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Dawn's picture

Complete Heart Block or High Grade AVB?

The patient:  This ECG was obtained from a 91-year-old woman who was complaining of weakness.  Unfortunately, we have no other information. 

The ECG:  This ECG has something for your basic students, and even more for the more advanced learners.  The first thing  that anyone should notice is the slow rate.  The ventricular rate is around 35 bpm, and regular.  If the patient is showing signs of poor perfusion, we would stop here and prepare to increase the rate with a temporary pacemaker (transvenous or transcutaneous). Why is the rate so slow?  There is no P wave in front of each QRS, so this is not sinus bradycardia.  Rather, we see P waves at a rate of approximately 100 bpm, wit a very regular rhythm.  Beginners should “march out” the P waves with calipers or by marking a straight edge piece of paper.  There are 15 P waves on this ECG – some are buried within QRS complexes (QRS #3) or T waves (QRS #4).

 Because there are two distinct, regular rhythms, but they do not track with one another, we know this is possibly third-degree AV block (complete heart block).  Another clue is that there are no steady, repetitive PR intervals, which means there is no relationship between the atrial rhythm and the ventricular rhythm.

 For more advanced learners, it is helpful to try to identify the origin of the escape rhythm.  If it is junctional, the AV block is above the junction.  If the escape is ventricular, the AV block is below the junction.  A junctional rhythm is usually between 40 – 60 bpm, with a narrow QRS.  Ventricular escape rhythms are usually less than 40 bpm and with wide QRS complexes.   This ECG will be a little challenging on this front, because the rhythm has some characteristics of junctional rhythm and of ventricular rhythm.

Dr A Röschl's picture

SICK SINUS SYNDROME

This EKG shows the classic features of sick sinus syndrome. Initially, there is an accelerated atrial rhythm/atrial tachycardia. After a pre-automatic pause of 2609 ms, a ventricular premature beat occurs, followed by a junctional escape rhythm. Pre-automatic pause is a pause after a tachycardia and before an automatic rhythm, like sinus rhythm or, in this case, junctional escape rhythm. Therefore, there is an alternation between tachycardic phases and very bradycardic rhythms, the classic bradycardia/tachycardia syndrome. Paper speed is 12.5 mm/sec.

Dawn's picture

Junctional or Low Atrial Rhythm

The Patient   This ECG was recorded from an 86-year-old man who was weak, pale, and diaphoretic. He was hypotensive, with a BP of 88/54.  He denied chest pain or shortness of breath.

The ECG   The 12-lead ECG shows a bradycardia at about 60 beats per minute and regular.  The QRS complexes are narrow, at a little less than .08 seconds (800 ms).  The P waves are negative in Leads II, III, and aVF and positive in aVR.  This is an indication that the P waves are traveling in a “retrograde” fashion – backward. The origin of the P waves has to be the AV junction or the lower atria for this to happen.  The PR interval is on the short side of normal at about .12 seconds (120 ms), possibly even less.  This is common in junctional rhythm, as the impulse starts at the AV junction, and travels back through the atria and forward through the ventricles at the same time.

There are no premature beats, and the ST segments are not elevated or depressed. There are no T wave inversions, except for aVR, where it is normal.

Assessment    One cause of junctional rhythm is sinus brady.  That is, the sinus node begins firing so slowly that the junctional pacemaker “escapes”, and takes control of the heart.  When the sinus node speeds up, it may once again take over the heart’s rhythm from the junction.  The fastest pacemaker controls the heart. A junctional rhythm may escape when the sinus node fails or there is a complete AV block in the AV node area.

Patient Outcome    This patient was diagnosed with orthostatic hypotension, bronchitis, and urinary tract infection. He was treated in the hospital and cleared by a cardiologist for discharge two days later.

Our thanks to Michael Francis and Chris Burden for donating this ECG.

Dawn's picture

Complete AV Block With Junctional Escape Rhythm

This ECG is from a 78-year-old woman.  We do not know any clinical details.

