Extended charge banking model of dual path shocks for implantable cardioverter defibrillators

<p>Abstract</p> <p>Background</p> <p>Single path defibrillation shock methods have been improved through the use of the Charge Banking Model of defibrillation, which predicts the response of the heart to shocks as a simple resistor-capacitor (RC) circuit. While dual path defibrillation configurations have significantly reduced defibrillation thresholds, improvements to dual path defibrillation techniques have been limited to experimental observations without a practical model to aid in improving dual path defibrillation techniques.</p> <p>Methods</p> <p>The Charge Banking Model has been extended into a new Extended Charge Banking Model of defibrillation that represents small sections of the heart as separate RC circuits, uses a weighting factor based on published defibrillation shock field gradient measures, and implements a critical mass criteria to predict the relative efficacy of single and dual path defibrillation shocks.</p> <p>Results</p> <p>The new model reproduced the results from several published experimental protocols that demonstrated the relative efficacy of dual path defibrillation shocks. The model predicts that time between phases or pulses of dual path defibrillation shock configurations should be minimized to maximize shock efficacy.</p> <p>Discussion</p> <p>Through this approach the Extended Charge Banking Model predictions may be used to improve dual path and multi-pulse defibrillation techniques, which have been shown experimentally to lower defibrillation thresholds substantially. The new model may be a useful tool to help in further improving dual path and multiple pulse defibrillation techniques by predicting optimal pulse durations and shock timing parameters.</p

His bundle activates faster than ventricular myocardium during prolonged ventricular fibrillation.

The Purkinje fiber system has recently been implicated as an important driver of the rapid activation rate during long duration ventricular fibrillation (VF>2 minutes). The goal of this study is to determine whether this activity propagates to or occurs in the proximal specialized conduction system during VF as well.An 8×8 array with 300 µm spaced electrodes was placed over the His bundles of isolated, perfused rabbit hearts (n = 12). Ventricular myocardial (VM) and His activations were differentiated by calculating Laplacian recordings from unipolar signals. Activation rates of the VM and His bundle were compared and the His bundle conduction velocity was measured during perfused VF followed by 8 minutes of unperfused VF. During perfused VF the average VM activation rate of 11.04 activations/sec was significantly higher than the His bundle activation rate of 6.88 activations/sec (p<0.05). However from 3-8 minutes of unperfused VF the His system activation rate (6.16, 5.53, 5.14, 5.22, 6.00, and 4.62 activations/sec significantly faster than the rate of the VM (4.67, 3.63, 2.94, 2.24, 3.45, and 2.31 activations/sec) (p<0.05). The conduction velocity of the His system immediately decreased to 94% of the sinus rate during perfused VF then gradually decreased to 67% of sinus rhythm conduction at 8 minutes of unperfused VF.During prolonged VF the activation rate of the His bundle is faster than that of the VM. This suggests that the proximal conduction system, like the distal Purkinje system, may be an important driver during long duration VF and may be a target for interventional therapy

A) Tissue receiving 20% of the shock received the highest weighting (1) while tissue receiving 10% and 100% of the shock received fixed weightings of 0

1. The cumulative weighting distribution (b) demonstrates that while approximately 80% of the tissue receives at least 24% of the full shock strength, only 20% of the tissue receives 60% of the full shock strength.<p><b>Copyright information:</b></p><p>Taken from "Extended charge banking model of dual path shocks for implantable cardioverter defibrillators"</p><p>http://www.biomedical-engineering-online.com/content/7/1/22</p><p>BioMedical Engineering OnLine 2008;7():22-22.</p><p>Published online 1 Aug 2008</p><p>PMCID:PMC2527568.</p><p></p

(A) For a single path shock and a critical mass of 80%, or for 80% of the area under the curve to achieve threshold, tissue that receives 24% of the maximum shock strength must reach threshold for the shock to successfully defibrillate

The area under the dashed line represents the 20% of tissue that would have a subthreshold response to a shock delivered at the DFT. (B) Critical mass criteria combined with a switched shock weighting function. For a critical mass of 80%, the combined response of the tissue must be at least 31% of the combined maximum response for the shock to successfully defibrillate. The removed section represents the 20% of tissue with a response of less than 31% of the maximum response. (C) A contour map of the dual path weighting function (shown in B) with the lowest model voltage 20% response is shown.<p><b>Copyright information:</b></p><p>Taken from "Extended charge banking model of dual path shocks for implantable cardioverter defibrillators"</p><p>http://www.biomedical-engineering-online.com/content/7/1/22</p><p>BioMedical Engineering OnLine 2008;7():22-22.</p><p>Published online 1 Aug 2008</p><p>PMCID:PMC2527568.</p><p></p

The side view (b) shows the same shape as the control waveform weighting function

The bottom figure (c) shows a contour map of the weighting function.<p><b>Copyright information:</b></p><p>Taken from "Extended charge banking model of dual path shocks for implantable cardioverter defibrillators"</p><p>http://www.biomedical-engineering-online.com/content/7/1/22</p><p>BioMedical Engineering OnLine 2008;7():22-22.</p><p>Published online 1 Aug 2008</p><p>PMCID:PMC2527568.</p><p></p

His and VM dV/dt of Laplacians during time course of VF.

<p>Early VF recording during perfused VF. Late VF is after 4</p

Mean and standard deviation of His and VM activation rate during eight minutes of unperfused VF.

<p>The average sinus rate for the rabbits was 3.46±0.61 activations/sec for both the His bundle and VM. *denotes p<0.05.</p