Electrical parameters for physiological His-Purkinje pacing vary by implant location in an ex vivo canine model.

BACKGROUND: Permanent His-bundle pacing (HBP) is an attractive, perhaps more physiological, alternative to traditional right ventricular pacing. OBJECTIVE: The purpose of this study was to utilize direct visualization to more comprehensively understand the anatomy central to HBP, correlating electrical lead performance to implant locations along the His-bundle (HB) pathway. METHODS: Canine hearts (n = 5) were isolated and reanimated using Visible Heart methodologies. Medtronic 3830 SelectSecure leads were fixated where His potentials were present. The location of each implant was mapped/binned into 4 regions approximately analogous to the proximal, penetrating, and distal HB. Locational differences in HBP capture and resultant QRS morphology were assessed. RESULTS: Average HBP capture thresholds did not significantly vary with respect to implant location (1.0-ms pulse width; P = .48). The resulting QRS morphologies from HB-paced beats varied in relation to implant location. As leads were placed further distally along the HB, the ratio of paced to native QRS complex duration increased (ΔQRSpaced/ΔQRSnative ratios-region 2: 0.84 ± 0.16; region 3: 1.04 ± 0.42; region 4: 1.74 ± 0.86). CONCLUSION: We demonstrated correlation between the anatomic locations of HBP lead placement and resultant QRS morphologies in a reanimated canine heart model. Proximal placement along the HB pathway resulted in more favorable QRS morphologies, suggesting improved selective HBP capture, with no significant increase in HBP capture thresholds. Pacing the HB in more proximal pathway locations improved the selectivity of HBP and may confer electrical and anatomic benefits relative to distal HBP.

Vascular conductance is reduced after menthol or cold application.

OBJECTIVE: To compare the effects of commercially sold menthol (3.5%) ointment and cold application on blood flow in the forearm. DESIGN: : Prospective counterbalanced design. SETTING: University research laboratory. PARTICIPANTS: Twelve (6 men and 6 women) college-aged students. INTERVENTIONS: Each participant had blood flow measured in the brachial artery for 5 minutes before and 10 minutes after menthol ointment or cold application to the forearm. MAIN OUTCOME MEASURES: Blood velocity, arterial diameter size, and blood pressure were recorded during testing procedures. Vascular conductance was calculated based on these measures and used to describe limb blood flow. RESULTS: We observed a significant reduction (35%; P = 0.004) in vascular conductance within 60 seconds of menthol and cold application to the forearm. Vascular conductance remained significantly reduced for 10 minutes by approximately 19% after both menthol and cold application [F(2.313, 43.594) = 10.328, P < 0.0001]. There was no significant difference between conditions [F(1, 19) = 0.000, P = 0.945]. CONCLUSIONS: The application of a 3.5% menthol ointment significantly reduces conductance in the brachial artery within 60 seconds of application, and this effect is maintained for at least 10 minutes after application. The overall decline in conductance is similar between menthol ointment and cold application.