Radionuclide Ventriculography and Diastolic Function

Gabriel Soudry, M.D.

Finn Manting, M.D., PhD

April 5, 1994

Case Presentation:

A 53-year-old man with a 15 year history of hypertension presented to the emergency room for progressively worsening shortness of breath. His chest radiograph showed pulmonary vascular congestion. Symptomatic relief was obtained with diuresis. An echocardiogram showed normal systolic function and moderate basal septal hypertrophy. Cardiac catheterization showed no significant coronary artery disease. He was referred to Nuclear Medicine for a radionuclide ventriculogram.

Findings:

The radionuclide ventriculogram (99k bytes) showed a normal ejection fraction of 72%, but a low peak diastolic filling rate of 2.06 EDV/seconds.

Discussion:

Clinical congestive heart failure (CHF) is traditionally associated with the triad of ventricular systolic dysfunction, loss of functional cardiac mass, and cardiac enlargement.

Left ventricular diastolic dysfunction in the absence of systolic dysfunction can also be a cause of congestive heart failure. Abnormal left ventricular diastolic performance can lead to substantial elevation in filling pressure, transudation of fluid into alveoli and pulmonary congestion. Up to 30-40% of patients who manifest CHF have normal systolic ejection fraction (1, 2, 3). Among those patients, abnormal diastolic function is the most frequent mechanism for the occurrence of congestive heart failure (4). The radionuclide ventriculogram not only provides an accurate assessment of the systolic ejection fraction but also measures left ventricular filling variables.

Several factors predispose to increased diastolic stiffness in a left ventricle with normal systolic performance. These include myocardial ischemia cardiac fibrosis, left ventricular hypertrophy, and elevated afterload (5). One condition in which many or all these factors coexist is chronic systemic hypertension.

Diastolic dysfunction may be secondary to altered passive elastic properties and/or impaired left ventricular relaxation (5). Diastole can be divided into four phases: the isovolemic relaxation phase, the rapid diastolic filling phase, the diastasis or slow filling phase and the atrial systole.

Left ventricular filling can be assessed with gated equilibrium ventriculography which generates a background-corrected time-activity curve for the left ventricle. The rate of left ventricular activity change is proportional to the rate of volume change with time which is expressed in end-diastolic volumes per seconds (EDV/s). Consecutive R waves are used as gating signals. The cardiac cycle is divided into a number of frames, typically 16 to 32, a separate image is stored for each of these frames and a periodic time/activity curve is generated. The following diastolic features can be determined:

Peak filling rate (PFR)

The most rapid change in ventricular volume is called peak filling rate. It usually occurs in the initial period of fast filling. The cardiovascular nuclear medicine computer can calculate the first derivative of the time-activity curve . The maximal value of this derivative during diastole is defined as the peak filling rate. It is important to assure that the point identified as the most rapid filling rate is included in the rapid diastolic filling phase.

Time to peak filling rate (TPFR)

The interval in milliseconds, between the point of minimal ventricular volume and the point at which the peak filling rate occurs is labeled as the time to peak filling rate.

Atrial systole

There is an artifact in the later part of the curve as a result of intrinsic variability of heart rate with the later frames of the acquisition containing less activity that may be anticipated. It is therefore difficult to generate accurate information about atrial systole.

The normal values for PFR and TPFR vary according to different published reports from 3.5 +/- 0.5 EDV/s and 145 +/- 20 ms to 2.63 +/- 0.39 EDV/s and 158 +/- 27 ms respectively (6). At Brigham and Women Hospital, normal values are PFR > 2.5 and TPFR < 150 ms.

Many studies have demonstrated a negative correlation between age and PFR and a positive correlation between heart rate and PFR in normal subjects (7,8,9). Thus the age and heart rate of the patient must be considered when diastolic measurements are assessed. In patients with impairment of LV systolic function, PFR is reduced in proportion to the fall in ejection fraction (10), suggesting that measurements of diastolic function do not provide additional information in patients with impaired systolic function.

PFR and TPFR can be measured with contrast ventriculography. In one study involving 10 patients, PFR and TPFR were similar when measured by contrast ventriculography and radionuclide ventriculography (11). An estimation of the diastolic filling can be obtained with Doppler echocardiography. Doppler mitral flow contours from a few representative beats are traced and analyzed for peak early flow velocity (E), peak atrial flow velocity (A), and A/E ratio. The Doppler PFR (ml/s) is derived by multiplying the peak early flow velocity by mitral valve area. In one study of 10 young normals (age 25 +/- 3 years) and 10 old normals (67 +/- 3), the mean A/E ratio was 0.54 +/- 0.15 and 1.09 +/- 0.29 respectively, the mean PFR was 448 +/- 152 ml/s and 274 +/- 62 ml/s respectively (12).

The major advantages of the radionuclide technique are its ability to measure relative volume changes with time without the geometric assumptions necessary with contrast angiographic and echocardiographic techniques, its ease of performance, lack of dependence on patient anatomy, production of data in a digitized format ready for computer processing and generation of the measurements of diastolic function, high reproducibility with recent Fourier fitting algorithms.

Conclusions:

References:

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12. Kitzman D, Sheikh K, Beere P, Philips J, Higginbottham M. Age-related alteration of doppler left ventricular filling indexes in normal subjects are independant of left ventricular mass, heart rate, contractility and loading conditions. J Am Cardiol 1991;18:1243-1250.

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J. Anthony Parker, MD PhD, Tony_Parker@bih.harvard.edu