#88: The EKG with Mike Fah-EY

July 5, 2023 | By Sam Masur

Audio

Summary:

Pediatric cardiologist Dr. Mike Fahey returns to teach us about the EKG. In our most ambitious episode yet, we discuss the what, where, why, and how of an EKG on an AUDIO podcast. Learn about how to approach an EKG read, what the electrical signal represents, and common pathologies that present with abnormal findings.

EKG Pearls

1. If the axis is abnormal in leads I and AVF in BOTH the P wave and QRS complex, then you either have situs inversus or a limb lead reversal. Most commonly it’s limb lead reversal!
2. We often obtain R leads to look at the right side of the heart in patients with complex congenital heart disease. For patients with a known structurally normal heart, Dr. Fahey will often ignore these and you can too
3. Never trust the machine! Not even the intervals
4. Atrioventricular Canal Defect, most commonly seen in patients with Trisomy 21, will give a characteristic Superior Axis (negative in AVF). This is because the VSD is located right where the His-Purkinje system should normally live, leading to the ventricles depolarizing from bottom-up rather than top-down.
5. The best place to look for bundle branch blocks is in the precordial leads.
6. When looking for the QTc, Dr. Fahey recommends looking at the leads where the end of the T wave is clearest
7. Inverted T waves in the left sided precordial leads (V4-V6) are never normal
8. Newborns will have the craziest repolarization abnormalities in the first 72 hours of life as they transition from fetal circulation to newborn circulation. If something doesn’t look right, repeat the EKG after 72 hours.
9. EKGs can be abnormal when the child has physiologic stress. You can always repeat the EKG a few weeks later in clinic to either reassure the family or confirm those abnormalities.

EKG Notes

What is the EKG?

Starting very basic, the terms EKG and ECG are interchangeable. The EKG is the measurement of the electrical signals of the heart through amplitude, direction, and time. It is a test best used to diagnose rhythm abnormalities, although we’ve adapted it to try to answer some structural questions because it is a quick non-invasive test. However, if you have any structural questions, the echocardiogram is your test of choice.  

Lastly, the spikes in the EKG represent certain events in electrical conduction. The P wave represents atrial depolarization; the QRS complex represents ventricular depolarization; and the T wave represents ventricular repolarization. The QRS is taller than the P wave because the ventricles are usually much larger than the atria. The QRS nomenclature is often confusing because we don’t always see a Q, R, and S. A Q wave is the first downward deflection, the R wave is the first upward deflection, and the S wave is another downward deflection. But not all QRS complexes start with a Q!

Lead Placement

The Limb Leads are considered to be AVR, AVL, and AVF. These physical leads on the body are used to create “measured” leads called the Bipolar Leads, I, II, and III. This is why we don’t actually have 12 stickers in a 12-lead EKG. Finally, the Precordial Leads are V1, V2, V3, V4, V5, and V6. The limb leads provide information about the heart in the coronal plane and the precordial leads provide information about the heart in the axial/transverse plane. For example, lead I travels directly to the patient’s left, which we call 0 degrees by convention. Lead AVF travels directly down to the patient’s feet, which we call 90 degrees by convention.

In pediatrics, we occasionally place extra precordial leads on the right side of the chest in a 15-lead EKG. These extra leads are the “R leads”, which can be helpful for dextrocardia or congenital heart disease with the need for extra information from the right side of the heart. In most cases, Dr. Fahey rarely uses these leads. 

When approaching an EKG, Dr. Fahey recommends looking at V1, which focuses on the right side of the heart, and V6, which focuses on the left side of the heart. Lastly, the coronary artery distributions are associated with the placement of our leads. The Left Anterior Descending (LAD) artery is seen in the precordial leads and the Right Coronary Artery (RCA) is seen in the inferior leads (II, III, AVF).

Dr. Fahey recommends keeping your eye out for limb lead reversals! Even the most experienced technicians will accidentally place the leads in the wrong spot. If the axis is abnormal in leads I and AVF in BOTH the P wave and QRS complex, then you either have situs inversus or a limb lead reversal.

Approach to Reading the EKG

Dr. Fahey recommends reading the EKG in whichever order you’d like, just make sure you do it the same way every time. In this episode, we’ll use Rate, Rhythm, Axis, Intervals, Hypertrophy, and Scanning/Repolarization.

