Biomedical subjects
Publications and source records attributed to D S Dymond.
Right ventricular rupture is rare. We report its identification by radionuclide ventriculography and subsequent confirmation by contrast angiography and at operation. The aetiology in this case was a primary cardiac malignancy.
The evolutionary changes in left ventricular function induced by cold pressor stimulation were investigated at 90 second intervals by rapid sequential first pass radionuclide angiography using the short half life tracer gold 195m. The results in 12 subjects with normal coronary arteries were compared with those in 12 patients with coronary artery disease. Left ventricular ejection fraction fell significantly from resting values in both groups after 1 minute of cold pressor, but only in patients with coronary disease was the significant fall maintained at 2.5 and 4 minutes. In both groups, the maximum decrease in ejection fraction occurred after 1 minute, whereas the maximum rise in systolic blood pressure occurred after 2.5 minutes. New abnormalities of regional ventricular function developed in 10 normal subjects after 1 minute of cold, with a total of 12 new abnormal segments. Only two such segments were seen at the later stages of imaging. Twenty one new segments developed after 1 minute in the coronary disease group, and 13 segments remained abnormal after 4 minutes. Three patients, two of whom had left main stem stenoses, showed persistent abnormalities of ventricular function after 2 minutes of recovery from cold stimulation. Thus left ventricular function changes rapidly during a period of cold stimulation in both those without and those with coronary disease. When the cold pressor test is used with multiple gated equilibrium imaging, the timing of imaging may be crucial to the results and interpretation of the test. The discordance between functional changes and rise in blood pressure is further evidence that alterations in afterload are not solely responsible for cold induced abnormalities.
Residual background activity following first-pass radionuclide angiography was assessed in 44 patients after eliminating activity in the right heart, left lung, and most of the right lung. The ejection fraction (EF) was calculated in two ways: (a) assuming background activity was present only in the right heart and lungs, and (b) correcting for scattered radiation by placing a circular region of interest around the left ventricle. With the first method, contrast EF was significantly underestimated in both AP and RAO views. With the second method, correlation was close in both views and absolute values agreed well with contrast EF. These results indicate that there is a substantial and measurable background component, due mainly to Compton scatter, even when activity from the right heart and lungs is eliminated.
A prospective randomized trial was conducted to evaluate the effects of exercise-based cardiac rehabilitation after myocardial revascularization surgery (MRS) on work capacity (measured in mets) and left ventricular function as determined from ejection fraction (LVEF). Twenty-eight patients undergoing MRS were randomly assigned to experimental (aerobic exercise, n = 19) or control (muscle relaxation and low-level exercise, n = 9) groups. Patients were studied before surgery (T1) and 2 (T2), 8 (T3), and 24 (T4) weeks after surgery with first-pass radionuclide angiography both while they were at rest and during maximal upright cycle ergometric exercise. Subsets of patients were also studied at T2, T3, and T4 at a standard workload of 75 W, and during maximal exercise 1 year after surgery (T5). Work capacity improved in both groups although significantly more so in the experimental group (3.9, 3.8, 6.0, and 7.3 mets and 3.7, 3.7, 4.9, and 5.7 mets at T1, T2, T3, and T4 in the experimental and control groups, respectively). The differences between groups were significant by T3. Peak exercise LVEF increased significantly in both groups from T1 to T2 then decreased at T3 and remained unchanged through T5. Peak exercise LVEF at T3 to T5 remained significantly above that observed at T1. LVEF responses were not related to the exercise program. During a standard workload, heart rate decreased, blood pressure increased, and LVEF did not change in either group. After conclusion of the formal protocol (T4), work capacity and LVEF did not change for either group throughout an additional 6 months (T5).(ABSTRACT TRUNCATED AT 250 WORDS)
The purpose of this study was to determine whether the left ventricular response during exercise radionuclide angiography would be influenced by exercise protocol. One hundred twenty healthy volunteers (aged 18 to 40 years) performed upright bicycle exercise using 1 of 5 protocols. Ejection fraction was measured using first-pass radionuclide angiography. Exercise protocols were as follows: (1) graded exercise (25 W increase every 2 minutes) to fatigue, heart rate greater than 85% of age-predicted maximum, n = 53; (2) graded exercise to 85% of age-predicted maximal heart rate or to fatigue with heart rate less than 85% of age-predicted maximum, n = 26; (3) graded exercise to fatigue, with "exercise" imaging performed immediately after exercise, n = 15; (4) abrupt presentation of a supermaximal work load (400 W), n = 10; (5) graded exercise to a work load of 75 W preceding the abrupt presentation of a supermaximal work load (300 to 400 W), n = 16. Protocols 2 and 3, representing less than maximal stress, yield higher ejection fractions than Protocol 1 and may reduce the sensitivity of exercise radionuclide angiography. Protocols 4 and 5, representing supermaximal stress, yield lower ejection fractions than Protocol 1 and may reduce the specificity of exercise radionuclide angiography. Thus, exercise protocol has a significant influence on the left ventricular response during exercise radionuclide angiography.
