Question:
Today, let’s go back to the basics and discuss catheter placement and waveforms.
In the following electrogram, none of the intracardiac channels are labeled. Identify each catheter location, the associated waveforms, and the rhythm.
Answer:
This is an example of sinus rhythm with high-to-low, right-to-left activation.
The purple channel displayed is from a catheter placed in the RV. Notice the RV activation lining up with the QRS on the surface ECG. Remember the QRS represents ventricular repolarization.
The next four yellow channels are from the His catheter. Since it is positioned partially in the atrium and ventricle right next to the bundle of His, there is an A (lining up with the P wave for atrial depolarization), His (H), and V (lining up with the QRS).
The duodecapolar (20 electrode) CS catheter is in the coronary sinus which is in-between the atrium and ventricle (AV groove). It originates in the RA on the posterior atrial septum and travels to approximately the left-lateral LA. With this placement, you will observe an A and V. Notice on the proximal aspect the A larger than the small far-field V. As the catheter is advanced further the V is slightly larger. If a ventricular branch is selected, there will be a large V and a small or no A. In that placement, the physician would be able to pace the LV from the epicardial approach much like with CRT devices.
The red channel is the first channel displayed (not on the original question image). This is the RF ablation catheter that is place somewhere in the right atrium. This was being utilized to pace the HRA; however, with poor signals observed, capture would not be likely in this position.
The atrial activation is observed from high-to-low (HRA, His, CS) and from right to left (CS proximal to CS distal). If the measurements are within the normal limits, this would be called Normal Sinus Rhythm.
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For more information: EP Essentials – Understanding EP: A Comprehensive Approach
