ECG Quiz 57 – Discussion – Incognito Paced Rhythm

Discussion – Incognito Paced Rhythm Click here for a larger image At one look it looks like left bundle branch block (blue arrows – lead I and aVL). But V5 shows negative complexes which is not typical of LBBB (violet arrow). There is left axis deviation as indicated by negative complexes in the inferior leads (green arrows). PR interval can be seen as varying on scrutiny of multiple beats. But PP interval is constant (red arrows). Atrial rate is higher than the ventricular rate (PP interval shorter than RR interval). Hence the four criteria for complete heart block are satisfied: Regular PP interval Regular RR interval Totally varying PR interval Atrial rate higher than ventricular rate But there is a catch here – it should be an infrahisian block as the QRS is wide. We would expect the ventricular escape rate to be around 40 per minute. But here it is 60 per minute. This should make us suspect that it is right ventricular apical paced rhythm in a person with complete heart block. Then where is the pacing artefact? It is hard to locate any pacing artefact even on close scrutiny. Why? Look at the low pass filter setting – 40 Hz (yellow arrow) at the bottom of the ECG. Low pass filter setting and pacing spike/artefact detection Pacing spike/artefact is a high frequency signal, which needs a low pass filter setting of 100 Hz for detection. Here since the low pass filter is set at 40 Hz, pacing signals are not displayed in the ECG. This is a common pro...
Source: Cardiophile MD - Category: Cardiology Authors: Tags: ECG / Electrophysiology ECG Library Source Type: blogs