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Prevention of sudden cardiac death: focus on the subcutaneous implantable cardioverter-defibrillator
No full textThe implantable cardioverter-defibrillator (ICD) is the most effective therapy to prevent sudden cardiac death (SCD) in high-risk patients. To overcome infections and failure of transvenous leads, the most frightening complications of conventional ICDs, a completely subcutaneous ICD (S-ICD) has been developed and is currently adopted in routine clinical practice. In view of their long life-expectancy, low competitive risk of dying from non-arrhythmic causes, and high lifetime risk of lead-related complications requiring surgical revisions, young patients with cardiomyopathies and inherited arrhythmia syndromes have traditionally been considered ideal candidates for the S-ICD. However, as growing evidence supported S-ICD safety and efficacy, initial niche implant indications were abandoned in favor of a widespread use of this technology, that is currently adopted in common ICD candidates with severe left ventricular dysfunction. Indeed, guidelines recommend S-ICD implantation as an alternative to TV-ICDs in all ICD candidates, unless pacing is required. This review focuses on the contemporary experience with the S-ICD and explores future scenarios in which device-to-device communication will enable to combine leadless therapies
An unusual pattern of Para-Hisian pacing. The role of infra-Hisian conduction delay
No full textA 26-year-old male athlete with a history of palpitations and intermittent preexcitation was referred to our center. The echocardiogram did not reveal any relevant abnormalities, while his basal 12-lead electrocardiogram showed sinus rhythm and incomplete left bundle branch block (LBBB).
An electrophysiological study was performed, and multipolar diagnostic catheters were positioned at the His bundle (HB) region and coronary sinus. The AH and HV intervals were 60 milliseconds and 45 milliseconds, respectively. Retrograde conduction was concentric and decremental. During Para-Hisian pacing (PHP) maneuver, an interesting phenomenon was observed (Figure 1A). The loss of direct HB capture at a lower pacing-output led to delayed retrograde HB activation, with a subsequent significant and homogenous delay in atrial activation, consistent with a nodal response (beat 2, Figure 1A). The H-A interval was slightly shorter (∼10 milliseconds) at beat 2, likely because the loss of HB capture caused a marked prolongation of the H-H interval compared to the basal pacing cycle length favoring faster retrograde conduction over the AV node (ie, decremental conduction).
However, the typical QRS widening was absent, and there was only a slight change in QRS morphology (earlier R/S transition in chest leads), while QRS duration remained nearly unchanged (∼120 milliseconds). Notably, the basal incomplete LBBB was observed to be more evident either spontaneously (Figure 1B), or at slightly faster rates of atrial pacing. Typically, direct HB capture at high pacing-output
produces a narrower QRS because of the support of His-Purkinje system providing faster and more synchronous activation of both ventricles. In particular, the LBB should play a dominant role in this scenery since it supports the activation of the left ventricle (LV) that is far from the pacing site. In our case, the status of HB capture during PHP (direct capture vs. delayed retrograde activation) did not affect LV timing nor had a major effect on ventricular activation time (QRS duration), likely due to the basal conduction defect at the LBB level. In this study, no inducible tachycardia or accessory pathways were observed even at high-dose Isoproterenol and ablation was not performed.
This case highlights an additional potential pitfall during PHP maneuver and how basal infra-Hisian conduction delay may affect the typical QRS changes that are essential criteria to recognize the status of HB capture. Multipolar HB recordings and the ability to detect retrograde HB potential, rather than relying on QRS changes, are the key for correct interpretation in such cases
Premature ventricular extrastimulus without His or ventricular capture. An unexpected response during AV nodal reentrant tachycardia
No full textA 52-year-old male was referred to our center for catheter ablation of recurrent episodes of paroxysmal supraventricular tachycardia. No relevant abnormalities were observed at his basal ECG and echocar- diogram. Electrophysiological study was performed, and multipolar diagnostic catheters were introduced via the femoral veins. Typical atrioventricular (AV) nodal reentrant tachycardia with a medium rate of 200 bpm was reproducibly induced and diagnosed according to the standard criteria. During ventricular resetting maneuver using the His catheter, an expected phenomenon was observed after applying an early premature ventricular extrastimulus (PVE) (Figure 1). At a first look, the stimulus occurred during the ventricular refractory period without any capture. However, a phase of right bundle branch block (RBBB) occurred immediately after this apparently noncapturing PVE and without any subsequent change in the tachycardia cycle length making rate-dependent RBBB unlikely as a mechanism. The PVE did not capture ventricular myocardium, nor the His bundle (H-H intervals remained unchanged), and the tachycardia was not reset (Figure 1A). The induced RBBB was likely due to local concealed capture of the proximal RBB during its relative refractory period by the applied PVE. The stimulus could generate only an attenuated action potential with slow conduction in the RBB (the asterisk, Figure 1B) unable to
advance the next QRS. Nevertheless, the local capture of proximal RBB rendered it unexcitable by the antegrade activation of the ongoing tachycardia. Another possible mechanism is local electrotonus after PVE causing local loss of membrane potential adjacent to the distal RBB and resulting in conduction block of the advancing wave coming down the RBB. Subsequently, RBBB was likely maintained through a linking effect and repetitive retrograde penetration of the RBB by impulses propagating antegradely over the contralateral left bundle (Figure 1C).
This case highlights intriguing electrophysiological phenomena that can still be observed during a classical pacing maneuver of a common reentry circuit including concealed capture of the His-Purkinje system, electrotonus, linking effect, and functional aberrancy
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Supraventricular arrhythmia with discordant electrocardiographic features. What is the arrhythmia mechanism?
No full textJunctional and AV nodal reentrant tachycardia share common electrocardiographic features, but they differ in their management and outcomes after catheter ablation. This case concerns a 60-year-old female who presented with recurrent episodes of a relatively slow, regular supraventricular arrhythmia. Electrocardiographic features of the arrhythmia were discordant regarding its underlying mechanism. However, careful analysis of 12-lead electrocardiograms, with focus on the effect of spontaneous premature beats, pointed out the arrhythmia etiology. Electrophysiological study and pacing maneuvers defined the arrhythmic substrate that was successfully treated by catheter ablation
Autonomic cardiovascular control and cardiac arrhythmia in two pregnant women with hypertrophic cardiomyopathy: Insights from ICD monitoring.
Full text linkDispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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