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
Headshot of Chris Anderson, MD · Clinical Education Director, Pediatrics
Chris Anderson
MD · Clinical Education Director, Pediatrics
envelope icon
Headshot of Kevin Hodges, Vice Chair, Emergency Medicine
Kevin Hodges
Vice Chair, Emergency Medicine
envelope icon phone icon
Table of Contents

Case 1: Sinus tachycardia in acute MI

Tap the arrow to view the case.
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!

Sinus bradycardia: Pathophysiology

Sinus bradycardia represents a relative imbalance in the normal sympathetic / parasympathetic balance of the heart. There are two basic causes of sinus bradycardia:

  1. Decreased sympathetic activity.
  2. Increased parasympathetic activity.

Parasympathetic activity is frequently the “relax and take your time” signal that counterbalances the sympathetic nervous system. Increasing parasympathetic activity slows down the heart rate. Decreased sympathetic activity does the same and is more common clinically. It is the result of the current common practice of using drugs that block the sympathetic nervous system in the treatment of hypertension, coronary artery disease, and heart failure. It is also possible to directly stimulate the parasympathetic nervous system. A common cause of

 increased parasympathetic activity is the vagal response. The vagal response can occur secondary to gastrointestinal (GI) stimulation during nausea and vomiting, drug treatment, the carotid reflex, or with direct therapeutic vagal stimulation for seizures or depression.

Case 2: The heart rate in atrial fibrillation

Tap the arrow to view the case.
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.

The heart rate reference table

Table 4.1 provides a quick reference for accurate determination of the heart rate when the patient is in a regular rhythm.

memorize this

Clinical significance of heart rates

The heart rate is a vital sign and conveys critical information.

Causes of sinus tachycardia Causes of sinus bradycardia
Shock
Beta blocker therapy
Heart failure
Vagal response (increased parasympathetic tone)
Bleeding
Hypothyroidism
Infection
Athlete’s conditioning
Hyperthyroidism
Pulmonary embolism
Sympathomimetic drug therapy
Anxiety
Hypoglycemia
Hypoxia
Asthma

Image credits

Unless otherwise noted, images are from Adobe Stock.

Warning: Copyright restrictions

This course content and all writings and materials provided to you at the Elson S. Floyd College of Medicine are protected by federal copyright law and Washington State University policy. The content is copyrighted by the Washington State University Board of Regents or licensed to the Elson S. Floyd College of Medicine by the copyright owner. Limited access to this content is given for personal academic study and review purposes of registered students and faculty of Elson S. Floyd College of Medicine. You shall not otherwise copy, share, distribute, modify, transmit, upload, post, republish, reuse, sell, gift, rent, lend or otherwise disseminate any portion of this course content without permission in writing, signed by an individual authorized by Washington State University.

 

The Digital Publishing team makes every effort to ensure these educational materials are accessible to all learners. If you run into problems, please contact us with your concerns at medicine.digipub@wsu.edu. We will respond within 2 business days.

Site Menu