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Supraventricular tachycardia

ECG BASICS, May 17, 2013: Supraventricular Tachycardia

Sat, 05/18/2013 - 00:20 -- Dawn

This strip is from a patient who experienced a sudden onset of palpitations and rapid pulse while at rest.  It shows a narrow-complex tachycardia, specifically a paroxysmal supraventricular tachycardia.  The subject of supraventricular tachycardias is a fascinating one, and is covered extensively throughout this website.  The mechanisms of SVT are many, and can be complex for the beginning student to understand.  Search the search terms on the left side of the page for entries from ASK the EXPERT and JASON's BLOG for more advanced information about SVT.

For the beginner, it is important to teach the difference between sinus tachycardia and "supraventricular tachycardia".  Of course, sinus tachycardia IS supraventricular - but current convention has us using the term "SVT" for atrial or junctional tachycardias, and especially for reentrant tachycardias.  Beginner students should understand the function of the sinus node, and it's ability to control the heart rate, based on direction given by the nervous system.  The sinus node increases and decreases the rate incrementally, or more gradually than the onset and offset of a reentrant tachycardia.  The appearance of a sudden onset of regular tachycardia following a PAC, producing a rhythm with a distinctly faster rate than the original sinus rhythm, is a sure sign of SVT.  When the onset or offset are caught on the rhythm strip, our job is SO much easier!

The heart rate helps with the diagnosis.  SVTs tend to be faster than sinus tachycardias.  SVTs tend to be faster than 150/min, while sinus rhythms TEND to be slower than 150.  And patients with sinus tachycardia usually have a readily determined reason for the tachycardia, such as fever, pain, fear, hypovolemia, hypoxia, or exertion.  So, a patient on a treadmill for an exercise stress test might very well have a heart rate over 150 / min.

When your students master the understanding of the different behaviors of the sinus node and the reentrant rhythms, and how important patient presentation is to the diagnosis, you will want to add atrial flutter and atrial fibrillation.  When these are mastered, be sure to remind your students that atrial flutter can conduct 2:1, and will mimic sinus tach.  A good rule of thumb is: Under 150/min.:  look for sinus tach first.  Around 150 / min.: look for atrial flutter with 2:1 conduction.  Over 150/min.: suspect PSVT.   

 

Spontaneously Changing Conduction In Wide Complex Tachycardia

Thu, 04/11/2013 - 00:23 -- Dawn

This ECG was donated to the ECG Guru by Dr. Arnel Carmona, one of our favorite Gurus.  You will not often see such a great example of this.  We are very grateful to Dr. Carmona for his contribution to learning. Dr. Carmona's new blog is EZG - ECG for beginners and enthusiasts.    

An adult patient was admitted due to palpitations.  What is this rhythm?This is a tachyarrhythmia that initially is regular wide complex (RBB morphology) and later became regular narrow complex at a rate of about 187 bpm. There is normalization of the QRS without a change in heart rate. In the latter part of the tracing (narrow complex), pseudo-r can be seen in V1. So, this is SVT with aberrancy with spontaneous normalization.

What is the cause of the intraventricular aberration during acceleration of heart rate? It could be due to failure of the refractory period to shorten or possible lengthening in response to acceleration. 

What is the cause of the normalization of the of the QRS? The normalization of intraventricular conduction could be due to the gradual shortening of bundle branch refractory period in response to the tachycardia. 

What is the possible mechanism maintaining the aberration? It is likely due to the transeptal concealed conduction blocking conduction in the contralateral bundle. With dissipation of transeptal conduction, the QRS complex normalizes. 

What happened to the case? Adenosine was given, terminating the arrhythmia.  

Ref: 

Fisch C. 1983. Aberration : Seventy-five years after Sir Thomas Lewis. BHJ 50:297-302 

Fisch C and Knoebel SB. 2000. Electrocardiography of Clinical Arrhythmia. New York. Futura Publishing Co

 

 

Sinus Tach vs SVT In An Inebriated Patient

Sat, 12/29/2012 - 16:21 -- Dawn

This series of ECGs was obtained from a 60-year-old man who was involved in a one-car accident.  He sustained no injuries, but his blood alcohol level was far above the legal limit for intoxication at over 300 mmol/L.  ECG No. 1 shows the ECG obtained by paramedics in the field, which they incorrectly interpreted to be atrial fibrillation.  No medication was given.  The ER physician obtained ECG No. 2, and considered sinus tachycardia as the diagnosis, but also, because of the fast rate and the fact that the rate had not changed for at least 15 minutes, he considered SVT or atrial flutter with 2:1 conduction.  The ERP administered diltiazem (Cardizem) to the patient, which resulted in ECG No. 3.  The transition to the slower rate was not captured on rhythm strips, but the nurse's notes showed a gradual change over 15 minutes from a rate of 160 to 105/min.  

Usually, on the Instructors' Collection ECGs, we like to give the "answer".  In this case, however, there will undoubtedly be some discussion regarding what went on.  This discussion can be useful if you are teaching intermediate to advanced students.  Questions to consider:  1) Is the fast rhythm an SVT and, if so, which one?  2) Is it sinus tachycardia and, if so, what are the effects of the car accident and the alcohol?  3) Is the left anterior fascicular block relevant? (Criteria are left axis deviation, slightly widened QRS complex at 110 ms, no other obvious reason for the axis deviation). 4) Is the ST elevation in the inferior wall during the tachycardia a sign of acute M.I.?  The patient was lost to followup, so it is not known whether the ST changes were investigated.  Note the flat ST segment and inverted T waves in V1 during the tachycardia that resolve when the rate decreases. 

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Wide-Complex Tachycardia Converted by Adenosine

Mon, 08/13/2012 - 15:58 -- Dawn

This ECG was presented earlier this week as an example of SVT with LBBB aberrancy, which was ultimately converted with one dose of adenosine in the Emergency Department.  It is the most shared and commented on ECG yet to appear on the Guru.  The diagnosis given was the one accepted by the medical staff who cared for the patient, who was a man in his 30's who presented to the Emergency Department complaining of a rapid heart rate.  He was ambulatory with stable vital signs, in spite of the tachycardia. He reported that he has had several episodes of fast heart rate which responded to either Valsalva maneuvers or, in some cases, medication in the ED.  He was told he might benefit from an ablation procedure, but he did not have health insurance and continued to use the ED as his primary source of medical care.  When he was admitted to the ED, the tech initially called for help, thinking the monitor showed ventricular tachycardia.  The ED physician felt that this represented LBBB aberrancy, possibly rate-dependent, and he treated the patient with adenosine.  The rhythm converted to sinus after one dose, and the patient remained stable throughout the process.  He was advised to undergo further observation and testing, but he declined due to financial concerns, and the fact that he usually succeeded in relieving his symptoms with "bearing down".  

Wide-complex tachycardias can be difficult to assess simply from an ECG. The patient's stability depends more upon general health and cardiac output issues than the origin of the tachycardia.  When we presented this ECG, we also presented the diagnosis he had upon discharge from the ED.

Subsequently, ECG Guru Dr. Ken Grauer, a frequent contributer to this site, offered his alternative diagnosis and his explanation of why he believes this to be v tach.  Other well-respected ECG experts have also questioned the original diagnosis.  Please refer to the comments below for this very helpful explanation.  Unfortunately, this patient is lost to followup, as this incident occurred some time ago.

WTCs remain a most fascinating topic, especially for those who enjoy "detective work".  We thank Dr. Grauer, Tom Bouthillet, and others for their contributions to the ECG Guru on this topic.
   

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