Keeping to the beat in rate control
Controlling tachycardia is an important element in regulating circulatory problems in AF, perhaps most importantly during the chronic phase of the disease, and ongoing trials continue to illuminate the merits of various drugs available to return rate to its normal range.
Speaking to Boston AF Symposium News, Kevin Heist (Massachusetts General Hospital, Boston, MA, USA) laid out the indications of different rate-controlling agents and his hopes as to what future research could address.
Rate control, the subject of Dr. Heist’s presentation taking place on Friday evening here at Boston AF, is actually the only session following this vein, as he observed: “From a big picture perspective, most of the meeting focuses on ablation and to a lesser degree, anti-arrhythmia drugs to maintain normal rhythm,” he said. “But for probably the majority, if not a very large minority of patients, rate control is the best strategy. People in the field recognize that, but very little is said about rate control, so it’s an under-appreciated but important aspect of AF treatment.”
Whilst neither dominate, there are clear factors that dictate their application under different circumstances. Dr Heist continued: “It’s generally believed that the older patients get, the more appropriate rate control becomes. So for people in their eighties and beyond, rate control is by far the common strategy. For people that are younger, especially much younger than that, rhythm control is much more heavily used. The second big factor is symptoms. If someone doesn’t have symptoms from AF when they’re rate controlled, there is no evidence that doing anything different benefits them. So if someone feels fine when they are rate controlled, we don’t have any evidence that either antiarrhythmic drugs or ablation benefits them.” Within the realm of rate control, conflicting data that have emerged from trials of different drugs may make it difficult for physicians to make balanced decisions. Describing the state of the research at present, Dr Heist said: “It’s clear that digoxin is not the best agent, that it is inferior to other agents. A very recent analysis which is still in press in the European Heart Journal actually shows higher potential mortality on digoxin. So it’s pretty clear that digoxin, at least as a soul therapy, is not the drug of choice.
“The other major classes of drugs are beta blockers and calcium blockers, and there are conflicting data on which of those are better; they are probably roughly equivalent, but you can find studies suggesting one or the other type of drug is better. Digoxin may be helpful in some cases as an add-on agent, especially for heart failure. But usually beta blockers or calcium blockers are the first line agent. An antiarrhythmic drugs called dronedarone was recently studied in people with permanent AF. Being used partially for rate control it showed worse outcomes. So it’s clear that dronedarone should not be used for rate control.”
Physician preference, therefore, may play a role when there is no other indication; however, considering other, sometimes unrelated, conditions that patients may have should give clearer indication as to the most suitable drug to prescribe. “Studies have been done and, at least for beta blockers and calcium blockers, it is not really clear if one or the other is superior,” Dr Heist explained. “So for a patient with no comorbidities, it probably doesn’t matter much. You try one, and if that works you stick with it; if they don’t feel well on it, then you go to something else.
“But there are specific classes of patients where one or the other drugs is not ideal. People with heart failure benefit from beta blockers for other reasons, so that should be the first line agent. But beta blockers can make asthma worse, so for people with asthma calcium blockers would be the drug of choice. But for a typical patient without comorbidities, it’s probably fine to choose either as an initial agent.”
Past studies have taught us that intuitive thinking about medications are not necessarily correct, but care must be taken in generalizing these data from one type of patient to another, especially those with comorbidities. “One of the studies that had somewhat surprising findings was published a couple of years ago now, called RACE-21, where they looked at strict versus lenient rate control, and many in the field – myself included – thought that the more strict rate control would be superior, and it was not. There was no measurable benefit to the strict rate control. But that was in a group of relatively healthy patients. There are data coming from a few different sources indicating that fast rates might be more harmful in heart failure patients, but we don’t have any studies really proving that, in AF patients with heart failure, stricter rate control is beneficial. So I would say that is one of the elements that is probably most lacking.
“The other issue is that there are now a large number of studies comparing medical rhythm control versus rate control (antiarrhythmic drugs versus rate control) and it’s pretty clear that in many patients rate control is at least as good. But similar studies haven’t been done comparing rate control versus rhythm control by ablation, and that’s another big unanswered question.”
1) Rate Control Efficacy in permanent atrial fibrillation, a comparison between lenient versus strict rate control in patients with and without heart failure. http://www.trialregister.nl/trialreg/ admin/rctview.asp?TC=425