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Friday, December 04, 2015

Left Bundle Branch Block (LBBB) is not just a EKG finding, it is a really big deal

The EKG pattern of left bundle branch block (LBBB) has been known for decades and that pattern was considered an indication of heart disease. In Dr. George Burch's text book, written over fifty years ago, A Primer of Heart Disease,  I read that LBBB was a pathognomonic sign of heart disease.

However,at the time, It was not known what was the role of LBBB  in altering cardiac function.Did it cause heart disease- this point is debated still. Did patients with heart disease and enlarged hearts develop LBBB or similar EKG patterns as their disease progressed? Some patients have LBBB secondary to coronary artery disease and an infarct involving the interventricular septum,some have heart failure and some  "just" have a LBBB, the so called lone  or isolated LBBB.

 We know the following about the cardiac functional consequences of LBBB in patient with lone LBBB:

1) Abnormal movement of the interventricular septum early in cardiac contraction ( systole) ie in the pre-ejection phase the septum moves to the left.
 (In most cases the septum moves to the left while lateral left ventricular wall relaxes.The septal movement is observed with cardiac echo and termed as "septal beaking")
2) delayed contraction of the left ventricular wall) reduced ejection fraction (EF)
4) Impaired filling of the left ventricle (diastolic dysfunction)
5) More time wasted with the heart valves  closed ( Technically  measured as prolonged IVCT and IVRT) and measured by the MPI or myocardial performance index
6) Mitral regurgitation due to asymmetrical contraction of the papillary muscles
7) increased in left ventricular end-diastolic  pressure
8) Increased pulmonary artery pressure during exercise in some patients with normal resting echo
9) impairment of the normal ventricular twisting motion

Basically the right and left ventricle are designed to contract at the same time. In LBBB they do not- the right contracts milliseconds before the left.So there is inter-ventricular loss of synchrony.

The heart's electrical wiring system is designed so that the impulses that cause muscle contraction spread out more or less simultaneously from the two bundle branches. In LBBB the activation pattern is markedly altered so that the  septum is activated from right to left and  there is delay of  the impulses arriving  at the lateral and posterior left ventricular wall delaying muscle  contraction.

There is also asynchrony within  the left ventricle  apart from that of the septum and lateral wall being out of sync. Various segments of the Left ventricle  also do not contract as an organized system , some segments contracting and relaxing out of tune with others.This is referred to as intra-ventricular  dysynchrony.

Consider what the development of LBBB does to an otherwise healthy heart and consider how that effect would be more manifest clinically in a diseased heart with failure.

Two studies have shown that the ejection fraction decreases about 10-15%. while another reported only 5.8%. The EF does not tell the whole story as there is also impaired filling of the left ventricle.So not only is the stroke volume diminished by a lower EF but impaired filling leads to less blood to eject.Cardiac output falls and is particularly evident during exercise.

Details regarding cardiac function in patients with LBBB and normal coronary arteries ( most were shown not to have coronary artery disease by angiography) were provided by Ozdemir who studied 45 cases of isolated LBBB ranging in age from 48 to 72.(Effect of isolated left bundle branch block on systolic and diastolic function of left ventricle),  see ref 3 below.

Although the ejection fraction was reduced  "only" 5.8% from controls,there were statistically significantly higher values in the LBBB group  for the left ventricular end-systolic diameter,and the isovolumic relaxation  time and the isovolumic counteraction time and importantly the invasively measured ( done at the time of  coronary angiography)left ventricular end- diastolic pressure ( 14+/-3 versus 10 +/-3) with a normal of 3-12.Earlier work had shown that some patients with "Lone" LBBB -those with no coronary artery disease or obvious heart failure- may have normal echocardiogams but have increased pulmonary artery pressure with exercise.

With increases in the IVRT and IVCT there is less time for the ejection time which leads to an elevated or abnormal MPI ( myocardial performance index).The failing heart  both contracts and relaxes more slowly and the MPI has been proposed as a useful prognostic indicator. There is more time spent with the aortic and mitral values in the closed position leaving less time for the basic work of the heart , which is  ejecting blood, to occur.But in lone LBBB it is not the muscle cells defects that are the problem but loss of the normal incredibly well coordinated contraction and relaxation of the ventricles.

I can add a personal story. When I  recently developed a LBBB my "comfortable "( age appropriate and consistent with what one might expect in an aging runner)  jogging times increased from about 12: 45 minutes per mile to 14 +  minutes per  miles. which represents a 12% decrease. in running speed. Similar stories can be found on the web describing what LBBB does to a person's exercise capacity.

But there is more to the functional consequences of LBBB. Some patients  ( many, most ?) with LBBB develop heart failure. Some of the evidence for this occurrence comes from the clinical experience of patients with heart block who have had pacemakers with the traditional right apical pacing electrode, which in effect is an iatrogenic  LBBB.It is thought that the abnormal contraction patterns due to LBBB may lead to a deleterious cardiac remodeling and ultimate heart failure.  

The introduction and advances in cardiac electrocardiography made it possible to gain important insights into what the functional consequences of LBBB were and ultimately provide a new treatment for heart failure.

Dr.  IG McDonald in 1973 demonstrated by echocardiography that the interventricular septum moved abnormally. The septal problems were defined more clearly by Curtis in 1983 who showed that various abnormal movements of the septum were associated  with lower cardiac ejection fraction.,some patterns being more detrimental than others. Curtis mentioned that cardiac pacing might mitigate the LBBB induced abnormal ventricular contraction pattern.

