Advanced Mapping for Advanced Cures

In the recent past, before 1985 and the FDA approval of the Automatic Implantable Cardioverter-Defibrillator (ICD), the primary treatment for life-threatening ventricular tachycardia was drug therapy.1 Unfortunately, many of the antiarrhythmic drugs also had a proarrhythmic side effect. Later, the technological advancement of the internal cardiac defibrillator was introduced. In the 16 years that internal cardiac defibrillators have been available, they have advanced from the original and simple shock-only devices, which were implanted abdominally and were the size of about 280 grams, 20 mm thick, 100 mm tall and 70 mm wide (10 ounces, 0.8˝ thick, 4˝ tall and 2.75˝ wide). The system included 2 epicardial screw-in electrodes on the left ventricle, two patches sewn onto either the myocardium or pericardium, and the generator. The procedure was done via open chest and additional abdominal incisions. Today we have available dual chamber pacemaker defibrillators with multiple features including anti-tachycardia pacing and shocking for both atrial and ventricular arrhythmias. These weigh in at as little as 77 grams (two and seven-tenths ounces). They are 13 mm thick, 70 mm tall and 50 mm wide, and are most often implanted pectorally with one incision about 3˝ in length. With these life-saving devices came their own set of problems. A certain population of patients receives frequent and multiple therapies even while receiving antiarrhythmic medications. The issue is that the ventricular tachycardia the patient experiences is at a rate that crosses into the programmed threshold of the device for ventricular fibrillation therapy, which results in frequent intracardiac direct current (DC) shocks. Usually, this occurs while the patient is still conscious and is quite painful to experience for many patients. However, more importantly, the frequent ventricular tachycardias are an indicator of increased mortality.2 Advances in technology once again came through. In 1997, Biosense Webster, Inc., (Diamond Bar, California) introduced the CARTO mapping system to the United States. The CARTO system was first introduced overseas in 1995. This system assists the physician to diagnose and treat many cardiac arrhythmias. One of the mechanisms of ventricular tachycardia that many of the patients with recurrent arrhythmias are plagued by is a macro-reentrant circuit.3 Scars on the ventricle from previous myocardial infarctions form these reentrant circuits. The CARTO system produces a three-dimensional endocardial reconstruction of the heart. Usually only the chamber being targeted as the culprit of the arrhythmia is mapped; in the case of recurrent ventricular tachycardias from scar tissue, most often this chamber is the left ventricle. The CARTO system displays various types of maps including one that measures voltage. The voltage map displays the electrical voltage of the heart tissue in different areas of the chamber. We know that scar tissue has little or no conductivity, thus having very low or no measurable voltage. After mapping the ventricle, by acquiring catheter tip contact points with the CARTO system software, a multi-colored, 3-dimensional display will be constructed on the display monitors. The colors are coded with red, denoting the lowest acquired voltage values, and purple, denoting the highest acquired voltage values in the map, with the remaining colors of the spectrum denoting values in between the extremes. By using the voltage map feature, it becomes easy to delineate scar tissue from healthy tissue, scars being the red areas on the map (Figure 1). Once the scar has been identified, a linear lesion can be deployed using radiofrequency (RF) energy from the scar to another area that does not conduct electrical signals, such as the mitral valve annulus or another area of the scar (Figure 2). This RF ablation line then interrupts the tachycardia circuit, thus curing the tachycardia. I have seen several patients who have undergone procedures using the CARTO system. The patients suffered from frequent shocks from their ICDs before the procedure. They have had no further therapies for their ventricular tachycardia from their devices since the procedure. A second type of ventricular tachycardia (VT) is idiopathic or automatic (abnormal impulse formation) VT. Figure 3 demonstrates a map of an idiopathic left ventricular tachycardia. Another form of idiopathic VT occurs in the right ventricular outflow tract (RVOT). RVOT-VT originates from, as the name indicates, the outflow tract. It is still unknown if this arrhythmia represents automaticity or a triggered focus. The CARTO system can identify the area of the origination site of the tachycardia by using the activation map feature of the CARTO system. This can be done by three different methods. The first is by acquiring catheter tip contact points in the right ventricle and outflow tract during sustained RVOT-VT. The second is by acquiring catheter tip contact points throughout the right ventricle and outflow tract while the patient has a premature ventricular contraction (PVC) or non-sustained VT from the RVOT. The third method is by marking pace map sites with the tag feature of the CARTO system. By using various colored tags, the physician can map the exit site of the VT with pacing maneuvers in order to find an area that corresponds to the culprit VT, using the body surface 12-lead electrocardiogram (ECG) as a guide. In this article, I will discuss the first two methods. With either of the first two methods, the color-coded activation map will indicate the exit site of the tachycardia in red (Figure 4). The RF ablation/mapping catheter, NAVISTAR (Biosense