ECG Guru - Instructor Resources

A gathering place for instructors of ECG and cardiac topics.


Subscribe to me on YouTube

Sinus tachycardia

Left Bundle Branch Block

Tue, 01/17/2017 - 18:36 -- Dawn

This ECG was taken from an unknown patient.  It shows sinus tachycardia with left bundle branch block. The ECG criteria for left bundle branch block are: 

* Wide QRS (.12 seconds or greater)

* Negative QRS deflection in V1

* Positive QRS in Leads I and V6 

* Supraventricular rhythm

In addition to these criteria, left bundle branch block will cause repolarization abnormalities.  This is because depolarization is altered through the left ventricle, which causes repolarization to also be altered.  Instead of the electrical impulse traveling down the left bundle branch to depolarize the left ventricle, it depolarizes the right ventricle first, then spreads cell-to-cell across the larger left ventricle. The ST and T wave changes caused by left bundle branch block are normally “discordant”.  That is, the ST segment will be elevated in leads with negative QRS complexes, and depressed in leads with positive QRS complexes.  This elevation and depression of the ST segment may “imitate” the changes caused by acute myocardial infarction.  They may also work to conceal M.I. changes, as we may not recognize  STEMI as we attribute the ST changes to the left bundle branch block itself. 

For more on determining the presence of acute M.I. when the patient has left bundle branch block, check out these links:  ECG Guru, LBBB with AMI; Life in the Fast Lane, Sgarbossa CriteriaEMS 12-Lead, Sgarbossa Criteria;  Dr. Smith's Modified Sgarbossa Criteria. 

Teaching Series - Tachycardia and Left Anterior Fascicular Block

Sat, 10/15/2016 - 15:48 -- Dawn

This series of three ECGs is from a 60-year-old man who was brought to the Emergency Department after being involved in a motor vehicle accident.  No injuries were found, but the patient was severely intoxicated by alcohol consumption.  He was conscious but agitated. 

ECG NO. 1     15:07:23

The first ECG was taken by fire-rescue personnel at the scene of the accident. His hemodynamic status was stable, and the rate was not addressed in the field. ECG No. 1 shows a supraventricular rhythm at 161 bpm, with a narrow QRS and P waves visible before each QRS. 

A notable feature of this ECG are the left axis deviation, by default diagnosed at left anterior hemiblock (left anterior fascicular block).  The .10 second QRS width is typical of LAHB, as is the rS pattern in Lead III.

Also  noted is the unusual R wave progression in the precordial leads.  The R waves are prominent in V2, and then fail to progress across the precordium, and the S waves persist. This is probably due to the hemiblock.  We do not know this patient’s medical history, except that he self-described as an “alcoholic”.  LAFB can be associated with coronary artery disease. 

ECG NO. 2      15:20:38

Now being evaluated in the Emergency Dept., we see the patient's heart rate is 163 bpm.  Some variability in the rate was noted with patient agitation and activity, so it was determined that the rhythm was probably sinus tachycardia.  There were no other significant changes in the ECG from the first one.  Unfortunately, we no longer have access to lab results, so we do not know his electrolyte or hydration status.  Labs confirmed ETOH intoxication. 

ECG NO. 3   15:43:26

ECG Basics: Sinus Tachycardia vs. PSVT

Thu, 04/21/2016 - 00:13 -- Dawn

Narrow-complex tachycardias can be very confusing to students of basic-level ECG.  There are very many rhythms that fall into the broad category of narrow-complex tachycardia.  We usually further divide them into sinus tachycardia and other "supraventricular tachycardias".  The basic student will want to make this distinction, as well as be able to differentiate atrial fib and atrial flutter from the other SVTs.  The more advanced student will want to go into more detail about which mechanism for supraventricular tachycardia is present.

Just the basics, please.   When the tachycardia is regular, it is most important to determine whether it is a SINUS TACHYCARDIA or a SUPRAVENTRICULAR TACHYCARDIA.  (Yes, we are aware that sinus rhythms are supraventricular, but the term "supraventricular tachycardia" or "SVT" is usually reserved for the fast, regular rhythms that are not sinus.)  So, what clues will be most helpful to our beginner students?