Rate

• Fast or Slow!

Rhythm

• Sinus Rhythm is the baseline rhythm of the heart when the electrical impulse originates from the sinus node, which is located in the right upper corner of the heart (right atrium).
• When in sinus rhythm, the electrical impulse travels from the patient’s right side to the left side and from superior to inferior in the coronal plane.
• Therefore, to be in sinus rhythm, our signal must be upright in lead I and upright in AVF
• Lastly, there must be a QRS complex that follows every P wave and a P wave before every QRS complex
• Want to learn more about abnormal rhythms? Check out Episode 37 to learn more about supraventricular tachycardias!

Axis

• Colloquially, the axis refers to the direction of the QRS complexes
• To understand axis, look at leads I and AVF. As a reminder, lead I points to the left of the patient, which is considered 0 degrees, and lead AVF points downward to the feet of the patient, which is considered +90 degrees.
• Rightward axis refers to conventional direction > 90 degrees*
• Leftward axis refers to conventional direction < -30 degrees*
• *Please see age appropriate reference standards for axis by age! (See below for link to reference book)
• The QRS complex is an average of electrical signals, creating a net force. Since the left ventricle is relatively bigger than the right, the LV tends to drive the axis. However, in infants, the RV is larger at time of birth due to fetal circulation, and so infants will often have a “rightward” axis deviation, which is demonstrated by a negative QRS deflection in lead I.
• Remember, axis shifts over time due to changes in pulmonary and systemic vascular resistance affecting the size of each chamber.
• Certain congenital heart diseases will have characteristic axis deviations. Dr. Fahey recommends the one to know is an Atrioventricular Canal Defect, most commonly seen in patients with Trisomy 21, will give a characteristic Superior Axis (negative in AVF). This is because the VSD is located right where the His-Purkinje system should normally live, leading to the ventricles depolarizing from bottom-up rather than top-down.

Intervals

• PR interval is the beginning of the P wave to the beginning of the QRS complex. This represents the time it takes for the atria to depolarize and the signal to move past the AV node
  • The AV node slows the electrical signal down because it needs to wait for the blood to catch up with the electrical signal.
  • Prolongation of the PR interval usually represents an abnormality in the AV node. 
  • Shortening of the PR interval usually represents either bypassing of the AV node, such as in Wolf Parkinson White Syndrome (WPW), or a shorter distance to travel, such as in ectopic atrial rhythm.
• QRS interval represents the time it takes for the ventricles to depolarize. This is driven by the function of the His-Purkinje System, including the 3 bundles in the bundle of His.
  • A bundle branch block will cause slowing/blocking of the electrical signal through the system, leading to a longer time to depolarize and a WIDER QRS complex
  • The best place to look for bundle branch blocks is in the precordial leads.
  • Right bundle branch block is most commonly seen after cardiac surgery due to the location of the patch used to close the heart.
  • In a right bundle branch block, the ventricular myocardium in the right side of the heart depolarizes slower than the left. At the tail end of the QRS complex, the left side will finish depolarizing first, leaving only rightward forces. Therefore, in V1, there will be an extra upward deflection called R’, and in V6, there will be a broad downward S wave.
  • In a left bundle branch block, the left side of the heart depolarizes slower than the right. Therefore, at the end of the QRS complex, there will only be leftward forces. So there will be a wide downward deflection/S wave in V1
  • Lastly, if you notice an RSR’ in V1 that is still considered narrow (according to age appropriate norms), this is called an Incomplete Right Bundle Branch Block. 
  • Another common cause of a widened QRS complex is if the beat originates in the ventricles and bypasses the bundle of His, like a premature ventricular complex or ventricular arrhythmia
• QT interval is measured from the beginning of the QRS complex to the end of the T wave. This represents repolarization of the heart. The QTc corrects the QT interval for the heart rate. As the heart rate speeds up, the QT interval is supposed to shorten because the heart is repolarizing quicker.
  • Dr. Fahey recommends looking at the leads where the end of the T wave is clearest
  • An approximation is the QT interval should be less than half the R to R interval
  • The most common causes for QT abnormalities include electrolyte abnormalities, such as hypocalcemia or hypokalemia, medications, or congenital channelopathies
  • See below for what to do with an incidental QTc prolongation
• Again, please remember to check age appropriate reference standards (See below for link to reference book)! Neonatal myocardium is super healthy and so everything moves very fast.

