13 Jun Atrial Fibrillation for exercise professionals part 2
Atrial fibrillation: medications, ablation therapies, case study (AVN ablation, PPM, AICD)
Medications for atrial fibrillation
Hi Steve Selig, founder of fit.test. I want to start by quickly summarizing the main medical interventions for people with atrial fibrillation. First, antiarrhythmic medications are designed to try to get people back into a rhythmic normal heart. The main class of drugs are the potassium channel blockers (e.g. amiodarone and sotalol) so you will see quite a lot of newly diagnosed people on one of these drugs; the interesting thing is that even if rhythm is not restored to sinus rhythm, these drugs can also help to control heart rate and prevent very high heart rates.
Other drugs are usually prescribed for the long term management of people with permanent AF. These drugs (beta blockers, digoxin) are geared to controlling and preventing very high heart rates, but are not prescribed to restore sinus rhythm.
Cardioversion refers to an elective defibrillation procedure under light anaesthetic, and this is designed to shock the upper chambers of the heart (atria) back into sinus rhythm, which is where the actual fibrillation is originating.
Moving onto ablation therapies, there are two main approaches. The first is called pulmonary vein isolation by deliberating scarring the tissue where the four pulmonary veins into the left atrium. The insertions of the four pulmonary veins into the left atrium are frequently the foci of the arrhythmia. Scarring prevents the arrhythmic foci from escaping from that region and dominating the rhythm of the atria, thereby enabling normal sinus rhythm to resume and persist. Scarring is achieved using either a heat stimulus (radioablation) or a freezing stimulus (cryoablation).
The second is called atrioventricular nodal ablation. The AVN is the second most dominant pacemaker cluster after the sinoatrial node (SAN) that is responsible for normal sinus rhythm. The purpose of the AVN is to control excitation traffic into the lower pumping chambers (left and righ ventricles) and in doing so, regulates and controls ventricular rhythm. In a healthy heart, ventricular rhythm slaves of atrial rhythm (and sinus rhythm). In atrial fibrillation, the AVN controls how much electrical chaos reaches the ventricles: too much and there will be very heart rates out of rhythm (tachyarrhythmias). The idea behind AVN ablation is to electrically isolate the ventricles by destroying the AVN “bridge” between the atria and the ventricles. Once the ventricles are isolated, then they MUST be paced using a permanent pacemaker (PPM) that is implanted either at the time of the AVN ablation or shortly before the ablation treatment. Without a PPM but after AVN ablation, the individual is exposed to ventricular arrhythmias and tachyarrhythmias which are dangerous and can lead to sudden cardiac death. Hence the need for PPM for all patients undergoing AVN ablation. The interesting thing for exercise professionals to recognise is that the patient who has undergone AVN ablation and PPM implantation, the atria remain in fibrillation for the rest of the individual’s life but the ventricles are paced and in rhythm. The lack of atrial function (because of the continuing AF) will make very little difference to overall cardiac performance and exercise performance. In other words, these patients can lead a normal active life, but will not make the Olympics! Finally, because the atria continue to fibrillate for the rest of the individual’s life, an oral coagulant (OAC) or other anti-coagulant must be prescribed for life to prevent intra-atrial thrombus from forming that could cause a stroke.
How do cardiologists select the ablation approach best suited to their patients? Most individuals will undergo PVI and this has good long term success rates of about 70-80% (i.e. patients not regressing back to AF). Some patients are assessed as PVI not likely to be successful due to very enlarged atria. For these individuals, AVN ablation and PPM implantation is often a good option because it does not matter that the atria are very enlarged (dilated) as the ventricles do not depend on the atria for either electrical stimulus or muscle performance.
Case study: AVN ablation, PPM, AICD
Case study: Now to my case study of a 53 year-old female with a family history of atrial enlargement who has been deeply troubled by atrial fibrillation for two years leading up to when I met her.
In 2019 a cardioversion (elective defibrillation under light anaesthesia) gave her some symptomatic relief for a couple of months. But she soon regressed back to AF. After one more unsuccessful attempt at cardioversion, it was decided that she undergo AVN ablation and PPM implantation.
I saw her a month after her AVN ablation and about five weeks after her pacemaker had been fitted, so the pacemaker was relatively new. To prevent intra-atrial thrombus forming, the atria need protection with lifelong prescription to an oral anti-coagulant. Hence rivaroxaban (Xarelto).
We did a multi-stage exercise test and you can see about 10 increments in exercise intensity (10 minute test) until she reached a fairly high level of exercise intensity. Her PPM had only recently been fitted and the PPM did not really respond to the increasing exercise intensities. This does not make exercise unsafe for her, but I was able to report this back to the primary care medical practitioner who then on-referred her for PPM tuning which happened. She then was able to resume exercise with more appropriate rises in heart rate in response to exercise.
I was able to use fit.test to assess her even with these inappropriately low heart rates. That is because unlike almost all fitness testing apps, fit.test does not depend on heart rates to gauge fitness or exertion levels.
Now if you had used any other app that had used the age-predicted HRpeak, three would have huge errors. The main error is an over estimation of her fitness which could make an exercise plan dangerous.
I hope you got something useful out of this topic. If you want to contact me as always, firstname.lastname@example.org. Bye for now. Have a great day.