Ablation Techniques Tips and Tricks
How to tell where esophagus is
- Primarily mapping. Use a catheter to map the esophagus and use a catheter to map the Left Atrium. This gives you an idea of where everything is this way. In some people the esophagus is going to be more to the right of the left atrium, in others it will be more to the left. It’s important to know because the atrial tissue that lies over the esophagus is thin and thus more prone to injury/puncture from the ablation tip. While the rate of this sort of even is less than 1% during an ablation procedure, it is a complication with a high rate of fatality should it occur and thus every precaution should be taken to avoid it. The esophageal mapping in conjunction with cardiac mapping are one such precaution.
- Additionally, a temperature probe is placed into the esophagus. This can measure the temperature of the area posterior to the part of the LA being burned (ablated). If the temperature rises too much, the ablation catheter can be moved. This comes into play also for something known as “boxing in the posterior wall.”
Boxing in the posterior wall (along with roof ablation)
- Sometimes ablation via isolation of the pulmonary veins alone is not effective and patients need repeat ablations. This is especially true with persistent AF. Thus, one approach that is sometimes taken in these patients is to “box out” the entire posterior wall of the left atrium. Since pulmonary vein isolation involves ablations along the antrums of the PVs this effectively creates the sides of the box. Another important structure often ablated in fibrillation and flutter is the left atrial roof, essentially the dome of the left atrial chamber with the superior pulmonary veins (L and R) on either side of the dome. Roof ablation is performed as a linear ablation connecting the superior edge of each ostia for the superior pulmonary veins (see figure at bottom)
How to tell LAA from Pulmonary veins
- The Left atrial appendage can be distinguished from the left pulmonary veins due to its proximity to the left ventricle. It is important to remember that the ablation procedures being discussed here are being performed using catheters inserted into the heart intravenously. In other words, the only way an interventional cardiologist can “see” anything is using ultrasound (sound wave energy), magnetic waves, or voltage variations. The basic principles underlying is that they integrate information from things that are known to produce a guide for the unknown. This known information, for example, is often in the form of electrophysiological wave morphology based on proximity of the catheters to certain structures. It can also be in the form of distance from catheter tips to magnets outside of the body. Specifically related to distinguishing the LAA from the pulmonary veins, since the LAA is closer to the ventricles, when a catheter is closer to the LAA, a ventricular waveform can be detected and visualized on the screen. In contrast, when the catheter is in the pulmonary veins as opposed to the LAA, this ventricular waveform is not seen because the veins are not as close in proximity to the ventricle.
Superior Vena Cava
- Similarly, how is one to distinguish the SVC from the left atrial area in proximity to the right pulmonary veins. In this case, the answer is a little different. However, the basic principles are similar in that the technique involves taking advantage of what is already known about the electrical behavior of the heart. This issue arises because the SVC lies directly anterior to the right pulmonary veins as it enters the right atrium. In this case, the interventional cardiologist can Pace the left atrium to distinguish signals coming from the SVC versus the left atrium. This is because the left atrial signals can be captured via pacing whereas signals from the SVC are not actual atrial signals and thus do not pace like the atrium.
In recent years, studies of multivessel coronary angioplasty have evaluated the fairness of randomization between surgery and intervention. The SYNTAX randomized trial compared multivessel PCI (including patients with left main stenosis) to CABG, demonstrating SYNTAX scores >34 appeared to do much better with CABG than those with lower SYNTAX scores, in whom PCI was just as good for major adverse cardiac events, with lower stroke rates.
What is the SYNTAX score?
The SYNTAX score published in 2005 is an angiographic grading tool to determine the complexity of coronary artery disease derived from multiple pre-existing classification systems. Higher scores correlate with increased complexity and higher risk in patients undergoing three vessel PCI, and worse prognosis if undergoing PCI rather than CABG.
The SYNTAX score is the sum of the points assigned to each individual lesion identified in the coronary tree with >50% diameter narrowing in vessels >1.5mm diameter. The coronary tree is divided into 16 segments, each given a score of 1 or 2 based on presence of disease and this score is then weighted, with values ranging from 3.5 for the proximal LAD to 5.0 for left main, and 0.5 for smaller branches.
Lesion Score: The SYNTAX lesion score is calculated by grading 11 types of lesions by answering sequential interactive questions
How do we use the SYNTAX scores?
The SYNTAX score is a useful differentiator for the outcome of patients undergoing three-vessel PCI. In general, patients with the highest scores have the highest risk and the lowest scores, the lowest risk. The SYNTAX scores can be divided into three groups. The high scores indicate complex conditions and represent greatest risks to patients undergoing PCI. High scores have the worst prognosis for revascularization with PCI compared to CABG. Equivalent or superior outcomes for percutaneous intervention were noted in comparison to coronary artery bypass graft surgery for patients in the lowest 2 groups.
Caveats and Measures to Correct
- Subjective visualization of stenosis – addressed by functional SYNTAX score (functional flow reserve)
- No clinical variables integrated – addressed by clinical SYNTAX score (age, renal function, heart failure)
|Online SYNTAX Score Calculator: http://ir-nwr.ru/calculators/syntaxscore.htm|
FUNCTIONAL SYNTAX SCORE (FFS)
The functional syntax score uses fractional flow reserve (FFR) at vessels with lesions. A study in 2011 by Nam et al. investigated whether an FFS guided syntax score would better predict clinical outcomes in comparison to the classic syntax score in patients with multi-vessel CAD undergoing percutaneous coronary intervention. Each lesion was graded and stratified based on the syntax score online calculator. The FFR was then measured for each lesion and FFS was calculated separately adding the individual scores of lesions with the actual value of FFR less than or equal to 0.80. Lesions with an FFR of greater than 0.80 were ignored.
Proportions of the study population according to the tertiles of the classic SYNTAX score (SS) (A) and those of the functional SYNTAX score (FSS) (B). After incorporating FFR into the SS to calculate FSS, 32% of patients moved from a higher-risk group to a lower-risk group as follows: 38% of the highest SS tertile moved to the medium- or lowest-risk FSS group, whereas 59% of the medium-risk SS tertile moved to the lowest-risk FSS group.
The rates of death or myocardial infarction (MI) (A), and the rates of major adverse cardiac events (MACE), as composite of death, MI, or any repeat revascularization including repeat percutaneous coronary intervention and coronary artery bypass graft (B) according to the tertiles of SS and FSS. The rate of death or MI as a critical hard endpoint was significantly different in the FSS groups unlike the SS groups. The rate of MACE was accordingly increased for the highest-risk group; this trend was attenuated in the FSS groups compared with the classic SS groups. *p < 0.01, **p < 0.001.
From the study results, the investigators concluded that recalculating the syntax score by only incorporating ischemia-producing lesions as determined by FFR decreases the number of high risk patients and better discriminates risk for adverse events in patients with multivessel CAD undergoing PCI.