Incomplete right bundle branch block (IRBBB), an entity undefined by a general consensus, can express a large pallet of both benign and pathological patterns. IRBBB is a common electrocardiogram (ECG) finding at all ages, more frequent in men and athletes. Usually, IRBBB does not need further evaluation; however, if abnormalities are found on the clinical exam, heart disease should be excluded. The RSR’ pattern and a QRS width below 100 ms define the crista supraventricularis (CSV) pattern. CSV is a right ventricular crest, one of the last structures to be depolarized by the Purkinje network. CSV pattern might result from posterior apex deviation, subpulmonic area delay, or late CSV activation. IRBBB can appear because of higher placement of electrodes V1 and V2 and pectus excavatum, in which P wave is negative, or in athletes, considered a benign pattern unless family history, symptoms, or left ventricular hypertrophy. It is necessary to differentiate IRBBB from pathological patterns such as type-2 Brugada ECG pattern, right ventricular enlargement, arrhythmogenic right ventricular cardiomyopathy, ventricular preexcitation—Wolf-Parkinson-White syndrome, and hyperkalemia. Examiners should be particularly alert to the splitting of the second heart sound because RBBB is a common finding in ostium secundum atrial septal defect. Therefore, clinicians need to be familiar with this ECG finding, which is not always a benign condition.
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