Low diastolic blood pressure
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Low Diastolic Blood Pressure: Implications for Cardiovascular Health and Mortality
Introduction to Low Diastolic Blood Pressure
Low diastolic blood pressure (DBP), typically defined as a DBP below 70 mmHg, has been a subject of extensive research due to its potential implications for cardiovascular health and overall mortality. While high blood pressure is a well-known risk factor for cardiovascular diseases, the effects of low DBP are less clear and have yielded mixed results in various studies.
Increased Mortality and Cardiovascular Risks
All-Cause Mortality and Major Adverse Cardiac Events
Several studies have demonstrated a significant association between low DBP and increased all-cause mortality (ACM) and major adverse cardiac events (MACE). A meta-analysis involving nearly 2 million participants found that a DBP below 60 mmHg was associated with a 48% higher risk of ACM and an 84% higher risk of MACE compared to a DBP of 70-80 mmHg. This risk was particularly pronounced in individuals with pre-existing cardiovascular disease (CVD).
Myocardial Infarction and Heart Failure
Low DBP has also been linked to an increased risk of myocardial infarction (MI) and heart failure. For instance, patients with a DBP below 60 mmHg had a 49% higher risk of MI. Similarly, in patients with heart failure with preserved ejection fraction (HFpEF), a DBP below 70 mmHg was associated with a significantly higher risk of adverse outcomes, including all-cause death and hospitalization for heart failure.
Specific Populations at Risk
Older Adults and Women
Older adults, particularly women, appear to be at higher risk when DBP is low. The Women's Health Initiative Long Life Study found that older women with a DBP of 50 mmHg had a 33% higher risk of mortality compared to those with a DBP of 80 mmHg. The study suggested that maintaining a DBP between 68 and 75 mmHg might minimize mortality risk in this population.
Patients with Coronary Artery Disease
In patients with chronic coronary artery disease (CAD), low DBP has been associated with increased odds of angina and myocardial infarction. Studies have shown a J-shaped relationship between DBP and angina, with the odds of angina increasing as DBP falls below 70-80 mmHg . This suggests that overly aggressive blood pressure control in CAD patients might exacerbate symptoms and increase cardiovascular risk.
Controversies and Considerations
The J-Curve Phenomenon
The J-curve phenomenon describes the paradoxical increase in cardiovascular events and mortality at very low levels of DBP. This has been observed in several studies, including the SPRINT trial, which found that intensive systolic blood pressure control did not significantly affect cardiovascular risk in patients with low DBP. However, the relationship between low DBP and adverse outcomes remains a topic of debate, with some studies suggesting that the risks may be overstated.
Cognitive Outcomes
Interestingly, intensive blood pressure control does not appear to negatively impact cognitive outcomes, even in individuals with low DBP. The SPRINT MIND trial found no significant difference in the incidence of dementia or mild cognitive impairment between intensive and standard blood pressure control groups, regardless of baseline DBP.
Conclusion
Low diastolic blood pressure is associated with increased risks of all-cause mortality, major adverse cardiac events, myocardial infarction, and heart failure, particularly in older adults and those with pre-existing cardiovascular conditions. While the J-curve phenomenon highlights the potential dangers of overly aggressive blood pressure reduction, the optimal DBP target may vary among individuals. Clinicians should carefully consider these risks when managing blood pressure, especially in vulnerable populations such as older adults and patients with CAD. Further research is needed to refine DBP targets and improve cardiovascular outcomes.
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