Rate    SVTs tend to be faster than sinus tachycardia.  More importantly, they are fast regardless of the patient's situation.  Sinus tachycardia almost always is reacting to the patient's situation.  For instance, a 22-year-old woman resting in a chair with a heart rate of 150 is likely to have an SVT.  A 22-year-old woman who is running in a 10 k marathon race and has a heart rate of 160 is responding appropriately to an increased need for oxygen and nutrients to her cells. Sinus tachycardia will ususally be 160 or less, and have an obvious reason for being, such as fever, pain, anxiety, exercise, hypovolemia, hypoxia, or drugs.  Unfortunately, many beginning students are told that any narrow-complex tachycardia with a rate of 150 or less is sinus, and over 150 is SVT. While they may be right most of the time, or on the written test they are about to take, this rule should not be applied in "real life".  Sinus rhythms can go over 150, and SVTs can be slower than 150.  So, what other clues should we be teaching beginners?

Consider the clinical situation    Look for an obvious cause for sinus tachycardia.  If none is found, strongly consider SVT.  Remember that pediatric patients have faster heart rates, especially infants.  If the strip is on a test, with no clinical information, consider these:

ECG Basics: Sinus Tachycardia, Peaked T Waves, and Baseline Artifact

Sun, 03/13/2016 - 21:45 -- Dawn

This strip offers several good teaching opportunities.  If it were a 12-lead ECG, no doubt it would be a bonanza!  First, there is sinus tachycardia at a rate of about 138 per minute.  The P waves are all alike and regular.  The T waves are tall and narrow, with a sharp peak.  This is often a transient sign of hyperkalemia, and should be investigated with serum electrolyte tests and with a 12-lead ECG.  In addition, the baseline shows a wandering type of artifact.  This is due to the patient's deep breathing, and the fact that the arm electrodes were placed on the chest.  This patient was a diabetic in ketoacidosis with hyperkalemia. 

Inverted T waves in Lateral Wall

Tue, 11/10/2015 - 20:45 -- Dawn

This ECG was obtained from a 49-year-old man who was a patient in an Emergency Dept.  We do not know his presenting complaint, only that he had a history of insulin-dependent diabetes mellitus (IDDM).  It was noted by the donor of the ECG that the patient had no chest pain, no shortness of breath, and no other cardiac symptoms.  We do not know his hydration or electrolyte status.  There are quite a few interesting abnormalities on this ECG, and the exact interpretation would, of course, depend upon the patient's clinical status.  It would definitely help to be there!

First, we note a sinus tachycardia at a rate of 118 bpm.  This could be due to very many causes, including but not limited to:  dehydration, pain, anxiety, high or low blood glucose, fever, or CHF.  The PR and QT intervals are within normal limits.  The QRS complexes are narrow.  The axis is normal at 0 degrees.  The QRS voltage in the lateral leads is on the high side of normal, but we do not know this patient's body type.  Voltage as read by the ECG can be influenced by a thin chest (making voltage look larger) or a large chest (making voltage lower).

There are T wave abnormalities in the lateral leads:  I, aVL, V5 and V6.  The T waves are inverted, which can have many meanings.  However, when inverted T waves are in the lateral leads, as opposed to the inferior or right chest leads, it is often a sign of ischemia.  The flat, horizontal ST segments can also signify coronary artery disease (CAD).  This patient denied cardiac symptoms, but his age and history of IDDM make it probably that CAD is a factor.  The leads with T wave inversion also have a small amount of ST segment depression.  The right precordial leads, V1 and V2, have a small amount of ST elevation,  This possibly represents a reciprocal change to the ST depression in V5 and V6.

Because we are not at the bedside of this patient, there are many details we do not know.  But these inverted T waves could be ischemic T waves, and this requires that the patient be further evaluated.

As always, we welcome comments, as this ECG probably has more to say!