 We break from our usual habit of removing the ECG machine’s interpretation of the ECG to serve as a reminder that the computer interpretation can be wrong.  ECGs should ALWAYS be interpreted by a knowledgeable person.  The machine interpretation can serve as a reminder, but should not take the place of human interpretation. 

Here is what we DO see:  There is a normal sinus rhythm present, as evidenced by the regular P waves that do not change their morphology.  Some of the P waves are “buried” behind QRS or T waves.  The atrial rate is 95 bpm. 

The ventricular rhythm, at 40 bpm, is also regular, but is separate from the atrial rhythm.  Even though some of the P waves LOOK like they have conducted to produce QRS complexes, they have not.  The PRIs are not all the same.  Neither do they “progressively prolong”.  There is no irregularity of the QRS rhythm or variation in QRS morphology.  We see the classic “AV DISSOCIATION” of complete heart block. 

When there is a third-degree AV block with a narrow-QRS escape rhythm, we can assume the block is in the AV node.  The junction is the escape focus, producing a narrow-complex rhythm between approximately 40-60 bpm.  In this case, the QRS is slightly wide at 112 ms (.11 sec), and the QRS complexes in several leads are fragmented.  Some might argue that there is an idioventricular escape mechanism.  But, with a normal frontal plane axis, borderline width,  and no T wave inversions, the rhythm looks more supraventricular.  The R wave progresson on the precordial leads shows a persistently negative QRS with late transition in V5.  The QRS complexes in V1 and V2 appear to have pathological Q waves.  When R wave progression is not normal, we should also consider electrode misplacement. 

Dawn's picture

Complete AV Block With Junctional Escape Rhythm

This ECG was taken from a 90-year-old woman.  We have no other history, unfortunately.  It is a good example of a sinus rhythm with complete AV block, also called third-degree AV block.

The defining characteristics of this rhythm include:   1) an underlying rhythm that is regular and with a physiological rate.  In other words, the P waves are not so fast that they would not be expected to conduct one-to-one.  2)  a second rhythm of regular QRS complexes that is unrelated to the P waves.

Occasionally, a P wave may occur before a QRS and appear to have a PR interval.  This is just a chance meeting, as both rhythms (P waves and QRS complexes) are regular AT DIFFERENT RATES, so we would expect them to occur near each other from time to time.  NONE of the P waves are being conducted to the ventricles to produce QRS complexes. This is a good ECG to demonstrate "marching out" the P waves to see that they are very regular, even though some are hidden in the QRS, ST segment, or T waves.

In this case, the "escape rhythm" occurs from the AV junction.  The AV junctional pacemakers are "set" at a rate of about 40 - 60 beats per minute.  Normally, the sinus rhythm arrives in the AV junction faster than that, depolarizing the junctional pacemakers and preventing them from firing spontaneously.  In complete AV block, the atrial impulse never arrives, so the junctional pacemaker is free to "escape" and become the primary pacemaker of the heart.  We recognize this rhythm as junctional because the QRS complexes are narrow, and the rate is around 40 bpm.  Knowing that the escape rhythm is from the junction tells us that the AV block is in the AV node.  The AV junction is the first available pacemaker below the block.  Had the complete AV block been lower, in the bundle branches, the QRS would have come from the ventricles and would have been wide and slower.

In very general terms, this "supra-Hisian" type of AV block is preferable to a "sub-Hisian" block.  The rate is faster, and the QRS complexes narrow, both conditions causing a better cardiac output than wide QRS complexes and extremely slow rates.  However, the effect of the block on the patient has a lot to do with the cause of the block and the symptoms the slow rate cause.  Emergency treatment of the rate may be necessary if it causes a drop in blood pressure and perfusion.  Some patients with this type of block will need a permanent implanted pacemaker, but not all. 

