Atrial fibrillation is the most common cardiac arrhythmia, and is a major risk factor for ischemic stroke. An ischemic stroke occurs when a blood clot from within the heart, or elsewhere, breaks loose and travels upward, through the carotid arteries, to the brain. The clot continues it upward track until the caliber of the artery is too small for it to travel farther. The clot lodges in the blood vessel, and immediately shuts off blood flow to the brain beyond that point. The blood carries oxygen to the brain, and when the oxygen supply is cut off, the brain cells die! An ischemic stroke is just like a heart attack. When a blood clot blocks the flow of blood, the brain tissue beyond the blockage is permanently damaged. The damaged brain tissue is called a cerebral infarction.
This factor alone is enough to make atrial fibrillation a potentially serious problem, so doctors watch these patients closely. They prescribe blood thinners (anticoagulants) to prevent blood clots, and use trans-esophageal echocardiography to be sure clots aren’t developing within the heart. It’s important for your doctor to know if you have atrial fibrillation. A large percentage of patients are asymptomatic and don’t realize they are in atrial fib. An equally large number of patients have symptoms and know when they’re in A fib. They are the easy ones! The difficult patients are the ones who have unexplained symptoms that are later found to be caused by A fib.
When a patient’s first sign of atrial fib is an ischemic stroke, it’s too late to help. The damage you’re trying to prevent has already occurred. Screening patients for atrial fib should go a long way toward preventing this disastrous outcome, if atrial fibrillation is detected. The problem is, it very often is not. In many people, Atrial fib occurs intermittently and isn’t occurring during the procedure done to find it. That’s a big problem and part of the reason screening for A fib is unproductive. However, if the doctor discovers a patient is in atrial fib, starting him on blood thinners is a must.
How then does the doctor “screen” for atrial fibrillation? There are several ways which involve hands-on examination or sophisticated technology. The easiest technique is to feel the patient’s radial (wrist) pulse and/or check his blood pressure. The doctor is trained to recognize an irregular pulse by feeling the artery in the wrist or hearing irregularity when checking the BP. Finding an irregular pulse then leads the doctor to listen to the patient’s heart and perform an electrocardiogram (ECG), a record of the electrical activity of the heart.
The ECG is the gold standard diagnostic test for a fib. It can be done using the standard 12-leads or a single lead called a rhythm strip. An ECG records the electrical activity of the heart from 12 locations on the body. The 12-lead ECG, in totality, gives a picture of the entire heart. A single lead, rhythm strip ECG can only tell the doctor the patient’s rhythm, which in the case of atrial fibrillation, is all you want to know.
If atrial fibrillation occurs intermittently, an ECG can easily miss it. The ECG must be done when the arrhythmia is occurring to capture and diagnose atrial fibrillation. To accomplish that, doctors have continuous monitoring devices the patient wears for a week or more. The Holter monitor is one such device. It attaches to the patient’s chest via wires and adhesive electrode patches and records every heart beat while it is attached. The monitor is later run through a computer to identify any abnormal rhythms. The patient keeps a diary and records his symptoms which are then correlated to rhythms on the monitor.
Another such recording device is an event monitor. The patient places the device against his chest whenever he feels some abnormal heart beats. The monitor records the heart activity and sends a report to the doctor. The patient carries the device with him and applies it against his chest whenever he feels “something funny” inside.
Other devices such as the “smart watch” and the smartphone can detect atrial fibrillation, but have a degree of unreliability. Automated blood pressure cuffs and finger touch pads are programmed to detect A fib, but again require confirmation with an ECG or other reliable recording device.
The techniques and devices mentioned previously are not screening procedures, but are actually diagnostic tools. There really isn’t a procedure used to screen for atrial fibrillation.
Routine ECG’s, monitoring devices, and vital sign instruments are programmed to detect atrial fibrillation, but only help if an abnormality is found. The diagnosis of Atrial fib is missed all the time, especially if it’s intermittent. There is little benefit to routine ECG’s because the yield of abnormal findings is very small. The United States Preventive Services Task Force, USPSTF, has extensively studied screening for atrial fib and finds insufficient evidence to recommend screening ECG’s. The yield does not justify the cost. Plus the vast majority of those ECG’s will be normal.
To diagnose atrial fibrillation, the doctor has to have a high index of suspicion, examine his patient closely, and listen to what the patient says. Also, the patient has to tell the doctor if, when, and how often he has the arrhythmia. The doctor can order tests to confirm the diagnosis, but may still not determine what’s going on. The diagnosis is made if the doctor tries hard enough to find it. If he blames symptoms on your “nerves,” don’t take that for an answer and insist on more tests. Atrial fibrillation will eventually be diagnosed.
Reference: USPSTF. Screening for Atrial Fibrillation. JAMA 2022 Jan 25;327(4):360-366.
