Yes, definitely it is. The risk is very high in patients with DCM and other structural heart diseases. (Typically bundle branch reentry-BBR Ref: Mazur A, Kusniec Indian Pacing Electrophysiol J. 2005)
What about in normal hearts?
However, In normal hearts without LV dysfunction the risk is dramatically lower, but still not totally risk free. (The term normality can be undermined now , because, in true sense , an echocardiogram is not sufffice to rule out a structural myocardial disease. MRI has become a basic requirment to R/O concealed or localised scars , which may not alter wall motion and show up in echocardiogram)
So, do you want to say all LBBBs are risky ?
No. But we can’t say they are not risky as well. This is because the slowing of conduction, mild prolongation of the QT interval (contributed more by prolonged depolarization), and desynchrony still are the common denominators. These changes increase vulnerability to arrhythmias under specific circumstances—like electrolyte imbalances, drug effects, or extreme stress. This can trigger a VT in potentially inappropriate circumstances.
Final message
Cardiac electrical highway from SA node to Purkinje fibers is expected to be smooth flowing without any bumps and humps. Any interruptions in the electrical circuit are a potential invite for misbehavior. Fortunately, most times the adjacent cells compensate and adapt to the subtle diversions.
Dr.S.Venkatesan MD 