UHFQRS physiology

Fig. ​Fig.22 demonstrates the physiological origin of UHF oscillations. The depolarization phase of myocardial cell action potentials (AP) serves as a main UHF transmitter (Fig. ​(Fig.2c).2c). Steep cell membrane potential gradients caused by the sodium ion current change (Phase 0 of AP) represent a unique source of UHF oscillations. The mass of myocardium, especially the left ventricle, defines the main location of UHF transmitters. UHFQRS can be simply interpreted as a histogram of UHF oscillation distribution in time (horizontal time axis) and location (V leads). The UHF transmitters work synchronously in the healthy heart (Fig. ​(Fig.2b,2b, HEALTHY). In a dyssynchronous left bundle branch block (LBBB) heart, the depolarization in the RV and septum (blue color in Fig. ​Fig.2b,2b, LBBB) precedes the depolarization in the LV lateral wall (green color).

Physiological origin of UHFQRS electrical activation pattern in ventricular dyssynchrony. Patient 1 with delayed activation of LV lateral wall (LBBB) and subject with HEALTHY conduction system. a Averaged ECG, V1-V6 leads. b Averaged UHF amplitude envelopes 500–1000 Hz (UHFQRS). c Schematic interpretation of myocardial cell action potentials—AP. Blue—V1 lead—mostly interventricular septum and RV, green—V6 lead—mostly LV lateral wall