Accessory Pathway-Mediated Tachycardias: Precision Electrocardiology Through Standard and Advanced Electrocardiogram Recording Techniques.

An accessory pathway (AP) can be apparent during sinus rhythm if it depolarizes part of the ventricles ahead of the normal wave front from the conduction system. An AP can generate an anatomic circuit able to sustain a macroreentrant atrioventricular reentrant tachycardia. This arrhythmia can engage the normal conducting system in an antegrade direction or retrogradely, generating, respectively, a narrow or a wide complex tachycardia. The combined use of a standard electrocardiogram and an esophageal recording-pacing can be particularly useful in the first approach to patients with Wolff-Parkinson-White syndrome, further stratifying patients requiring electrophysiology study and transcatheter ablation.

Bidirectional ventricular tachycardia induced by caffeine poisoning.

Bidirectional ventricular tachycardia (BVT) is a tachyarrhythmia characterized by 180-degree beat-to-beat alteration in the QRS axis. BVT is traditionally known as an electrocardiography (ECG) finding pathognomonic of digitalis poisoning and a hallmark of catecholamine-induced ventricular tachycardia. Apart from digitalis poisoning, aconitine poisoning is the only reported cause of poisoning-related BVT, and no report of caffeine-poisoning-related BVT is as yet available. A-27-year-old woman was transported to hospital with cardiac arrest from ventricular fibrillation after taking a massive dose of a caffeine-containing supplement (corresponding to 6 g of caffeine) 6 h before presentation. Return of spontaneous circulation (ROSC) was achieved by defibrillation. She developed BVT after ROSC. Hemodialysis was performed to remove the causative drug from the blood, with subsequent resolution of BVT and hemodynamic stabilization. At presentation, she had a blood caffeine concentration of 232 µg/mL. A suggested mechanism of development of BVT is that increased intracellular calcium concentration causes delayed afterdepolarization, which induces alternate occurrence of triggered activities within different His-Purkinje fibers, and thereby produces characteristic ECG findings. Caffeine acts on the ryanodine receptor to promote calcium release from the sarcoplasmic reticulum, and thus can induce BVT via the same mechanism. Caffeine poisoning can be treated by dialysis. In cases of BVT induced by caffeine poisoning, hemodynamic stabilization can be achieved by emergency dialysis.

Advanced Cardiac Signal Recording.

Implantable loop recorders allow prolonged and continuous single-lead electrocardiogram recording, with the pivotal addition of remote monitoring. They have significantly shortened time to electrocardiographic diagnosis and appropriate therapy of many bradyarrhythmias/tachyarrhythmias and proved helpful in arrhythmia burden definition, offering invaluable information in the diagnostic workup for syncope and atrial fibrillation. Advanced cardiac signal recording is also possible by transesophageal catheters. They have been used to orient diagnosis during wide and narrow QRS complex tachycardias and also to perform minimally invasive pacing. Intracardiac electrophysiologic study remains, however, essential for diagnosis of several arrhythmias in the perspective of curative catheter ablation.

High-Density Mapping and Ablation of Primary Nonfocal Left Atrial Tachycardia: Characterizing a Distinct Arrhythmogenic Substrate.

OBJECTIVES: This study sought to characterize primary left atrial tachycardia (LAT) mechanisms, electrical properties and substrate using high-density mapping. BACKGROUND: Nonfocal LAT can be found in patients without prior substrate modifying interventions. METHODS: Of 223 catheter ablation procedures for LAT 15 patients (60% male, age 74 ± 6 years) had nonfocal AT and no history of LA ablation or cardiac surgery. RESULTS: AT (mean cycle length 244 ± 32 ms) were identified as macro-re-entry (12 of 15) or localized re-entry (3 of 15). High-density electroanatomical mapping (EAM, performed in 13 patients) revealed a high proportion of low voltage areas (LVA, <0.45 mV, 41 ± 22%). Anterior LVA regions were predominantly related to the macro-re-entry and directly perpetuating the re-entrant circuit in 8 patients by formation of a conductive channel (width: 14 ± 7 mm, length: 11 ± 3 mm) between the inferior pole of the scar and the mitral valve (MV) annulus with electrophysiological features of diseased tissue. A tailored anterior ablation line successfully terminated AT in 9 patients (6 dominant circuit MV dependent, 3 dominant circuit scar dependent AT), while a lateral isthmus line was performed in 2 patients. Localized re-entries were successfully targeted by local ablation. Acute successful ablation could be achieved in 14 of 15 patients leading to a freedom from any arrhythmias in 9 of 15 patients (60%) after follow-up of 343 ± 203 days. CONCLUSIONS: Patients with nonfocal left atrial tachycardia without previous iatrogenic interventions show evidence for advanced atrial myopathy. High-density mapping revealed involvement of the anterior LA and allows for an individualized ablation approach beyond strategies usually applied in consecutive AT.

