Diastolic dysfunction (DD) is a type of heart failure where the heart’s main pumping chamber, the left ventricle, struggles to relax and fill correctly with blood during the resting phase (diastole). Unlike the more commonly understood systolic failure, which involves weak contraction, DD is a problem caused by stiffness. When the heart muscle is stiff, the filling process is impaired, causing pressure to build up in the heart. This pressure eventually backs up into the pulmonary circulation, leading to symptoms. The severity of DD is classified using a progressive grading system.
The Basics of Diastolic Function and Grading
The cardiac cycle involves a precise sequence of events, and diastole is the heart’s filling phase. This phase begins with isovolumic relaxation, followed by the rapid filling phase, and finally, the atrial contraction provides an “atrial kick.” Cardiologists use a four-grade scale to classify diastolic dysfunction based on how severely this filling process is impaired.
Grade I represents the mildest form, known as impaired relaxation, where the stiffening of the ventricle causes slower initial filling. As the condition worsens, it can progress to the severe stages, Grade III and Grade IV, which are characterized by a restrictive filling pattern. In these advanced stages, the heart muscle is so stiff that it rapidly fills with blood, but pressure quickly equalizes.
Grade III, or restrictive filling, typically indicates significantly elevated pressures within the left atrium. The most severe form, Grade IV, is referred to as fixed restrictive filling, signifying that the severe stiffness and high pressures are irreversible. Grade II occupies an intermediate position in this continuum, representing a moderate stage of the disease where the body’s compensatory mechanisms mask the underlying dysfunction.
Specific Characteristics of Grade II Dysfunction
Grade II diastolic dysfunction is often called “pseudonormalization” because the heart’s filling pattern appears deceptively normal on an echocardiogram despite underlying disease. This pattern results from two opposing forces: impaired ventricular relaxation and a compensatory increase in left atrial pressure. The ventricle remains stiff, a characteristic carried over from Grade I.
In Grade I, the Doppler measurement of blood flow across the mitral valve shows a reduced early filling wave (E wave) and an increased atrial contraction wave (A wave), resulting in an E/A ratio less than 0.8. As the disease progresses to Grade II, the heart’s inability to accept blood elevates the left atrial pressure. This increased pressure forces blood across the mitral valve faster, artificially boosting the E wave velocity.
This high pressure normalizes the E/A ratio, bringing it into the range of 0.8 to 2.0, mimicking a healthy heart. Because this normal-appearing ratio is achieved through high driving pressure rather than healthy relaxation, the E/A ratio alone cannot reliably differentiate a normal heart from a Grade II pattern.
To confirm the diagnosis, physicians must look beyond the E/A ratio to other non-invasive Doppler measurements. Tissue Doppler Imaging (TDI) measures the velocity of the heart muscle itself, specifically the early diastolic velocity (e’). Because the e’ velocity is less dependent on filling pressure, it remains low in Grade II dysfunction, reflecting the true underlying stiffness of the ventricle.
The ratio of the E wave velocity to the e’ velocity (E/e’ ratio) is then calculated, and an elevated value, often greater than 10 to 14, is a strong indicator of the high left ventricular filling pressures characteristic of Grade II DD. Furthermore, a non-invasive maneuver, such as the Valsalva maneuver, may be performed to transiently reduce the preload. This often unmasks the underlying impaired relaxation pattern by causing the E/A ratio to revert to the abnormal pattern seen in Grade I.
Underlying Causes and Patient Symptoms
The development of diastolic dysfunction, including Grade II, is linked to chronic medical conditions that cause structural changes and stiffening of the left ventricular muscle.
The primary causes include:
- Poorly controlled high blood pressure (hypertension), causing the heart muscle to thicken (hypertrophy).
- Diabetes mellitus, promoting microscopic changes that increase stiffness.
- Coronary artery disease (CAD), where reduced blood flow can lead to scarring or fibrosis, decreasing muscle compliance.
- Aging, as the heart muscle progressively loses elasticity over time.
Symptoms of Grade II DD result directly from elevated left atrial pressure and fluid backup.
Common symptoms include:
- Dyspnea, or shortness of breath, especially with physical exertion, as high pressure forces fluid into the lungs.
- Orthopnea, which is difficulty breathing when lying flat, relieved by sleeping propped up.
- Generalized fatigue and reduced exercise tolerance because the stiff ventricle cannot fill adequately to supply oxygenated blood.
- Fluid retention, noticeable as swelling (edema) in the legs and ankles.
Diagnosis and Treatment Approaches
The diagnosis of Grade II diastolic dysfunction relies on a comprehensive echocardiogram using Doppler technology to quantify the heart’s filling velocities. The technician uses pulsed-wave Doppler to measure the E and A waves, and Tissue Doppler Imaging (TDI) to obtain the e’ velocity. The calculated E/e’ ratio, combined with an assessment of left atrial size, confirms the elevated filling pressures and the pseudonormal pattern.
Treatment focuses primarily on managing the underlying conditions that caused the heart muscle to stiffen. Aggressive control of blood pressure, often using medications like ACE inhibitors or Angiotensin Receptor Blockers (ARBs), is essential to reduce strain on the left ventricle. Tight regulation of blood sugar levels in diabetic patients is also a central component of therapy.
Medications are also used to manage symptoms caused by fluid backup. Diuretics are commonly prescribed to eliminate excess fluid, reducing elevated left atrial pressure and easing symptoms like shortness of breath and edema. Although Grade II DD is a moderate stage requiring continuous medical attention, its progression can often be slowed or stabilized by rigorous management of these underlying health issues.