As a nurse you want to be familiar with all the types of heart blocks. The types include:
Second-Degree Type I (Mobitz type I or Wenckebach)
Second-Degree Type II (Mobitz type II)
Third-Degree (Complete Heart Block)
Before you review this material be sure to check out the lecture on Second-Degree Type I Heart Block and the comprehensive ECG lecture that details how to analyze heart rhythms.
Second-Degree Type I AV Heart Block (Mobitz I or Wenckebach)
Characteristics and Criteria of Second-Degree Type I
The key with this rhythm is that the PR interval follows a pattern where they gradually lengthen. Therefore, you will see that the p wave is getting further and further away from the QRS complex, and then all of the sudden there is a p wave without a QRS complex. Then this pattern will repeat itself again.
What you will see?
- Normal p-waves
- Atrial rate normal and rhythm regular
- Normal QRS complex <0.12 seconds
- Ventricular rate is slower than atrial rate and rhythm will be irregular (this is because QRS complexes are missing)
- Gradually lengthening or prolonged PR intervals until a QRS complex is dropped and then the cycle repeats
ECG/EKG Study Guide and Workbook for Nursing Students
“ECG/EKG Interpretation Study Guide and Workbook by Nurse Sarah”. This book contain 100 pages of content featuring 26 ECG rhythm break downs, 51 ECG rhythm analysis practice problems, 100 comprehensive ECG practice questions, worksheets, chart summaries, and more.
You can get an eBook version here: “Nurse Sarah ECG Book” or a physical copy here: “ECG/EKG Interpretation Study Guide by Nurse Sarah“.
Causes of Second-Degree Type I
Myocardial infarction (especially during an active inferior wall MI due to active ischemia depriving the tissue of oxygen), medications that delay AV conduction like calcium channel blockers, Digoxin, beta blockers, rheumatic fever, and increased vagal tone
Treatment for Second-Degree Type I
Assess if having symptoms? If not, continue to monitor and an order may be given to consult with a cardiologist for further evaluation. Some medications may need to be stopped that slow AV conduction.
If patient is have signs and symptoms associated with a myocardial infarction (chest pain, dyspnea, sweating, clammy etc.) with this rhythm, get patient treatment FAST.
Therefore, if symptoms are presenting where cardiac output if falling (low blood pressure, weak pulse, mental status change, pale etc.) you need help so activate the emergency response team. Atropine or temporary pacing may be needed.
Now test your knowledge on this material by taking the free Second-Degree Type I Heart Block Quiz.
References:
American Heart Association | Algorithms. (n.d.). Retrieved September 2, 2022, from https://cpr.heart.org/en/resuscitation-science/cpr-and-ecc-guidelines/algorithms#adult
Mangi MA, Jones WM, Mansour MK, et al. Atrioventricular Block Second-Degree. [Updated 2022 May 22]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK482359/