I don't normally pick favorites...so do you wanna know why I pick the CS as my favorite? Many times, I have found myself referencing (pun intended, mappers) the CS catheter to figure out what’s going on with the rhythm!! There are incredible insights you can glean when the CS is in proper position, both anatomically and electrically.
Proper placement...let’s talk about that. So, where is the CS really located?
ANATOMY: The CS is considered an external cardiac structure, meaning it’s outside of the main pumping chambers. Just to fill in the blanks...CS stands for coronary sinus. This sinus (cavity) is a network of veins that return coronary blood flow to the RA. The main body of the CS runs from the ostium (in the RA) along the back of the left heart, following the AV groove. The specific location in the lower posterior RA serves as a landmark for catheter access and placement, mapping and ablations.
You know the High to Low, Right to Left mantra in the EP lab? No?...Just me?! Well, one of my favorite things about the CS is seeing atrial and ventricular signals propagate from Right to Left. During an electrophysiology (EP) procedure, how can we possibly obtain atrial (A) and ventricular (V) signals from a structure that is accessed from the right atrium??
ISOLATED BUT HEARD: The fibrous skeleton of the heart electrically isolates the atria from the ventricles, however as the CS is outside the heart so a catheter inside the CS can “hear” electrical activity from both atria and ventricles as a product of laying in the AV groove.
EGMs: If you are new to EP, it may be difficult at first to discern which electrogram signals are “A” or “V”. This may help…Atrial signals are sharp and discrete, whereas ventricular signals are wider and less sharp. When in doubt, look up – no not at the ceiling!! –look at the Body Surface ECG. The A will line up with the P-wave and the V signal will align to the QRS. (You’re welcome, just don’t be tricked during Atrial Flutter!!)
APPLICATION: So, whether in tachycardia, eccentric activation or retrograde activation, understanding the “reasoning” for what we see in the EP lab will help you better observe and interpret CS EGMs.