 "The early studies described how the abnormal and/or delayed left ventricular activation wave front could lead to a reduction in left ventricular efficiency and performance that is largely independent of myocyte contractile function" Ref 1 see below.

 But it was not until 1994 that his theorizing was proven true when two clinical  studies demonstrated that pacing targeted to the site of the most delayed left ventricular contraction could improve overall cardiac function. The dyssynchrony could be "fixed" by resynchronization  ( or at least could  provide an effective work around) which became known as CRT or cardiac re-synchronization therapy.( also known as Bi-ventricular pacing, or Bi-V).About 1/3 of HF patients treated with CRT do not show improvement, the 2/3 who do are those with  LBBB because in them the dyssynchrony is a major factor in the cardiac impairment and is often improved with Bi-V.

Cardiac pacemakers are nothing new-the first totally implementable pacemaker (PM) was introduced in 1958 and for decades were used to treat patients with heart block .Now a new use for pacing has improved the outlook for many patients with heart failure. It turns out that that the ones benefited are those with LBBB so would not patients with lone LBBB also benefit from CRT? Is it necessary for a patient with LBBB to develop overt heart failure before pacing is considered or could/should the patient with NYHA class 1 be offered the implant?What about the patients with normal cardiac echo studies and shortness of breath on exercise? On further thought if a patient with LBBB has shortness of breath I would not expect the echo to be perfectly normal.The EF might not be less than the lower limits of normal but there would at least be delayed relaxation evident on echo . If PM implantation were a completely benign procedure the answer would be easy.


1)Breihardt,G,and Breithhardt ,O "Left Bundle  Branch Block-an Old-New Entity". J of Cardiovasc Trans. Res. 2012 5: 107-116

2)Grines,CL et al, Functional abnormalities in isolated left bundle branch block. The effect of interventricular asynchrony.  Circulation 1989. 79:845-853

3)Ozdenir,V Effect of the isolated left bundle branch block on systolic and diastolic functions of left ventricle. J Am Soc Echocardiog, 2001 Nov 14, 11 , 1075-9

4) Vaillant, C Resolution of Left Bundle Branch Block-induced cardiomyopathy by cardiac
 resynchornization therapy. J. of Amer College of Cardiology.2013, 61, 1089-1095

5)Yu,cm et al Biventricular pacing in patients with bradycardia and normal ejection fraction. NEJM 2009,363

addendum 12/28/15. Minor editing and addition of a 9th abnormality in LBBB,.
addendum 1/17/16 minor editing.5/22/16 Several spelling errors corrected.
addendum 3/19/17 Three sentence were added to the last paragraph.


Tommy B said...


I'd love to hear more of your thoughts on stand alone LBBB and it's effects on endurance athletes. I am a 39 yr old cyclist and was diagnosed with stand alone LBBB roughly 3yrs ago. I underwent significant testing, wearing a portable ECG machine for 30 days, treadmill test, sonograms, etc and the finding of the cardiologist was that my pulse was phasing into LBBB above resting rate during exercise and even sometimes at random. I exhibited no other symptoms of heart disease or any other conditions often associated with LBBB and so it was recommended that i make annual checkup visits and that's it. During that period my wife and I were having a baby, life was busy and so I wasn't riding and racing all that much anyways. I've since returned to competetive racing this season. While I understand that life with wife and kids allows for less training and riding I am generally finding that my threshold seems nowhere what it was. I consider myself to be a fairly talented endurance athlete, having raced competitively at the highest levels of international cycling for some years in my late 20's. generally that ability and "fitness memory" to some degree stays with most guys who have competed a this level even as they age, but I am getting my butt whipped!

Age and lifestyle aside, is LBBB a real contributing factor or is it in my head? Are there real concerns moving forward when it comes to high stress activity? Is there something that can be done? It is really hard to find material on this subject and I found this post to be compelling and informative (and alarming!). Looking for any insight or help where available, happy to chat.


Anonymous said...

Hi,I am in the same boat as you,I find I am 1minute a mile slower than 2 years ago since I found I had left bundle branch block,not sure if I was born with it or just acquired it,have you got any more info on it?are you going any faster or have you just quit?

james gaulte said...

Reply to anonymous 7:12am and Tommy B
My story is a little different.Not only had I developed LBBB I also had an intermittent exercise induced second degree heart block with a decrease in my heart rate occurring suddenly while running. This was a accepted indication for a pacemaker (PM). Because my electrophysiology cardiologist realized that a regular PM could not improved my cardiac function he opted for a type of pacing called Bundle of His pacing.This some how or other basically not only protects me from a too low heart rate but it in effect "fixes" the LBBB providing a sequence of activation and contraction of the left ventricle that is basically normal. So actually after I recovered from the implantation I was able to run at a speed very close to what I could do before I developed the LBBB. Had I only had the LBBB I would not have had a currently recognized indication for Bundle of HIs pacing it being a big deal to get a PM.Ironically those folks with LBBB who then develop heart failure ( all do not and all LBBB patients do not have the same degree of heart pumping function reduction))would be eligible at some point for CRT (cardiac resynchronization therapy)to correct or mitigate the malfunctioning left ventricle. CRT can be done with either a left ventricular lead ( bringing about bi-ventricular pacing or Bi-V) or with Bundle of His Pacing. It has only been in the last 2 years that His pacing is becoming more standard and many EP cardiologists have not adopted the procedure. I was fortunate as it seems better than Bi-V. It just happened by EP doc was the first one in town to do His bundle pacing.

James Gaulte