MECHANISMS OF IDIOPATHIC LEFT-VENTRICULAR TACHYCARDIA

Idiopathic left ventricular tachycardia (ILVT) differs from idiopathic right ventricular outflow tract (RVOT) tachycardia with respect to me chanism and pharmacologic sensitivity. ILVT can be categorized into th ree subgroups. The most prevalent form, verapamil-sensitive intrafasci cular tachycardia, originates in the region of left posterior fascicle of the left bundle. This tachycardia is adenosine insensitive, demons trates entrainment, and is thought to be due to reentry. The tachycard ia is most often ablated in the region of the posteroinferior interven tricular septum. A second type of ILVT is a form analogous to adenosin e-sensitive RVOT tachycardia. This tachycardia appears to originate fr om deep within the interventricular septum and exits from the left sid e of the septum. This form of VT also responds to verapamil and is tho ught to be due to cAMP-mediated triggered activity. A third form of IL VT is propranolol sensitive. It is neither initiated or terminated by programmed stimulation, does not terminate with verapamil, and is tran siently suppressed by adenosine, responses consistent with an automati c mechanism. Recognition of the heterogeneity of ILVT and its unique c haracteristics should facilitate appropriate diagnosis and therapy in this group of patients.