 

Dawn's picture

ECG Basics: Pacemaker Failure to Capture

This ECG is taken from a patient with an implanted pacemaker who was experiencing near-syncope.  She was taken to the hospital by EMS, where the pacemaker was adjusted to obtain ventricular capture.  This ECG did not have a Lead II rhythm strip, so the 12-lead ECG is being presented.  The P waves have been marked with a "P", pacemaker spikes marked with an arrow, and the QRS complexes marked with a "J" because they are junctional.  Because we can see 12 leads, or viewpoints, the morphology of the P waves and QRS complexes changes each time the machine switches to a new lead.

The underlying rhythm is sinus, with nearly regular P waves occuring at a rate of about 72 beats per minute.  The QRS complexes are also regular, but they are dissociated from the P waves.  Because the rate is near or just under 40 bpm, and the QRS complexes are narrow, this represents a slow junctional rhythm.  Because both atrial and ventricular rhythms are regular, but not associated with each other, an interpretation of complete heart block (third-degree AV block) can be made.  This explains why the patient had a pacemaker implanted.

The pacer spikes, for the most part, track the P waves, which is how this pacemaker is programmed.  They are not followed by a paced QRS complex, however.  This is failure to capture.  The second and fourth P waves did not stimulate a pacer spike because of their proximity to the T wave of the junctional beat.  The mA (energy setting) was adjusted in the Emergency Dept., and the pacemaker did not require repositioning.  The patient regained a reliable paced rhythm.

This section of the ECG Guru is meant to be for your basic students.  Pacemakers now have become very complex, with many options and variable settings.  So complex, that I would not feel comfortable getting into any more detail than I have here (although visitors to the site are welcome to).  It is important that, if you deal with patients in an emergency setting, you do not tell the patient that "something is wrong with their pacemaker" until it has been evaluated by a qualified person who can electronically interrogate the device.  It can be very difficult to determine from an ECG how a pacemaker is programmed, and how it should be reacting.  Since this patient had symptoms related to the bradycardia, and since pacemaker spikes occurred free of any refractory period and did not produce QRS complexes, it is safe to say there needs to be an adjustment.

In an emergency, with serious symptoms present, a transcutaneous or transvenous temporary pacemaker can be used.  Medications such as Atropine, epinephrine, and norepinephrine are also used, depending upon the type of AV block and the resources available.

 

jer5150's picture

Jason's Blog: ECG Challenge of the Week for April 7th - 14th.

At this time of posting, I currently have no clinical data for this patient.  This ECG is of interest because of its arrhythmic and nonarrhythmic elements. 

I can think of at least two possible explanations for the mechanism of this rhythm and both would benefit from being illustrated by a laddergram. 

One mechanism is rather exotic and has not been previously seen here on this website or discussed in the various FB forums.   

Dawn's picture

Inferior Wall M.I. With Third-degree AV Block

This ECG was obtained from an elderly woman who suffered a complete right coronary artery occlusion and inferior wall M.I.  In her case, the AV node was also affected, and she developed a third-degree AV block with a junctional escape rhythm.  A good ECG for ACLS classes as well as for ECG classes.  A lively discussion can be had regarding "types" of complete heart block and the nature of the escape rhythm - when to treat and when to leave the rhythm alone.  In this case the rate of the junctional escape rhythm was adequate for perfusion, and the patient's blood pressure was stable. Priority for treatment in this situation is restore blood flow through the coronary artery, if the patient is a candidate for PCI.  You might want to review Christopher Watford's contribution to the Ask the Expert page on AVB vs. AV Dissociation.

jer5150's picture

Jason’s blog: ECG Challenge of the Week for June 24 – July 1, 2012. Pinpoint the primary disturbance.

This patient was seen by his primary care provider (PCP) on an outpatient basis.  The PCP decided to send her patient over to me to perform a routine ECG and establish a baseline, hince the computer's statement below of "No previous ECGs available".  I printed out the above 12-lead ECG and became slightly concerned with the rhythm I was seeing.  Consequently, I also recorded six full pages of continuous rhythm (not shown here).  I don’t ordinarily resort to doing this except on those rare

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