A 56-year-old man with an implantable cardioverter-defibrillator (ICD) presented with unexplained heart palpitations, which were usually aggravated after ingesting alcohol. He had a history of coronary artery bypass graft surgery 8 years ago, and an ICD was placed (i.e. a single ventricular shock coil with integrated atrial-sensing rings [VDD ICD lead]) 1.5 years ago for primary prevention of sudden cardiac death associated with ischemic cardiomyopathy. Repeated electrocardiograms and echocardiograms showed no evidence of atrial flutter-fibrillation; this was clearly demonstrated using several atrial electrogram strips during the ICD analysis.
Atrial Fibrillation ; Cardiomyopathies ; Coronary Artery Bypass ; Death, Sudden, Cardiac ; Defibrillators* ; Defibrillators, Implantable ; Electrocardiography ; Electrophysiologic Techniques, Cardiac ; Heart ; Humans ; Middle Aged ; Primary Prevention ; Shock ; Stroke ; Transplants

Atrial fibrillation (AF) is a common arrhythmia, and restoration of sinus rhythm is very important in treating this condition. Recently, we experienced a rare case of immediate cardioversion from AF after successful revascularization in a patient with chronic total proximal part of the right coronary artery (RCA) occlusion. A 72-year-old woman with hypertension and diabetes mellitus experienced chest discomfort. An electrocardiogram (ECG) revealed AF. Despite 3 months of appropriate pharmacologic therapy for AF, she continued to complain of effort angina, which was relieved by sublingual nitroglycerin. She subsequently underwent cardiac catheterization, which revealed chronic total occlusion of the proximal RCA with grade III collateral vessels from the left anterior descending (LAD) artery. Balloon angioplasty and stenting restored the blood flow of the RCA, and the AF promptly reverted to sinus rhythm. There was no recurrence of AF over 12 months of follow-up at the outpatient clinic.
Aged ; Ambulatory Care Facilities ; Angioplasty, Balloon ; Arrhythmias, Cardiac ; Arteries ; Atrial Fibrillation* ; Cardiac Catheterization ; Cardiac Catheters ; Coronary Occlusion ; Coronary Vessels ; Diabetes Mellitus ; Electric Countershock ; Electrocardiography ; Female ; Follow-Up Studies ; Humans ; Hypertension ; Myocardial Ischemia ; Nitroglycerin ; Perfusion* ; Recurrence ; Stents ; Thorax

BACKGROUND AND OBJECTIVES: In cases of radiofrequency catheter ablation (RFCA) for patients with atrioventricular nodal re-entrant tachycardia (AVNRT), complete elimination of slow pathway is not always achievable. Furthermore, in situations of the so-called modified slow pathway, the underlying mechanism of tachycardia elimination remains unclear. SUBJECTS AND METHODS: Patients who underwent RFCA for AVNRT, and showed persistence of dual atrioventricular nodal physiology but no induction of AVNRT after ablation were enrolled. We measured electrophysiologic parameters before and after the ablation procedure. RESULTS: The study subjects included 31 patients (39% men; mean age 43±19 years). The RR interval, Wenckebach cycle length of AV node, slow pathway effective refractory period, maximal AH interval of fast pathway and slow pathway showed no significant changes before and after ablation. However, fast pathway effective refractory period (360±67 vs. 304±55, p<0.001) and differences between slow pathway effective refractory period and fast pathway effective refractory period (90±49 vs. 66±35, p=0.009) were decreased after slow pathway ablation. CONCLUSION: We suggest a possible relationship between the mechanism of tachycardia elimination in AVNRT and an alteration of the re-entrant circuit by removal of the atrial tissue in Koch's triangle. This may be a critical component of providing the excitable gap for the maintenance of tachycardia rather than the electrical damage of slow pathway itself.
Atrioventricular Node* ; Catheter Ablation ; Humans ; Male ; Physiology* ; Tachycardia*

