Atrial Fibrillation

Atrial Fibrillation (AKA AFib, AF, or fib)

This is the most common rhythm disorder in the Unites States, and it’s incidence is constantly on the rise. Unfortunately, even many physicians are confused about the nature of this disease, it’s causes, symptoms, and most importantly it’s treatment. Needless to say patients are not any better off in their understanding of the disorder. In the coming paragraphs I will outline the most important facets of atrial fibrillation in a simplified, clear manner.

Mechanism – (What is AFib?)

In contrast to almost all other rhythm problems of the heart, the mechanism of AFib is the least well understood. We do know that the left atrium is where the trouble starts in most cases, and that the veins that return blood to that chamber (Pulmonary Veins) often play a critical role. Instead of the normal coordinated conduction sequence (described in the introductory section dealing with normal conduction) from the right upper chamber (sinus node) and forward, the left atrium takes over. There can be one or more areas in the left upper chamber that emit electrical signals in a very rapid, and often chaotic manner. This results in a very rapid heart in the upper chambers (400-600 bpm!). Luckily, that rate is not translated to the lower chambers of the heart because the AV node (the electrical connection between the upper and lower chambers) slows this down a bit. However, the effective heart rate may be quite rapid (between 100-170 bpm in most cases) and is always irregular in rhythm (see figure 3).

Atrial Fibrillation Definitions

Not all AFib is the same. There may be many underlying causes and other diseases that trigger AFib. These include High Blood pressure (hypertension), Heart failure, Heart Valve disease among many others. Of course, the physician must not lose sight of the ‘big picture’, and ignore these potentially important diseases that are the ‘real’ culprit resulting in AFib.

  1. Paroxysmal – This means that the AFib is not always there and that it stops by itself in less than 7 days.
  2. Persistent – This means that the AFib lasts for more than 7 days continuously.
  3. Longstanding – In this case, the AFib has been there continuously for more than 1 year.
  4. Permanent – AFib for over a year AND have failed Cardioverion (using an electrical shock to restore sinus rhythm- see below – Cardioversion). The term ‘permanent’ is  a bit of a misnomer, as even in these cases normal rhythm can often be restored.

The problem for patients

Although patients may feel completely normal while in AFib (see below – section on symptoms), there are several consequences of this arrhythmia that can cause trouble.

  1. STROKE – The most concerning aspect of this disease is the risk of stroke that is associated with it. Undetected or untreated Afib is the most common cause for stroke in the US. This can occur because when the atria are being activated so rapidly, they do not actually produce a strong contraction, rather they merely ‘fibrillate’, allowing blood to collect in the nooks, and crevices of the inner walls of the atria. If a clot forms and then dislodges to the brain, this will cause diminished or no blood flow to a particular area of the brain resulting in stroke. This complication can be easily avoided as we shall learn in the treatment section below.
  2. The heart beating TOO fast – As noted the actual lower chamber heart rate can also become quite rapid with Heart rates greater than 100 bpm while at rest. One can imagine that with a little physical activity that heart rate can accelerate to even faster rates, essentially mimicking significant exertion and causing shortness of breath and fatigue. In certain instances if the heart rate is very rapid for sustained periods of time, the heart may actually weaken as a result. All of these symptoms are certainly worse if there is pre-existing weakness of the heart.
  3. Upper and lower chamber are not beating in a coordinated fashion – This can cause a sense of palpitations, facial flushing, and generalized uneasiness.

Symptoms

Symptoms can vary quite a bit between patients. Some do not feel the AFib all, while others cannot function while in this rhythm, although most people fall somewhere in the middle of these 2 extremes. Patients can have palpitations, shortness of breath, fatigue, and lightheadedness as some of the many manifestations of AFib.

Treatment - Blood thinning medication

In many instances in order to prevent stroke in AFib, one must be treated with blood thinning medication. To determine when this is required physicians utilize a risk stratifying tool of some sort. What this means is that there are certain risk factors for stroke in patients with AFib and these have to assessed to determine if the benefit of blood thinning outweighs the potential risk (bleeding complications). There are different tools that are currently used that coalesce the risk factors into a unified score. One should keep in mind that this is merely a statistical analysis, and that the rules may not work for every single patient.

