Saturday, August 6, 2011

Atrial flutter in the human heart

The cardiologist view of the human heart is often reported as a structural entity with valves that pumps blood around. It has these arteries that run along the outside of the heart that when they get plugged up, can cause a heart attack, or lead to a catheter intervention or bypass surgery. Essentially it is a pump with fuel lines. I see it in a slightly different way, looking at it also from its electrical standpoint. This is often under-appreciated by the medical community, as cardiac electrophysiologists are looked at as the nerds and geeks of the cardiac world. For years, no one, except for the electrophysiologists themselves, really understood what the hell they did. Many of the pioneers of the EP world were locked up in academic centers for 12 to 24 hours at time studying a single patient without much to offer as a cure. That changed in the late 1980s and early 1990s as ablation of cardiac arrhythmic pathways became the new treatment paradigm. In other words, the nerds actually did something that could make money. Here's a case I worked on today. Three or four years ago, I could create something like this in a matter of a couple of hours (see figure below). Today, this electroanatomical map of a cardiac arrhythmia was created in a matter of minutes. Pretty amazing.

Here 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.

Atrial flutter map in a clockwise direction shown in the right atrium of the human heart. In this view, we are looking down on heart. The entire heart is not shown, only the right atrium (seen as H in the figure below). The round structure is the superior vena cava (seen as G in the figure below).

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.

Here is another view from our case today. This is an anterior view with the superior vena cava being that structure on top. This is just the right atrium. The arrhythmia is moving from the anterior-lateral part of the heart across the top in a clockwise manner and down along the posterior-medial part of the heart across the cavo-tricuspid isthmus (CTI in figure above). Ablation from the CTI to the inferior vena cava terminated the arrhythmia.

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.

No comments:

Post a Comment