This is a good strip to demonstrate the change in the appearance of a T wave when a premature P wave occurs on the preceding T wave. The PACs found the atria ready to depolarize and produced a P wave that landed on top of the preceding T wave, making it appear taller than the others. The PACs also reset the sinus node, causing a slight delay before the next sinus discharge. The PACs occurred while the ventricles were still refractory, so no QRS complexes followed.
This 92-year-old patient was diagnosed with left bundle branch block on ECG, and left ventricular hypertrophy on echocardiogram. The two conditions are very often seen together, in fact, a majority of LBBB patients have LVH. Since the two conditions can have similar ECG changes, it is difficult from the ECG alone to determine the presence of LVH when LBBB is present. If the ECG criteria for LVH are present, it can be assumed that LVH is present, even in the presence of LBBB. For determining LVH by ECG criteria, the Sokolov-Lyon criteria are commonly used ( S wave in V1 + R wave in V5 or V6 > 35 mm).
The common criteria for left bundle branch block include: wide QRS complex, frontal plane axis normal or leftward, negative QRS in V1, and positive QRS in leads I and V6. LBBB is only found in supraventricular rhythms (not ventricular rhythms). The ST segment and T wave will be negative in leads with positive QRS complexes, and positive in leads with negative QRSs (discordant).
Left ventricular hypertrophy also widens the QRS, although not often as much as LBBB does. There will be discordant ST segments and T waves, which is called the "strain" pattern. It also is easier to diagnose in supraventricular rhythms, because ventricular rhythms usually have large QRS complexes due to the depolarization wave being in one direction across the heart.
For confirmation of LVH, an echocardiogram is recommended.
This ECG also has an interesting rhythm. The first beat appears normal, the second beat is a PAC. The third beat appears to arise from a different focus, which would make it an escape beat, but it is very difficult to determine this due to the very tiny P waves. After a pause, a regular sinus rhythm resumes. To see the P waves, look at the right chest leads: V1, V2, V3. Since left bundle branch block only occurs in SUPRAVENTRICULAR rhythms, it is important to determine the rhythm, and P waves are a definite sign of SV rhythm. We wish the P waves here were taller.
This ECG is a good example of sinus rhythm with aberrantly-conducted PACs. The tracing was donated to the ECG Guru several years ago by Dr. Ahmed from Sanjiban Hospital in India. We have no patient data for this tracing.
The underlying rhythm here is normal sinus rhythm. Most of the parameters – rate, PR interval, and QRS duration – are normal. The QTc interval, which is the QT interval corrected to a rate of 60 bpm, is prolonged at 568 ms. We do not know the patient’s clinical condition or medications, so we cannot guess at the reason. However, a prolonged QTc is associated with an increased risk of Torsades de pointes, a type of polymorphic ventricular tachycardia.
The first three beats appear the same (Leads I, II, and III). However, the first R-to-R interval is shorter than the second one. This could be due to rate variation, a concealed sinus block, or a premature atrial contraction (PAC). The P wave of the “early” beat, marked #1, looks slightly different from the other P waves in Lead II, but, because of the slow rate, there is no way to be sure without a longer rhythm strip. After the possible PAC, the rhythm becomes coupled, probably atrial bigeminy, where every other beat is a PAC. There are several mechanisms that cause grouped beating, but atrial ectopic bigeminy is the most common. Normally, PACs have different-looking P waves compared to the sinus beats. In this ECG, the P waves are often buried in the preceding T waves, and are hard to evaluate.
This strip shows an underlying sinus bradycardia with a rate less than 40/min. There is one "premature" beat, which can be considered to be ectopic, because it interrupts an otherwise regular rhythm. The interesting thing is that the premature beat is not terribly early - it is about 740 ms from the previous beat. If all the beats were spaced like this, the heart rate would be about 84/min. There is probably an element of "escape" here, in that the ectopic beat is able to express itself due to the slow rate. A faster sinus rate would override this ectopic focus. So, we could view this early beat as a help, rather than a problem. The most important consideration here is to address the cause of the bradycardia, and treat appropriately.
This is a good example of sinus rhythm with left bundle branch block. There is some irregularity due to a PAC at the beginning. The QRS is wide at 144 ms (.14 seconds). There is also first-degree AV block, with a prolonged PR interval of 228 ms. The criteria for diagnosis of left BBB are: wide QRS, supraventricular rhythm, and a negatively-deflected QRS in V1 with a positive QRS in Leads I and V6.
Left bundle branch block can be associated with many forms of heart disease, including CHF. It can be permanent, transient, intermittent, or rate-related. The wide QRS of LBBB significantly decreases cardiac output, causing poor perfusion symptoms in some people.
This ECG is a good one for your students who are just transitioning from reading rhythm strips to reading 12-lead ECGs. It shows the value of multi-lead assessment of rhythms. You will notice that P waves are difficult to see in some leads. Armed with the knowledge that the four channels on this ECG are run simultaneously, you can show the students how finding P waves in one lead will allow you to find them in the leads that are above and below that lead.
Similarly, it can be difficult to see the QRS width in some leads. The leads in the same vertical column can help you see the QRS's true width, even if part of the QRS is "flat" in the isoelectric baseline.
A good example of aberrantly conducted premature beats (PACs or possibly PJCs) that are conducted with a left anterior fascicular block. The underlying rhythm is sinus at about 80/min. The timing of the premature beats is best seen in the Lead II rhythm strip at the bottom, as this ECG machine does not print the 12 leads in an uninterrupted manner. You will see interruptions each time the leads change.
The first beat on the ECG is one of the premature beats. You can observe the left axis deviation without pathological Q waves. Lead I shows the premature beats with an Rs pattern, and Leads II and III have rS. The early beats have caught the anterior fascicle of the left bundle branch refractory from the preceding beat. It recovers for the normally-timed sinus beats.
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