This paper describes the preparation and characteristics of a 195mHg-195mAu generator for clinical use in first-pass radionuclide angiography of the heart. The generator has an efficiency of elution of 20-30% which is maintained over the whole of its useful life. Over 100 patients have taken part in clinical trials with the generator.
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The development of a mercury-195m/gold-195m radionuclide generator system is described, together with the results of preliminary experiments in animals and in man. The daughter radionuclide has a half-life of 30.5 s with a principal gamma emission at 262 keV, ideal for use with the multicrystal camera but suitable also in conjunction with the Anger design. The half-life of the parent radionuclide is 40 h. The eluant in current use is 2.5 mM sodium cyanide, the column being stored under 2% sodium nitrate solution when not in use to prevent radiation damage. Generators capable of delivering 550 MBq of 195Aum in a 0.4 ml bolus have been used for first-pass nuclear angiocardiography, the half-life being long enough to permit administration via peripheral intravenous injection. The radiation dose associated with this radionuclide is much lower than that from conventional 99Tcm-labelled radiopharmaceuticals, permitting multiple sequential studies, even on children.
A case of aortic valve stenosis is reported with progressive left ventricular dysfunction demonstrated by radionuclide angiography. A gradient of 120 mmHg was present across the aortic valve. At the time of surgery, the patient was in severe cardiac failure with a left ventricular ejection fraction of 22%. Two months postoperatively, the patient was asymptomatic, and repeat radionuclide angiography demonstrated an ejection fraction of 93%. The reversible nature of this patient's ventricular dysfunction suggests that the cardiac failure was related to 'afterload mismatch' caused by the stenotic valve, rather than due to depressed contractility. The encouraging result in this patient reinforces the view that surgical intervention is warranted in some patients with critical aortic stenosis and extreme impairment of left ventricular function, and that the close relation between ejection fraction and operative survival may not hold true in aortic stenosis.
Rupture of the left ventricle after myocardial infarction results either in sudden death from cardiac tamponade or, when pericardial adhesions are present, in bleeding that is confined to a limited space, which gradually expands as the blood flows through a small communicating orifice under high pressure, forming a false aneurysm. In three such patients a false aneurysm of the left ventricle after myocardial infarction was successfully treated by operation. The interval from the initiating event to the time of surgery averaged 10 months. Two of the patients had pericarditis and all presented at some stage of the illness with tachyarrhythmias and cardiac failure. All the patients survived operation and have improved functionally. Because of the propensity of false aneurysms to rupture, early diagnosis and aggressive surgical treatment are recommended.
This study compared functional capacity during treadmill exercise testing and during bicycle exercise radionuclide angiography. 262 patients performed maximal upright bicycle exercise and also performed maximal graded exercise testing using either the Bruce (n = 158) or Naughton (n = 104) treadmill protocols. The functional capacity was well correlated between bicycle and treadmill for Bruce (r = 0.89), Naughton (r = 0.93), or combined treadmill (r = 0.90) protocols. However, the functional capacity was significantly lower during bicycle than during treadmill testing for Bruce (8.3 vs. 10.5 METs), Naughton (7.8 vs. 8.7 METs), or combined treadmill (8.1 vs. 9.8 METs) protocols. Treadmill functional capacity could be predicted from bicycle functional capacity using the following equations: Bruce METs = 1.00 X (bike METs) + 2.23, Naughton METs = 0.94 X (bike METs) + 1.40, and combined treadmill METs = 0.98 X (bike METs) + 1.85.
Twelve patients were studied by rest and exercise radionuclide ventriculography following left ventricular aneurysmectomy (LVA). Left ventricular filling pressure (LVFP) was also measured. Nine patients had been studied pre-LVA at rest and exercise before and after isosorbide dinitrate (ISDN). Resting ejection fraction (LVEF) improved after LVA (p less than 0.25), but exercise LVEF did not. End-diastolic volume (EDV) and resting LVFP also fell after LVA (p less than 0.25 for EDV, p less than 0.05 for LVFP) and although exercise LVFP fell (p less than 0.02), the values were abnormal in all patients. Ejection fraction of contractile segment (EFCS) from the resting radionuclide study pre-LVA was related to resting LVEF post-LVA (r = 0.71 p less than 0.02), although postoperative LVEF could not be predicted from preoperative EFCS in individual patients. Deterioration in LVEF and LVFP from rest to exercise post-LVA occurred both in patients with single-vessel occlusion and in those with multivessel coronary disease, irrespective of whether or not revascularization had been performed. Thus LVA is effective in improving resting ventricular function; exercise performance may remain abnormal even in patients without residual coronary disease.
