Mitral flow derived Doppler indices of left ventricular diastolic function.
Heart failure has been identified as a major health care initiative for the millennium. In the United States alone there are more than 4·9 million people with heart failure and 450 000–700 000 new cases are diagnosed each year. Heart failure is currently the most frequent cause of hospital admission for patients over 65 years of age. The concept that heart failure is defined as ventricular systolic contractile dysfunction and inability to meet the metabolic requirements of the body tissues is no longer tenable, because almost one third of all patients with heart failure have normal systolic function but abnormal left ventricular diastolic function. Diastolic ventricular relaxation is an energy requiring process involving sequestration of cytosolic calcium by the sarcotubular system and not simply passive elastic recoil. Today’s definition of heart failure needs to embrace diastolic ventricular dysfunction, that is, failure to receive blood at normal intracardiac filling pressures. Normal ventricular filling is a prerequisite for normal ventricular emptying, and the relationship between diastolic filling and contractile function is described by Frank–Starlings law. Perturbations in myocardial perfusion and ventricular hypertrophy induced by chronically increased afterload due to valvular heart disease or hypertension often result in abnormalities of ventricular function which are first manifest in diastole. Thus, there is an important need for techniques to accurately and unequivocally diagnose abnormalities of ventricular diastolic function. Left ventricular diastolic dysfunction was assessed initially in terms of impaired relaxation by measurement of the time constant of left ventricular pressure decay (tau), or altered ventricular compliance, both of which required haemodynamic and/or angiographic measurement at cardiac catheterization to construct pressure decay curves or pressure–volume/dimension relations. However, serial evaluation of left ventricular diastolic function by cardiac catheterization has never been a practical proposition. The introduction of echocardiography and subsequently Doppler has provided non-invasive methods of quantitating left ventricular diastolic function in terms of chamber filling dynamics and left atrial pressure. M-mode echocardiograms of the left ventricular dimension or the two-dimensional echocardiographic left ventricular short axis area with simultaneous left ventricular pressure tracings have been digitized to construct pressure–dimension loops, estimate peak filling rates and the duration of the rapid diastolic filling phase. However, these measurements can only be utilized when the region of the left ventricle sampled is representative of the whole ventricle, so that their use is precluded in ventricles with regional wall motion abnormalities. In contrast, Doppler techniques enable measurement of blood flow velocities across the mitral valve throughout diastole which reflect global left ventricular filling, and do not require assessment of ventricular size, shape or regional wall motion abnormalities. Initial Doppler studies measured peak blood flow velocities during rapid passive filling phase (E wave) and during atrial systolic contraction (A wave) and demonstrated that these measurements describing diastolic left ventricular function changed with age even in normal subjects. The velocity during the passive rapid filling phase peak velocity decreased in amplitude with concomitant prolongation of passive filling. This was accompanied by augmentation of the peak velocity during atrial systole, indicating that a greater proportion of left ventricular diastolic filling volume resulted from atrial systole with increasing age, and this could be expressed as a progressive decline in the ratio of peak velocities E/A or the ratio of their respective velocity time integrals EVTI/AVTI. There followed a burgeoning literature of Doppler studies describing small numbers of patients in whom measurements of E and A wave blood flow velocities were made in a wide spectrum of diseases in which abnormal left ventricular diastolic function was suspected. These studies showed that transmitral E and A blood flow velocities and their ratio (E/A) were sensitive to variations in left ventricular loading conditions, heart rate, body weight, age and gender. More recently quantitation of the deceleration time of the early (E wave) passive filling velocity transient has been shown to correlate with left atrial pressure. Because interpretation of Doppler measurements of diastolic ventricular function may be complicated by a number of confounding factors, recommendations have been formulated to assist in the diagnosis of left ventricular diastolic function. A notable deficiency in the Doppler literature was the