I expect you are the same, I find it quite reassuring when there is no clear agreement amongst my Consultant colleagues to a clinical question because it’s then most likely that there is no scientific right or wrong. Last month, I mentioned asymptomatic left bundle branch block (LBBB) with a good LV, and as my colleagues gave me varying answers to the question about whether and when to follow-up, I thought I would explore this a little bit further.
Asymptomatic, isolated LBBB is not an unusual reason for referral to a general cardiology clinic, often coming from occupational or screening medicals, pre-operatively, etc.
Of course, we all recognise that LBBB is abnormal. The activation of the interventricular septum, which is left-sided in physiologic conditions, originates on its right side, with the electrical impulse propagating inferiorly and to the left, thus resulting in a non-homogeneous and delayed depolarization of the left ventricle, which over time may be detrimental to systolic contraction. But, it has not been clearly established over what time course this may become clinically relevant, nor with clear accuracy, in what percentage of patients; although, it is clearly a minority.
Of course, not only is there the effect on the myocardium, but there is a higher risk of developing spontaneous AV block.
We know the prevalence of LBBB in the general population has been reported to range from 0.1–0.8%, and there is a large amount of strong data out there about the significance of LBBB on prognosis.
In the Framingham Study, coincident with or subsequent to the detection of LBBB, 48% of individuals developed symptomatic CAD or CHF. Within 10 years from LBBB detection, CV mortality was 50%; and at 18 years follow-up, only 11% of LBBB patients remained free of detectable CV abnormalities.
Azadani, et. al. in 2012 found that in asymptomatic LBBB patients during 6 years of follow-up, 4.8% of people developed new CHF. A higher mortality from cardiovascular diseases was also found in participants with LBBB after adjusting for potential confounders (OR: 2.35).
The significance of asymptomatic LBBB in those over 45/50 years old, and certainly in those with CV risk factors, seems quite well established, but outside these groups, it does appear less certain.
Clearly, with our new referral, we are going to rule out obstructive coronary disease. My routine is to go beyond symptoms and the resting ECG and more often do a CTCA, certainly in all those with CV risk factors. Is this going too far in an asymptomatic patient?
We recognise that even with good LV contraction on echo there could still be myocardial disease, and I would routinely do an ESR, ACE level, and occasionally Lyme serology, following on with a cardiac MRI; and also, a holter for occult higher level conduction abnormalities.
Interestingly, my EP colleagues don’t seem terribly interested in doing an EP study in an asymptomatic patient unless persuasive abnormalities on holter, although there is some data that suggests patients with a prolonged HV time are at higher risk of future heart block.
If these investigations are normal, after reassuring your patient and counselling on minimising CV risk factors, what next?
Do you follow them routinely, and over what time-interval; just for symptoms or also periodic echocardiograms to establish they haven’t developed sub-clinical LVSD, or just periodic echos? Should this be different for those under and over 45/50 years, and in those with CV risk factors or not?
I share with my patients what I know on LBBB and what are the potential future problems. As a routine I give them a copy of their ECG, to ease their path through future medical contacts, and I counsel them to report any symptoms consistent with heart failure, and any syncopal episodes.
In those over 55 yrs, I more often arbitrarily see them in two years time. I must confess I don’t know how consistent I am with this approach, nor can I truthfully say what has happened to those I review; I think I’ll need to start auditing this now! Finding asymptomatic LVSD is important, but is it not more likely they will present with a change in symptoms?
What do you do, and why, for this patient group?