Left bundle branch block with intermittent QRS axis switching: observation of a hypertensive patient for 18 years

Area of Science:

• Cardiology
• Autonomic Nervous System Physiology

Background:

• A 64-year-old male patient with a history of hypertension since 1971 presented with electrocardiographic abnormalities.
• Antihypertensive medication was prescribed starting in 1971.

Observation:

• Electrocardiogram (ECG) in 1988 showed left axis deviation (LAD).
• Slightly prolonged PQ intervals were noted in 1993.
• Complete left bundle branch block (CLBBB) with LAD emerged in May 1995.
• The wide QRS of CLBBB persisted, intermittently alternating between LAD and a normal axis.
• PQ intervals were longer during LAD compared to normal axis.
• QRS complexes in leads V1-V3 showed an R wave during LAD and a QS pattern during normal axis.
• The QRS axis shifted from normal to LAD during forced expiration and post-exercise testing.

Findings:

• The QRS axis exhibited dynamic shifts, alternating between LAD and normal axis.
• These axis shifts were observed to be triggered by physiological stimuli like deep breathing and exercise.
• A correlation was found between the QRS axis status (LAD vs. normal) and PQ interval duration.

Implications:

• The findings suggest a potential relationship between autonomic nervous system tone and the dynamic changes in QRS axis.
• This case highlights the complex interplay between cardiac conduction, axis variation, and autonomic regulation.
• Further research may elucidate the mechanisms underlying autonomic influence on cardiac electrical activity and axis determination.