Diastolic dysfunction (point of care ultrasound)
Assessment for diastolic dysfunction is an advanced application of point-of-care ultrasonography, most commonly used as a supplemental non-invasive estimate of left atrial pressure in hemodynamically complex patients . Of note, this article will discuss the simplified, binary approach used in critical care and emergency ultrasound, and will not address the more comprehensive formal echocardiography protocol, which is the gold standard in clinical practice.
- isovolumetric relaxation
- rapid filling
- late filling
Diastolic dysfunction is exceedingly prevalent among the critically ill, occurring in 20-57% of patients with sepsis. In the community, diastolic dysfunction is a major pathophysiologic mechanism in heart failure .
Factors which influence diastolic function include ;
- atrial compliance and contractility
- mitral valve function
- ventricular recoil and relaxation
- ventricular compliance
- left ventricular systolic function
- right ventricular function
- interventricular dependence
Derangement of any of these variables may contribute to diastolic dysfunction. While a linear progression is not generalizable to all patients, the progression from an early, reversible state in which the left ventricle becomes less effective at suctioning an incipient preload to an end-stage, irreversible state in which a volume overloaded left atrium pushes a preload into a stiff, non-compliant left ventricle by virtue of extremely high pressure may be a useful pathophysiological model to correlate with measured pressures .
Cardiology literature promotes an approach by which one must follow two divergent paths of inquiry based on the classification of the left ventricular ejection fraction as reduced (LVEF < 40%) or preserved;
- for those patients with an EF less than 40% the following mitral inflow parameters are used
- E wave velocity
- if E < 50 cm/s with an E/A ratio <1, left atrial pressure is normal
- E wave deceleration time
- A wave velocity
- E/A ratio
- if E/A > 2 with a deceleration time < 150 ms, the left atrial pressure is elevated
- if no definitive result is derived from the abovementioned parameters, the mitral annulus must be interrogated with tissue doppler imaging to yield an e'
- an E / e ′ ratio is calculated
- an E / e ′ < 8 corresponds to a normal left atrial pressure
- an E / e ′ > 15 corresponds to an elevated left atrial pressure
- an E / e ′ ratio is calculated
- in patients with preserved left ventricular systolic function (LVEF > 40%), one forgoes analysis of the mitral inflow parameters in isolation, and begins with the calculation of the E/e' ratio
- E/e' < 9 indicates a normal left atrial pressure
- E/e' > 14 indicates a normal left atrial pressure
- E wave velocity
Indeterminate results require further measurement of parameters that are technically challenging, such as pulmonary venous Doppler, in the critically ill and lack clinical utility. Furthermore, there is no use for grading diastolic dysfunction at the bedside. A simplified protocol is suited to bedside application and will be described in the following section, which seeks to determine simply whether diastolic dysfunction is present or absent, and by proxy, whether elevated left-sided filling pressure could be present.
After basic goal-directed transthoracic echocardiography one may note supportive evidence of occult diastolic dysfunction, these findings include;
- left atrial enlargement
- increased left ventricular wall thickness
After basic goal-directed transthoracic echocardiography, assessment of diastolic dysfunction may take place in the apical 4 chamber view. A pulsed wave Doppler gate is placed just distal to the tips of the mitral valve leaflets, and the diastolic left ventricular inflow pattern with two positive deflections (the E and the A wave, respectively) are noted. Settings are then adjusted for tissue Doppler sampling, and the gate is placed over the septal (and/or lateral) annulus of the mitral valve, the target variable being the velocity of the mitral annulus during early ventricular filling, referred to as the e' wave.
Measurement of the peak velocities of the "E wave" and the "e' wave" are recorded and used to derive a third variable, the "E/e' ratio."
The "E wave" represents early diastolic filling, and is determined by the pressure gradient between the left atrium and ventricle when the mitral valve opens. The e' velocity is used as a measure of the lusitropic properties of the ventricle. As two important factors actuating left ventricular diastolic filling, the ratio derived from these variables provides a conceptual, rough estimate of filling pressure. An E/e' > 14 and/or an e' < 8 indicates the presence of diastolic dysfunction, and may be integrated into hemodynamic findings to;
- increase confidence that diffuse, bilateral B-lines represent cardiogenic pulmonary edema by demonstrating an increased left atrial pressure
- in the presence of bilateral A-lines, which are specific for wedge pressures under 18, and an otherwise normal goal-directed echo, rule out significant diastolic dysfunction
- identify patients with diastolic dysfunction before volume resuscitation
- rely on left atrial pressure to fill left ventricle, exquisitely sensitive to hypotension