Further Insight into Mechanisms of Ventricular Tachycardia from the Clinical Electrophysiology Laboratory

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72003/1/j.1540-8167.1991.tb01319.x.pd

Direct cooling of the catheter tip increases safety for CMR-guided electrophysiological procedures

<p>Abstract</p> <p>Background</p> <p>One of the safety concerns when performing electrophysiological (EP) procedures under magnetic resonance (MR) guidance is the risk of passive tissue heating due to the EP catheter being exposed to the radiofrequency (RF) field of the RF transmitting body coil. Ablation procedures that use catheters with irrigated tips are well established therapeutic options for the treatment of cardiac arrhythmias and when used in a modified mode might offer an additional system for suppressing passive catheter heating.</p> <p>Methods</p> <p>A two-step approach was chosen. Firstly, tests on passive catheter heating were performed in a 1.5 T Avanto system (Siemens Healthcare Sector, Erlangen, Germany) using a ASTM Phantom in order to determine a possible maximum temperature rise. Secondly, a phantom was designed for simulation of the interface between blood and the vascular wall. The MR-RF induced temperature rise was simulated by catheter tip heating via a standard ablation generator. Power levels from 1 to 6 W were selected. Ablation duration was 120 s with no tip irrigation during the first 60 s and irrigation at rates from 2 ml/min to 35 ml/min for the remaining 60 s (Biotronik Qiona Pump, Berlin, Germany). The temperature was measured with fluoroscopic sensors (Luxtron, Santa Barbara, CA, USA) at a distance of 0 mm, 2 mm, 4 mm, and 6 mm from the catheter tip.</p> <p>Results</p> <p>A maximum temperature rise of 22.4°C at the catheter tip was documented in the MR scanner. This temperature rise is equivalent to the heating effect of an ablator's power output of 6 W at a contact force of the weight of 90 g (0.883 N). The catheter tip irrigation was able to limit the temperature rise to less than 2°C for the majority of examined power levels, and for all examined power levels the residual temperature rise was less than 8°C.</p> <p>Conclusion</p> <p>Up to a maximum of 22.4°C, the temperature rise at the tissue surface can be entirely suppressed by using the catheter's own irrigation system. The irrigated tip system can be used to increase MR safety of EP catheters by suppressing the effects of unwanted passive catheter heating due to RF exposure from the MR scanner.</p

Interaction between Alpha-1 Adrenergic and Vagal Effects on Cardiac Rate and Repolarization 1

ABSTRACT Alpha-1 adrenergic stimulation modulates ventricular automaticity via an alpha-1 adrenoceptor (AR) subtype blocked by the alpha-1B antagonist chloroethylclonidine (CEC) and alters repolarization via receptor subtype(s) (alpha-1A and alpha-1D) blocked by WB4101. Our objective was to determine alpha-1 AR subtype specific effects and vagal interactions on heart rate and ventricular repolarization. We studied right vagally innervated Langendorff-perfused guinea pig hearts, beta-blocked with propranolol, 5 ؋ 10 ؊7 M. Heart rate and QT interval were measured from bipolar epicardial electrodes. In some experiments rate corrected QT interval (QT c ) (Bazett formula) was calculated, as well. Phenylephrine (PE) alone, 10 ؊8 M, reduced sinus rate significantly (P &lt; .05) in 8 of 13 preparations. A decrement in rate occurred in all preparations in the presence of WB4101 and was blocked by CEC. Vagal stimulation, at 1 to 20 Hz slowed heart rate (P &lt; .05) in a frequency-dependent fashion. Addition of PE alone or in the presence of WB4101 further reduced rate (P &lt; .05). However, with vagal stimulation ؉ PE ؉ CEC, rate did not differ from that in the presence of vagal stimulation, alone (P &gt; .05). In studies of repolarization, QT c shortening was elicited by PE alone (P &lt; .05) and CEC ؉ PE (P &lt; .05). In the presence of WB4101, no QT c shortening occurred (P &gt; .05). QT c shortening induced by vagal stimulation was attributable to the heart rate change rather than to a direct effect on ventricular repolarization. In conclusion, in the setting of beta adrenergic blockade, an alpha-1B receptor appears responsible for the alpha-1 adrenergic decrease in heart rate and facilitation of vagal responsiveness. A receptor subtype blocked by WB4101 (alpha-1A or alpha-1D) is responsible for the QT and QT c shortening. Whereas right vagal stimulation shortens the QT c interval, this action reflects the change in sinus rate rather than an effect on the ventricle

Communicating the organizational identity of the Girl Scouts of the Philippines through an event

Girl Scouts of the Philippines (GSP) is a non-profit organization situated in Padre Faura, Manila with a mission and vision of instilling the principle of womanhood, promoting holistic growth in girls aged 4 to 21 years and molding them to become responsible Filipino citizens. GSP follows themes as the 8-Point Challenge, which are programs and activities dedicated to fulfill their mission and vision. Through the interviews, surveys and qualitative content analysis, the group discovered that there is lack of awareness of the 8-Point Challenge from GSP’s the target public. The organization’s communication efforts are not enough as it was revealed that majority of their communication efforts are not enough as it was revealed that majority of their communication efforts regarding the 8-Point Challenge are directed towards their internal public (e.g Girl Scouts and GSP employees). In addition to this, there are misconceptions regarding the programs and activities that GSP conducts and there is failure to generate return visits in their social media accounts. In order to solve the organization’s problem, the group created an (1) event called 2Challenge the Girls3 which served as medium in introducing the 8-Point Challenge, the organizational identity of GSP, to its public. It was patterned after the game Amazing Race where there were 8 stations representing each of the 8-Point Challenge. For the event to be sustainable, (2) a 32-page step-by-step guidebook was designed. The guidebook was made in order to serve as a template for GSP in their future efforts in conducting the same kind of event for the same target public