Evaluation of Electrophysiological Mechanisms of Post-Surgical Atrial Tachycardias Using an Automated Ultra-High-Density Mapping System.

OBJECTIVES: This study aimed to evaluate the electrophysiological mechanisms of post-surgical atrial tachycardias (ATs) during mapping with an automated high-resolution mapping system (Rhythmia, Boston Scientific, Marlborough, Massachusetts). BACKGROUND: Mapping and ablation of post-operative ATs following previous open-heart surgery is often challenging because the potential mechanisms remain incompletely understood. METHODS: Fifty-one consecutive patients underwent mapping and ablation of post-surgical ATs. RESULTS: A total of 64 ATs were identified, and the mechanism was macro re-entry in 58 of 63 (92.1%) ATs, focal in 4 ATs, localized micro re-entry in 1 AT, and undetermined in 1 AT. Of 11 patients who underwent surgical repair of congenital heart disease, 6 (54.5%) had peri-tricuspid re-entrant AT, 5 had either right atrial (RA) free-wall incisional ATs or figure-8 re-entrant ATs, with an isthmus between the tricuspid annulus and the RA free-wall incision or between the incisions, and none had left atrial (LA) or focal ATs. In 32 patients with valve replacement and 8 who underwent valvuloplasty, peri-tricuspid ATs were observed in 14 (43.4%) and 6 (75%) patients, RA free wall or septal incisions-related ATs were seen in 7 and 2 patients, and LA macro re-entrant ATs were observed in 12 patients and 1 patient, respectively. A macro pseudo re-entry pattern was identified in 8 of 51 patients (15.7%). All these activations could be easily excluded by manually moving the window of interest, except in 2 cases with a figure-8 re-entrant configuration. CONCLUSIONS: RA macro re-entrant ATs predominate, irrespective of the types of initial surgical procedures, but LA ATs occur more frequently in patients with valve replacement. Pseudo re-entry atrial activation is common and easily recognized by adjusting the mapping window.

A Fatal Case of Amlodipine Toxicity Following Iatrogenic Hypercalcemia.

Using calcium salts in management of amlodipine overdose is challenging. A 25-year-old male with known history of adult polycystic kidney disease presented with hypotension, tachycardia, and intact neurological status after ingestion of 450 mg of amlodipine. Immediately, normal saline infusion and norepinephrine were initiated. Two grams of calcium gluconate was injected, followed by intravenous infusion of 1.16 mg/kg/h. The patient was put on insulin-glucose protocol to maintain euglycemia and hyperinsulinemia. Electrocardiography demonstrated junctional rhythm. Serum creatinine was 2.5 mg/dL with metabolic acidosis. By the end of 24 h post-admission, his consciousness, blood pressure, and urine output were normal. Almost 32 h post-admission, he became disoriented and his oxygen saturation decreased and therefore was mechanically ventilated. Second chest X-ray showed pulmonary edema. Serum calcium level increased to 26.1 mg/dL. Calcium was discontinued, and furosemide infusion and calcitonin were intravenously administrated. Urine output increased and hemodialysis improved pulmonary edema and serum calcium level with no change in consciousness. Three days after admission, the patient became anuric and developed multi-organ failure and died 5 days post-admission. To avoid the consequences of excessive infusion of calcium in renal failure patients, the minimum calcium dose with close monitoring is recommended.

Validation of device algorithm to differentiate pacemaker-mediated tachycardia from tachycardia due to atrial tracking.

