Anthony R. Magnano

Autonomic nervous system influences on QT interval in normal subjects

OBJECTIVES We sought to determine whether the relationship between heart rate (HR) and QT interval (QT) differs as HR increases in response to exercise, atropine and isoproterenol. BACKGROUND Autonomic nervous system influences on repolarization are poorly understood and may complicate the interpretation of QT measurements. METHODS Twenty-five normal subjects sequentially underwent graded-intensity bicycle exercise, atropine injection and isoproterenol infusion. Serial 12-lead electrocardiograms were recorded at steady state during each condition and analyzed using interactive computer software. The HR-QT data were modeled linearly and the slopes (quantifying QT adaptation to HR) as well as the QT intervals at 100 beats/min for each intervention were compared by repeated-measures analysis of variance. RESULTS As HR increased, QT was longer for isoproterenol in comparison to exercise or atropine, which were similar. The HR-QT slope (ms/beats/min) was less steep for isoproterenol (-0.83 +/- 0.53) than for atropine (-1.45 +/- 0.21) or exercise (-1.37 +/- 0.23) (p < 0.0001). In comparison to men, women had more negative HR-QT slopes during all interventions. At 100 beats/min, the QT was 364 ms during isoproterenol, which was significantly longer than that during exercise (330 ms) or atropine (339 ms) (p < 0.0001). Isoproterenol produced a dose-dependent increase in U-wave amplitude that was not observed during exercise or atropine. CONCLUSIONS In comparison to exercise and atropine, isoproterenol is associated with much less QT shortening for a given increase in HR and, therefore, greater absolute QT intervals. Our findings demonstrate that autonomic conditions directly affect the ventricular myocardium of healthy subjects, causing differences in QT that are independent of HR.

Sympathomimetic Infusion and Cardiac Repolarization: The Normative Effects of Epinephrine and Isoproterenol in Healthy Subjects

Introduction: Catecholamines are known to affect cardiac repolarization, and provocation with either isoproterenol or epinephrine has been proposed as a tool for uncovering latent repolarization abnormalities. This study systematically compares the effects of isoproterenol and epinephrine infusions on QT interval (QT), T waves and U waves in normal subjects.

Mechanisms of Atrial Tachyarrhythmias Following Surgical Atrial Fibrillation Ablation

Introduction: Typical and atypical atrial flutters (AFLs) and atrial tachycardias (ATs) have been reported in patients with prior surgical atrial fibrillation ablation. The underlying mechanisms for this group of atrial tachyarrhythmias have not been well characterized and the efficacy of catheter ablation in their treatment is unknown.

Neurogenic stunned myocardium in Guillain–Barré syndrome

Article abstract Neurogenic stunned myocardium (NSM), a syndrome of reversible left ventricular dysfunction best described after subarachnoid hemorrhage, has not been associated with peripheral neuropathy. We describe a woman with Guillain–Barré syndrome in whom a syndrome compatible with NSM developed in the setting of a physiologically documented increase in sympathetic cardiovascular tone. This case supports the presumed unifying role of excessive sympathetic nervous system activation in the pathogenesis of NSM.

Catheter ablation of supraventricular tachycardia in the transplanted heart: a case series and literature review.

Clinically important supraventricular arrhythmias are occasionally encountered in patients following cardiac transplantation and the use of catheter ablation as a treatment has been reported. The following three cases are described: (1) atrial flutter, including electroanatomic mapping of the donor and recipient components of the right atrium, (2) a mid‐septal accessory pathway, and (3) atrioventricular nodal reentrant tachycardia (AVNRT). A Medline database search was performed and articles addressing catheter ablation following cardiac transplantation were reviewed. The efficacy of RFA for treating various arrhythmia mechanisms was evaluated based on a summary of published case reports. (PACE 2003; 26:1878–1886)

Cyclic Tachycardia and Hypotension

A 60-year-old man presented to the emergency department with multiple episodes of palpitations, dyspnea, diaphoresis, and lightheadedness. One episode was associated with a syncopal event 1 week before admission. His symptoms recurred during hospitalization, at which time telemetry documented a narrow complex tachycardia at 160 bpm accompanied by hypotension. During the next 24 hours, he developed sinus tachycardia and hypotension followed by normal sinus rhythm and hypertension, which alternated in a cyclic pattern with a periodicity of ≈8 minutes (Figure …

Autonomic modulation of the u wave during sympathomimetic stimulation and vagal inhibition in normal individuals.

Prolonged repolarization time, an important contributor to the pathogenesis of ventricular arrhythmias, is usually identified by a long QT interval (QT) on the ECG but is frequently confounded by the presence of a U wave. The physiological basis and clinical relevance of the U wave is unresolved. To better understand the relationship between the T and U waves, this study examined their behavior during nonresting autonomic conditions. Twenty‐five healthy subjects were evaluated during sympathomimetic infusion with isoproterenol and vagal inhibition with atropine. As heart rate (HR) increased in response to isoproterenol, the QU interval (QU) decreased by an eightfold greater extent than QT. Furthermore, a marked increase in U wave amplitude and decrease in T wave amplitude were observed with T and U wave fusion at higher HRs. During atropine, QU decreased by only a threefold greater extent than QT, T and U wave amplitudes were affected only minimally, and T‐U wave fusion was not observed. These results demonstrate that sympathomimetic stimulation causes striking alterations in the timing and amplitude of U waves that differ from effects on the T wave. These effects are not observed during vagal inhibition. Thus, the U wave represents a component of cardiac repolarization that is electrocardiographically and physiologically distinct from the T wave with a unique response to sympathomimetic stimulation.

Balloon Dilatation of Coronary Sinus Spasm During Placement of a Biventricular Pacing Lead

A 48-year-old man with a history of idiopathic dilated cardiomyopathy, Class 3 symptoms of congestive heart failure, and left bundle-branch block with QRS duration of 164 ms was referred for revision of his implantable cardioverter-defibrillator to a biventricular pacing device. At the time of initial cardioverter-defibrillator implantation at an outside hospital, a coronary sinus (CS) lead was not placed because of …