Unlike other muscles in the body, the heart contracts in a very specific manner according to the propagation of electrical signals through its tissue. These contractions can be measured using an Electrocardiogram, or ECG. ECGs can be used to detect arrhythmias, which are abnormal contractions. Watch the video below to learn about how the heart contracts and how we can measure the signals causing it to do so.
Self-Assessment Questions:
Click here to test your understanding of Heart Contractions, ECGs, and Arrhythmias.
Discussion Questions:
- The cardiac muscle surrounding the left ventricle is thicker and stronger than the cardiac muscle surrounding the right ventricle. Why is this? Now imagine a patient whose right ventricular wall is thicker than their left ventricular wall. What could cause this?
- How is cardiac muscle different from skeletal muscle? Why do these differences make sense? Use the literature to support your response.
- Consider the locations of the SA and AV nodes within the heart. Why does the directionality of electrical impulses in cardiac tissue make sense given the heart’s blood-pumping function?
- The heart is covered with a layer of fibrous connective tissue called the pericardium. Imagine a fictional organism, whose pericardium is made of a metal, such as aluminum. Would we be able to collect an ECG signal from this organism? Why or why not?
- Consider a patient who is getting an ECG. The nurse accidentally reversed the leads when setting up the ECG (positive lead placed where negative lead should go, and vice versa). Assuming the patient has a normal sinus rhythm, what will the displayed ECG waveform look like?
- Why do you think ventricular fibrillation causes the ECG waveform that it does?
- Why does atrial flutter cause a characteristic sawtooth pattern on the ECG trace?
Continue Reading:
- Samol A, Bischof K, Luani B, Pascut D, Wiemer M, Kaese S. Single-Lead ECG Recordings Including Einthoven and Wilson Leads by a Smartwatch: A New Era of Patient Directed Early ECG Differential Diagnosis of Cardiac Diseases? Sensors. 2019;19(20):4377. doi:10.3390/s19204377
- As smartwatches offering one-lead ECG capabilities are becoming increasingly common, this paper delves into how accurate these ECGs are and their potential use in healthcare.
- Vaidya GN. Application of exercise ECG stress test in the current high cost modern-era healthcare system. Indian Heart J. 2017;69(4):551-555. doi:10.1016/j.ihj.2017.06.004.
- This article describes an exercise ECG stress test (compared to that taken at rest), and its use in modern healthcare system.
About the Creator:
This video was created by a student in the Rice Bioengineering Class of 2023 (used with permission).
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