Epidemiology and Novel Oral Anticoagulants: a summary
Atrial fibrillation (A-Fib) could result in death, stroke, hospitalizations, reduce the quality of life and exercise capacity, or result in left ventricular dysfunction. 12–16 million Americans will be affected by A-Fib by 2050. Prevalence of A-Fib is greater in men than women in all age groups. Congestive heart failure, hypertension, age, diabetes mellitus and stroke (CHADS2) are the risk factors for A-Fib. A score of two or more on CHADS2 indicates a moderate to high risk of stroke.
Aspirin and Warfarin are common drugs used as blood thinners. Studies have shown that Warfarin is more effective than Aspirin. The quality of anticoagulation control is of critical importance. Some common problems associated with Warfarin are delayed onset/offset, unpredictable dose response, narrow therapeutic index, drug-drug and drug-food interactions, problematic monitoring, high bleeding rate and slow reversibility.
Top novel oral anticoagulants include Dabigatran, Rivaroxaban, Apixaban and Edoxaban. Studies have shown that Dabigatran is approximately 30% more effective than Warfarin in reducing the stroke rate. It also reduces mortality by over 10%. Patients should know that the effectiveness of blood thinners has tradeoffs with bleeding complications. Novel anticoagulants will provide more choices even though more expensive, while Warfarin will continue to be one of the choices because of its low cost and long track record.
To understand atrial fibrillation, we must have a frame of reference to what normal rhythm is, because atrial fibrillation is abnormal rhythm. The heart has its own electrical system, as it has its own plumbing. The SA mode is called the heart’s pacemaker, which beats 60-70 times a minute normally. The AV node relays the pacemaker signal and sends it down through white cables called bundle branches to electrically activate the bottom chambers and tell them to squeeze. Normally, one impulse from the pacemaker gets transmitted down to the pumps. So each depolarization, each impulse in the pacemaker causes a heartbeat. In atrial fibrillation, everything breaks down; patients develop these tiny circuits that spin chaotically, causing the top chambers to beat continuously. Instead of being a 60-70 beats per minute in a normal state of relaxation, the heart rate is about 500 beats a minute. An open heart in the operating room simply quivers if it has atrial fibrillation. Because it is beating so rapidly, the AV node gets bombarded with electrical impulses; not every impulse gets down, and the AV node slows down those impulses so only every third to fifth beat gets down, resulting in a highly irregular rhythm.
Atrial fibrillation is chaos in the top chambers, which causes chaos in the bottom chambers. Short circuits and extra beats in the upper half circumvent the normal pacemaker. In the majority of cases, these extra beats originate from the pulmonary veins, which connect the heart and lungs together, like glue, so that oxygen can get to the heart from the lungs. There are two sets of veins: the upper vein and lower vein on the left, and the same on the right. These little veins have muscle strands that develop irritable firing that conduct from the veins into the heart. When that happens, it triggers atrial fibrillation. This is the mechanism that underlies atrial fibrillation. It was a seminal observation from the late 1990s from Bordeaux, France, to understand why people went into atrial fibrillation; before, no one really knew. This understanding underlies a lot of the therapies that we now offer patients with atrial fibrillation.
When patients are taken to electrophysiology labs to try and eliminate atrial fibrillation, random firings can be seen. It’s the dominant mechanism in the majority of patients. Why do people get these skip beats? We don’t know—we see them in people that are 15, and people that are 90. They tend to become more frequent over time; they tend to become more frequent when there are diseased parts in the heart—people with heart attacks, high blood pressure, diabetes, sleep apnea; other things can make them fire, but in some people there is no rhyme or reason. It just happens.
When looking at the prevalence of atrial fibrillation based on age, one sees that as people age, the prevalence of atrial fibrillation becomes higher. 15% above the age of 70 are documented to have atrial fibrillation. This is old data, however, so the number has likely gotten a lot higher. Some practices span from teenage years to the nineties, so it’s a common disease. Part of treatment is related to symptoms. The most common reason that people get to doctors is because they have atrial fibrillation and have symptoms, so the most common types of symptoms that people with this disease have are: palpitations, when the heart rate is fast and pounding or beating irregularly; shortness of breath, particularly in patients with very fast rhythms; fatigue, feeling tired, the inability to do what one wants to do; lightheadedness; and chest pain, from blockages in heart arteries. An EKG from a typical patient tells us that this patient had atrial fibrillation, and had a very fast heart rate. Almost everybody that has atrial fibrillation that would have a heart rate so fast would feel it, and the symptoms can run the whole gamut. Most commonly, they feel rapid palpitations. This is probably the most common scenario with atrial fibrillation.