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How Fast Does the Electrical Impulse Travel Within the Myocardium? The Need for a New Clinical Electrophysiology Tool: The Conduction Velocity Mapping

In the genesis of flutter as well or any reentrant tachycardia, substrate is a critical component. Reentry may result from myocardial disease or anatomical anomalies.1 Seminal works brought the clinical proof2-4 that partially scarred areas are localized by low-voltage and are associated with local slowing of conduction. When contained within a narrow isthmus, targeting these regions with catheter ablation allows the cure of the arrhythmia. How do we approach myocardial conduction velocity (CV) in the electrophysiology lab? In the absence of a clinical tool to assess directly this parameter, manual computations5,6 and assumptions based on the morphology of the intracardiac electrograms5,7,8 allow us generally to link the slow conducting areas to the low voltage or fractionated regions. CV during atrial flutter has been previously correlated with the peak negative voltage of the unipolar electrogram.9 In this issue of the Journal, Itoh et al.10 studied using detailed electroanatomical mapping 26 right atrial (RA) flutters and found a logarithmic relationship between the CV and the local bipolar electrogram amplitude (EA). The logarithmic relationship is very interesting in that it is easy to understand that for a narrow interval of bipolar EA (e.g., <0.5 mV representing 10% of the maximum mapped voltage), a broad spectrum of CV is scattered (covering more than half of the conduction velocities axis—see Fig. 1). This makes the CV a more discriminative parameter than mere voltage within the low voltage areas. As original as this approach is, it should not be forgotten that the method of manual computation of the CV as well as point-by-point electroanatomical mapping are of limited interest in obtaining a detailed analysis of the CV along the circuit or in the entire map. Although, for anatomical reasons, the circuit length of the typical atrial flutter is longer than for atypical RA flutters, it is worth noting that the mean CV is almost twice as fast in typical flutters than during atypical RA flutters (0.80 ± 0.07 m/s for typical flutter versus 0.51 ± 0.19 m/s and 0.43 ± 0.10 m/s for postoperative and idiopathic atypical flutters, P < 0.01).10