Bruce B. Lerman

Chapter 72 – Ventricular Tachycardia in Patients with Structurally Normal Hearts

Idiopathic ventricular tachycardia is a generic term that refers to ventricular arrhythmias that originate in hearts without structural disease. Several discrete forms of idiopathic ventricular tachycardia have been identified, and electropharmacologic data suggest that multiple arrhythmogenic mechanisms may account for these arrhythmias. 1 2 Idiopathic ventricular tachycardia has been classified with respect to the ventricle of origin, the response to pharmacologic agents, evidence for catecholamine dependence, and the morphologic features of the arrhythmia (QRS configuration and axis and whether repetitive, nonsustained, or sustained). A mechanistically oriented classification has also been developed and is summarized in Table 72-1 . In general, the response of the arrhythmia to programmed stimulation and to adenosine, verapamil, and propranolol differentiates nearly all forms of idiopathic ventricular tachycardia.

Seizures and Syncope

Syncope, defined as an abrupt loss of consciousness and postural tone caused by cerebral hypoperfusion with spontaneous recovery, is a common clinical problem, accounting for 3% of emergency room visits and 6% of general hospital admissions in the United States (1). A subset of these patients (up to 12%) have an associated convulsive reaction, which may be difficult to differentiate from epilepsy (2). This entity has been designated convulsive syncope. It is estimated that as many as 20–30% of patients diagnosed with epilepsy may in fact suffer from convulsive syncope (3,4). The intent of this chapter is to review the approach to the patient with syncope, with an emphasis toward differentiating syncope from seizures.

993-44 The Ventricular Response in Atrial Fibrillation is Not Chaotic

In nonlinear dynamics, chaos refers to a system that is aperiodic but deterministic (nonrandom). Although the ventricular response during atrial fibrillation (AF) is commonly described as chaotic, it has yet to be demonstrated that this represents chaos in the mathematical sense. A defining characteristic of chaotic systems is sensitive dependence on initial conditions; i.e. similar sequences evolve similarly in the near future, but then diverge exponentially. We developed a nonlinear predictive forecasting algorithm to search for evidence of short-term predictability and sensitive dependence on initial conditions in recordings of 2000 ectopy-and artifact-free RR intervals obtained during routine activity in 5 pts with AF. The algorithm: 1) uses the technique of lags to reconstruct phase spaces with embedding dimensions from 3 to 10,2) the 3 nearest neighbors of a given trajectory are used to predict the evolution of the trajectory from 1 to 10 intervals into the future and 3) the correlation coefficient between predicted and actual evolution is computed for all RR intervals in the time series. The results were compared to test sequences from linear oscillators with high and low signal-noise ratios and a system with chaotic dynamics (the logistic map). Distinct from each of the test sets, the ventricular response in AF was only weakly predictable at all time scales, and did not exhibit sensitive dependence on initial conditions. Conclusion The irregular ventricular response during AF is not governed by a low-dimensional chaotic attractor. Download : Download high-res image (91KB) Download : Download full-size image