Hypertrophy

• Before getting into further discussion, Dr. Fahey reminds us that the EKG is not a good screening test for hypertrophy.
• Hypertrophy is identified using the precordial leads. Dr. Fahey recommends looking at lead V1 for the right ventricle and V6 for the left ventricle.
• Voltage criteria (amplitude of the S and R waves) is used to screen for left ventricular hypertrophy, right ventricular hypertrophy, and atrial enlargement
• Check age appropriate reference standards for diagnostic criteria (See below for link to reference book)!
• Please remember that all rules go out the window if there is a bundle branch block. The assumption is the ventricles are depolarizing at the same rate

Scanning/Repolarization

• When scanning, Dr. Fahey first looks at the T waves in the precordial leads
  • Inverted T waves in the right sided precordial leads (V1-V3) can be normal
  • In children age > 10 and all adults, T waves should be upright in all the precordial leads
  • All children through age 10 should have inverted T waves in at least V1
  • Infants will have inverted T waves from V1 through V3. As the myocardium matures, the T waves will gradually turn upright
  • When you see upright T waves in V1 in a child under 10, think right ventricular hypertrophy
  • Inverted T waves in the left sided precordial leads (V4-V6) are never normal
  • Flattened T waves can be due to medications, but should be evaluated
• Next, Dr. Fahey looks at the ST segments, which is the end of the S wave to the beginning of the T wave.
  • In children, ST segment elevation is often NOT due to myocardial ischemia
  • Commonly, it’s due to early repolarization, where the myocardium is so healthy that it begins to repolarize before the rest has even depolarized
  • Truthfully, it’s almost impossible to tell the difference on EKG alone. Clinical history and other laboratory workup is needed to ultimately distinguish the two.
• Lastly, Dr. Fahey points out that newborns will have the craziest repolarization abnormalities in the first 72 hours of life as they transition from fetal circulation to newborn circulation. If something doesn’t look right, repeat the EKG after 72 hours.

Incidental QTc Prolongation

As discussed earlier, the differential diagnosis for prolonged QTc is electrolyte abnormalities, medications, or congenital conditions. After finding an incidental prolonged QTc, Dr. Fahey recommends asking about medications in the house, which could be a sign of accidental ingestion, and ordering electrolytes (+/- thyroid studies). If the above testing is normal, this is likely a channelopathy, known as congenital prolonged QT syndrome. Echocardiogram is not helpful for this type of disease process because it is not a structural abnormality. However, there is an overlap between patients with inherited channelopathies and inherited cardiomyopathies, so echocardiogram can be helpful in finding an associated cardiomyopathy.

For congenital prolonged QT syndrome, treatment should be determined by a pediatric electrophysiologist. This patient should be seen immediately. However, the most common channelopathies that make up congenital prolonged QT syndrome tend to respond to beta blockers. Lastly, first degree family members should also be screened with a baseline EKG.

Links

Medicine Related

• CredibleMeds.Org for a list of QTc prolonging medications
• Dr. Fahey uses The Harriet Lane Handbook as his reference standard

Not Medicine Related

• Crimetown Podcast
• These Vital Signs By Sayed Tabatabai
• Fake Doctors Real Friends (Scrubs Rewatch Podcast)
• Shrinking (TV Show)
• Meow Wolf

Goal

Listeners will learn how to approach an EKG, the physiologic mechanisms behind the lines, and identifying abnormal findings. 

Learning objectives

After listening to this episode listeners will…  

1. Identify the leads on a 12 lead EKG
2. Learn the systematic approach to reading an EKG
3. Understand the physiology behind changes in axis
4. Learn why T waves change as kids grow older 
5. Workup and treat incidental QTc prolongation

Disclosures

Dr Fahey reports no relevant financial disclosures. The Cribsiders report no relevant financial disclosures. 

Citation

Masur S, Fahey M, Chiu C, Berk J. “88: The EKG with Mike Fah-EY”. The Cribsiders Pediatric Podcast. https:/www.thecribsiders.com/ July 5, 2023.