November 28, 2021

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Heart Blocks Explained – First, Second, Third Degree and Bundle Branch on ECG

3 min read

Heart blocks illustrated clearly with Dr. Seheult. See the other videos in this ECG Interpretation series at:

This video includes 1st degree heart blocks, 2nd degree heart blocks (Mobitz type 1 or wenckebach, mobitz type 2), 3rd degree heart blocks (complete heart block), hemiblocks, bundle branch blocks, 2:1 heart block, and more. Also, learn the pathophysiology of heart blocks as they relate to the SA node, AV node, ventricles, and atrium.

See the complete ECG Interpretation course. Confidently interpret EKGs and EKG rhythms in a systematic way, including:

– The physiology of the heart
– EKG leads and vectors
– Leads and EKG paper
– The ECG tracing
– EKG waves, complexes, and intervals (p waves, QRS complexes, PR interval etc.)
– Axis on EKG and precordial leads
– The autonomic nervous system and the heart
– Heart rate and automaticity on the ECG
– The R to R interval
– Rhythm, arrhythmias, and escape rhythms,
– Premature beats and pauses on EKG
– Bigeminy, trigeminy, and tachyarrhythmias
– V-tach and torsades de points
– Atrial and ventricular flutter
– Atrial fibrillation and ventricular fibrillation on ECG
– Heart blocks and escape rhythms (1st, 2nd, and 3rd degree heart block)
– Bundle branch blocks, hemiblocks, and fascicular blocks
– Hypertrophy (LVH) and atrial enlargement
– COPD, PE, Hyperkalemia, Digoxin and the EKG
– How to systematically read an EKG (and what a normal ECG looks like)
– Many practice EKG (that Dr. Seheult interprets step by step)
– EKG quizzes follow each video.

This video is part of the “MedCram Remastered” series: A video we’ve re-edited & sped up to make learning even more efficient.

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Speaker: Roger Seheult, MD
Co-Founder of
Clinical and Exam Preparation Instructor
Board Certified in Internal Medicine, Pulmonary Disease, Critical Care, and Sleep Medicine.

MedCram = More understanding in less time

Medical education topics explained clearly including: Respiratory lectures such as Asthma and COPD. Renal lectures on Acute Renal Failure, Urinalysis, and The Adrenal Gland. Internal medicine videos on Oxygen Hemoglobin Dissociation Curve / Oxyhemoglobin Curve and Medical Acid Base. A growing library on critical care topics such as Shock, Diabetic Ketoacidosis (DKA), aortic stenosis, and Mechanical Ventilation. Cardiology videos on Hypertension, ECG / EKG Interpretation, and heart failure. VQ Mismatch and Hyponatremia lectures have been popular among medical students and physicians. The Pulmonary Function Tests (PFTs) videos and Ventilator-associated pneumonia lectures have been particularly popular with RTs. NPs and PAs have provided great feedback on Pneumonia Treatment and Liver Function Tests among many others. Mechanical ventilation for nursing and the emergency & critical care RN course is available at Dr. Jacquet teaches our EFAST exam tutorial, lung sonography & bedside ultrasound courses. Many nursing students have found the Asthma and shock lectures very helpful. We’re starting a new course series on clinical ultrasound & ultrasound medical imaging in addition to other radiology lectures.

Recommended Audience – Medical professionals and medical students including physicians, nurse practitioners, physician assistants, nurses, respiratory therapists, EMT and paramedics, and many others. Review and test prep for USMLE, MCAT, PANCE, NCLEX, NAPLEX, NBDE, RN, RT, MD, DO, PA, NP school and board examinations.

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#MedCram #ECG #HeartBlocks

Please note: MedCram medical videos, medical lectures, medical illustrations, and medical animations are for medical education and exam preparation purposes, and not intended to replace recommendations by your doctor or health care provider.


36 thoughts on “Heart Blocks Explained – First, Second, Third Degree and Bundle Branch on ECG

  1. Hello I know this is a little old but I need some reassurance. I'm a 37 year old female and out of nowhere 3 days ago I ended up being taken by ambulance to hospital. I had a really bad turn out of the blue. I went dizzy, hot, pale, my heart was racing, I was lethargic, my speech was drowsy and I felt drowsy, I had a weird sensation in my face and neck and generally felt awful. I had an ECG on the way to hospital & it turns out I had a left bunch branch block. As I understand it usually blocks don't present themselves with symptoms, and if they do it suggests an underlying heart condition. I'm also aware it's more serious to get these blocks on the left but not so serious in the right. I just want to know can blocks by themselves kill you? I have such bad anxiety about this. I'm scared its going to happen again. I have a heart scan soon but I just need some reassurance that I'm not in danger. Thank you.

  2. Thank you very much for this lecture. You explain concepts so well. I'm watching this on loop as I prepare for the CVRN-BC exam

  3. Wow, your lectures are really informative. They really encourage me to make more videos for Medical students on my channel. Def subscribing

  4. The explanation is phenomenal, thank you for that.
    But the title of the video and the description is extremely misleading. This video DOES NOT cover 3rd degree AV blocks, BBB, or hemiblocks.

  5. I am not asking for a diagnosis, just some advice. I am 68, 5’11”, workout regularly, eat clean. For the past 15 years or so, a couple of times a week my my heart rate increases from the high forties (resting) to the high 130’s for a few seconds, then stops for about 2 full seconds and resets to the normal rate. Anyone have any idea what, if anything, I should do?

  6. Thanks for the video it's incredibly helpful. Only thing I was confused about …. @10:47 I think you meant PRs are becoming longer in length as opposed to QRSs ? Or am I wrong?

  7. i am consfused. you said because the PR interval is getting longer as the block in AV gets worse the QRS gets narrowers but then on the ECG exaple you said QRS is normal. please can you help me on this

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