is a model of the heart showing atrial flutter in the right atrium of
the heart. In our patient today, the rhythm actually rotated in an
opposite (or clockwise) direction. |
Here's how it works. This is the CARTO system that is sold by a company called Biosense-Webster. There is another company called ESI-Navx that produces a similar product. Patches are placed on the outside of the body: this is essentially a GPS system, where the heart is the planet, and the platinum-tipped catheter is the body on (in) the planet. The catheters have a magnetic location tip. The catheter is a very long wire inserted through the femoral vein inside the right (and left) groins, and run up the vein into the heart, much like a very long intravenous line. However, this line is connected to a recording and pacing device that is also run through the CARTO system.
When the catheter tip touches the inside wall of the heart, the impedance changes, and the computer is told to make a point. As the catheter is drawn across the inside of the heart, the point becomes a line, which becomes a plane, which becomes a shell, which becomes a chamber of the heart.
In this case the catheter(s) were contained within the right atrium. The patient arrived to the lab with an underlying cardiac arrhythmia called atrial flutter. We were pretty sure it was well-contained within the right atrium, but we wanted to make certain. The total time of the procedure to terminate the arrhythmia took approximately 15 minutes, but we liked playing around with the arrhythmia just to make sure we ablated in the right spot.
Atrial flutter is the electrical energy of the heart that is caught in a closed loop, much like when your computer does the spinning hourglass (Windows) or spinning pinwheel (Mac). This is a re-entrant arrhythmia, meaning that it goes round and round inside of the heart. In the 1970s, scientists didn't have clue on how this worked, until somebody one day opened up a dog or a pig or a human and actually measured the timing cycles of this electrical energy moving around and around in a circle. Fortunately with computers, this can be easily demonstrated. This patient was in the arrhythmia for nearly a year. The top figure is that of the right atrium looking down from the superior vena cava. The colors are assigned to time, so that red is early and purple is late. As you look down on the heart you can see the energy spinning in a clockwise fashion. Think of it has a millions of cells performing the 'wave' inside the right atrium.
Fortunately this arrhythmia has to travel across a bridge. This bridge is the cavo-tricuspid isthmus. Get rid of the bridge, and you break the circuit. You don't have to cut the heart open, just apply radiofrequency energy (or heat) to this ridge to lightly scar this tiny area. Ablation is accomplished by drawing a line of RF energy from the cavo-tricuspid isthmus (CTI in figure below) to the inferior vena cava. Magically the cardiac rhythm was restored, and the patient went home without complication.