The tachycardia which presents with regularly irregular rhythm consists of a broad set of differential diagnoses. We present a case of cycle length alternans tachycardia in a patient, with Ebstein\'s anomaly and describe how a diagnosis was arrived at after careful analysis of electrocardiogram and EGMs.

In the field of cardiac electrophysiology, there is a universal desire: the discovery of a flawless diagnostic maneuver for supraventricular tachycardias (SVTs). This is not merely a wish but a shared odyssey. To improve diagnostic accuracy and achieve sufficient sensitivity and specificity, numerous diagnostic maneuvers have been proposed. However, each has its limitations and prompts a search for new diagnostic techniques. This continuous cycle of discovery and refinement, which we titled \"SVT Quest\" is reviewed in chronological sequence. This adventure in diagnosing narrow QRS tachycardia unfolds in 3 steps: Step 1 involves differentiating atrial tachycardia from other SVTs based on the observations such as V-A-V or V-A-A-V response, ΔAA interval, VA linking, the last entrainment sequence, and response to the atrial extrastimulus. Step 2 focuses on differentiating orthodromic reciprocating tachycardia from atrioventricular nodal reentrant tachycardia based on the observations such as tachycardia reset upon the premature ventricular contraction during His refractoriness, uncorrected/corrected postpacing interval, differential ventricular entrainment, orthodromic His capture, transition zone analysis, and total pacing prematurity. Step 3 characterizes the concealed nodoventricular/nodofascicular pathway and His-ventricular pathway-related tachycardia based on observations such as V-V-A response, ΔatrioHis interval, and paradoxical reset phenomenon. There is no single diagnostic maneuver that fits all scenarios. Therefore, the ability to apply multiple maneuvers in a case allows the operator to accumulate evidence to make a likely diagnosis. Let\'s embark on this adventure!

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BACKGROUND: The impact of the His bundle location and distance from the ablation site on ablation efficacy and complication risk remains unexplored. We determined the correlation between age, height, body mass index (BMI), and the His bundle location, and whether the distance between the His bundle and ablation target (DHIS-ABL) affects ablation safety and efficacy.
METHODS: Overall, 346 patients with atrioventricular nodal re-entrant tachycardia (AVNRT) and 96 with atrioventricular re-entrant tachycardia (AVRT) were retrospectively analyzed. The distance between the His bundle and the coronary sinus ostium (DHis-CS), the height of the His bundle (HHIS), and DHIS-ABL were measured. Electrocardiograms were obtained 3 months post-ablation to assess recurrence and complications.
RESULTS: Multiple linear regression showed that HHIS was negatively correlated with age in both groups. In AVNRT patients, DHIS-ABL was associated with age, height, and BMI; DHIS-CS was only negatively correlated with age. In AVRT patients, there was no significant correlation between the DHIS-ABL and age, height, or BMI. The recurrence rates in the AVNRT and AVRT groups were 0.9% and 8.7%, respectively. Subgroup analysis showed that patients with DHIS-ABL ≤ 10 mm had a higher recurrence rate than those with DHIS-ABL > 10 mm (p = .013). The incidence of third-degree atrioventricular block (AVB) complications was 0.2%.
CONCLUSIONS: HHIS was negatively correlated with age but not with height and BMI. The DHIS-ABL correlated with age, height, and BMI in AVNRT patients. A short DHIS-ABL led to a higher rate of supraventricular tachycardia recurrence; whether this affects AVB risk warrants further studies with larger sample sizes.

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Paediatric supraventricular tachycardia (SVT) is a common arrhythmia of great clinical significance. If not treated promptly, it can cause heart failure and cardiogenic shock. Depending on the patient\'s condition, SVT treatment involves vagal manoeuvres, pharmacological, or direct current cardioversion. The goal of acute SVT management is to immediately convert SVT to a normal sinus rhythm (NSR) and prevent its recurrence. Adenosine is recommended as the first-line treatment for stable SVT by the European Resuscitation Council (ERC) and American Heart Association (AHA) guidelines, when vagal manoeuvres have proven ineffective. The ERC and AHA guidelines recommend the intravenous route of administration. The intraosseous (IO) administration technique is also possible, but still relatively unknown. The aim of this paper is to describe a 3.5-year-old child with SVT that was converted to NSR following IO administration of adenosine. Successful conversion was achieved after the second attempt with the adenosine dose. In the described case, there was no recurrence of SVT.

Primary cardiac tumors in children are rare and mostly benign but can cause significant cardiovascular complications, including arrhythmias. We present a rare case of fetal and neonatal refractory supraventricular tachycardia linked to a probable mitral valve hemangioma, resulting in severe neonatal and maternal morbidity. Despite challenges, pharmacological therapy ultimately successfully managed the condition, highlighting the importance of individualized treatment in such complex cases.

OBJECTIVE: There is no consensus on the best prophylaxis for supraventricular tachycardia (SVT) in infancy. We studied the efficacy and safety of sotalol.
METHODS: This retrospective study comprised infants diagnosed with SVT before 1 year of age and treated with sotalol during 2002-2018 in Stockholm, Sweden. The patients\' characteristics, comorbidities, sotalol dosages, QT intervals and outcomes were extracted from their medical records.
RESULTS: We studied 85 infants (65% boys) with a median age of eight (range 0-288) days at the time of diagnosis, including 78 with re-entry tachycardia. Sotalol was completely or partially successful in the 67/75 patients who completed the treatment, as well as in four of the seven patients with other tachycardia mechanisms. The 48 infants with postnatal debut had significantly higher success rates than the 27 with foetal debut (96% vs. 78%, p = 0.04). Prolongation of corrected QT (QTc) intervals of ≥450 ms occurred in 16% of the total cohort and two patients with QTc intervals of ≥500 ms had their treatment changed. There were no cases of proarrhythmia after sotalol treatment.
CONCLUSIONS: Sotalol provided effective and safe prophylaxis for SVT during infancy. QTc prolongation rarely caused treatment discontinuation and there were no cases of proarrhythmia.

BACKGROUND: Heart disease and strokes are leading global killers. While atrial arrhythmias are not deadly by themselves, they can disrupt blood flow in the heart, causing blood clots. These clots can travel to the brain, causing strokes, or to the coronary arteries, causing heart attacks. Additionally, prolonged periods of elevated heart rates can lead to structural and functional changes in the heart, ultimately leading to heart failure if untreated. The left atrium, with its more complex topology, is the primary site for complex arrhythmias. Much remains unknown about the causes of these arrhythmias, and computer modeling is employed to study them.
METHODS: We use N-body modeling techniques and parallel computing to build an interactive model of the left atrium. Through user input, individual muscle attributes can be adjusted, and ectopic events can be placed to induce arrhythmias in the model. Users can test ablation scenarios to determine the most effective way to eliminate these arrhythmias.
RESULTS: We set up muscle conditions that either spontaneously generate common arrhythmias or, with a properly timed and located ectopic event, induce an arrhythmia. These arrhythmias were successfully eliminated with simulated ablation.
CONCLUSIONS: We believe the model could be useful to doctors, researchers, and medical students studying left atrial arrhythmias.