The Lack Of New Drugs For Rhythm Control Of Atrial Fibrillation: A Stagnant Pipeline

“It does not matter how slowly you go as long as you do not stop”
– Confucius
Atrial fibrillation (AF) is the most common arrhythmia in the world1. This potentially malignant condition can dramatically raise the risk for stroke. Many patients are symptomatic, and those with congestive heart failure may suffer worse outcomes when afflicted with AF2. Undoubtedly with these patients, avoidance and prevention of AF is desirable. Anticoagulants are a mainstay for stroke prevention, and there are several to choose from. Today my article addresses the rhythm control drugs, or lack of. Here lies the problem: the (few) available oral agents are often not well tolerated, and antiarrhythmic drugs (AAD) are notorious for their potential for adverse effects.
Patients nowadays are internet savvy and very commonly will “research” their prescription medications. I cannot even begin to estimate how many patients with highly symptomatic AF I have met who were reluctant or downright refused to take a prescribed antiarrhythmic after reading the potential side effect profile. Amiodarone is one such drug. Largely accepted as effective, many practitioners are wary of long-term use and the development of pulmonary toxicity or hepatic insufficiency although rare. Other agents such as flecainide and propafenone may cause fatigue and dizziness due to bradycardia and ancillary effects. These agents are contraindicated in patient’s structural cardiac abnormalities given concerns for heart failure and risk for ventricular tachycardia.
Sotalol, a “potassium” (Ikr) blocker is also a very old drug which needs close monitoring to identify electrocardiographic QT prolongation and the proarrhythmic risk of torsades de pointes, a potentially fatal consequence of inadvertently prolonging ventricular repolarization (more on this below). Dofetilide is another Ikr blocker which functions in similar fashion. The protocol for drug initiation requires mandatory hospitalization for the very same reason I just described.
Other agents such as disopyramide and quinidine are rarely used. Dronedarone, a form of “amiodarone light” proved to be largely ineffective and cannot be used in heart failure. Ranolazine, a delayed sodium-blocker is being studied for AF control, but its use outside the treatment for angina is off-label. Unfortunately as a whole, the current available antiarrhythmic arsenal cause electrophysiologic effects on ventricular myocardium. To negate the risks associated with the latter, the ideal AAD would have effects solely on atrial tissue.
Catheter ablation for AF has emerged has a viable treatment option for AF. The treatment paradigms generally focus on isolation of the pulmonary veins, and occasionally AF triggers outside these structures. With that being said, AF has proven to be a very formidable problem to treat, and not uncommonly repeat procedures or continued antiarrhythmic therapy is required to achieve a favorable result3. Hence the use of an AAD is done with the purpose of lowering AF burden and frequency.
Clinicians who care for AF patients were encouraged when the initial studies of vernakalant were published4. The novel drug prolonged atrial refractoriness by blocking multiple channels, including Ikur. The Ikur channel is found exclusively in the atria which made the availability of such a drug in oral form highly attractive4,5 Finally, an atrial-selective AAD with purportedly a very low risk of torsades de pointes might be available. Unfortunately, during a follow-up trial, ACT V, the trial was stopped due to concerns of drug safety. The FDA required revisions to the study protocol. The sponsor could not agree to those terms, and in March 2012 Merck abandoned development of oral vernakalant. It must be noted that the intravenous form of the drug is available in the European Union6.
Vanoxerine, a potent dopamine reuptake inhibitor was being studied in the treatment of cocaine addiction. It also was evaluated for and proved to be unsuccessful in treating Parkinsonism and depression7. However, this agent was observed to prolong ventricular repolarization as evidenced by prolongation of the QT on the surface EKG. This lead to interest as a possible antiarrhythmic. The COR-ART trial published in 2015 suggested a high rate of conversion to sinus rhythm. The medicine was in oral form and generally well tolerated. There were no episodes of torsades de pointes8. However, RESTORE SR, a small randomized trial found the drug to pose a risk for ventricular proarrhythmia in patients with structural heart disease [9]. Out of safety concerns, recruitment was terminated, and the manufacturer, Laguna Pharmaceuticals closed operations10,11.
While there continue to be marked improvements in mapping and ablation technologies for AF, clinicians are still left with the same limited medical arsenal. Perhaps greater collaboration and determination among the pharmaceutical industry may lead to finally new medical options for AF.

  1. January CT, Wann LS, Alpert JS, Calkins H, Cigarroa JE, Cleveland JC Jr, Conti JB, Ellinor PT, Ezekowitz MD, Field ME, Murray KT, Sacco RL, Stevenson WG, Tchou PJ, Tracy CM, Yancy CW; ACC/AHA Task Force Members. 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation: executive summary: a report of the American College of Cardiology/American Heart Association Task Force on practice guidelines and the Heart Rhythm Society. Circulation. 2014;130:2071-104
  2. Leong-Sit P, Tang AS. Atrial fibrillation and heart failure: a bad combination. Current Opinion in Cardiology. 2015;30:161–167
  3. Duytschaever M1,2, Demolder A1, Philips T3, Sarkozy A3, El Haddad M1,2, Taghji P1, Knecht S1, Tavernier R1, Vandekerckhove Y1, De Potter T4.PulmOnary vein isolation With vs. without continued antiarrhythmic Drug trEatment in subjects with Recurrent Atrial Fibrillation (POWDER AF): results from a multicentre randomized trial. Eur Heart J. 2017 Dec 2. doi: 10.1093/eurheartj/ehx666. [Epub ahead of print]
  4. Torp-Pedersen C, Raev DH, Dickinson G, Butterfield NN, Mangal B, Beatch GN .A randomized, placebo-controlled study of vernakalant (oral) for the prevention of atrial fibrillation recurrence after cardioversion. Circ Arrhythm Electrophysiol. 2011;4:637-43
  5. Camm AJ, Capucci A, Hohnloser SH, Torp-Pedersen C, Van Gelder IC, Mangal B, Beatch GN, AVRO Investigators. A randomized active-controlled study comparing the efficacy and safety of vernakalant to amiodarone in recent-onset atrial fibrillation. J Am Coll Cardiol. 2011;57:313-21
  6. Camm AJ. The Vernakalant Story: How Did It Come to Approval in Europe and What is the Delay in the U.S.A?Curr Cardiol Rev. 2014; 10:309–314
  7. Preti A. New developments in the pharmacotherapy of cocaine abuse. Addict Biol. 2007;12:133-51
  8. Dittrich HC, Feld GK, Bahnson TD, Camm AJ, Golitsyn S, Katz A, Koontz JI, Kowey PR, Waldo AL, Brown AM. COR-ART: A multicenter, randomized, double-blind, placebo-controlled dose-ranging study to evaluate single oral doses of vanoxerine for conversion of recent-onset atrial fibrillation or flutter to normal sinus rhythm.Heart Rhythm. 2015;12:1105-12
  9. Piccini JP, Pritchett EL, Davison BA, Cotter G, Wiener LE, Koch G, Feld G, Waldo A, van Gelder IC, Camm AJ, Kowey PR, Iwashita J, Dittrich HC. Randomized, double-blind, placebo-controlled study to evaluate the safety and efficacy of a single oral dose of vanoxerine for the conversion of subjects with recent onset atrial fibrillation or flutter to normal sinus rhythm: RESTORE SR. Heart Rhythm. 2016;13:1777-83

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Christian Perzanowski is an electrophysiologist in Tampa, FL. His main interests are in ablation techniques for atrial fibrillation and device therapy for congestive heart failure.

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