Introduction
Beta-Blockers
Calcium Channel-Blockers
Digoxin
Sodium and Potassium Channel-Blocking Drugs
Summary
Antiarrhythmic medications are, as the name suggests, a group of medications used to treat cardiac arrhythmias, which are any abnormalities in the heart’s rate or rhythm. Given the many types of medicines used for the prevention and control of arrhythmias, this can be a very complicated area, even for doctors.
I would like to organize this section on antiarrhythmic medicines into groups. First, I will identify a category of medicines and briefly explain how they act on the heart. Next, I will name the main examples of medicines from each group. I will always name the generic name, with the brand name in parentheses. For the most common medicines, I will discuss the reasons doctors use them and the main side effects seen.
This article may not discuss a medicine that you have been prescribed. I advise all of my patients to save a package insert from their medicines in a folder. If you think you are experiencing a side effect, you can quickly check to see whether your medicine may be causing it. This is a useful practice for all of your medicines, not just antiarrhythmics. However, I will warn you that package inserts will list many, many side-effects (or adverse reactions). This does not necessarily mean that the medicine is as dangerous as it sounds, since many side effects (such as headache, dizziness, fatigue, nausea, etc.) occur even with placebo (fake) pills during research studies. Nevertheless, you should understand each and every medicine you use and bring up any concerns with your doctor. Always speak with your doctor before starting or stopping any prescription or over-the-counter medicine.
Health
Beta-blockers may be the most common antiarrhythmic medicines used by doctors. They block the nervous system from exciting the heart and tend to slow the heart rate slightly. These medicines are used for treating high blood pressure, coronary artery disease, and congestive heart failure in addition to arrhythmias. Part of the reason they are such helpful medicines for patients with coronary artery disease and congestive heart failure is that they help prevent cardiac arrhythmias.
Some examples of beta-blockers include propranolol (Inderal), metoprolol (Lopressor or Toprol XL), atenolol (Tenormin), nadolol (Corgard), timolol (Blocadren), bisoprolol (Zebeta), labetolol, (Normodyne or Trandate) and carvedilol (Coreg).
Beta-blockers are used to slow the abnormally fast heart rate in certain arrhythmias, such as atrial fibrillation and atrial flutter. Atrial fibrillation and atrial flutter are two arrhythmias that arise from the atrium (upper chambers of the heart) and usually cause the pulse to be rapid and irregular. In addition, beta-blockers can prevent certain rhythms all together, most notably supraventricular tachycardia (SVT), an arrhythmia that is associated with frequent rapid bursts of palpitations. Finally, beta-blockers have been shown to prevent arrhythmias that lead to sudden cardiac death. Sometimes, doctors like to combine beta-blockers with other antiarrhythmics for enhanced effects.
Beta-blocker side effects
Although most patients are able to take beta-blockers without difficulty, there are a number of important side effects. First, these drugs should be used cautiously if you have asthma, emphysema, or other lung diseases. The reason is that beta-blockers can worsen the wheezing or airway obstruction seen in these disorders. There are a group of "selective" beta-blockers available that act on the heart much more strongly than they act on the lungs. These are useful when mild lung disease is present. Examples of these selective beta-blockers include metoprolol, bisoprolol, and atenolol.
The second important side effect of beta-blockers is impotence (or erectile dysfunction) in men. This is a fairly common problem, especially since most men who need beta-blockers may already be prone to have erectile dysfunction (because of the presence of chronic illnesses such as diabetes, hypertension, and atherosclerosis). Next, beta-blockers can cause blood pressure to become too low. This may not come as a surprise since these same medicines are used to lower high blood pressure in patients with hypertension. If you have diabetes, it is possible that a beta-blocker could make it harder to notice the symptoms of low blood sugar. Beta-blockers can still be very helpful for diabetics, but I recommend careful blood glucose monitoring. Finally, beta-blockers may cause what we call "constitutional symptoms," which refer to feelings of fatigue, mild depression, or lack of energy. In each case, it is important to discuss any side effects with your doctor. It is always a case-by-case issue whether the benefits of a medicine outweigh the side-effects or risk.
Calcium channel-blockers are medicines that bind to a calcium channel in the heart and blood vessels. Some calcium channel-blockers may slow the heart rate slightly, these medications are useful in treating arrhythmias. The two calcium channel-blockers that are most often used as antiarrhythmics are diltiazem (Cardizem, Dilacor, or Tiazac) and verapamil (Calan or Isoptin). Other calcium channel-blockers such as nifedipine (Procardia or Adalat), amlodipine (Norvasc), nisoldipine (Sular), and nicardipine (Cardene) are good blood pressure medicines, but are less helpful in controlling arrhythmias. They are also useful in slowing the heart rate in atrial fibrillation and/or preventing episodes of SVT. However, they are probably less useful (except in rare cases) than beta-blockers for ventricular arrhythmias.
Calcium channel-blocker side effects
Side effects occur less often with calcium channel-blockers than with beta-blockers. But they also have fewer proven benefits in patients with various heart diseases. In fact, some calcium channel-blockers may even be dangerous in certain heart conditions such as congestive heart failure, so check with your doctor to make sure that your calcium channel-blocker is not harmful if you have an underlying heart problem. Some of the side-effects seen include leg swelling, low blood pressure, abnormally slow heart rhythms, constipation, headache, or dizziness.
