What happens to the heart when diastolic blood pressure is critically high?

Effects of Critically High Diastolic Blood Pressure on the Heart

When diastolic blood pressure is critically high, it causes increased cardiac workload, left ventricular hypertrophy, impaired coronary perfusion, and accelerated atherosclerosis, all of which significantly increase the risk of cardiovascular mortality and morbidity.

Pathophysiological Changes

High diastolic blood pressure affects the heart through several mechanisms:

1. Increased Cardiac Workload

• Elevated diastolic pressure increases peripheral resistance that the heart must pump against
• This creates a higher afterload, forcing the heart to work harder with each contraction 1
• The increased workload leads to greater myocardial oxygen demand

2. Left Ventricular Hypertrophy (LVH)

• The heart responds to chronic high diastolic pressure by developing left ventricular hypertrophy
• This compensatory mechanism initially helps maintain cardiac output but becomes pathological over time
• LVH is an independent risk factor for cardiovascular events and mortality 1

3. Impaired Coronary Perfusion

• While coronary arteries fill primarily during diastole, critically high diastolic pressure paradoxically reduces coronary blood flow
• This occurs through:
  • Compression of coronary vessels due to increased ventricular wall tension
  • Structural changes in coronary microvasculature
  • Endothelial dysfunction limiting vasodilation 1

4. Accelerated Atherosclerosis

• High diastolic pressure increases mechanical stress on arterial walls
• This promotes endothelial damage and dysfunction
• The resulting inflammation and lipid deposition accelerates atherosclerotic plaque formation 2
• Both large and small coronary vessels are affected, increasing risk of myocardial infarction

Cardiovascular Risk

The relationship between diastolic blood pressure and cardiovascular risk is well-established:

• For every 10 mmHg increase in diastolic BP, there is a doubling of mortality risk from both ischemic heart disease and stroke 1
• The risk increases progressively and linearly from diastolic levels as low as 75 mmHg upward 1
• Critically high diastolic pressure (≥110 mmHg, classified as Stage 3 hypertension in older guidelines) poses immediate risk of target organ damage 1

Cardiac Complications

Critically high diastolic blood pressure can lead to several serious cardiac complications:

• Coronary Heart Disease: Accelerated atherosclerosis and impaired coronary perfusion increase risk of myocardial ischemia and infarction
• Heart Failure: Chronic pressure overload leads to pathological cardiac remodeling, eventually causing systolic and/or diastolic dysfunction
• Arrhythmias: LVH and myocardial fibrosis create substrate for dangerous arrhythmias
• Sudden Cardiac Death: Combination of ischemia, structural changes, and electrical instability increases risk 2

Clinical Significance

The 2017 ACC/AHA guidelines classify diastolic BP ≥90 mmHg as Stage 2 hypertension, requiring prompt pharmacological intervention 1. Critically high diastolic BP (≥110 mmHg) represents a hypertensive emergency if accompanied by signs of acute target organ damage.

When evaluating patients with critically high diastolic pressure:

• Look for evidence of acute cardiac damage (chest pain, ECG changes, elevated troponin)
• Assess for other target organ damage (neurological symptoms, renal dysfunction)
• Evaluate for secondary causes of hypertension
• Begin appropriate antihypertensive therapy promptly 1

Treatment Considerations

While treatment details are beyond the scope of this question, it's worth noting that:

• Drug treatment should be initiated promptly in patients with critically high diastolic BP 1
• The goal is to reduce diastolic BP to <90 mmHg in most patients 1
• Care must be taken not to reduce diastolic pressure too rapidly or excessively, as this may compromise coronary perfusion, especially in patients with existing coronary artery disease 3, 4

In summary, critically high diastolic blood pressure places tremendous strain on the heart through multiple mechanisms, significantly increasing cardiovascular risk and requiring prompt medical intervention to prevent serious complications.