Journal of electrocardiology
-
This study employs a bifurcation analysis approach to elucidate the effect of the key ion channels on cardiac arrhythmias and thereby explain the efficacy of antiarrhythmic drugs in controlling arrhythmias. The model used for the analysis contains the key ion channels involved in the ventricular action potential--fast sodium, slow calcium, and background potassium channels. The cardiac tissue is modeled by a ring structure. ⋯ In the neighborhood of the CRS, the cycle length oscillates with an interesting pattern that depends on ring size and drug type. Although a critical reentrant loop length for stable reentrant excitation has been investigated for a long time, this study is the first demonstration of how the key ion channels in the plasma membrane affect the loop length. Furthermore, the analysis approach provides a theoretical basis for the increased mortality associated with class I drug use in the Cardiac Arrhythmia Suppression Trial Team.
-
A mathematic description of the behavior of the Bazett-corrected QTc interval during exercise was developed from the underlying relationship between the unadjusted QT interval and heart rate in 94 normal men. Measurements were made from digitized precordial lead V5 complexes that were averaged by computer over 20-second periods at upright control (mean rate, 78 beats/min), during moderate exercise (mean rate, 125 beats/min), and at peak effort (mean rate, 162 beats/min), using a gently graded treadmill protocol that produces small heart rate increments between 2-minute stages. ⋯ As a consequence of this linearity, the behavior of the QTc interval over a range of heart rates generally found during exercise could be modeled as a function of the slope (m) and intercept (b) of the observed relationship, since the Bazett relationship QTc = QT[ms]/R-R0.5 can, in this context, be rewritten simply as QTc = (481 - 1.32HR)/(60/HR)0.5, which reproduces the observed biphasic QTc interval behavior. Plots of the generalized equation QTc = (b - mHR)/(60/HR)0.5 allow theoretical exploration of QTc interval behavior that might result from varied disorders with different slopes (m) and intercepts (b), and these regression-based descriptors of the QT-heart rate relationship may provide useful, additional definitions of normal and abnormal QT interval behavior during exercise.