BACKGROUND: The Htr3a antagonist, ondansetron, has been reported to prolong the QT interval and induce Torsades de pointes in the treatment of postoperative nausea and vomiting. To explore the mechanisms underlying these findings, we examined the effects of ondansetron on the mouse cardiac voltage-gated K⁺ (Kv) channel. METHODS AND RESULTS: Ondansetron increased QT intervals in late pregnant (LP) mice. We measured the Kv channels in freshly isolated left ventricular (LV) myocytes from non-pregnant (NP) and late pregnant (LP) mice, using patch-clamp electrophysiology. Ondansetron blocked Kv current at a dose of 50 µM, and reduced the amplitude of peak current densities in a dose-dependent manner (0, 1, 5, 50 µM), in LP but not in NP mice. In contrast, serotonin and the Htr3 agonist, m-CPBG, increased Kv current densities in NP, but not in LP mice. Interestingly, during pregnancy, serum serotonin levels were markedly increased, suggesting the saturation of the effect of serotonin. Immunostaning data showed that Kv4.3 protein and Htr3a co-localize at the membrane and t-tubule of cardiomyocytes. Moreover, Kv4.3 membrane trafficking was enhanced in response to Htr3a-mediated serotonin stimulation in NP, but not in LP mice. Membrane analysis showed that serotonin enhances Kv4.3 membrane trafficking in NP, but not LP mice. CONCLUSION: Ondansetron reduced Kv current densities, and reduced the Kv4.3 membrane trafficking in LP mouse ventricular cardiomyocytes. This data suggests that QT prolongation by ondansetron is mediated by the reduction of Kv current densities and Kv4.3 membrane trafficking.
Animals ; Electrophysiology ; Membranes ; Mice* ; Muscle Cells* ; Myocytes, Cardiac ; Ondansetron* ; Postoperative Nausea and Vomiting ; Pregnancy ; Serotonin ; Torsades de Pointes

No abstract available.
Defibrillators, Implantable* ; Humans ; Magnetic Resonance Imaging*

The use of both magnetic resonance imaging (MRI) and pacing devices has vastly increased worldwide in recent years. A significant number of implanted patients will likely need monitoring using magnetic resonance imaging (MRI) over the course of the lifetime of their device. Some studies have demonstrated that with appropriate precautions, MRI can be safely performed in patients with selected implantable pacemakers. However, MRI is still contraindicated in patients with pacemakers. Recently, new pacing systems have been specifically designed for safe use in the MRI environment. The first reported experience suggests that the technology is safe and may allow patients with these new pacemakers to undergo MRI. This review will describe the outstanding issues and controversies surrounding the safety of MRI in patients with pacemakers, and the potential benefits of the new MRI-conditional technology. We will also discuss how to decide whether an MRI-conditional system should be implanted, and highlight key issues that warrant further studies.
Humans ; Magnetic Resonance Imaging*

Magnetic resonance imaging (MRI) is increasingly becoming a standard of care and hence, an unmatched and irreplaceable diagnostic method. However, patients with implantable cardiac devices have not been guaranteed safety when exposed to the MRI environment. For this reason, Medtronic has taken the initiative and developed SureScan™ devices, which are MRI compatible devices for patients that would enable them to undergo MRI scans safely. The current technological developments in magnetic resonance (MR) and their clinical applications are discussed.
Cardiology ; Humans ; Magnetic Resonance Imaging* ; Methods ; Safety Management ; Standard of Care

Gaining a complete understanding of the physics of magnetic resonance imaging (MRI) is a daunting task. However, as cardiac MRI is being increasingly used in cardiovascular medicine, understanding the basics of MRI physics has become necessary for appropriate assessment of the images and correct interpretation of the findings. MRI is an imaging modality that utilizes the magnetic potential of the body. When the body is placed inside an extremely strong magnetic field, the protons of the water molecules inside the body align along the field, after which, the proton spins are exposed to a radiofrequency pulse with a frequency that matches the precession frequency of the protons in the body. This causes the precession of the protons to resonate and increase in amplitude. Simultaneously, three-dimensional magnetic gradients are applied for targeting specific slices of the body and discriminating the two-dimensional orientation of the organs; this is followed by emission of electromagnetic pulses generated by the resonance with varying frequencies and phases from various parts of the body. As soon as the input pulse has ceased, the machine starts absorbing the electromagnetic pulses that are being emitted by the body. These waves are mathematically converted into images of the internal organs and are visualized through rapid computer processing. To improve the contrast between tissues and abnormal structures, specific pulse sequences and weighting of the images are applied. This review summarizes the principles of MRI physics for clinicians who lack an understanding of fundamental physics.
Magnetic Fields ; Magnetic Resonance Imaging ; Magnets ; Protons ; Water

