; in all 3 patients, the Q waves were intermittent. No patient had a history of arrhythmia or had Wolff-Parkinson-White pattern on the ECG. Diagnostic and therapeutic interventions for suspected myocardial infarction included cardiac catheterization in 2 patients, intravenous thrombolytic therapy in 1 patient, and heparin in 2 patients. Ischemic heart disease was excluded in all. Patients underwent pharmacological testing and/or electrophysiologic study for suspected preexcitation. Despite the absence of ECG markers of preexcitation, the presence of a latent accessory atrioventricular connection was confirmed in each patient by pharmacological or electrophysiologic studies. In patients who present with intermittent noninfarction Q waves, the most likely diagnosis is latent preexcitation. Clinicians need to be educated about this clinical diagnosis and encouraged to pursue confirmatory testing. Such patients should be informed about the nature and importance of their electrocardiographic abnormality.