The Patient:  This ECG was taken from a 14-year-old girl with a complaint of palpitations.  Her medical history is not known.

The ECG:  The rate is about 160 bpm, with an irregularly-irregular rhythm.  There are no P waves.  This is atrial fibrillation.  There are several different morphologies noted in the QRS complexes.  First, a narrow QRS with normal axis, as demonstrated in beats #5 and #7.  There are distinctly wide QRS complexes with a right bundle branch block pattern.  See beats #2, #3, and #19.  This represents aberrant conduction.  Atrial fib often displays aberrant conduction, especially when a beat follows closely after a long R-R cycle followed by a short R-R cycle. The refractory period is set by the preceding cycle.  So a lont R-R causes a longer refractory period.  The short R-R that follows finds itself in a relative refractory period - not refractory enough to prevent conduction altogether, but in this case, the right bundle branch has not yet recovered, so the impulse continues down the left bundle, bypassing the right bundle branch.  The right ventricle depolarizes late, causing a widening of the QRS.

There is a sliight variation seen in the aberrant beats, notably in #1 and #2.  This may represent varying amounts of aberrancy, where the pathways change slightly from beat to beat.  Atrial fibrillation is rare in children and adolescents, but can be caused by many factors, including stress, caffeine, endocrine disorders, obesity, and heart infections.  

This ECG was published by me on Facebook nearly a decade ago, and received some excellent comments from Dave Richley and Dr. Ken Grauer (two of our favorite Gurus).  I will reproduce them here to spare them re-writing their comments.

The Patient:     This excellent teaching case was donated to the ECG Guru by our friend, Sebastian Garay (who is an ECG Guru himself).  It was taken from a 33-year-old man who was complaining of chest pain and palpitations. He reported a similar episode about six months prior, but failed to follow up with cardiology. Was told by his medical care provider that he had atrial fib.

The ECG:      We are able in this case to provide a 12-lead ECG with each lead recorded for the entire width of the paper. This has the advantage of producing twelve ten-second rhythm strips.  Page one contains the limb leads, and page two shows us the precordial leads.

The rhythm is atrial fibrillation, with a heart rate of 133 bpm and an irregularly irregular rhythm. The QRS axis is extreme left at about -75 degrees.  This has caused Leads II, III, and aVF to be negatively deflected, and aVR and aVL to be positive. Lead I is biphasic, low voltage, and mostly positive, indicating that the axis travels almost perpendicular to Lead I, but slightly toward it.

The machine mistakenly gives us a reading for PR interval and P wave axis, even though there are no P waves.  The QRS is on the wide side without being abnormal at .10 seconds (100 ms). The QTc is within normal limits, although it might be considered “borderline”, with 431-450 usually considered borderline.

This strip shows the onset of atrial fibrillation.  A fib can be "paroxysmal," meaning that it has a sudden onset, but then stops spontaneously, usually within 24 hours to a week.  A fib can also be classified as "persistent", meaninging that the a fib lasts more than a week.  It can stop spontaneously, or be halted with medical treatment.  "Permanent" a fib is a fib that is resistent to treatment.  

The first three beats in this strip represent sinus rhythm at 75 beats per minute.  At the onset of atrial fibrillation with beat number four, the rhythm becomes irregularly irregular, and the rate is around 140-150 bpm. We can expect new-onset a fib to have a fast ventricular rate, as the atria are sending hundreds of impulses to the AV node every minute. The AV node will conduct as many of those impulses as it can to the ventricles.  Most AV nodes can easily transmit 130-160 bpm.  In a fib, the atria are quivering, not contracting. Because of this fibrillation of the atrial muscle, a fib has no P waves, and therefore, no "atrial kick".  The contribution of the atria to cardiac output (25-30%) is lost. An extremely fast rate can also lower output and overwork the heart, so one treatment goal for a fib is to lower the rate.  This can be done independently of attempts to convert the rhythm.

During a fib, blood clots can form in parts of the atria, especially the left atrial appendage.  If sinus rhythm is restored after these thrombi form, they can embolize and travel to the brain, causing stroke.  Before electively converting atrial fib to a sinus rhythm, the patient may need to be anticoagulated.