In ECG interpretation, what does the 'M' pattern suggest regarding the QRS wave?

The 'M' pattern in the context of ECG interpretation is a hallmark feature often associated with left bundle branch block (LBBB). This pattern, characterized by a prominent double-peaked appearance, typically indicates a delay in the electrical conduction through the left bundle branch of the heart's conduction system.

In LBBB, there is a disruption in the normal sequence of ventricular depolarization, leading to a specific morphology of the QRS complex. The presence of the 'M' pattern illustrates that the electrical impulse is travelling through the right bundle branch before it travels through the left ventricle, resulting in the characteristic changes in the QRS complex. This can include a widened QRS complex and a notched or slurred appearance.

When analyzing ECGs, it is crucial to recognize that the 'M' morphology is a significant indicator that may prompt further investigation or management of conditions related to the heart's left ventricle, including potential hypertrophy or ischemic changes, but primarily signals the conduction abnormality inherent to left bundle branch block.