Broadening of QRS complexes

It has been mentioned to me by a cardiac physiologist that people with pacemakers will have broader QRS complexes on ECG. Does anyone know why? 


broad QRS complex

by Gemita - 2023-05-24 06:08:31

Penguin, I get broad QRS complexes during intermittent left bundle branch block.  I also get broad QRS complexes during an arrhythmia when I am paced in my right ventricle because ventricular pacing causes wide QRS complexes with left bundle branch block appearance.  Broad QRS is either caused by the ventricular conducting system not working properly (as in bundle branch block) or the electrical circuit not involving the atrioventricular (AV) node correctly.  Broad complex tachycardias for example may be ventricular or supraventricular in origin. 

Of course there are other causes for broad QRS complexes so make sure they look for other causes too!

It can happen

by Lavender - 2023-05-24 12:12:43

I asked my cardiologist about this at my last visit. He did give an explanation which I got lost in 😜

Bottom line is he said something about the length of time transmitting. (Slower spread of ventricular depolarization.) 

I have left bundle branch block and a no longer functional AV node. I think the signal gets longer. He said not to worry about it-in my case🌺💕

Broad/Wide QRS

by Gemita - 2023-05-24 13:41:39

Broad/Wide QRS more than 100 ms is not normal.  A QRS duration of more than 120 ms is required for the diagnosis of bundle branch block or ventricular rhythm, see attached link for more details.  

I see from my last Pacemaker Check that fast AF with aberrancy was seen (right bundle branch block) up to 220 bpm in some traces.  Left bundle branch block morphology was clearly noted from “ventricular pacing”.

Wide QRS with pacing

by Selwyn - 2023-05-24 13:44:13

Normal electrical heart activity sequence is atrial, then septum, then left ventricle, and lastly right ventricle. The Purkinje fibres act as the wiring of the heart to quickly conduct electrical activity.

If you are paced from your right ventricle lead ( the normal situation) then the sequence is right ventricle, septum and left ventricle. The Purkinje fibres are by-passed.

In effect this slower conduction widens the QRS ( which is made up of the combination of the septum, LV and RV activity) as the majority of the heart muscle ( therefore the biggest swing in electrical voltage) is from the left ventricle. ( This looks similar to left bundle branch block which has the effect of giving the same sequence as RV pacing).

Bundle of His pacing gives a more physiological QRS complex.

I hope this offers a clear explanation.

I would see as this has a nice graphic showing heart conductivity and explains about the Bundle of His etc.



Thank you All

by Penguin - 2023-05-24 17:25:31

Thank you Selwyn, Gemita and Lavender. 

Am I right to gather from this that various factors affecting ventricular conduction can broaden the QRS as mentioned by Gemita and Lavender, but in general someone with a pacemaker will have slightly broader QRS complexes than someone without a pacemaker due to the way that the device paces the heart and it's circuitry? 

The question leading on from that is, would this broadening affect the overall QT interval and could this be the cause of a prolonged QT interval which appears abnormal on ECG?  


Thank you all

by AgentX86 - 2023-05-24 22:32:48

Not necessarily.  As noted above, if the ventricular lead is placed in the bundle of HIS, the conduction is "normal" and the QRS complex will also be more normal.  If tuned properly a CRT pacemaker should be similar.

That's what I thought too...

by FG - 2023-05-24 23:16:35

 I am supposed to have Left Bundle Branch pacing. But It took him FIVE TRIES to "get LBB capture". Is that why my QRS is 134? I am supposed to have an RBBB pacing pattern. Does this cause a wide QRS in and of itself or I am I really just paced at the septum??? 

LBB pacing

by AgentX86 - 2023-05-25 01:08:36

Could be but it seems HIS pacing would be a better choice.

Here is an active diagram of the heart's conduction system.  It's show backwards (note the blood going our the aorta on the right) but it gives the normal sequence.  The bundle of HIS (details shown at the bottom of the page) is the short, single, piece of nerve fiber from the A/V node to where the RBB and LBB split.


You can see here why apical pacing into the Purkinje fibes wouldn't be optimum.  The distance across the heart would take a while (hence the wide QRS).

Ventricular Lead Position

by Penguin - 2023-05-25 03:13:30

My v.lead is on the septum and it's never been a great connection - but apparently adequate.

Does this make a difference to conduction times?

Ventricular lead position/broadening, lengthening etc of QRS/QT

by Gemita - 2023-05-25 05:15:37

Penguin, I considered your questions carefully.  My rhythm disturbances certainly came before my pacemaker, although these have been relieved to some extent by my pacemaker pacing me at a steadier, higher heart rate. 

I am 100% atrial paced with very little ventricular pacing and I feel completely normal until my arrhythmias start and I experience a sudden mode change and a withdrawal of atrial pacing which I absolutely hate.  During "atrial" pacing my QRS appears normal whereas with a switch to "ventricular" pacing I will always have a broader QRS complex. 

My RV lead tip is also placed in the RV Septal area.  Yes it does make a difference to conduction times which should be faster I was told since septal pacing, if lead tip is well positioned, may use the normal conduction system route.  RV septal pacing is certainly thought to be better than RV apical pacing.

While a well placed lead will provide the best chance of a natural, comfortable pacing experience, there are other factors that could cause QT prolongation that cannot be corrected by lead position alone, and let us not forget our pacemaker settings will affect our pacing experience too. 

Our QT interval is clearly prolonged by slower heart rates and shortened by faster ones, so the typical measurement of the QT interval for most of us is subject to substantial variability.  We need also to consider other factors that could increase the likelihood of broadening, lengthening the QRS/QT too and these might include (!) getting older, low left ventricular EF, dehydration, electrolyte imbalances, ischaemia, slow heart rate and other arrhythmias, some antibiotic/antidepressant meds, autonomic disorders, raised blood cholesterol, diabetes, thyroid disorders, left ventricular hypertrophy, heart disease to name but a few.  Your question . . . "would this broadening affect the overall QT interval and could this be the cause of a prolonged QT interval which appears abnormal on ECG?" is therefore difficult to answer because of the many variables.

Update: I attach a link which contains a full size diagram (if you keep following the download links) of the possible lead tip positions in conduction system pacing (see Figure 1), which I found helpful:-

This is the direct link to the full size diagram:-*y4rezr*_ga*MTczODkwMjc2Mi4xNjg1MDE1Mzcx*_ga_T874FCJ3LG*MTY4NTAxNTM3MC4xLjEuMTY4NTAxNjA2NC4wLjAuMA

Thank you

by Penguin - 2023-05-25 18:02:01

Thank you for this -  I'll go away and try to digest all of this. LBB and RBB are not diagnoses on my radar.  I've never been told that either apply to me.

I was told that Septal pacing makes pacing induced cardiomyopathy less likely by one EP and then told by another EP that he didn't rate it and that it had been hyped up but doesn't deliver!  

In terms of the QR interval and septal pacing information - understood - thanks Gemita and thanks to you again and AgentX and Selwyn for the web links.  I've obviously heard of these pieces of cardiac anatomy but have never looked into them. I'll read to overcome my ignorance! 

Not sure I need any further info right now. It will take me a while to get my head round the info offered, so I'll close this thread here. 

Many thanks 

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