Sudden strenuous exercise (SSE) has been shown to produce ischemic electrocardiographic (ECG) responses, abnormalities of myocardial blood flow, and decreases in left ventricular ejection fraction. Prior exercise taken as warm-up has been shown to ameliorate the ECG and myocardial blood flow abnormalities induced by SSE. The purpose of this study was to determine whether warm-up would normalize the responses of the left ventricular ejection fraction to SSE. Twenty healthy male volunteers performed SSE (400-W bicycle exercise) either with (group A, n = 10) or without (group B, n = 10) warm-up. Ejection fraction was measured using first-pass radionuclide angiography under control conditions and during SSE. During SSE ejection fraction decreased from control values in both group A (70.5 +/- 6.3 to 64.8 +/- 8.2%) and group B (70.3 +/- 10.1 to 57.7 +/- 7.7%), although ejection fraction was significantly higher during SSE in group A. The results are consistent with the hypothesis that the abnormal responses to SSE are attributable to subendocardial ischemia secondary to a delay in autoregulation of myocardial blood flow. However, the decrease in ejection fraction during SSE even following warm-up suggests that the mechanism for the abnormal response to SSE is more complicated than previously hypothesized.
To determine whether the temporal sequence of imaging could influence the results of exercise radionuclide angiography, 15 healthy volunteers were studied at rest, during peak bicycle exercise and immediately postexercise using first pass radionuclide angiography. Responses at rest, peak and postexercise included: heart rate (67 to 174 to 170 bpm), double product (7.4 to 31.5 to 27.5 mm Hg X bpm X 10(3)), left ventricular ejection fraction (68 to 69 to 80%) and mean normalized left ventricular ejection rate (3.63 to 6.56 to 8.56 s-1). The results indicate that left ventricular ejection fraction and mean normalized ejection rate were different during exercise and immediately postexercise although heart rate and double product were not. The results indicate that the temporal sequence of imaging is a significant procedural variable in the conduct of exercise radionuclide angiography.
To examine which factors affect the reproducibility of ejection fraction (EF), pulmonary transit time (PTT) and segmental wall motion assessed from first-pass radionuclide angiograms (FPRA), 32 patients who had FPRA were randomized for site of injection of isotope (right or left arm) and projection (right or left anterior oblique [RAO or LAO]). The quality of injected bolus was measured from the full width at half maximum (FWHM) of the bolus time-activity curve in the superior vena cava. All patients had two sequential studies on each of two consecutive days, and each study was analyzed independently by two observers. For EF, inter- and intraobserver correlations ranged from 0.94-0.98. EF was higher in the RAO than the LAO projection (mean 47.4% vs 40.3%, p less than 0.001), but neither injection site nor bolus FWHM affected the results. For PTT, interobserver correlations ranged from 0.75-0.93 and intraobserver correlations from 0.61-0.85. Variability in PTT was large, and inter- and intraobserver variabilities were directly related to bolus FWHM (mean 0.60 +/- 0.21 second for interobserver differences in PTT of less than 2.0 seconds, mean 1.55 +/- 0.86 seconds for interobserver differences in PTT of greater than 2 seconds [p less than 0.005]). Differences in FWHM between sequential studies were 0.28 +/- 0.29 second when intraobserver differences in PTT were less than 2 seconds and 1.04 +/- 0.67 seconds when differences in PTT were greater than 2.0 seconds (p less than 0.005). Variations in PTT were not related to differences in projection or injection site. Wall motion was highly reproducible for both projections. In the RAO projection, one of 116 anterior segments (0.9%), one of 116 apical segments (0.9%), and four of 116 inferior segments (3%) were judged normal from one observer's images and abnormal from another. In the LAO view, discrepancies occurred in one of 126 septal segments (0.8%), two of 126 apical segments (1.6%) and four of 126 posterolateral segments (3%). This study shows that EF and wall motion are highly reproducible in any projection, but the choice of projection significantly affects the values for EF from FPRA. PTT measurements are less reliable, highly bolus dependent, and their use in clinical practice depends on quality control of the bolus of injected radionuclide.
Thirty-seven patients undergoing contrast left ventriculography were studied by first-pass radionuclide angiography (FPRA) in the right anterior oblique view. Ejection fraction (LVEF) was calculated from FPRA using (a) a spatially and temporally varying background correction (BGC) based on a matrix of activity in lung and left atrium and (b) BGC with temporal fluctuation but with no allowance for spatial variations. The two methods were performed on both raw and temporally smoothed data. All four LVEFs correlated well with contrast LVEF (r = 0.90 - 0.94). Absolute values differed significantly from contrast values except for the method using the spatially and temporally varying BGC on smoothed data, which provided the closest overall agreement at all levels of LVEFs, despite occasional large individual variations. The same method on raw data overestimated low LVEFs and the method applying only temporal fluctuation in background underestimated high LVWFs. Allowance for spatial and temporal variations in background is therefore important when first-pass radionuclide angiography is performed in the RAO view.
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