ECG Pointers: A Dynamic Approach to Tachydysrhythmias

Authors: Lloyd Tannenbaum, MD (EM Attending Physician, Geisinger Wyoming Valley, PA); Mai Saber, DO (EM Attending Physician, Hackensack University Medical Center, NJ); Rachel Bridwell, MD (EM Attending Physician, Charlotte, NC) // Reviewer: Brit Long, MD (@long_brit)

Hello and welcome back to ECG Pointers, a series designed to make you more confident in your ECG interpretations.  This week, we are introducing part 1 of a 4-part series tackling tachydysrhythmias.  These are commonly encountered in the emergency department, so being able to correctly identify the rhythm is extremely important.  Let’s dive in!

When you are presented with a tachycardic ECG, there are two major factors we want you to focus on right away.  Ask yourself, is the QRS narrow or wide and is the R-R interval regular or irregular?  To review, for adults, a narrow QRS complex is one that is less than 120 msec (3 little boxes) and a wide QRS complex is greater than 120 msec.  A regular R-R interval is one where the QRS complexes are marching out at a regular, predictable rate, whereas an irregular R-R interval is constantly changing.  The following rhythm strips demonstrate several real-life examples of narrow versus wide QRS complexes and regular versus irregular R-R intervals:

Figure 1: Two rhythm strips, the top one shows a narrow complex QRS interval while the bottom one shows a wide complex QRS interval.

Figure 2: Two rhythm strips, the top one shows a regular R-R interval (blue lines are all the same) while the bottom one shows an irregular R-R interval.

Now let’s put it all together.  The following chart should be used as a starter guide for any tachydysrhythmia.  It’s not all inclusive, but it should be enough to get you a start in the right direction.  Over the course of the next few weeks, we will be breaking down each box and talking about each of the different rhythms below:

Table 1.  Differential for tachydysrhythmias.  Remember, this chart is not all encompassing, just designed to give you a start in the right direction.  Defining the terms, SVT = Supraventricular Tachycardia; Aflutter = Atrial Flutter; Sinus Tach = Sinus Tachycardia; Vtach = Ventricular Tachycardia; Afib with RVR = Atrial Fibrillation with Rapid Ventricular Rate; MAT = Multifocal Atrial Tachycardia; Vfib = Ventricular Fibrillation; Torsades = Torsades de Pointes

The First Box: Narrow and Regular

Table 2: Differential for narrow and regular tachydysrhythmias

This week we are going to hit Narrow and Regular tachydysrhythmias.  For this box, please keep Supraventricular Tachycardia (SVT), Aflutter (Atrial Flutter) and Sinus Tach (Sinus Tachycardia) in your differential.

This ECG comes from a 22-year-old female presenting with palpitations.  Take a look at her ECG:

What do you notice about this ECG?  Take a second and read it yourself before we reveal the answer.

Here’s what we saw:

Rate: around 120-130

Rhythm: Sinus Tachycardia (P before each QRS, QRS after each P and an upright P in lead II)

Axis: Normal axis

Intervals: narrow QRS complexes, rest look reasonable

Morphology: Looks mostly normal

Final read: Sinus tachycardia with a rate around 120s-130s.

Here’s a marked-up version of the ECG to help you see what we’re seeing:

This next case comes from a 78-year-old male presenting with palpitations.  Take a look at his ECG:

What do you notice about this ECG?  Take a second and read it yourself before we reveal the answer.

Here’s what we saw:

Rate: around 150

Rhythm: Atrial Flutter (more on that below)

Axis: Normal axis

Intervals: narrow QRS complexes

Morphology: sawtooth P waves (best seen in the inferior leads)

Final read: Atrial flutter with a rate of 150. The rate and sawtooth waves push towards this diagnosis.

Here’s a marked-up version of the ECG to help you see what we’re seeing:

Final case for this box comes from a 37-year-old female presenting with palpitations and shortness of breath. Take a look at her ECG below:

What do you notice about the ECG?  Take a second and read it yourself before we reveal the answer.

Here’s what we saw:

Rate: around 190

Rhythm: NOT Sinus.  No obvious P waves

Axis: Rightward axis

Intervals: narrow QRS complexes

Morphology: diffuse ST segment depression consistent with a strain pattern

Final read: Supraventricular tachycardia.

Here’s a marked-up version of the ECG to help you see what we’re seeing:

Takeaways

• When presented with a tachydysrhythmia, start by asking yourself if the QRS complexes are WIDE (>120 msec) or NARROW (<120 msec) and if the R-R intervals are REGULAR or IRREGULAR
• A good initial differential in the NARROW and REGULAR category is Sinus Tachycardia, Atrial Flutter, and Supraventricular Tachycardia
• Tips to recognize Sinus Tach
  1. Regular R-R interval
  2. P Waves are present and upright in lead II
  3. Patient is in SINUS rhythm
• Tips to recognize SVT
  1. Fast rate
  2. Regular R-R interval
  3. No visible P waves
  4. Narrow QRS
• Tips to recognize Aflutter
  1. Sawtooth Waves
  2. Predictable rate (300-150-100-75)

References
– Tannenbaum L, Bridwell R, Inman B.  EKG Teaching Rounds. Springer. 2022.