671Assessment of irrigated-tip radiofrequency catheter ablation lesion characteristics using different irrigation fluids on ex-vivo bovine myocardium

Introduction Certain arrythmias, particularly of ventricular origin, necessitate deep lesions in order to achieve clinical success. The introduction of irrigated-tip radiofrequency (RF) catheters has allowed creation of deeper lesions and has decreased char formation. Although normal saline has been used as a standard solution, recent observations have suggested less ionic solutions may increase lesion depth. In this in-vitro study we aimed to characterize lesions created by irrigated-tip RF catheters using standard normal saline(NS), half-normal saline (HNS), and HNS-%2.5Dextrose (HNS-DEX/2) combination solutions. METHODS Bovine myocardium was placed firstly in ringer-lactate bath. Using irrigated-tip RF catheter ablation lesions were created serially using 30, 40, 50, 60, 70Watts with NS, HNS and HNS-DEX/2 as irrigation solutions. Lesion depths, steam pops and impedance drops were measured. Subsequently the experiment was repeated in normal saline bath. RESULTS Both HNS-DEX/2 and HNS irrigation solutions increase lesion depths when compared to normal saline (Table 1, Figure 1). Steam pops were more common and earlier with HNS-DEX/2 and HNS. DISCUSSION AND CONCLUSION Our findings suggest that less ionic irrigation solutions lead to increased lesion depths using similar RF power. If confirmed in-vivo, HNS and, particularly, HNS-DEX/2 as irrigation solution may increase ablation success for intramural/deep myocardial arrhythmic foci. Additionally, studies to assess safety of this strategy are necessary as intuitively deeper lesions may lead to more complications. Table 1 Irrigation Solution/Bath solution 30W/30ml(Lesion depth mm)(Impedance drop) 40W/30ml(Lesion depth mm)(Impedance drop) 50W/30ml(Lesion depth mm)(Impedance drop) 60W/30ml(Lesion depth mm)(Impedance drop) 70W/30ml(Lesion depth mm)(Impedance drop) HNS+%2.5D / Ringer Lactate 470->61 4.583->63 5.074->62SP+(32s) 6.080->66SP+(27s) 7.577->65SP+(26s) HNS/ Ringer Lactate 3.590->65 4.580->63SP+(34s) 5.073->59SP+(33s) 5.580->56SP+(28s) 6.583->64SP+(22s) NS/ Ringer Lactate 3.077->60 472->59 4.576->61 5.081->56 674->55 SP+(30s) HNS+%2.5D/Normal saline 3.573->67 598->63 5.573->58SP+(28s) 697->76SP+(26s) 7.570->58SP (25s) HNS/Normal saline 3.563->58 4.066->52 4.567->52 5.575->52 788->60SP+(28s) NS/Normal saline 2.566->58 3.063->52 4.073->58 5.077->55 5.568->44 Lesions created by irrigated tip radiofrequency catheter with bovine myocardium Abstract Figure 1

Tropomyosin Period 3 Is Essential for Enhancement of Isometric Tension in Thin Filament-Reconstituted Bovine Myocardium

Tropomyosin (Tm) consists of 7 quasiequivalent repeats known as “periods,” and its specific function may be associated with these periods. To test the hypothesis that either period 2 or 3 promotes force generation by inducing a positive allosteric effect on actin, we reconstituted the thin filament with mutant Tm in which either period 2 (Δ2Tm) or period 3 (Δ3Tm) was deleted. We then studied: isometric tension, stiffness, 6 kinetic constants, and the pCa-tension relationship. N-terminal acetylation of Tm did not cause any differences. The isometric tension in Δ2Tm remained unchanged, and was reduced to ~60% in Δ3Tm. Although the kinetic constants underwent small changes, the occupancy of strongly attached cross-bridges was not much different. The Hill factor (cooperativity) did not differ significantly between Δ2Tm (1.79 ± 0.19) and the control (1.73 ± 0.21), or Δ3Tm (1.35 ± 0.22) and the control. In contrast, pCa50 decreased slightly in Δ2Tm (5.11 ± 0.07), and increased significantly in Δ3Tm (5.57 ± 0.09) compared to the control (5.28 ± 0.04). These results demonstrate that, when ions are present at physiological concentrations in the muscle fiber system, period 3 (but not period 2) is essential for the positive allosteric effect that enhances the interaction between actin and myosin, and increases isometric force of each cross-bridge.