Electroanatomical Characteristics of Idiopathic Left Ventricular Tachycardia and Optimal Ablation Target during Sinus Rhythm: Significance of Preferential Conduction through Purkinje Fibers

PURPOSE: We hypothesized that Purkinje potential and their preferential conduction to the left ventricle (LV) posteroseptum during sinus rhythm (SR) are part of reentrant circuits of idiopathic left ventricular tachycardia (ILVT) and reentry anchors to papillary muscle. MATERIALS AND METHODS: In 14 patients with ILVT (11 men, mean age 31.5+/-11.1 years), we compared Purkinje potential and preferential conduction during SR with VT by non-contact mapping (NCM). If clear Purkinje potential(SR) was observed in the LV posteroseptum and the earliest activation site (EA) of preferential conduction at SR (EASR) was well matched with that of VT (EAVT), EASR was targeted for radiofrequency catheter ablation (RFCA). Also, the anatomical locations of successful ablation sites were evaluated by echocardiography in five additional patients. RESULTS: 1) All induced VTs exhibited clear Purkinje potential(VT) and preferential conduction in the LV posteroseptum. The Purkinje potential(VT) and EAVT was within 5.8+/-8.2 mm of EASR. However, the breakout sites of VT were separated by 30.2+/-12.6 mm from EAVT to the apical side. 2) Purkinje potential(SR) demonstrated a reversed polarity to Purkinje potential(VT), and the interval of Purkinje potential(SR)-QRS was longer than the interval of Purkinje potential(VT)-QRS (p<0.02) 3) RFCA targeting EASR eliminated VT in all patients without recurrence within 23.3+/-7.5 months, and the successful ablation site was discovered at the base of papillary muscle in the five additional (100%) patients. CONCLUSION: NCM-guided localization of EASR with Purkinje potential(SR) matches well with EAVT with Purkinje potential(VT) and provides an effective target for RFCA, potentially at the base of papillary muscle in patients with ILVT.

Efectos de la adenosina sobre el automatismo y las oscilaciones post-potencial en fibras de Purkinje de mamífero / The effects of adenosine on automacity and after potential oscillations on canine cardiac Purkinje fibers

Se estudiaron los efectos de la adenosina (ADO) sobre el automatismo y las oscilaciones post-potencial de fibras de Purkinje de corazones de perro. Se emplearon concentraciones de ADO desde 10-8 hasta 10-5 M. Se obtuvieron registros de la actividad eléctrica celular mediante microelectrodos. La ADO en concentraciones mayores de 10-8 M produce durante los dos primeros minutos un incremento súbito de la longitud del ciclo básico (LCB), de alrededor del 50 por ciento de su valor control, lo que después progresa hacia un estado estable. La curva dosis-respuesta en la fase estable es sigmoidal típica y semeja a las curvas de ocupación de receptores. Las pendientes del potencial de marcadores tienden a disminuir junto con la depresión de la LCB. Las oscilaciones post-potencial inducidas por tener de estimulación muestran que la pendiente de despolarización de la oscilación post-potencial disminuye con ADO 10-8 M pero no con concentraciones mayores. Los resultados encontrados sugieren que la ADO provoca un incremento en la corriente de potasio tiempo independiente. Este efecto parece depender de la estimulación de receptores específicos. El que la adenosina tenga un curso temporal bifásico sugiere la existencia de receptores purinérgicos con afinidades y constantes de disociación distinta pero con efectos similares y que podrían ser subtipos de receptores A1

Mechanism of Low K+-induced Depolarization in Mammalian Cardiac Muscle

The membrane permeability to potassium at a resting state is greater than to any other ions and the maintenance of resting membrane potential is largely dependent on K+ concentration of outside medium (Hodgkin and Horowicz 1959), i.e. an increase of K+ concentration of medium induces a depolarization, vice versa. However, on the contrary to this prediction, in some mammalian heart muscle a reduction of external K+ concentration induces a depolarization of membrane potential rather than a hyperpolarization (Vassalle 1965). In this study it was aimed to elucidate the possible mechanism of spontaneous depolarization induced by low external K+ in canine Purkinje fibers. The membrane potential was constantly recorded while components of cations in the bathing medium were replaced one by one by equimolar sucrose until the low K+ induced depolarization was blocked. The results are summarized as follows; The membrane potential of canine Purkinje fibers was spontaneously depolarized by low external K+, and the magnitude of depolarization was not affected by verapamil TEA, and a partial replacement of external Na+ and Ca2+ with choline chloride. But the membrane potential was hyperpolarized only when the all external cations were substitued with sucrose; and this hyperpolarization was disappeared again by substitution of sucrose with choline chloride. From these results, it may be concluded that the depolarization induced by low external K+ in canine Purkinje fibers is due to the nonspecific increase of membrane permeability to external cations and/or combinations with decreased K+ conductance.