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Dr A Röschl's picture

Sinus Bradycardia and More

Let's analyze the ECG. It comes from a pacemaker patient whose pacemaker was briefly switched to VVI at 30 bpm due to a stimulation threshold test. The first 3 beats show a sinus rhythm with a frequency of approx. 40 bpm. This is followed by a premature ventricular contraction (PVC). The P wave of the next sinus node beat lands exactly on the T of the PVC. This cannot be conducted to the ventricles, either because the ventricular myocardium is still unexcitable or the PVC has conducted retrogradely into the AV node and this is therefore still refractory.

Dawn's picture

Anterior Wall M.I. With Bifascicular Block

This ECG is taken from an 82-year-old man who called 911 because of chest pain.  He has an unspecified “cardiac” history, but we do not know the specifics. 

WHAT IS THE RHYTHM?  The heart rate is 69 bpm, and there are P waves before every QRS complex. The underlying rhythm is regular, with one premature beat that is wide without a P wave.  The PR interval is slightly prolonged at .25 seconds.  The rhythm is normal sinus rhythm with first-degree AV block and one PVC. 

WHY THE WIDE QRS?   The QRS complex is wide at .14 seconds. The QRS in V 1 has a wide R wave after a small Q wave.  This in consistent with right bundle branch block pattern, with loss of the normal initial small r wave (pathological Q waves).  The diagnosis of RBBB is further corroborated by the wide little S waves in Leads I and V6.  The QRS frontal plane axis is -66 degrees per the machine, and clearly “abnormal left” because the QRS in Lead II is negative, while the QRS in Leads I and aVL are positive.  This is left anterior fascicular block, also called left anterior hemiblock.  The combination of RBBB and LAFB is a common one, as the two branches have the same blood supply.  It is also called bi-fascicular block. 

WHAT ABOUT THE ST SEGMENTS?  The ST segments in leads V2 through V6 are elevated, and their shape is very straight, as opposed to the normal shape of coved upward (smile). Even though the amount of ST elevation at the J points appears subtle, the shape of the segments, the fact that they appear in related leads, and the fact that the patient is an elderly male with chest pain all point to the diagnosis of ANTERIOR WALL ST elevation M.I. (STEMI).  Additional ST changes include a straight shape in Leads I and aVL and ST depression in V1 and aVR.  

PATIENT OUTCOME  The patient was transported to a cardiac center, where he received angioplasty in the cath lab.  The left coronary artery was found to be occluded, and was repaired and stented.  He recovered without complications and was sent home in a few days.

Dawn's picture

ECG Basics: Sinus Rhythm With Ventricular Bigeminy

This rhythm strip offers two leads taken at the same time, Lead II and Lead V1.  The Lead II strip may not look "typical" to a beginning student, because the sinus beats are very small and biphasic.  This is due to an axis shift, which cannot be evaluated without more leads.

One of the best teaching opportunities in this strip is the concept of "underlying rhythm" with ectopy.  The underlying rhythm here is sinus.  But there are sinus P waves which are hidden, making the sinus rate twice what it appears to be.  The P waves are invisible in the Lead II strip, with baseline artifact making them even harder to see.  But in V1, we are able to find them at the end of the PVCs' T waves.  The sinus rhythm is a bit irregular toward the end of the strip.  There are probably many things a more advanced practitioner could say about this strip, but it usually requires more than one or two leads to do a complete evaluation.  For your basic student, it is a good example of sinus rhythm with ventricular bigeminy.

Dawn's picture

ECG Basics: Normal Sinus Rhythm With Premature Ventricular Contractions

This ECG shows an underlying rhythm of normal sinus rhythm at a rate of 80 / min.  There are two premature ventricular contractions (PVCs).  The sinus rhythm actually continues uninterrupted, causing a “compensatory pause”.  If you march out the P waves, you may even see hints of the hidden P waves in the ST segments of the PVCs.  The P waves that occur in the ST segments of the PVCs land in the refractory period of the ventricles, and so are unable to continue into the ventricles and cause a QRS. 


It is also permissible to call these beats “ventricular premature beats (VPBs)” or “ventricular premature complexes (VPCs)”.  