BACKGROUND: Current cardiac devices cannot always differentiate between pacemaker-mediated tachycardia (PMT) and tracking of sinus or atrial tachycardia. We previously derived a novel algorithm for distinguishing the 2 mechanisms based on the specific termination response to postventricular atrial refractory period extension, atrial rates, and changes in atrial electrogram morphology. OBJECTIVE: The purpose of this study was to evaluate how this algorithm would have performed in a clinical setting based on previously recorded PMT events. METHODS: We applied our algorithm to a database of 122 de-identified stored electrograms that were classified as PMT by 43 remotely monitored devices. RESULTS: Of the 122 events stored as "PMT," 3 episodes were excluded because the device recording was consistent with atrial fibrillation. Of the remaining 119 episodes, our algorithm was able to correctly reclassify 92 events (77%) as tracking of sinus or atrial tachycardia rather than true PMT. The VAV response following postventricular atrial refractory period extension, which is specific to tracking of atrial or sinus tachycardia, was seen in 72% of these cases. Changes in atrial rate and atrial electrogram morphology were able to reclassify the remainder of episodes. Finally, we observed that 12 of 83 episodes (14%) misclassified as PMT in cardiac resynchronization devices resulted in loss of cardiac biventricular pacing. CONCLUSION: Applying a novel diagnostic algorithm to current cardiac devices improves the proper diagnosis of true PMT rather than tracking of atrial or sinus tachycardia. Enhanced accuracy of diagnosis reduces the likelihood of inappropriate clinical decisions.

Diagnosis and management of phantom tachycardias based on an electrophysiologically guided approach.

BACKGROUND: Non-documented palpitations, or phantom tachycardias, are palpitations deemed to be of unknown origin after evaluation with conventional diagnostic tools, such as 12-lead electrocardiogram and Holter recordings. Our aim was to determine the diagnostic value of an electrophysiologic study (EPS) and its role in the management of patients presenting with non-documented palpitations. METHODS: We performed EPS in 78 consecutive patients with repeatable, poorly tolerated symptoms of paroxysmal, non-documented tachycardia, the absence of structural heart disease and at least one 24-h Holter recording. The duration and frequency of palpitations was registered in each patient. RESULTS: Long-lasting palpitations (>1 hour) were present in 15.4% of patients. Half of patients reported symptoms less often than once per week. Only 13/78 patients (16.6%) had normal EPS findings, while dual pathways at the AV node ± echo beats were identified in another 13 patients without inducible tachycardia. At least one tachycardia event was induced in 52 patients (66.6%). AVNRT was provoked in 32 patients (41.2%). Ablation was performed in 14/52 patients with inducible tachycardia (26.9%). Slow pathway ablation was also performed in three patients with dual AV pathways and atrial echo-beats but without provoked tachycardia. Follow-up data were available in 52 patients, and 84.6% had fewer or no clinical recurrences. CONCLUSIONS: EPS is safe and of enhanced diagnostic value in patients with unexplained palpitations because only 1/6 had negative results. EPS also provided an explanation about the mechanism of arrhythmia and successfully guided the management of these patients, as well as enhanced improvement in the quality of life.

An 88-year-old man with syncope and an alternating axis.

CLINICAL INTRODUCTION: An 88-year-old man, admitted to the emergency room (ER) after three episodes of syncope within 1 day, reported a precursory of syndrome of light-headedness with rapid palpitations that led to an abrupt loss of consciousness. After undergoing percutaneous and surgical revascularisation, he started complaining of chest and back discomfort for the past 20 years and searching for help from Chinese medicine, Fuzi. He had history of chronic renal failure and heart failure, but denied neither taking digitalis nor having family history related to sudden death.On arrival, heart rate was 150 bpm and blood pressure (BP) by cuff was 91/81 mm Hg (non-invasive BP could not be accurately obtained during tachycardia) plus oedema on both lower extremities. There were diffuse crackles and indistinct heart sounds on auscultation.The admission ECG was performed in the ER (figure 1). His serum creatinine was 139.7 mmol/L, serum K(+) was 4.7 mmol/L, N-terminal of the prohormone brain natriuretic peptide was highly elevated (12 000 pg/mL) and troponin I was negative. QUESTION: What is the most likely diagnosis suggested based on the patient's ECG and history? Aconite poisoningDigitalis toxicityCatecholaminergic polymorphic ventricular tachycardia (CPVT)Andersen-Tawil syndrome (ATS).