Key result
Amplitude-normalized electrogram area strongly correlates with local conduction delay induced by flecainide, carbenoxolone, and ischemia.
Why the study?
Re-entrant ventricular tachycardia may be non-inducible or haemodynamically compromising, requiring substrate mapping during sinus rhythm to identify slow conduction areas for ablation.
Effect estimate: r2 = 0.92
p-value: p=<0.0001
The amplitude-normalised electrogram area (norm_EA) is a novel, validated quantitative measure of local conduction delay that may aid in electrophysiological substrate mapping of tachyarrhythmias.
Hypothesis-generating for norm_EA in arrhythmia substrate mapping; prospective human studies needed before clinical use.
Background Re-entrant ventricular tachycardia may be non-inducible or haemodynamically compromising, requiring assessment of the electrophysiological properties of the myocardium during sinus rhythm (i.e. substrate mapping). Areas of heart tissue with slow conduction can act as a critical isthmus for re-entrant electrical excitation and are a potential target for ablation therapy. Aim To develop and validate a novel metric of local conduction delay in the heart, the amplitude-normalised electrogram area (norm_EA). Methods A computational model of a propagating mouse action potential was used to establish the impact of altering sodium channel conductance, intracellular conductivity, fibrosis density, and electrode size/orientation on bipolar electrogram morphology. Findings were then validated in experimental studies in mouse and guinea pig hearts instrumented for the recording of bipolar electrograms from a multipolar linear mapping catheter. norm_EA was calculated by integrating the absolute area of a bipolar electrogram divided by the electrogram amplitude. Electrogram metrics were correlated with the local conduction delay during sodium channel block, gap junction inhibition, and acute ischaemia. Results In computational simulations, reducing sodium channel conductance and intracellular conductivity resulted in a decrease in signal amplitude and increase in norm_EA (reflecting a broadening of electrogram morphology). For larger electrodes (3mm diameter/ 7.1mm2 area), the change in norm_EA was essentially linear with the change in local conduction delay. Experimental studies supported this finding, showing that the magnitude of change in norm_EA induced by flecainide (1-3M), carbenoxolone (10-50M), and low-flow ischaemia (10% of initial flow rate) was linearly correlated with the local conduction delay in each condition (r2=0.92). Qualitatively similar effects were observed in guinea pig hearts perfused with flecainide. Increasing fibrosis density also resulted in a decrease in signal amplitude and increase in norm_EA. However, this remains to be validated using experimental/clinical data of chronic infarct. Conclusion norm_EA is a quantitative measure of local conduction delay between the electrode pair that generates a bipolar electrogram, which may have utility in electrophysiological substrate mapping of non-inducible or haemodynamically compromising tachyarrhythmia.
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Costa et al. (2020) studied Ventricular tachycardia / Cardiac arrhythmia. Conduction slowing interventions (flecainide, carbenoxolone, low-flow ischemia) vs. Baseline was evaluated on Correlation between norm_EA and local conduction delay (r2 = 0.92, p=<0.0001). The amplitude-normalized electrogram area (norm_EA) was strongly linearly correlated with local conduction delay induced by flecainide, carbenoxolone, and ischemia (r2 = 0.92, p < 0.0001).
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