Some Risk Factors for clot formation in AFib:

  1. Age >75
  2. High Blood Pressure
  3. Previous Stroke or TIA (mini stroke)
  4. Diabetes
  5. Structural Heart Disease (such as weak heart function or valve heart problems)


Maintaining Sinus Rhythm or staying in AFib? Do you have Symptoms?- The next question to consider is must we restore normal sinus rhythm (the normal rhythm of the heart) or can one stay in AFib for the rest of one’s life  as long as the heart rate is controlled. These 2 approaches are commonly referred to as the sinus rhythm vs. rate control approaches respectively. This is a critical question that the physician and patient must discuss thoroughly  as the therapy must be highly individualized depending on a myriad of circumstances. The most important question, however, is does the patient feel unwell with their AFib. There exists a wide spectrum of symptoms in patients from the totally unaware, asymptomatic patient to the opposite extreme, of the patient who cannot function when in AFib, while most patients fall somewhere in the middle of these 2 poles.

The question of approach is easy to answer for the patients at either side of the spectrum. If one is totally asymptomatic, opt for rate control, and likewise for the very symptomatic patient do everything to restore sinus rhythm. Now on to how this can be achieved.

Rate Control Approach

This essentially means that medication will be used to ensure that the heart rate does not go too fast in AFib. This can usually be achieved with simple medications such as beta blockers or calcium channel blockers (same medications that are commonly used to treat high blood pressure). Of course, this will be independent of blood thinners. Also keep in mind that one will potentially remain in AFib indefinitely with this approach.

Sinus Rhythm Approach

There are several modalities for that can be utilized for this approach. At the outset one must realize that none of them are perfect and that a total 100% ‘cure’ for Afib is difficult to achieve.

Cardioversion (CVN)

This is a procedure that is done in the hospital under general anesthesia. Electrical patches are placed on the patient, and once asleep a current of energy is delivered in hopes of restoring normal sinus rhythm. One should understand that a cardioversion is not treating the underlying AFib, it is simply getting rid of it for a period of time. The success of the CVN, and the maintenance of normal rhythm will depend on many factors, including the duration of AFib prior to CVN. The longer one has been in AFib the  more difficult it will be to maintain normal rhythm. This procedure is often repeated periodically in cases of recurrent AFib.

Antiarrhythmic Drugs (AADs)- More Medicine!

There are many different AADs that can help treat AFib, however none are completely successful, and none are without side effects. That being said, one can do quite well with AAD therapy for prolonged periods with occasionally requiring a cardioversion (see previous section). One could actually  expect recurrence of AFib at some point while taking AADs , and this SHOULD NOT be considered failure of the medication. A cardioversion once or twice a year while taking AADs is good therapy.

There are many different AADs with different efficacies, and side effect profiles that is beyond the scope of this overview, however, whenever choosing such a medication it is critical that an ultrasound (Echocardiogram) , and a stress test be obtained prior.

Ablation Therapy

This is an invasive therapy in which a variety of catheters (wires) are inserted through veins in the groin into the heart. The purpose is to ablate (or “zap” away) different areas of the left atrium (the left upper chamber). As noted previously, the precise mechanism for AFib has yet to be discovered, however we do know that the Pulmonary Veins (PVs) are often involved as are the junctions of the PVs, and left atrium as they insert ( see figure 3). Most ablative therapy focuses on electrically isolating these veins from the rest of the Left Atrium. Additionally other lines of ablation are often created to modify the Left Atrium, and thereby prevent recurrence.

Several important factors to keep in mind:

  1. The success of ablation in patients with paroxysmal AFib is between 60-70%. This is much lower than most other ablations for other heart rhythm disorders. If one has more persistent or permanent AFib that rate drops even further.
  2. It is not uncommon to require more than one ablation for AFib. Usually 20-30% of patients will require a second or even third procedure
  3. This procedure is generally not considered first line therapy , and should be reserved for patients that are quite symptomatic, and have often failed medical treatment.
  4. One may still have AFib post ablation, and yet have reduced symptoms. The patient may feel better, but may still require blood thinning medication.
  5. Often, post ablation AADs that were previously unsuccessful now work well. This is know as hybrid therapy  – combining more than one treatment modality.

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