Michael H. Kim

Diagnostic value of tachycardia features and pacing maneuvers during paroxysmal supraventricular tachycardia.

OBJECTIVESnThe purpose of this prospective study was to quantitate the diagnostic value of several tachycardia features and pacing maneuvers in patients with paroxysmal supraventricular tachycardia (PSVT) in the electrophysiology laboratory.nnnBACKGROUNDnNo study has prospectively compared the value of multiple diagnostic tools in a large group of patients with PSVT.nnnMETHODSnOne hundred ninety-six consecutive patients who had 200 inducible sustained PSVTs during an electrophysiology procedure were included. The diagnostic values of four baseline electrophysiologic parameters, nine tachycardia features and five diagnostic pacing maneuvers were quantified.nnnRESULTSnThe only tachycardia characteristic that was diagnostic of atrioventricular (AV) nodal reentry was a septal ventriculoatrial (VA) time of <70 ms, and no pacing maneuver was diagnostic for AV nodal reentry. An increase in the VA interval with the development of a bundle branch block was the only tachycardia characteristic that was diagnostic for orthodromic tachycardia, but it occurred in only 7% of all tachycardias. An atrial-atrial-ventricular response upon cessation of ventricular overdrive pacing was diagnostic of atrial tachycardia, and this maneuver could be applied to 78% of all tachycardias. Burst ventricular pacing excluded atrial tachycardia when the tachycardia terminated without depolarization of the atrium, but the result could be obtained only in 27% of patients.nnnCONCLUSIONSnThis prospective study quantitates the diagnostic value of multiple observations and pacing maneuvers that are commonly used during PSVT in the electrophysiology laboratory. The findings demonstrate that diagnostic techniques rarely provide a diagnosis when used individually. Therefore, careful observations and multiple pacing maneuvers are often required for an accurate diagnosis during PSVT. The results of this study provide a useful reference with which new diagnostic techniques can be compared.

Effect of Chronic Amiodarone Therapy on Defibrillation Energy Requirements in Humans

Amiodarone Effect on Defibrillation Energy Requirement. Introduction: The effect of oral amiodarone therapy on defibrillation energy requirements in patients with an implantable defibrillator has not been established.

Complete atrioventricular block after valvular heart surgery and the timing of pacemaker implantation

The natural history of patients who developed complete atrioventricular block after valvular heart surgery was investigated to determine the optimal timing for pacemaker implantation. Patients who developed complete atrioventricular block within 24 hours after operation, which then persisted for > 48 hours, were unlikely to recover; such patients could potentially undergo earlier pacemaker implantation if otherwise ready for discharge.

Effects of Digoxin on Acute, Atrial Fibrillation–Induced Changes in Atrial Refractoriness

BackgroundAtrial fibrillation (AF) shortens the atrial effective refractory period (ERP) and predisposes to further episodes of AF. The acute changes in atrial refractoriness may be related to tachycardia-induced intracellular calcium overload. The purpose of this study was to determine whether digoxin, which increases intracellular calcium, potentiates the acute effects of AF on atrial refractoriness in humans. Methods and ResultsIn 38 healthy adults, atrial ERP was measured at basic drive cycle lengths (BDCLs) of 350 and 500 ms after autonomic blockade. Nineteen patients had been treated with digoxin for 2 weeks. After a several-minute episode of AF, atrial ERP was measured serially at alternating BDCLs. Compared with pre-AF ERPs, the first post-AF ERPs were significantly shorter in both the digoxin and the control groups (P <0.001). The post-AF ERP at a BDCL of 350 ms shortened to a greater degree in the digoxin group (37±16 ms) than in the control group (20±13 ms, P <0.001); similar changes occurred at a BDCL of 500 ms. During post-AF determinations of the atrial ERP, secondary AF episodes occurred significantly more often in the digoxin group (32% versus 16%;P <0.04). ConclusionsAfter a brief episode of AF, digoxin augments the shortening that occurs in atrial refractoriness and predisposes to the reinduction of AF. These effects occur in the setting of autonomic blockade and therefore are more likely to be due to the effects of digoxin on intracellular calcium than to its vagotonic effects.

