New research indicates that the benefits of lowering blood pressure to less than 120/70 mm Hg remain questionable, as low blood pressure could increase the risk of cardiovascular diseases.
Coronary artery disease (CAD), or coronary heart disease, is the most common of the heart and blood vessels diseases, called cardiovascular diseases. The condition increases the risk of stroke, heart attack, and cardiac arrest. In 2013, CAD was the most common cause of death worldwide and was responsible for approximately 16% of fatalities. The risk factors for developing CAD include high blood pressure, smoking, diabetes, inactivity, being overweight, elevated cholesterol, poor diet and unreasonable alcohol intake.
Treatment for coronary artery disease involves improving the lifestyle measures listed above as well as taking medication to regulate blood pressure. The ideal blood pressure target for those with CAD remains debatable.
Blood pressure is expressed in terms of systolic pressure over diastolic pressure and is measured in millimeters of mercury (mm Hg). Systolic pressure is the force the heart uses to pump the blood around the body. Diastolic pressure is the resistance to blood flow in the blood vessels. Optimal blood pressure is usually considered to be in the range of 120-140 over 70-80mm Hg.
While elevated blood pressure puts extra strain on the heart and is associated with an increased risk of stroke, heart attack and death, blood pressure that is too low may generate insufficient blood flow to the heart, particularly in patients with coronary artery disease, and may cause similar outcomes.
A new study, published in The Lancet, examined the association between blood pressure and cardiovascular outcomes in patients with coronary heart disease.
The authors analyzed data collected over a period of five years from 22 672 coronary artery disease patients in 45 countries who were being treated for high blood pressure. Medical records were reviewed for strokes, heart attacks, or cardiac arrest. Average systolic and diastolic blood pressures at each event were categorized into 10mm Hg increments. A statistical analysis was conducted comparing the blood pressure and the incidence of each undesired cardiac event using 120-129 mm Hg systolic and 70-79 mm Hg diastolic blood pressures as references.
The results of the study are as follows:
- Systolic blood pressure of 140 mm Hg or more and diastolic blood pressure of 80 mm Hg or more were each associated with an increased risk of stroke, heart attack and cardiac arrest;
- Systolic blood pressure of less than 120 mm Hg and diastolic blood pressure of less than 70 mm Hg were associated with an increased risk of heart attack and cardiac arrest;
- Systolic blood pressure of less than 120 mm Hg and diastolic blood pressure of less than 70 mm Hg were not associated with an increased risk of stroke;
- Patients older than 75 years had an increased risk of a cardiovascular event for systolic blood pressure of 150 mm Hg or more and systolic blood pressure of 120 mm Hg or less, but not for systolic blood pressure of 140–149 mm Hg, which seems to confirm guidelines advocating a higher systolic blood pressure target of 150 mm Hg in older adults.
Previous research suggested a paradox: patients with CAD whose blood pressure was lowered to less than 120/80 mm Hg seemed to suffer heart attacks and cardiac arrests at rates comparable to patients with elevated blood pressure. This has been referred to as the J-Curve phenomenon. Study results support this concept.
The authors conclude that caution should be taken in the use of blood pressure lowering treatments in patients with CAD. While the benefits of lowering blood pressure to less than 140 mm Hg remain obvious, the benefits of lowering blood pressure to less than 120 mm Hg are questionable. Study results apply to patients with coronary heart disease and high blood pressure and may not apply to patients with hypertension and other conditions. Physicians should remain vigilant in their effort to improve patient care as about half of the population with hypertension has blood pressure that remains uncontrolled.
Written By: Lynn Kim