What is the importance of adequate diastole in maintaining optimal cardiac function?

The Importance of Adequate Diastole in Maintaining Optimal Cardiac Function

Adequate diastole is critical for optimal cardiac function as it enables proper ventricular filling, maintains normal stroke volume, and prevents elevated filling pressures that could lead to pulmonary congestion and heart failure symptoms. 1

Physiological Role of Diastole

Diastole is the portion of the cardiac cycle that begins with isovolumic relaxation and ends with mitral valve closure, comprising both active and passive processes:

• Active relaxation (early diastole): Energy-dependent process that allows the ventricle to rapidly expand and create a pressure gradient for efficient filling 2
• Passive filling (mid to late diastole): Determined by ventricular compliance, loading conditions, and atrial contraction 2
• Coronary perfusion: Myocardial perfusion occurs almost exclusively during diastole, making adequate diastolic time essential for coronary blood flow 1

Hemodynamic Consequences of Diastolic Function

Proper diastolic function maintains a delicate balance between:

• Filling pressures: Adequate diastole prevents elevated left ventricular filling pressures, left atrial pressure, and pulmonary venous pressure 1
• Cardiac output: Ensures sufficient ventricular filling to maintain stroke volume, particularly during increased demand (e.g., exercise) 1
• Coronary perfusion: Maintains coronary blood flow through adequate diastolic time and pressure 1

Diastolic Function During Exercise

Normal diastolic response to exercise includes:

• Enhanced myocardial relaxation: Normal subjects increase stroke volume without significantly increasing filling pressures due to augmented relaxation and early diastolic suction 1
• Proportional increases: In healthy individuals, both mitral E velocity and annular e' velocity increase proportionally during exercise, maintaining a stable E/e' ratio 1
• Exercise capacity: The faster the myocardial relaxation (e' velocity), the higher the exercise capacity 1, 3

Consequences of Diastolic Dysfunction

Impaired diastolic function leads to:

• Elevated filling pressures: Patients with diastolic dysfunction can only achieve required cardiac output at the expense of increased left ventricular filling pressures 1
• Reduced exercise tolerance: Diastolic dysfunction limits the ability to augment cardiac output during exercise 1
• Pulmonary congestion: Elevated filling pressures can lead to pulmonary venous congestion and symptoms of dyspnea 1
• Heart failure with preserved ejection fraction: Approximately 30% of heart failure patients have normal systolic function but predominantly diastolic dysfunction 1

Assessment of Diastolic Function

Diastolic function can be evaluated through:

• Echocardiography: Key parameters include mitral inflow velocities, mitral annular e' velocity, E/e' ratio, tricuspid regurgitation velocity, and left atrial volume index 1
• Diastolic stress testing: Particularly valuable when resting echocardiography doesn't explain symptoms of dyspnea or heart failure, especially with exertion 1
• Invasive hemodynamic assessment: Gold standard for measuring relaxation (using micromanometer catheter) and compliance (combining with conductance catheter) 4

Clinical Implications

Diastolic dysfunction is prevalent in various cardiovascular conditions:

• Coronary artery disease: Myocardial ischemia consistently reduces ventricular relaxation 1
• Hypertension: Hypertensive heart disease impairs diastolic function 1
• Hypertrophic cardiomyopathy: Characterized by significant diastolic abnormalities 2
• Aging: Diastolic function commonly declines with age 2

Management Considerations

Treatment approaches for diastolic dysfunction include:

• Diuretics: Judicious use to reduce elevated filling pressures without significantly reducing cardiac output 1
• Nitrates: Help lower elevated filling pressures 1
• Rate control: Drugs suppressing AV conduction to control ventricular rate in patients with atrial fibrillation 1
• Calcium channel blockers and beta-blockers: May improve diastolic filling by reducing heart rate and potentially augmenting ventricular relaxation 1
• ACE inhibitors: Frequently used, though studies demonstrating their effectiveness specifically for diastolic dysfunction are limited 1

Common Pitfalls in Diastolic Assessment

• Heart rate effects: Fusion of E and A velocities at higher heart rates can complicate assessment 1
• Conduction abnormalities: Left bundle branch block, right ventricular pacing, and cardiac resynchronization therapy reduce the accuracy of diastolic parameters 1
• Loading conditions: Many diastolic parameters are load-dependent and should be interpreted with caution 5
• Mitral valve disease: Significant mitral valve disease can confound diastolic assessment 1