Second degree heart block Type 2, which is also called Mobitz II or Hay, is a disease of the electrical conduction system of the heart. Second-degree AV block (Type 2) is almost always a disease of the distal conduction system located in the ventricular portion of the myocardium.
This rhythm can be recognized by the following characteristics:
- non-conducted p-waves (electrical impulse conducts through the AV node but complete conduction through the ventricles is blocked, thus no QRS)
- P-waves are not preceded by PR prolongation as with second-degree AV block (Type 1)
- fixed PR interval
- The QRS complex will likely be wide
Click here to see why.
The QRS on an ECG will most likely be wide because the block occurs in the His bundle or bundle branches and conduction through the ventricles is slowed. This slowing of conduction appears as a wide QRS complex on the ECG.
Second-degree heart block type 2 is usually caused by structural damage to the conduction system of the heart. Causes of the structural damage to the conduction system include the following:
Causes:
- Myocardial infarction that damages the conduction system
- Idiopathic fibrosis
- Cardiac surgery
- Infections and inflammatory conditions
- Hyperkalemia
- Autoimmune diseases affecting the heart
Second-degree AV block (Type 2) should be treated with immediate transcutaneous pacing or transvenous pacing because there is risk that electrical impulses will not be able to reach the ventricles and produce ventricular contraction.
Second-degree AV block (Type 2) is clinically significant because this rhythm can rapidly progress to complete heart block.
Atropine may be attempted if immediate TCP is not available or time is needed to initiate TCP. Atropine should not be relied upon and in the case of myocardial ischemia it should be avoided.
Below is a short video which will help you quickly identify second-degree heart block type 2 on a monitor. Please allow several seconds for the video to load. (2.65 mb)
Click for next Rhythm Review:
Complete Heart Block (3rd Degree Block)
Top Questions Asked On This Page
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Q: The video says “sometimes has wide QRS.” What else would you see with 2nd-degree if the block is occurring in the bundled His? I have seen the portrayed rhythm many times and was not sure what it was.
A: For 2nd-degree block type II you will see:
non-conducted p-waves (electrical impulse conducts through the AV node, but complete conduction through the ventricles is blocked, thus no QRS)
P-waves are not preceded by PR prolongation as with second-degree AV block (Type 1)
fixed PR interval -
Q: Having trouble differentiating between Mobitz II and third-degree block.
A: The main difference is this:
Mobitz II: There will be a P-wave with every QRS. There may not always be a QRS complex with every p-wave. The rate will usually be regular. Also, the PR interval will be regular.
3rd Degree Block: There may not be a p-wave with each QRS, and the PR interval will not be the same with each PQRS.
These videos may help you.
They are kind of hard to hear, but the content is good. -
Q: Your video says pace right away for 2nd degree? TCP should only take place if the patient is symptomatic or showing signs of inadequate perfusion? Correct?
A: Correct. If the patient is unstable which is defined as “showing signs of poor perfusion.”
Rfraser says
This site is so helpful and great to use, thank you! Regarding the PR interval for second degree heart block, I know it stays consistent but timing wise, will it also always be greater than 0.20 seconds, the normal 0.12- 0.20, or could both occur?
Jeff with admin. says
It can be either one.
Kind regards,
Jeff
Rhonda Gaines says
If a second degree block can occur at the His bundle, or bundle branch, is a bundle branch block similar to a second degree? I had a patient within the past 2 weeks who converted to a bundle branch block from NSR in the OR. Came to PACU like this. I had to argue to get his new wide complex EKG that wasn’t dropping beats, any extra help. Finally got an EKG and labs ordered, his K was high. Just before he left the PACU hours later to higher level of care, and to a Hospitalist, in the last 10 minutes he converted back. So, he wasn’t blocked he had a disease process? His QRS looked just like your video, no dropping….
Jeff with admin. says
2nd° AV block type II is a temporary complete failure in the conduction system below the level of the bundle of His. This means that that neither the left or right bundle branch conducts the electrical impulse. Therefore, The ventricle does not receive the electrical impulse and there is no QRS complex on the ECG.
A bundle branch block is a complete failure of one of the two branches that are below the bundle of His. Either the left branch or the right branch not both. If a person has a bundle branch block and develops 2nd° AV block type, this can rapidly lead to third-degree block since the normal conduction system would be completely blocked.
So in a sense they are similar. In one case there is a block in one branch of the conduction system (BBB), and in the other there is a temporary complete block of both branches of the conduction system.
Kind regards,
Jeff
Lorna says
I realize this is an older article but I was wondering if you could answer my question. I am 39years old & have been diagnosed with late stage Lyme disease with a recurrent (and nasty) active infection – all labs positive for old & new infection. I was first bit & had bulls-eye rash with illness 2yrs ago. 4wks of oral antibiotics back then. Just had lumbar puncture other day & waiting for results due to CNS symptoms.
Anyhow I am going in for heart monitoring because I have been having significant sporadic arrhythmias (majority of the day) which are worsening and also worsening chest pain, clammy sweats, arm pain, dizziness to almost fainting at times, nausea, fatigue and shortness of breath – feels like I haven’t had a good breath of oxygen in over a month.
Anyhow, I am not asking for diagnoses as I was just reading up heart block in case (but hopeful it is not) since it is associated with Lyme especially if symptomatic indicating heart issues. My question is –
How is the pulse rate with second degree heart block? Both Mobitz 1 and 2? Does it have to be consistently slow like with 3rd degree? I don’t ask about 1st degree because I have read that it is asympotmatic. But any insight if I am wrong would be appreciated.
