Heart Rate Case Studies

Home » MEDCLIN530 » EKG » 12-Lead EKG Confidence » II. Methodology: Measurements and their clinical significance » 4. Heart Rate: A mandatory part of an EKG interpretation » Heart Rate Case Studies
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Chris Anderson
Vice Chair, Pediatrics
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Kevin Hodges
Vice Chair, Emergency Medicine
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Table of Contents

Case 1: Sinus tachycardia in acute MI

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The finding of sinus tachycardia on the EKG, as in Figure 4.8, enables visualization of an imbalance in the normal sympathetic / parasympathetic balance. Underlying clinical possibilities should be considered. The sympathetic stimulation may have increased, or the parasympathetic stimulation may have decreased (Figure 4.9).
  1. For example, the ED admission of a patient with an acute MI and sinus tachycardia can have several causes.
  2. Shock, congestive heart failure (CHF), pain, anxiety, hypoxia, and bleeding (secondary to anticoagulation) may be present singly or in combination.
  3. The vital signs document the blood pressure and heart rate.
  4. Physical examination of the lungs for rales helps to confirm the presence of congestive heart failure.
  5. Pulse oximetry, if available, confirms the presence or absence of hypoxemia.
  1. The chest x-ray helps to confirm CHF, or a pneumothorax.
  2. An echocardiogram determines systolic and diastolic function, as well as the presence or absence of mechanical complications of acute MI. This is clinically oriented critical thinking. It all begins with the heart rate, a vital sign right there on the EKG!

Case 2: The heart rate in atrial fibrillation

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When the RR intervals are irregular, the best way to estimate the heart rate is by counting the number of QRS complexes in a 6-second block of time and multiplying that number by 10. (Five large boxes measure 1 second of time. Thirty large boxes measure 6 seconds of time.) The result is the heart rate in beats per minute. In the example below, there are 7 QRS complexes in the 6-second block. Multiplying 7 complexes (in 6 seconds) by 10 yields a heart rate of 70 per minute. Of course, since the rhythm is atrial fibrillation, this rate of 70 represents the ventricular rate. Memorize this method. It’s an essential skill.

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