BACKGROUND AND OBJECTIVES: Previous studies have demonstrated an association between several single nucleotide polymorphisms and atrial fibrillation (AF). We hypothesized that the phenotypes of AF patients were associated with common AF susceptibility alleles. SUBJECTS AND METHODS: A total of 659 patients (57±9 years, 76% male) with AF who underwent catheter ablation and 659 age, and sex-matched controls were genotyped for the common AF susceptibility alleles rs2200733 and rs6843082 at 4q25, rs2106261 at ZFHX3, and rs13376333 at KCNN3. The phenotypes of AF patients, including electroanatomical characteristics of the left atrium and recurrence after ablation, were compared. RESULTS: The rs2200733 variant allele carriers have larger left atrium volume (128.5±40.7 vs. 113.5±29.2 mL, p=0.020), longer PR interval (185.9±32.6 vs. 174.8±21.9 ms, p=0.018), and higher amplitude of negative P-wave terminal force in Lead V₁ (0.07±0.04 vs. 0.05±0.04 mV, p=0.015) on electrocardiography than those without the variant allele. When the patients were assigned to three groups according to the number of variant alleles (Group A: no variant, n=15; Group B: 1 variant, n=158; Group C: 2 variants, n=439), incremental prognostic value, according to the number of variant alleles, was demonstrated (Log Rank p=0.015). Multivariate Cox regression analysis showed that persistent AF (OR 1.677, 95% CI 1.176-2.381, p=0.004) and the number of variants (OR 1.552, 95% CI 1.099-2.222, p=0.015) were independent predictors for recurrence of AF. CONCLUSION: This study showed the common AF susceptibility alleles at 4q25 and ZFHX3 are associated with electroanatomical characteristics of the left atrium and the clinical outcomes of catheter ablation in Korean patients with AF.
Alleles ; Atrial Fibrillation* ; Catheter Ablation* ; Electrocardiography ; Heart Atria* ; Humans ; Phenotype ; Polymorphism, Single Nucleotide* ; Recurrence

BACKGROUND AND OBJECTIVES: Myocardial wall stretch is the main trigger for pro-brain natriuretic peptide (pro-BNP) secretion. The reduced heart rate associated with bradyarrhythmia increases stroke volume, resulting in increased wall tension. Therefore, we propose that bradyarrhythmia could increase plasma N-terminal pro-BNP (NT-pro-BNP) levels. SUBJECTS AND METHODS: We enrolled 125 patients who received a temporary pacemaker because they had sinus node dysfunction (SND) or atrioventricular blocks (AVBs). Patients with renal dysfunction, hyperkalemia, reduced left ventricular systolic function (left ventricular ejection fraction [LVEF], <40%), and atrial fibrillation were excluded. Heart failure (HF) was defined as an NT-pro-BNP level of >300 pg/mL. We evaluated history of hypertension, diabetes mellitus, and ischemic heart disease, plasma NT-pro-BNP levels, body mass index (BMI), LVEF, left atrial diameter (LAD), and escape rhythm rate. RESULTS: The log plasma NT-pro-BNP level of the patients with AVBs was significantly increased compared to that of the patients with SND (3.17±0.55 vs. 2.93±0.64 pg/mL, respectively; p=0.03). The incidence of HF was 72.5% (106 patients; 44 male patients). Further, the incidence of HF was significantly higher among patients with AVBs than among patients with SND. The type of bradyarrhythmia was found to be the only predictor of HF after adjusting for age, history of hypertension, LAD, and LVEF. The LVEF, LAD, and ventricular rate were similar between the 2 groups. CONCLUSION: As in the case of patients with tachyarrhythmia, bradyarrhythmia may increase plasma NT-pro-BNP levels, leading to HF. Therefore, the possibility of HF should be considered in patients with bradyarrhythmia.
Arrhythmias, Cardiac ; Atrial Fibrillation ; Atrioventricular Block ; Body Mass Index ; Bradycardia* ; Diabetes Mellitus ; Heart Failure ; Heart Rate ; Humans ; Hyperkalemia ; Hypertension ; Incidence ; Male ; Myocardial Ischemia ; Plasma* ; Sick Sinus Syndrome ; Stroke Volume ; Tachycardia ; United Nations