Radionuclide evaluation of left ventricular function with nonimaging probes

Evaluation of cardiac function by echo-Doppler studies in critically ill patients

Measurements of stroke volume (SV) by echo-Doppler techniques (2D-echocardiography, continuous and pulsed Doppler) were compared to those obtained by thermodilution in 116 critically ill patients. The best correlation was obtained with pulsed Doppler positioned in the left ventricular (LV) outflow (r = 0.78, p less than 0.001). In a subgroup of 12 patients who had LV ejection fraction less than 60% and LV end-diastolic pressure greater than 15 mmHg, we also measured the peak aortic blood velocity (PABV) and acceleration (PABA) by continuous and pulsed Doppler as indexes of myocardial contractility before coronary artery bypass graft. When compared to healthy volunteers, these patients had decreased PABV and PABA, measured by continuous Doppler (91 +/- 16 vs 79 +/- 9 cm/s, p less than 0.05 and 913 +/- 202 vs 660 +/- 149 cm/s/s, p less than 0.05, respectively). These data therefore indicate that in critically ill patients pulsed Doppler placed in the LV outflow is an adequate echo-Doppler technique to measure SV, while continuous Doppler placed in the suprasternal notch can be used to assess LV performance.

Dissociation between global and regional systolic and diastolic ventricular function during coronary occlusion and reperfusion

Indexes of global ventricular function such as the ejection fraction (EF) and the peak diastolic filling rate (PDFR) are often used to assess the effects of coronary recanalization in patients with myocardial infarction. In this investigation we assessed the relationship between these global indexes and directly measured indexes of regional function during 15 minutes of coronary occlusion followed by 120 minutes of reperfusion in 22 open-chest dogs. A computerized nuclear cardiac probe was used to assess EF and PDFR. Indexes of regional function were measured by Doppler ultrasonic wall-thickening probes. During coronary occlusion, paradoxical systolic thinning occurred and the EF and PDFR decreased an average of 31.6% and 24.4%, respectively. During reperfusion the EF and PDFR improved rapidly and at 60 minutes were similar to baseline. Systolic wall thickening improved more gradually and remained abnormal throughout reperfusion. Likewise, indexes of diastolic function (mean rate to half end-diastolic thinning and late diastolic thinning fraction) recovered slowly and remained abnormal throughout reperfusion (78% and 69.7%, respectively). The correlation between the rate of change of global and regional function was poor during both coronary occlusion and reperfusion. Thus, during coronary occlusion the global and regional indexes of ventricular function undergo directionally similar changes. However, during coronary reperfusion the global indexes do not reflect the slow recovery of the stunned myocardium.

Significance of the pericardium in human subjects: effects on left ventricular volume, pressure and ejection

To assess the effect of the pericardium, left ventricular systolic function and diastolic compliance were studied in 15 patients before and after pericardiotomy during coronary artery surgery. Using first pass radionuclide angiography, curves for left ventricular systolic function (stroke work versus end-diastolic volume) and a measure of diastolic compliance (pulmonary capillary wedge pressure versus end-diastolic volume) were generated by changing body position to alter venous return. Left ventricular end-diastolic volume ranged from 41 to 111 ml/m2 and pulmonary capillary wedge pressure from 0 to 24 mm Hg. No significant changes were found in blood pressure (150/83 to 148/82 mm Hg), heart rate (66.7 to 67.1 beats/min), cardiac index (2.38 to 2.41 liters/min per m2), ejection fraction (0.56 to 0.54), end-systolic volume index (31.4 to 32.2 ml/m2), end-diastolic volume index (65.9 to 69.5 ml/m2) or pulmonary capillary wedge pressure (7.5 to 7.3 mm Hg). The pericardium did not affect the curves relating stroke work and end-diastolic volume or those relating pulmonary capillary wedge pressure and end-diastolic volume. Thus, when filling pressure and volume are normal or only moderately elevated, the pericardium does not appear to affect left ventricular systolic function or diastolic compliance in patients.

Continuous monitoring of left ventricular performance with the computerized nuclear probe during laryngoscopy and intubation before coronary artery bypass surgery

Left ventricular performance was monitored serially in 25 patients during laryngoscopy and intubation in the anesthetic induction period before elective coronary artery bypass surgery using the labeled equilibrium blood pool and the computerized nuclear probe. Left ventricular ejection fraction was obtained preoperatively, after induction of anesthesia but before endotracheal intubation, immediately after intubation, and at 1 minute intervals thereafter for 10 minutes. In all patients, there was an immediate decrease (mean 16%) in left ventricular ejection fraction accompanying the reflex hypertension and tachycardia occurring during laryngoscopy and endotracheal intubation; it was significantly depressed for 3 minutes with the concomitant hemodynamic changes. Seven patients did not demonstrate a recovery of left ventricular ejection fraction to the preintubation value. In 10 healthy noncardiac patients undergoing orthopedic surgery, after an identical anesthetic induction sequence and intubation, there was a similar decrease in ejection fraction, but of shorter duration. In these patients the recovery of left ventricular performance preceded the recovery of blood pressure and heart rate. This study demonstrates that profound decreases in left ventricular performance accompany the reflex hypertension and tachycardia occurring during endotracheal intubation and that there is persisting depression of left ventricular function in some patients with coronary artery disease. These findings indicate the potential utility of the computerized nuclear probe for monitoring ventricular performance during this critical period.

Beat-to-beat left ventricular performance assessed from the equilibrium cardiac blood pool using a computerized nuclear probe

The feasibility, accuracy and reproducibility of continuous beat-to-beat evaluation of left ventricular performance with a computerized nonimaging scintillation probe was assessed in 71 patients. This portable instrument has enough sensitivity to generate a real-time relative left ventricular volume curve using the labeled equilibrium blood pool without electrocardiographic gating. The probe was positioned at the left ventricular and background regions of interest using a systematic series of computerized algorithms and operator routines that were developed and standardized during the initial phase of this study. In each patient, left ventricular ejection fraction was calculated manually from the strip-chart recording in 10 consecutive sinus beats. Beat-to-beat left ventricular ejection fraction determined by the probe correlated well with first-pass studies obtained using a computerized multicrystal scintillation camera (r = 0.92). There was no systematic over- or underestimation, and the correlation was evident over a wide range of first-pass values (15-81%). There was excellent agreement between initial and repeat analyses (n = 58, r = 0.97) and between initial and repeat studies (n = 48, r = 0.94). The absolute variability of beat-to-beat ejection fraction measurements determined from all 710 beats was +/- 5.9% (expressed in ejection fraction units as +/- 2 SD). This technique should provide a reliable means of addressing pathophysiologic questions that require sampling of data directly on a beat-to-beat basis.

A perspective on the usefulness of computers in nuclear medicine

A computer system in clinical nuclear medicine has a wide variety of operations which it can perform. These range from simple data acquisition and tabulation to elaborate temporal and spatial reconstructions. Simultaneous recording of physiological data has also expanded the number of nuclear medical studies possible. The multiple-gated cardiac equilibrium analysis is the primary example of this format which has evolved rapidly with the availability of inexpensive central memory. Decreasing size and cost of processor units recently have led to the development of multiple processor systems. In some cases, the peripheral devices have a microprocessor already built in. The total cost of the computer system is essentially dictated by the number of peripheral devices.