Right ventricular radiofrequency ablation of ventricular tachycardia after myocardial infarction.

Radiofrequency transcatheter ablation of ventricular tachycardia in the setting of a prior myocardial infarction is typically performed with application of energy to the left ventricular endocardium. In this article, two cases are described in which successful radiofrequency transcatheter ablation of ventricular tachycardia occurred with energy delivery to the right ventricular septum after failed ablation attempts from the left ventricle. Both patients had tachycardias with a left bundle branch block morphology and markedly presystolic activity recorded from the right ventricular septum.

Contractile properties of single isolated feline ventriculocytes.

Isolated single cardiac myocytes are becoming an increasingly popular experimental preparation. To date, however, the mechanical properties of these isolated adult mammalian cardiac myocyte preparations have not been thoroughly evaluated. The aims of this research were to 1) define the basic contractile properties of externally unloaded single feline ventriculocytes, 2) determine their response to standard inotropic stimuli, and 3) determine whether contractile properties vary as a function of cell size.

Comparison of slow response action potentials from normal and hypertrophied myocardium.

Previous studies have shown that papillary muscles from hypertrophied cat right ventricles (RVH) exhibit altered mechanical properties which may be associated with defects in the excitation-contraction coupling process. Since calcium influx [as slow inward current (Isi) during the cardiac action potential is thought to be a major determinant of contractile state, we compared Isi-mediated slow response action potentials ( SRAPs ) in papillary muscles from cats with RVH, induced by chronic pulmonary artery constriction, to SRAPs from sham-operated controls. The results show that 1) when depolarized by elevated extracellular potassium (K+o, 22 mM), RVH muscles became inexcitable (as defined here) significantly faster than control muscles; 2) inexcitable RVH muscles required significantly more isoproterenol than controls to restore slow response activity; 3) at all isoproterenol concentrations tested, SRAPs from RVH muscles were reduced in amplitude and duration compared with controls; 4) SRAPs evoked by long duration stimulus pulses in the absence of isoproterenol were also markedly reduced in RVH; and 5) the relationship between resting potential and K+o was the same in both groups.