Therefore left ventricular abnormalities cannot be reliably interpreted.
With a left bundle branch block left ventricular activation is no longer though the His-Purkinje system but results from direct myocardial activation coming from the right bundle and right ventricle. More precisely this system consists of the bundle of His, the left and right bundle branch and the fascicles of the left bundle branch ( Figure 1 ). Therefore, abnormalities of the left ventricle can be interpreted on the ECG. The intraventricular conduction system is composed of the His-Purkinje system. With an IVCD, left ventricular activation still occurs through the normal His-Purkinje system, but conduction is slowed. When the complex is this wide, the IVCD is the result of a dilated cardiomyopathy (cardiomyopathic QRS complex). Frequently, an IVCD will look like a LBBB in lead V1 with a rS complex or monomorphic S wave, and it appears like a RBBB in leads I and V6 with a broad. Therefore, the presence of septal forces means that widened QRS complex is the result of an intraventricular conduction delay (IVCD) and not a left bundle branch block. With a left bundle branch block there is no septal activation occurring as the septal branch is no longer functional there are no septal forces seen. This accounts for the small septal R wave in lead V1 and small septal Q waves in leads I, aVL, and V5-V6. The first part of the ventricles to be activated is the septum, with the impulse going in a left to right direction. Septal activation results from an impulse conducted via the septal or medial branch that comes off of the left bundle. Most importantly there is a prominent septal R wave in lead V1 (→) which indicates normal septal activation. Also noted is prominent notching of the QRS complex in leads I, aVR, and V1-V6. It can also be distinguished as can have delta wave (upslurring of QRS wave) and changing QRS morphologies. It often has a very fast rate (which can help differentiate it from other wide complex tachycardias) with rates often between 200 and 300. However, the QRS complex with a left bundle branch block is not usually this wide. Pay attention to how the wide-QRS tachycardia begins and ends. Since conduction occurs outside the AV node, it appears as a wide complex tachycardia. The QRS complex is wide (0.18 sec) and there is a morphology that resembles a left bundle branch block with a broad R wave in leads I and V6 (↑) and a deep S wave in lead V1 (←). The P waves are positive in leads I, II, aVF, and V4-V6 hence this is a normal sinus rhythm. There is a P wave (+) before each QRS complex with a stable PR interval (0.20 sec). Circulation - Circulation ECG Challenge Response! Regarding the 69 y/o man with a gout flare: Diagnosis-normal sinus rhythm, intraventricular conduction delay (cardiomyopathic QRS complex) There is a regular rhythm at a rate of 60 bpm.
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