Webster, Inc.) can be manipulated into the red area to deliver the RF lesion. One of the greatest advantages of the CARTO system is that it provides real-time, 3-dimensional anatomical reconstructions of the heart chamber being mapped with a spatial resolution of less than 1 mm.4 Often in a two-dimensional view (fluoroscopically right anterior oblique), it appears that the catheter is lined up appropriately with the location in which a lesion is wanted. When a second 2-dimensional view (fluoroscopically left anterior oblique) is obtained, it is clear that the catheter is not where it needs to be. The CARTO system can display two views simultaneously, with the ability to manipulate the main view in a three-dimensional space at all times. This feature makes it easy for the operator to quickly confirm if the catheter is in the desired position prior to administering RF therapy. The NAVISTAR catheter also indicates good catheter position by providing the operator with a catheter icon that can be constantly viewed during real-time mapping and therapy delivery. This is important and time-saving, because an effective lesion cannot be applied if the catheter is not in good position with adequate tissue contact.3 Another advantage of using the CARTO system for mapping and ablating is that it is easy to reposition the NAVISTAR catheter to a previously mapped location. Often, after the initial mapping process, the physician will want to revisit an interesting area. This is quickly accomplished by using the previously mentioned tag feature and applying a colored tag to the interesting point that is acquired during the mapping process. This marks the point with a specific color. A narrative comment can also be assigned to any specific point for use of identification at another time. The CARTO system also automatically adds tags to all RF applications. This feature allows for visual tracking of RF lesion progress. This feature is very useful when deploying linear RF lesions. When using fluoroscopic guidance, it is not possible to anatomically track lesion deployment with any degree of reliability. Often, this visual aid will assist the physician when targeting a specific region for RF therapy. Other tachycardias that are often very difficult and time-consuming to ablate without the assistance of CARTO are ectopic atrial tachycardias (EAT). Using the activation map feature of the CARTO system, the time spent curing atrial tachycardia has been greatly reduced. By systematically taking points throughout the atrium while the patient is in sustained tachycardia, the CARTO will create a map identifying the earliest activation area or area of origin of the tachycardia. Once this area has been identified, RF energy can be applied to the area via the NAVISTAR catheter, eliminating the arrhythmia. I would like to share an ectopic atrial tachycardia case with you. The patient is a young woman, status post two prosthetic mitral valve replacements. When in tachycardia, she was very symptomatic with a very rapid ventricular response. With the prosthetic valve, when in tachycardia the valve is also very loud, making a clicking noise. Once while attending a college class, she went into tachycardia; during this time, the other students she was with in the class were looking around the room saying, What is that noise? This, as you can imagine, gave this woman a significantly embarrassing moment. In spite of multiple antiarrhythmic drug therapies, she presented repeatedly for external direct current cardioversions. She underwent an electrophysiology study in 1999; at this time, it was determined that her atrial tachycardia was originating in the left atrium. Due to her prosthetic valve (unable to do a retrograde access) and not being previously consented for a transseptal approach, it was decided to try a new antiarrhythmic drug. Over the next several months, her tachycardia recurred more frequently. The CARTO system became available at the hospital where she went for treatment for her arrhythmia. Her physician immediately scheduled her for an atrial transseptal approach, CARTO mapping and RF ablation procedure. The tachycardia was easily induced and mapped to the left atrium using CARTO with an easily identified focus of origin (Figures 5 and 6). The tachycardia was terminated with the first application of RF energy, and has not returned in the eighteen months since the ablation. A third arrhythmia type that CARTO has assisted us with is typical atrial flutter. Once the flutter has been diagnosed, one approach that can be taken to decrease time in the lab for the ablation is to use the CARTO system to make an anatomical map. The superior vena cava, inferior vena cava, tricuspid valve ring and coronary sinus os are identified with tagged points and colored rings are constructed to show these structures. The ablation catheter is placed at a starting point on the sub-eustachian isthmus and lesions are applied to create a line of conduction block of the flutter circuit (Figure 7). Creating a limited activation map, acquiring catheter tip contact data on the medial and lateral aspects of the linear lesion during coronary sinus pacing, can then prove conduction block in the sub-eustachian isthmus. The CARTO mapping system has given the electrophysiology lab a new approach to several old problems. One of the goals with the CARTO system is to decrease the amount of fluoroscopy time used. A physician can now see 2 three-dimensional views at all times without the use of fluoroscopy. In many cases, the CARTO system has enabled arrhythmias to be cured in a more timely fashion. These arrhythmias would previously have either taken much longer to treat or been unsuccessful in curing.