Dawn's picture

Left Bundle Branch Block With Left Atrial Enlargement

This ECG, kindly donated by Dr. Ahmed from India, is from a 70-year-old man shows a sinus rhythm at 80 bpm with left bundle branch block (LBBB), left atrial enlargement (LAE), and a premature ventricular contraction (PVC). The ECG criteria for LBBB is:  1) Wide QRS  - greater than or equal to .12 seconds;  2) Supraventricular rhythm;  3) QRS that is negative in V1 and positive in Leads I and V6. In leads with a positive QRS, we will see some ST depression, and in leads with a negative QRS, some ST elevation.  This is "normal" for the wide QRS rhythm, and does not indicate injury or ischemia, although it does not rule it out, either.  LBBB is an indicator of cardiac disease, but not specific to one etiology.

There is a PVC seen as the 8th beat from the left, and it gives you a chance to show your students a wide-complex beat that is NOT associated with a P wave and is premature, compared to the wide-complex SINUS beats with LBBB.  The PVC, being wide-complex, also has similar ST changes:  the ST segments and T waves are DISCORDANT with the QRS complexes.

The P waves show some signs of enlargement of the left atrium.  The P waves in Lead II are tall and pointed, and the P waves in V1 are biphasic.  Left atrial enlargement in a patient with LBBB would not be surprising, as both are associated with left ventricular dysfunction.  Patients with these ECG patterns should be thoroughly evaluated for congestive heart failure.  Patients with LBBB, low ejection fractions, and heart failure are treated with cardiac resynchronization therapy, using a pacemaker that paces the atria and each ventricle, synchronizing both the A-V coupling interval and the depolarization of the ventricles for optimum cardiac output.

Dawn's picture

ECG BASICS: Sinus Rhythm With Ventricular Bigeminy

Nice, clear example of ventricular bigeminy with an underlying sinus rhythm.  We do not know from this strip if the sinus rhythm is a bradycardia at a rate of about 42 per minute, or if the underlying sinus rhythm is actually at a rate of 85 per minute, with every other sinus beat inhibited by the occurance of a PVC.  In the first possibility, the ventricular beats would be considered "escape" beats, positively contributing to the patient's heart rate.  In the second instance, the rather late-occurring PVCs would cause the heart to be refractory, preventing the sinus P wave from conducting it's impulse to the ventricles.   Sometimes, we can see signs of the sinus P wave "hiding" in the PVC, but in this case, if P waves exist, they fall almost exactly in the middle of the ventricular beats' QRS complex, making them invisible.  A good strategy would be to watch the strip continuously for some time, hoping to catch the conduction of two sinus beats in a row, solving the dilemma.

Dawn's picture

Sinus Rhythm With Left Bundle Branch Block, PVCs, and Fusion Beats


This is a great ECG for teaching your students about some of the different causes of wide QRS.  This 89 year old man has a sinus rhythm that is around 100 bpm, and his QRS is widened at 148 ms (.148 sec).  Leads I and V6 are positive, and Lead V1 is negative, meeting the criteria for left bundle branch block. There is a left axis deviation, which is common with LBBB, although it is not always this pronounced, indicating that there is possibly another cause for LAD.  In this ECG, there are also PVCs and probable fusion beats.  The 14th beat is a PVC.  Complexes 1, 6, and 9 are possibly fusion beats. Fusion can be described as an almost simultaneous sinus beat and ventricular beat.  The depolarization waves, one coming from the top of the heart and one coming from the bottom, meet and "fuse" on the ECG.  Fusion beats will have some characteristics of the supraventricular beats and some of the ventricular beats.  They are not significant except that fusion can be said to "prove" the existence of a ventricular pacemaker - either a natural pacemaker or an electronic one.

Do you see anything else interesting in this ECG?  How would YOU describe this rhythm?  Please do not hesitate to add your comments, or ask questions of the experts who contribute to this site.  We will respond quickly to all questions.

Dawn's picture

Left Bundle Branch Block In Patient With Severe Aortic Stenosis

This ECG is from a 91-year-old man who was being evaluated for replacement of his aortic valve, which was severely calcified. It shows a classic LBBB pattern: wide QRS, supraventricular rhythm (normal sinus rhythm with first-degree AV block), a negative QRS in V1, and a positive QRS in Leads I and V6.

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