Jane Caldwell

Heterogeneity of Ventricular Fibrillation Dominant Frequency During Global Ischemia in Isolated Rabbit Hearts

Introduction : Ventricular fibrillation (VF) studies show that ECG‐dominant frequency (DF) decreases as ischemia develops. This study investigates the contribution of the principle ischemic metabolic components to this decline.

Amplitude Changes during Ventricular Fibrillation: A Mechanistic Insight.

Introduction: Clinically in ventricular fibrillation (VF), ECG amplitude, and frequency decrease as ischemia progresses and predict defibrillation success. In vitro ECG amplitude declines without ischemia, independent of VF frequencies. This study examines the contribution of cellular electrical activity and global organization to ECG amplitude changes during VF. Methods and Results: Rabbit hearts were Langendorff-perfused (40u2009mL/min, Tyrode’s solution) and loaded with RH237. During VF, ECG, and epicardial optical action potentials were recorded (photodiode array; 256 sites, 15u2009mmu2009×u200915u2009mm). After 60u2009s of VF, perfusion was either maintained, global ischemia produced by low-flow (6u2009mL/min), or solution [K+]o raised to 8u2009mM. Peak-to-peak amplitude was determined for all signals. During VF, in control, ECG amplitude decreased to a steady-state (∼57% baseline), whereas in low-flow steady-state was not reached with the amplitude continuing to fall to 33% of baseline by 600u2009s. Optically, LV amplitude declined more than RV, reaching significance in control (LV vs. RV; 33u2009±u20095 vs. 63u2009±u20098%, pu2009<u20090.01). During VF in 8u2009mM [K+]o, amplitude changes were more complex; ECG amplitude increased with time (105u2009±u200913%), whilst LV amplitude decreased (60u2009±u200915%, pu2009<u20090.001). Microelectrode studies showed amplitude reduction in control and 8u2009mM [K+]o (to ∼79 and ∼93% baseline, respectively). Evaluation of electrical coordination by cross-correlation of optical signals showed as VF progressed coordination reduced in control (baseline 0.36u2009±u20090.02 to 0.28u2009±u20090.003, pu2009<u20090.01), maintained in low-flow (0.41u2009±u20090.03 to 0.37u2009±u20090.005, pu2009=u2009NS) and increased in 8u2009mM [K+]o (0.36u2009±u20090.02 to 0.53u2009±u20090.08, pu2009<u20090.05). Conclusion: ECG amplitude decline in VF is due to a combination of decreased systolic activation at the cellular level and increased desynchronization of inter-cellular electrical activity.

Relative timing of near-field and far-field electrograms can determine the tachyarrhythmia site of origin

BACKGROUNDnDespite improving algorithms, inappropriate shocks for supraventricular tachycardia (SVT) still occur in a significant number of patients with implantable cardioverter-defibrillators (ICDs). This makes the discovery of novel discriminators that use existing ICD hardware an attractive proposition.nnnOBJECTIVEnWe hypothesized that the delay of activation onset from the device-detected, far-field electrogram (EGM) to the near-field, bipole EGM would allow the differentiation of ventricular tachycardias (VTs) from SVTs.nnnMETHODSnProof of principle was demonstrated by rapid pacing in the right atrium, right ventricle, and left ventricle in healthy patients undergoing atrial fibrillation ablation procedures (n = 17). Using real-life ICD recordings, the equivalent measurements were made in a derivation cohort (n = 26) and cutoff predictive values obtained. Finally, the selected values were validated in a separate group of recordings (n = 82).nnnRESULTSnIn healthy patients, significant differences in the far-field to near-field EGM activation onsets were observed between right atrial (14.7 ± 2.7 ms), right ventricular (36.3 ± 8 ms), and left ventricular (57.8 ± 10.3 ms; P < .001) pacing. In the derivation ICD cohort, the median far-field to near-field onset delay wasxa0significantly shorter in SVT (24.5 ms; interquartile range, 15.3-47.5 ms) than in VT (118.5 ms; interquartile range, 102.5-131.5 ms) (P < .001). Using a cutoff of 100 ms in the validation cohort, SVT was successfully discriminated from VT with a sensitivity and specificity of 88% and a negative predictive value of 94.2%.nnnCONCLUSIONnThe delay between far-field and near-field EGMs offers a potential new discrimination tool to reduce inappropriate ICD therapies and aid interpretation of single-lead device tracings.