REFERENCES:  Dr. Ken Grauer,  Life In The Fast Lane, World Journal of Cardiology 

ECG Basics: Sinus Tachycardia

Wed, 06/10/2015 - 20:53 -- Dawn

This is a good teaching strip on many levels.  At the BASIC level, we see a strip that clearly meets all the criteria for sinus tachycardia:  a regular rhythm over 100/min. with P waves that look normal and all look alike.  The rate is 110 per minute.  The PR interval is just at the upper limits of normal at .20 second, or 200 ms.  The QRS complex is within normal limits, but slightly wide at .10 seconds.

This strip is good for teaching rate determination by several different methods.  It is helpful that QRS complexes 1, 5, and 10 fall on the dark lines of the paper.

This is a Lead II rhythm strip, and it is helpful to show students that not ALL Lead II strips produce an upright QRS complex.  Of course, correct lead placement should be confirmed.  In this particular case, the patient had suffered an anterior - septal wall M.I., and has a left anterior hemiblock, also called left anterior fascicular block.  This shifts the frontal plane axis to the left, causing Lead II to have a negative QRS.  Axis can't be accurately determined from one lead, but axis shift explains the negative QRS in this strip.

Sinus Tachycardia in a Child

Wed, 07/17/2013 - 23:02 -- Dawn

A six-year-old girl was found with her two younger siblings and her mother, unconscious, in a room filled with carbon monoxide.  The mother had been using a charcoal grill inside the house.  She managed to call 911 before losing consciousness, and the fire rescue paramedics broke into their house, saving them.  This six-year-old required treatment in the pediatric intensive care unit, but recovered completely.  The lesson for our students is to judge rate in the setting in which it is found.  The heart rate here is 136/min.  Normal for a child of six is usually between 80 and 100 at rest.  This child is severely hypoxic, and she has sinus tachycardia.  It would be a mistake to assume her rate is normal because "all children have fast heart rates".  Also, children with sinus tachycardia can be so fast, they appear to have PSVT.  The onset and offset can be excellent clues to the origin of the rhythm.  Sinus rhythms can be expected to speed up and slow down gradually, unlike PSVTs, which have sudden onset and offset.  The most important consideration is that sinus tachycardia usually has an APPARENT CAUSE:  exercise, anxiety, hypoxia, hypovolemia, fear ,,,, the list is a long one.  Once it is determined that the patient has sinus tachycardia, efforts usually focus on the elimation of the cause.


We welcome any comments on this ECG, perhaps taking the discussion to a more advanced level.

ECG BASICS: Sinus Tachycardia in a Toddler

Wed, 05/01/2013 - 17:24 -- Dawn

Here is a nice example of sinus tachycardia taken from a 2-year-old in the post-anesthesia care unit after a short GI endoscopic procedure.  Would you call this NSR, since it is from a child?  The pre-op heart rate in this child was 120/min.

For your more advanced students, remind them that, in adults especially, a heart rate close to 150/min. should cause them to examine the ECG in several leads, looking for the presence of atrial flutter with 2:1 conduction.  Another important teaching point, most ADULTS with sinus tach at 150/min. would  manifest an obvious reason for the rapid heart rate (dehydration, pain, anxiety, shock, etc.)  Challenge your basic students to come up with as many causes for sinus tach as they can.

jer5150's picture

Jason's Blog: ECG Challenge of the Week for March 24th - 31st.

Patient's clinical data:  47-year-old black man.  Another serial ECG (seen below) showed a supraventricular tachycardia (SVT) at a rate of 164/min that was diagnosed by an Electrophysiologist as atrioventricular nodal reentrant tachycardia (AVNRT).  How does knowing the mechanism of AVNRT help you in determining the nature of the mechanism in this week's ECG.  

jer5150's picture

Jason's Blog: ECG Challenge of the Week for Feb. 24th - March 3rd.

Patient's clinical data:  55-year-old white man admitted to the surgical intensive care unit (SICU). 

Part of the computer's interpretation was:
Sinus tachycardia 1st degree AV block Occasional
Premature supraventricular complexes


All our content is FREE & COPYRIGHT FREE for non-commercial use

Please be courteous and leave any watermark or author attribution on content you reproduce.

Subscribe to RSS - Sinus tachycardia