Diastolic dysfunction (DD) occurs when the left ventricle cannot relax or fill with blood effectively during the resting phase of the cardiac cycle. This failure causes a pressure backup, which can lead to fluid congestion in the lungs and other symptoms of heart failure. Echocardiography, a non-invasive ultrasound of the heart, is the standard method used to diagnose and assess the severity of this condition. It uses Doppler technology to analyze blood flow patterns and tissue movement, providing detailed measurements of the left ventricle’s filling properties and allowing clinicians to determine the presence and grade of diastolic impairment.
Understanding Diastolic Function
The heart operates through a continuous cycle of contraction (systole) and relaxation (diastole). Systole is the active phase where the left ventricle squeezes to eject blood into the body, while diastole is the subsequent phase where the ventricle relaxes and refills. The primary goal of healthy diastole is to allow the ventricle to fill completely with an adequate volume of blood while maintaining low pressure within the chamber. This process involves the muscle’s ability to actively untwist and relax (active relaxation) and the passive physical properties of the ventricular wall (compliance or stiffness).
Active relaxation begins immediately after contraction and is an energy-dependent process that rapidly lowers the pressure inside the ventricle, creating a suction effect that pulls blood from the left atrium. Following this rapid early filling, the passive properties of the ventricular wall become more important. Compliance describes the heart muscle’s elasticity, or its ability to stretch and accommodate increasing blood volume without a significant rise in internal pressure. When the myocardium becomes stiff, its compliance decreases, meaning even small increases in volume cause a sharp rise in filling pressure.
Key Echocardiographic Measurements
The assessment of diastolic function relies on a comprehensive set of Doppler and two-dimensional echocardiographic measurements that reflect the mechanical and pressure changes within the left heart chambers. The American Society of Echocardiography (ASE) and the European Association of Cardiovascular Imaging (EACVI) recommend focusing on four primary parameters to determine the presence of left ventricular diastolic dysfunction. These measurements provide non-invasive estimates of the left ventricular filling pressure.
Mitral Annular Velocity (Tissue Doppler Imaging)
Tissue Doppler Imaging (TDI) measures the velocity of the heart muscle movement at the mitral valve annulus. The early diastolic velocity, labeled e’, directly reflects the speed of the left ventricle’s active relaxation. Lower e’ velocities indicate impaired relaxation, suggesting a stiffer ventricle. The measurement is typically taken at both the septal (medial) and lateral sides of the mitral annulus, with a septal e’ velocity less than 7 cm/s or a lateral e’ velocity less than 10 cm/s considered abnormal.
The ratio of the mitral inflow E-wave velocity to the e’ velocity (E/e’ ratio) is a valuable tool for estimating the left ventricular filling pressure. The E-wave represents the driving force of blood from the left atrium. When the E-wave is high relative to the low e’ of a stiff ventricle, the resulting elevated E/e’ ratio suggests high filling pressures. An average E/e’ ratio greater than 14 is used as a cutoff suggesting elevated left ventricular filling pressures.
Mitral Inflow E/A Ratio and Deceleration Time (DT)
Mitral inflow is measured using Pulsed Wave Doppler placed at the tips of the mitral valve leaflets, creating a characteristic two-peak waveform. The first peak, the E-wave, represents the rapid, passive filling of the ventricle during early diastole. The second peak, the A-wave, is generated by the active contraction of the left atrium near the end of diastole.
The E/A ratio compares the velocity of early filling to atrial contraction, and its pattern changes predictably as diastolic dysfunction progresses. In healthy young individuals, the E-wave is usually faster than the A-wave, leading to an E/A ratio greater than 1. The Deceleration Time (DT) is the time it takes for the E-wave velocity to drop from its peak back to zero, reflecting the rate of pressure equalization between the atrium and ventricle. A prolonged DT, typically greater than 200 to 240 milliseconds, is a sign of impaired relaxation and a common finding in the mildest form of diastolic dysfunction.
Left Atrial Volume Index (LAVI)
The Left Atrial Volume Index (LAVI) is a measurement of the left atrium’s size, adjusted for the patient’s body surface area. The left atrium collects blood returning from the lungs before it enters the left ventricle. When the left ventricle is unable to accept blood efficiently due to stiffness or high filling pressures, the blood backs up into the left atrium, causing it to enlarge over time.
Because the left atrium is chronically exposed to the elevated pressure from the dysfunctional ventricle, its enlargement serves as a marker of the duration and severity of the condition. An indexed volume greater than 34 mL/m² is considered enlarged and represents structural evidence of chronic diastolic stress. The LAVI is a robust, time-averaged parameter that is less affected by acute changes in heart rate or volume status than the Doppler measurements.
Peak Tricuspid Regurgitation (TR) Velocity
The velocity of blood flowing backward through the tricuspid valve (Tricuspid Regurgitation, or TR) is used to estimate the pressure in the pulmonary artery. This estimation is an indirect measure of the overall pressure load on the heart, as elevated left ventricular filling pressures are transmitted backward to the right side of the heart.
A high peak TR velocity, specifically greater than 2.8 m/s, indicates high pulmonary artery systolic pressure, which is often a consequence of chronically elevated left atrial and left ventricular filling pressures. This parameter serves as one of the four main criteria in the standard algorithm for assessing diastolic function.
The Grading System for Diastolic Dysfunction
The echocardiographic measurements are synthesized using a standardized algorithm to assign a specific grade of diastolic dysfunction. This grading system provides a concise description of the severity and helps predict the patient’s clinical outcome. Diastolic function is typically classified as normal, indeterminate, or one of three grades of dysfunction, based on whether left ventricular filling pressures are elevated.
Grade I: Impaired Relaxation
Grade I, or Impaired Relaxation, represents the mildest form of diastolic dysfunction, where the ventricle’s active relaxation is slowed but filling pressures remain normal or near-normal. The characteristic Doppler pattern is a reversal of the mitral inflow E/A ratio, with the E-wave velocity dropping below the A-wave velocity (E/A ratio less than 0.8). The e’ velocity is typically low, reflecting the impaired relaxation, and the Deceleration Time is often prolonged. This pattern is common in older individuals without overt heart failure symptoms.
Grade II: Pseudonormalization
Grade II is labeled Pseudonormalization because the mitral inflow pattern superficially resembles a normal heart, with an E/A ratio between 0.8 and 1.5. This deceptive normalization occurs because the underlying impaired relaxation is coupled with elevated left atrial pressure. The high pressure in the atrium pushes blood into the ventricle faster, artificially boosting the E-wave velocity. The combination of a normalized E/A ratio with an abnormal E/e’ ratio (greater than 14) and an enlarged LAVI (greater than 34 mL/m²) confirms moderate dysfunction with elevated filling pressures.
Grade III: Restrictive Filling
Grade III, or Restrictive Filling, represents severe diastolic dysfunction associated with significantly elevated left ventricular filling pressures and poor prognosis. The ventricle is extremely stiff and non-compliant, leading to a large, forceful rush of blood from the atrium into the ventricle during early filling. This results in a highly restrictive pattern characterized by a very tall E-wave and a small A-wave (E/A ratio greater than 2). The Deceleration Time is markedly shortened, often less than 150 milliseconds, as the pressure equalizes almost instantaneously due to the ventricle’s stiffness.