P waves in the electrocardiogram recording of tachycardia: 'You can run, but you cannot hide'

Abstract

This editorial refers to ‘A new method of filtering T waves to detect hidden P waves in ECG signals’ by D. Goldwasser et al ., on page 1028. The history of the evolution of recording of cardiac electrical activities by electrocardiogram (ECG) is quite fascinating.1 The initial ECG recording systems used by Waller, Einthoven, and Lewis consisted of mercury capillary electrometers and string galvanometers that were cumbersome to use and provided limited information.1–3 In Waller's demonstration of the human ECG, only ventricular activities were recorded and the P waves were not discernible.1 Interestingly, even today there are situations where in the ECG recordings obtained with modern and sophisticated ECG machines the P waves may not be easily discernible. Interpretation of ECG recordings remains fundamental to the clinical investigation of cardiac arrhythmias. To confirm the diagnosis of ventricular tachycardia from the ECG tracing of a wide complex tachycardia would require accurate detection of the P waves to determine atrioventricular (AV) dissociation. Likewise, detection of the P waves, their morphological characteristics, axis, and timing relationships with the R waves would be important to confirm and further differentiate supraventricular tachycardias (SVTs) into AV nodal reentrant tachycardia (AVNRT), accessory bypass tract-mediated AV reentrant tachycardia (AVRT), atrial tachycardia, junctional ectopic tachycardia, or sinus tachycardia. However, simple as it sounds, the task of finding P waves let alone their characterization may be extremely difficult, if not impossible. In an approach to make a correct diagnosis of SVT recorded by 12-lead ECG, general criteria such as RP intervals, QRS alternans, pseudo-r′, pseudo-S-wave, etc. although frequently used, lack robustness in their sensitivity and specificity. Because the P waves are generated by the atrial chambers that have lower muscle mass, they are of lower amplitude when compared with the QRS complexes. As such, during SVT …