Electrogram Polarity and Cavotricuspid Isthmus Block During Ablation of Typical Atrial Flutter

Electrogram Polarity in Atrial Flutter Ablation. Introduction: The atrial activation sequence around the tricuspid annulus has been used to assess whether complete block has been achieved across the cavotricuspid isthmus during radiofrequency ablation of typical atrial flutter. However, sometimes the atrial activation sequence does not clearly establish the presence or absence of complete block. The purpose of this study was to determine whether a change in the polarity of atrial electrograms recorded near the ablation line is an accurate indicator of complete isthmus block.

Effects of β-Adrenergic Blocking Therapy on Left Ventricular Diastolic Relaxation Properties in Patients With Dilated Cardiomyopathy

Background—The hemodynamic mechanism for the improvement in left ventricle (LV) end-diastolic pressure in cardiomyopathy patients treated with β-adrenergic blocking agents is controversial. We hypothesized that the salutary effect of this kind of therapy on LV end-diastolic pressure would be indicative of an improvement in late, passive diastolic relaxation properties. Methods and Results—We studied 14 cardiomyopathy patients in normal sinus rhythm with no arteriographic evidence of coronary artery disease and an LV ejection fraction of ≤40% by radionuclide angiography both before and after 6 months of metoprolol therapy with simultaneous micromanometry and biplane cineventriculography. Four comparable patients who were not treated with metoprolol were studied in a similar fashion and served as control subjects. In those receiving metoprolol, LV end-diastolic pressure decreased (P=0.001). The isovolumic relaxation index, τln, shortened (P=0.03). In a similar fashion, the LV chamber stiffness constant, κ, ...

Electrocardiographic predictors of successful ablation of tachycardia or bigeminy arising in the right ventricular outflow tract

Among various electrocardiographic variables, the QRS duration in V2 was found to be the best discriminator of outcome in patients undergoing radiofrequency catheter ablation of the right ventricular outflow tract tachycardia and/or bigeminy. If the QRS duration is <160 ms in lead V2, the probability of successful ablation is lower than if the QRS duration is longer.

Atrial fibrillation after coronary surgery: comparison between different health care systems

AIMSnNo studies have evaluated the influence of management strategies in different health insurance environments on atrial fibrillation (AF). This observational study compared the incidence of and treatment strategies for postoperative AF after primary coronary bypass surgery.nnnMETHODS AND RESULTSnOne insurance and one public funded location was compared: University of Michigan Health Center (USA, n=272) and Tampere University Hospital (Finland, n=314). USA patients had more co-morbidities and were treated more aggressively after acute myocardial infarction. More Finns were on beta-blockers both preoperatively (93 vs. 68%, P<0.001) and postoperatively (97 vs. 66%, P<0.001). However, AF was more frequent among Finns (38 vs. 29%, P=0.037) and present on 4.6% of cases when transferred postoperatively. No USA patients had AF at time of discharge. Mean length of stay was 8.6 days at USA, and not affected by AF. The incidence of in-hospital death, strokes and multiorgan failures was similar. Multivariable analysis, adjusted for site and selection biases (propensity analysis) revealed increasing age [OR=1.063 (1.042, 1.084), P<0.0001] and use of radial arteries [OR=2.175 (1.071, 4.417), P=0.032) to be independent predictors to the incidence of postoperative AF.nnnCONCLUSIONSnWe found several major differences in patient selection and treatment strategies among primary coronary bypass patients managed in the two institutions. Despite the marked practice variation, the incidence of postoperative AF was rather similar. Despite routine use of beta-blockers, AF occurred in 29-38% of patients. However, the length of stay was not particularly affected by postoperative AF.

Prevalence and significance of Exit Block During Arrhythmias Arising in Pulmonary Veins

Exit Block. Introduction: Recent studies described the occurrence of conduction block within pulmonary veins. The purpose of this study was to evaluate the prevalence of exit block during arrhythmias that arise in pulmonary veins.

Effect of electrode polarity on the energy required for transthoracic atrial defibrillation.

Two hundred patients with atrial fibrillation underwent transthoracic cardioversion using adhesive electrodes positioned at the apex and right infraclavicular area, and the apex electrode was randomly selected to serve as the cathode or anode. The mean defibrillation energy requirement with the cathodal configuration was significantly lower than with the anodal configuration.