What are the causes of left posterior hemiblock in adults with a history of hypertension, diabetes, or hyperlipidemia?

Causes of Left Posterior Hemiblock

Primary Etiologies

Left posterior hemiblock (LPH) is most commonly caused by extensive coronary artery disease, particularly involving both the right coronary artery and left anterior descending artery, and represents a marker of severe myocardial damage. 1, 2

Coronary Artery Disease (Most Common)

• Acute myocardial infarction is the predominant cause, with LPH appearing within hours of the acute event and carrying an 87% hospital mortality rate due to pump failure 1
• Extensive coronary disease is nearly universal: all patients with LPH demonstrate significant right coronary artery disease (most with complete occlusion) plus critical disease of at least one major left coronary branch 2
• The left anterior descending artery is critically diseased in 80% of cases (4 of 5 patients had complete LAD occlusion in angiographic studies) 2
• Infarction typically involves both anterior and inferior ventricular walls, with septal involvement being particularly common 1
• The pathophysiology involves acute histologic changes affecting posterior septal and midseptal fibers 1

Hypertension

• Arterial hypertension is the second most important cause after coronary disease, particularly in patients with chronic conduction abnormalities 3
• Hypertension contributes to left bundle branch system disease through chronic pressure overload and fibrosis 3

Degenerative Conduction System Disease

• Heavy calcification of the left cardiac skeleton is found in chronic cases, particularly affecting the posterior fibers of the left bundle branch 4
• Lev and Lenègre diseases (progressive degenerative diseases of the conduction system) are recognized causes 3
• Histopathologic studies show that lesions underlying LPH are more severe and more proximally located than in left anterior hemiblock, though less widely distributed 4

Cardiomyopathies

• Various cardiomyopathies can cause LPH through diffuse myocardial involvement affecting the conduction system 3
• One documented case involved diphtheritic myocarditis causing chronic LPH 4

Valvular Heart Disease

• Aortic valve disease can lead to LPH through hemodynamic stress and associated conduction system involvement 3

Congenital Heart Disease

• Congenital cardiopathies, particularly those involving the ventricular septum, may cause LPH 3

Critical Clinical Context for High-Risk Patients

In Patients with Hypertension, Diabetes, or Hyperlipidemia

These cardiovascular risk factors accelerate coronary atherosclerosis, making extensive coronary disease the likely mechanism when LPH develops in this population 5. The combination of:

• Hypertension contributes both directly (through conduction system fibrosis) and indirectly (through accelerated coronary disease) 5, 3
• Diabetes mellitus compounds risk by promoting both coronary atherosclerosis and microvascular disease affecting the conduction system 5
• Hyperlipidemia accelerates coronary disease, which is the primary substrate for LPH 5

Prognostic Implications

• LPH is an ominous electrocardiographic finding with incidence of only 0.5% even among patients with significant coronary disease, indicating its association with particularly severe pathology 2
• When associated with right bundle branch block (occurs in 60-67% of cases), there is great propensity to develop complete atrioventricular block and Adams-Stokes seizures 3, 4
• Isolated LPH is extremely rare and almost always indicates underlying structural heart disease, unlike left anterior hemiblock which can be benign 3

Key Distinguishing Features from Left Anterior Hemiblock

• LPH lesions are more severe, more proximally located, but less widely distributed than those causing left anterior hemiblock 4
• LPH is much rarer than left anterior hemiblock and virtually never occurs as an isolated benign finding 3
• The posterior fascicle requires more extensive disease to be interrupted due to its anatomical characteristics 4