What is the common cause of ST depression in patients with hypertension?

Common Causes of ST Depression in Hypertension

Left ventricular hypertrophy (LVH) is the most common cause of ST depression in hypertensive patients, followed by coronary artery disease (CAD) and subendocardial ischemia. 1

Pathophysiological Mechanisms

• LVH develops as an adaptive response to chronic pressure overload in hypertension, causing structural modifications of cardiac muscle including alterations in gene expression, loss of cardiomyocytes, defective vascular development, and fibrosis 1
• These structural changes in the myocardium alter normal repolarization patterns, leading to ST-segment depression on ECG 1
• Hypertension is a major risk factor for CAD, which can cause demand ischemia primarily limited to the endocardium, contributing to ST depression on the surface ECG 1
• ST-segment depression recorded on the body surface represents electrical gradients generated by ischemic vectors across the endocardium and epicardium 1

Prevalence and Clinical Significance

• Studies show that 15-23% of patients with mild-to-moderate hypertension who are free of clinical signs of coronary artery disease experience episodes of ST-segment depression 2, 3
• Most of these episodes are asymptomatic and not associated with symptoms 2
• Women with hypertension have a higher prevalence of ST-segment depression than men during Holter monitoring (17.5% vs 5.2%) 2
• Hypertensive patients with ST depression show significantly higher combined intima-media thickness of carotid and femoral arteries and more arterial plaques compared to hypertensives without ST depression 4

Relationship Between LVH and ST Depression

• LVH is present in approximately 57% of hypertensive patients with ST-segment depression 2
• In hypertensives with transient ST-segment depression, a significant relation exists between left ventricular mass and ischemic burden (r=0.51) 4
• The specificity of exercise ECG for detecting CAD is significantly reduced in patients with LVH (69% specificity) compared to those without LVH (78% specificity) 5

Distinguishing Features

• Standard criteria for ischemic ST depression include horizontal or downsloping ST depression ≥1 mm (0.1 mV) at 60 to 80 ms after the J point 1
• Upsloping ST depression is generally considered an "equivocal" test response and is not usefully predictive for myocardial ischemia in general populations 1
• The anatomic and functional severity of CAD can be related to the time of appearance of ischemic ST-segment depression - the lower the workload at which it occurs, the worse the prognosis 1

Clinical Implications

• Ambulatory blood pressure load is greater in hypertensive patients with ST-segment depression than those without (135±14 vs 129±15 mmHg systolic and 84±8 vs 79±10 mmHg diastolic) 3
• BP variations, particularly elevations, may trigger episodes of ST-segment depression in hypertensive patients 3
• Exercise echocardiography is more accurate than exercise electrocardiography for the detection of coronary artery disease in patients with known or suspected LVH (85% vs 60% accuracy) 5

Monitoring and Management Considerations

• 24-hour Holter ECG monitoring can be useful for detecting silent ST depression episodes in hypertensive patients 3
• Circadian distribution of ST depression episodes in hypertensives shows two peaks: on awakening and in the late afternoon periods 3
• Effective blood pressure control may prevent the development of arrhythmias and ST-segment abnormalities 1
• Thiazide diuretics commonly used to treat hypertension may result in electrolyte abnormalities (hypokalaemia, hypomagnesaemia) that can contribute to ST-segment changes 1

Understanding these mechanisms is crucial for proper interpretation of ECG findings in hypertensive patients and for distinguishing between benign ST depression related to LVH and potentially concerning ischemic changes that may require further evaluation.