Observations on conduction in a case of intermittent left bundle branch block

Incomplete Left Bundle-Branch Block

“…With an increase in heart rate (illustrated as RI to R3 in Fig. 1), consecutive impulses find one bundle branch-usually the, right-refractory and the other fully recovered; conduction to the ventricles thus proceeds through one bundle branch only, resulting in an aberrant or bundlebranch block pattern.Examples of this arrhythmia have been reported by Vesell (1941), Shearn andRytand (1953), andGardberg andRosen (1958): in all these cases the transition from the bundle-branch block pattern to normal intraventricular conduction and vice-versa was sudden. We report another example of this arrhythmia where the aberrant pattern was in the form of left bundle-branch block…”

“…Examples of this arrhythmia have been reported by Vesell (1941), Shearn andRytand (1953), andGardberg andRosen (1958): in all these cases the transition from the bundle-branch block pattern to normal intraventricular conduction and vice-versa was sudden. We report another example of this arrhythmia where the aberrant pattern was in the form of left bundle-branch block…”

Inefficacy of Carotid Sinus Stimulation in Atrial Fibrillation*

“…A similar mechanism is observed in intermittent left bundle‐branch block. In this condition the conductivity of the bundle of His is depressed but not abolished, and the bundle is able to conduct when the cycle is long enough to allow for recovery from the increased refractory period (12). Gardberg and Rosen (13) demonstrated that in a patient with aninitial left bundle‐branch block but no evidence of heart disease or hypertension, stimulation of the carotid sinus caused the block to convert to normal QRS conduction.…”

Diabetes Mellitus, Idiopathic Myocardial Hypertrophy and Paroxysmal Atrial Flutter

“…Accordingly, incomplete right bundle-branch block may appear when the rate is increased and disappear when the rate is diminished. Once bundle branch block is abolished by slowing the rate, it may remain absent after the heart rate has again increased to a rate with which the block was originally present (7). In the presence of coronary atherosclerosis with a rapid ventricular rate, coronary flow can be impaired sufficiently to produce an incomplete right bundle-branch block.…”