It is possible to experience a heart attack or stroke while having blood pressure levels that fall within the normal range. While high blood pressure (hypertension) is a leading risk factor for both events, it is not the only cause of life-threatening blockages in the body’s arteries. Normal blood pressure is generally defined as a systolic reading below 120 mm Hg and a diastolic reading below 80 mm Hg. The mechanisms leading to a heart attack or stroke often involve issues with plaque stability, blood clotting, or vessel integrity that are independent of systemic pressure.
Heart Attack Causes Beyond Hypertension
The most common cause of a heart attack (myocardial infarction or MI) is the sudden rupture of an atherosclerotic plaque inside a coronary artery. This event is driven by the internal composition of the plaque, not the external pressure exerted by the blood. Vulnerable plaques have a large, soft lipid core and a thin, fragile fibrous cap, a condition promoted by chronic inflammation and high cholesterol.
Plaque rupture immediately exposes the highly thrombogenic core material to the bloodstream, triggering a cascade that rapidly forms a blood clot (thrombus). This clot completely blocks the artery, causing the heart muscle tissue downstream to die from lack of oxygen. Most fatal plaque ruptures occur in arteries that were only mildly narrowed, often less than 50% blocked, meaning a person would have had no prior symptoms.
Other mechanisms involve issues with the artery wall itself. Spontaneous Coronary Artery Dissection (SCAD) is a tear in the inner layer of a coronary artery that allows blood to pool between the layers, creating a blockage. SCAD commonly affects women in their 40s and 50s who lack traditional risk factors for heart disease. It is frequently associated with underlying conditions like Fibromuscular Dysplasia (FMD) or extreme emotional or physical stress.
Coronary artery spasm, also known as Prinzmetal’s angina, is another non-hypertensive cause where the smooth muscle in the artery wall suddenly constricts. This temporary but complete closure of the vessel cuts off blood flow to the heart muscle, leading to an MI. These spasms often occur at rest, particularly between midnight and early morning. They are linked to triggers like smoking and cocaine use, not chronic high blood pressure.
Stroke Causes Beyond Hypertension
Like a heart attack, a stroke can occur from a sudden blockage in a cerebral artery, which may originate elsewhere in the body, bypassing blood pressure issues. Cardioembolic stroke is a prime example, accounting for a significant portion of ischemic strokes in normotensive individuals. This occurs when a blood clot forms in the heart and travels to the brain, lodging in a smaller vessel.
The most common cardiac source for these clots is Atrial Fibrillation (AFib), an irregular heart rhythm that causes blood to pool and stagnate, predominantly in the left atrial appendage. Even with normal blood pressure, the chaotic electrical activity of AFib creates an environment where a clot can form, detach, and travel to the brain. The resulting stroke is often severe because the clot is typically large and blocks a major cerebral artery.
Another cause, particularly in younger adults, is Cervical Arterial Dissection (CAD), a tear in the wall of the carotid or vertebral arteries located in the neck. The dissection allows blood to enter the artery wall, leading to the formation of a clot that subsequently breaks off and travels to the brain. This event is often preceded by minor neck trauma or associated with inherited connective tissue disorders, rather than chronic high blood pressure.
A third mechanism is paradoxical embolism, which can occur with a Patent Foramen Ovale (PFO). This is a small opening between the heart’s upper chambers that failed to close after birth. If a blood clot forms in the venous system (e.g., in a leg vein), it can pass through the PFO from the right side of the heart to the left side, bypassing the lungs’ filtration system. Once on the left side, the clot travels to the brain, causing a stroke despite normal systemic pressure.
Silent Contributors and Underlying Conditions
A number of systemic conditions act as silent drivers for heart attack and stroke, predisposing a person to these events even with normal blood pressure readings. Dyslipidemia, particularly high levels of Low-Density Lipoprotein (LDL) cholesterol, is the primary factor promoting atherosclerotic plaque formation. The total cholesterol level may be misleading; the ratio of LDL to HDL cholesterol, and elevated triglycerides, are more directly involved in creating the vulnerable, lipid-rich plaques that rupture.
Insulin resistance, a metabolic state that precedes Type 2 Diabetes, is a major independent risk factor. This condition is linked to a pro-thrombotic and pro-inflammatory state, promoting endothelial dysfunction and accelerating the development of unstable plaques. Individuals with insulin resistance may exhibit a cluster of risk factors, including high triglycerides and low HDL, which collectively increase cardiovascular risk regardless of normal blood pressure.
A strong Genetic Predisposition is another factor that bypasses traditional risk calculations. A family history of premature cardiovascular events significantly elevates risk. This is defined as a first-degree male relative experiencing an event before age 55 or a female relative before age 65. This suggests inherited tendencies for poor lipid processing or underlying defects in artery wall structure, such as those that make a person susceptible to SCAD.
Chronic Systemic Inflammation, measurable by a blood test for high-sensitivity C-reactive protein (hs-CRP), is a powerful predictor of future events. An hs-CRP level above 3.0 mg/L indicates a high level of low-grade inflammation that actively destabilizes atherosclerotic plaques, making them prone to rupture. This inflammatory process is an independent mechanism that turns a stable plaque into a life-threatening one, demonstrating that cardiovascular risk extends beyond the simple measurement of blood pressure.