I ask because I often read bradycardia as the heart rate in 2nd degree but mine becomes extremely tachy with walking only a few steps, but does drop around 50 on occasion – tough to catch it in time to check as I work in health care & so far have been trying to continue to work through this until I no longer can. It is steadily starting to drop at rest so I am trying to be proactive. Hopefully my scheduled IV antibiotics treatment will fix everything – just waiting on the dreaded insurance for approval still.. almost a week & half and still no approval. Gotta love health insurance these days!
Thank you for any explaination and information you can give me on the heart rate for degrees of heart block.
Lorna
Jeff with admin. says
Thanks for the question. Typically 2nd degree heart blocks will lead to a very slow heart rate. The heart rate wil not always be extreemly slow (less than 30), and it can be nomal (60-80) as well.
Saying a prayer for your right now with regard to your treatment and cure. Blessings to you.
Kind regards,
Jeff
Tammy says
So kind of you.
Nima Mathew says
Thanks Jeff!! This is a great site. Used it two years ago and came back now for my recert. You are doing a great job. God bless you!
Jeff with admin. says
You are very welcome. So glad that the site has been helpful for you.
Barbara Lee says
If atropine is not to be used or avoided in case of myocardial infarction – how would you be able to determine myocardial infarction quickly so you would know not to use atropine? Barb
Jeff with admin. says
This would most likely need to be determined by someone how can read 12-lead EKG’s. Also, the symptoms may guide the care. If the patient is clearly having chest pain or other symptoms that indicate MI then you could defer the atropine.
Kind regards,
Jeff
George says
Also, atropine in 2nd and 3rd heart blocks is rarely successful. It will usually increase only the atrial rate. Due to the block in AV node, the ventricular rate will often remain low. In symptomatic (i.e., bradycardic, hypotensive, & aloc) patients with heart block 2nd degree or 3rd degree pacing is recommended.
JChandler says
Thanks again Jeff for your knowledge, skill and website!
bfaroni says
Hi Jeff,
Can you explain the difference of the 2 rhythm images to me? Are they both what I should expect to see for this type of rhythm?
V/R
Briana
Jeff with admin. says
With respect to the definition of 2nd degree block type II there is no difference between the two rhythm strips.
Kind regards, Jeff
lullrich says
Hi Jeff –
On the Second degree (AV) heart block – Type 2 explanation … Under the reasons why the rhythm can be recognized. #1 says … Non-conducted p-waves … conduction through the ventricles is blocked therefore no QRS. Then under reason #4, it says the QRS complex will be wide … can you please explain how one explanation says there is no QRS, but then the explanation goes on to say the QRS complex will be wide. What am I missing here? How can there be no QRS but then a wide QRS?
Thank you. Linda
Jeff with admin. says
Some QRS complexes are conducted. Not all of the QRS complexes are conducted. The QRS complexes that are conducted may have a wide QRS complex.
Kind regards,
Jeff
ligerber says
When new AV block occurs think about testing the patient for Lyme disease in the work-up.
Gary Grubbs says
I have a 2nd° heart block. There are no symptoms with mine. The first time I was sitting in church and just fell over dead two times. There were paramedics there and they got to me quickly. They transported me to the Med Center and after about six hours all the tests came out normal unable to find anything. They transported me to the VA hospital for observation and they had to use atropine twice to bring me back during transport. Within about 10 minutes of arriving at the VA , I sat up and was talking with the doctor then the nurse started putting in the IV and I coded. In a matter of a few seconds I flatlined and woke up with them doing CPR on me. They then put pacer pads and defibrillator pads on me as a precaution after that. It happened again in the middle of the night and they were able to use atropine to bring me back up again. The doctors were baffled because all the testing came back negative. The next morning the doctors were talking trying to figure out what to do and had just left the room when I looked at the monitor and watch myself crash again. They got in the room and got me stabilized again quickly and were able to see the whole block on the monitor finally. They then New what they needed to do. They implanted the Boston scientific pacemaker with two leads. If my heart rate drops below 60 it turns on. It’s a weird feeling when it happens because my heart drops so quick that it has to bring it back up again quite fast and it feels like I’ve run a sprint. Some days I feel little or no activity with the pacemaker and other days I feel it quite often. I’m getting accustomed to it but not sure if I’ll ever get used to the feeling. The pacemaker is doing its job and I am doing everything I used to do again. Although not quite up to the same degree that I used to.
I am thankful that there was no actual physical damage to my heart. EKGs, CAT scans, bloodwork, chest x-rays, tests on my arteries, all were normal. It is really quite baffling how everything can look so good and have something like this happen. The body heals good but the mental side takes a little while to get through it all.
I am 60 years old and was going to the gym 3 to 4 times per week and was in the best health since I was a teenager. I had a clean diet and everything seems about as good as it could be. I feel so blessed that the VA had such fabulous doctors and staff. They are my miracle workers. They saved my life numerous times. I am happy to give the VA a good story.
Jeff with admin. says
I’m glad to hear everything worked out well! Blessings, Jeff
Marion Penfold says
Happy to hear your good…and pacemaker is doing it”s job ,life is too short…LIVE for each day. Smile and don”t sweat the small stuff! God Bless-
Leticia A Gosline says
Hi Jeff,
I suffered a second degree heart block after I had gastric bypass surgery in February. I want to have a tummy tuck, however I’m afraid of suffering another heart block or it progressing to a 3rd degree.
Is this possible? If I suffered one, will I suffer another one? Is getting a pacemaker a solution?
Regards,
Letti
Jeff with admin. says
I cannot provide medical advice on this site. The site is designed to educate health care providers regarding advanced cardiac life support.
I can say that I’m not sure why the heart block occurred after your first surgery and I would definitely speak with a cardiologist prior to any other surgical intervention.
Kind regards,
Jeff