Digoxin is in a class of its own. Its brand name is Lanoxin. Digoxin acts on a protein in the heart that pumps sodium and potassium. It works on arrhythmias by slowing the heartbeat slightly. It also makes the heart contract a little more forcefully, which explains why it originally was prescribed to patients with congestive heart failure (CHF), a disease where the heart does not contract strongly enough.
In treating arrhythmias, I use digoxin to slow the heart rate in atrial fibrillation or atrial flutter. However, digoxin is rarely strong enough to slow the heart rate sufficiently by itself. It usually needs to be combined with a beta-blocker or calcium channel-blocker. Also, digoxin is often used to prevent episodes of SVT. The side effects of digoxin are most pronounced when the blood level becomes too high. For this reason, I give older patients or patients with kidney problems a lower dose. Also, it is a good idea to check blood levels occasionally to make sure that the level is not dangerously high. Particularly when the blood level becomes too high, digoxin can cause a variety of cardiac arrhythmias, which may be either too fast (called tachyarrhythmias) or too slow (called bradyarrhythmias). In addition, digoxin can cause nausea, poor appetite, fatigue, or visual disturbances. If you take digoxin and notice these side effects, I recommend that you contact your doctor to have the digoxin blood level checked.
Sodium and Potassium Channel-Blocking Drugs
Sodium and potassium channel-blocking drugs have been in use for many years. They bind to proteins in the heart that allow either sodium or potassium to pass into and out of cells. There are many of these medications on the market and some even have "combined activities," meaning they bind to other channels in the heart as well. This group of medicines is most useful in stopping or preventing a variety of arrhythmias including atrial fibrillation, atrial flutter, SVT, and ventricular arrhythmias.
One very important point: all of these medicines can cause arrhythmias even though they are used to suppress arrhythmias! We call this the pro-arrhythmic effect and this is one of the main problems with many anti-arrhythmic medicines. For this reason, it is often a good idea to have a cardiologist involved with your care if you need sodium or potassium channel-blocking drugs. In addition, patients using these medicines generally require occasional blood testing and ECGs (also called an EKG or electrocardiogram). An ECG is a recording of the heart’s electrical activity from small adhesive pads placed on the arms, legs, and chest.
Since it is more difficult to make generalizations about this group of medicines, I will review the side effects for each drug individually.
Quinidine (Quinaglute or Quinalan) can cause an upset stomach (including nausea and diarrhea), ringing in the ears, dizziness, and tremor. Since quinidine can cause abnormal blood counts, patients using quinidine should have periodic blood tests done.
Procainamide (Pronestyl or Procanbid) can also cause nausea and diarrhea. In addition, patients taking procainamide occasionally complain about a bitter taste in the mouth or a depressed mood. Like quinidine, procainamide can cause low blood counts, so occasional blood tests are important—both to check on the level of the medicine in your blood and to monitor your blood count. Finally, up to one-third of all people using procainamide develop symptoms that resemble lupus (rashes, arthritis, kidney malfunction), which generally requires stopping the medicine.
Disopyramide (Norpace) can cause dry mouth, blurred vision, and in older men, difficulty urinating. In addition, certain types of glaucoma can worsen on disopyramide and congestive heart failure can become more difficult to control.
Lidocaine (Xylocaine) is only available for use in the hospital. It can cause confusion, nervousness, dizziness, seizures, and fatigue. Most of these side effects become evident when the blood level gets too high, so you would have frequent blood tests if you were in the hospital on lidocaine.
Mexiletine (Mexitil) can cause stomach upset, nausea, vomiting, dizziness, and tremors. Patients using mexiletine may very rarely experience seizures, rashes, or hepatitis (liver inflammation).
Flecanide (Tambocor) can cause blurred vision, headache, dizziness, tremors, rashes, stomach pain, diarrhea, and impotence. Flecanide should not be used if you have certain underlying heart problems, such as coronary artery disease (CAD) or congestive heart failure (CHF).
Propafenone (Rythmol) can cause stomach upset, dizziness, lightheadedness, nausea, and a metallic taste. Like flecanide, propafenone should not be used if you have certain underlying heart problems.
Sotalol (Betapace) actually combines a potassium channel-blocking medicine with a beta-blocker. Therefore, all the side-effects seen with beta-blockers can be seen with sotalol. Unlike beta-blockers, sotalol can cause abnormal fast heart rhythms.
Amiodarone (Cordarone) does it all—it binds to sodium, potassium, and calcium channels in addition to being a beta-blocker. It is one of the most powerful antiarrhythmic medicines in suppressing arrhythmias, but it also has a large number of frequent side effects. In fact almost every part of the body may eventually be affected by amiodarone. Common side effects seen early after starting amiodarone include nausea, vomiting, constipation, and fatigue. Side effects seen with long-term use (several years) include thyroid dysfunction, lung disease, visual problems, discoloration of the skin and inflammation of the liver. Some of these side effects may not resolve even after amiodarone is stopped. Amiodarone also can affect the level of other medications. It is important to review all of your medicines with your doctor, adjusting the doses or closely monitoring the levels, when starting amiodarone.
Hopefully, this introduction has provided you with useful information about the treatment of cardiac arrhythmias with medications. It would be impossible to discuss every medicine in complete detail. I encourage you to keep careful track of all of your medications and discuss any concerns or possible side effects with your doctor. This advice is especially important for antiarrhythmics. If you are using an antiarrhythmic medicine, it is a good idea to read the information that the pharmaceutical company includes with the medication and keep it handy for reference as needed.
