What is ventricular diastole?

Ventricular Diastole

Ventricular diastole is defined as the relaxation and filling phase of the cardiac cycle that occurs after aortic valve closure and before aortic valve opening. 1 During this period, the ventricle relaxes and fills with blood in preparation for the next contraction.

Phases of Ventricular Diastole

Ventricular diastole consists of four distinct phases:

1. Isovolumic relaxation: The initial phase immediately following aortic valve closure when the ventricle begins to relax but before the mitral valve opens. During this phase, ventricular pressure drops rapidly while volume remains constant.

2. Early rapid filling: Begins when the mitral valve opens as ventricular pressure falls below atrial pressure, allowing blood to flow rapidly from the atrium into the ventricle.

3. Diastasis: A period of slow filling when atrial and ventricular pressures are nearly equal.

4. Atrial systole: The final phase when atrial contraction provides an additional 25-30% of ventricular filling, often called the "atrial kick." 1

Physiological Determinants of Diastolic Function

Several factors influence ventricular filling during diastole:

• Active relaxation (lusitropy): An energy-dependent process that requires ATP to remove calcium from the cytosol and allow myocardial relaxation
• Passive compliance: The elastic properties of the ventricular wall that determine its ability to stretch during filling
• Loading conditions: Preload and afterload affecting ventricular filling
• Heart rate: Determines the duration available for diastolic filling
• Atrial function: Contributes to late diastolic filling
• Ventricular interdependence: The influence of one ventricle's filling on the other through shared septum and pericardial constraint 2

Clinical Assessment of Diastolic Function

Diastolic function is primarily evaluated using echocardiography, with several key parameters:

• Mitral inflow patterns: E wave (early filling) and A wave (atrial contraction) velocities and their ratio
• Tissue Doppler imaging: Measurement of mitral annular velocities (e' and a')
• E/e' ratio: An important indicator of left ventricular filling pressures
• Pulmonary vein flow patterns: Systolic (S) and diastolic (D) velocities
• Left atrial size: Often enlarged in chronic diastolic dysfunction 1

Grading of Diastolic Dysfunction

Diastolic dysfunction is typically classified into three grades:

• Grade 1 (mild): Impaired relaxation pattern with reduced early filling
• Grade 2 (moderate): Pseudonormal filling pattern due to increased left atrial pressure compensating for impaired relaxation
• Grade 3 (severe): Restrictive filling pattern with markedly decreased ventricular compliance 1

Clinical Significance

Diastolic dysfunction plays a crucial role in several cardiovascular conditions:

• Heart failure with preserved ejection fraction: Often primarily a disorder of diastolic function
• Hypertensive heart disease: A common cause of diastolic dysfunction due to left ventricular hypertrophy
• Coronary artery disease: Ischemia can impair active relaxation
• Aging: Normal aging is associated with progressive diastolic dysfunction 3

Pitfalls in Assessment

• Fusion of E and A waves: Can occur with tachycardia or first-degree AV block, making interpretation difficult
• Pseudonormalization: Grade 2 dysfunction can appear normal on basic measurements, requiring additional parameters for correct identification
• Atrial fibrillation: Absence of atrial contraction alters filling patterns and requires different assessment approaches 1

Understanding ventricular diastole is essential for proper evaluation of cardiac function, as diastolic abnormalities often precede systolic dysfunction and contribute significantly to symptoms of heart failure even when ejection fraction is preserved.