Steven C. Port

Coronary vasodilator reserve. Comparison of the effects of papaverine and adenosine on coronary flow, ventricular function, and myocardial metabolism.

To evaluate coronary flow reserve during cardiac catheterization, intracoronary adenosine and papaverine have been used in the clinical setting. Although papaverine maximizes coronary blood flow, it induces several toxic side effects that reduce its desirability as a coronary dilator. This investigation was designed to compare the subselective intracoronary administration of papaverine with that of adenosine in an animal model. In dogs (n = 34), we studied the effects of each agent on hemodynamics, regional myocardial blood flow, contractility (sonomicrometric and echocardiographic), metabolism (coronary arterial and venous lactate and tissue high-energy phosphates), and electrocardiographic (ST and QT intervals) parameters. Barbiturate and morphine anesthesia/analgesia was induced, and a left thoracotomy was performed. An arterial shunt was created from the left carotid artery to the left anterior descending coronary artery. Two separate groups were studied: group 1 (n = 16) for regional myocardial blood flow and mechanical function and group 2 (n = 18) for biochemical measurements. Adenosine (67 +/- 2 micrograms/min) or papaverine (6 +/- 1 mg/min) was infused into the coronary shunt at a rate of 0.5 + 0.1 ml/min for a maximum duration of 3.5 minutes. Regional myocardial blood flows were determined at control (predrug) and maximal coronary flow using radiolabeled microspheres. All hemodynamic, wall motion, biochemical, and electrocardiographic parameters were also measured at these times. Both drugs produced comparable increases in total and regional coronary blood flows (adenosine, 1.21 +/- 0.15 to 4.83 +/- 0.36 ml/min/g; papaverine, 1.21 +/- 0.05 to 4.89 +/- 0.28 ml/min/g) upon infusion into the left anterior descending coronary artery. Papaverine produced significant (p less than 0.05) changes in subendocardial ST segment electrocardiogram (-2.5 mm), QT prolongation (8 +/- 2%), myocardial creatine phosphate (47% decrease), and coronary sinus serum lactate (277% increase) compared with control. In addition, intracoronary papaverine induced an abnormal contractile pattern. No significant changes in any of these parameters (i.e., ST segment, QT prolongation, myocardial creatine phosphate level, or lactate level) were observed with intracoronary adenosine infusions. We conclude that intracoronary adenosine is comparable to papaverine for maximizing coronary blood flow without the deleterious properties observed with intracoronary papaverine.

Assessment of single vessel coronary artery disease: Results of exercise electrocardiography, thallium-201 myocardial perfusion imaging and radionuclide angiography

The sensitivity of the commonly used stress tests for the diagnosis of coronary artery disease was analyzed in 46 patients with significant occlusion (greater than or equal to 70% luminal diameter obstruction) of only one major coronary artery and no prior myocardial infarction. In all patients, thallium-201 perfusion imaging (both planar and seven-pinhole tomographic) and 12 lead electrocardiography were performed during the same graded treadmill exercise test and radionuclide angiography was performed during upright bicycle exercise. Exercise rate-pressure (double) product was 22,307 +/- 6,750 on the treadmill compared with 22,995 +/- 5,622 on the bicycle (p = NS). Exercise electrocardiograms were unequivocally abnormal in 24 patients (52%). Qualitative planar thallium images were abnormal in 42 patients (91%). Quantitative analysis of the tomographic thallium images were abnormal in 41 patients (89%). An exercise ejection fraction of less than 0.56 or a new wall motion abnormality was seen in 30 patients (65%). Results were similar for the right (n = 11) and left anterior descending (n = 28) coronary arteries while all tests but the planar thallium imaging showed a lower sensitivity for isolated circumflex artery disease (n = 7). The specificity of the tests was 72, 83, 89 and 72% for electrocardiography, planar thallium imaging, tomographic thallium imaging and radionuclide angiography, respectively. The results suggest that exercise thallium-201 perfusion imaging is the most sensitive noninvasive stress test for the diagnosis of single vessel coronary artery disease.

Effects of intraaortic balloon counterpulsation on myocardial blood flow in patients with severe coronary artery disease

The purpose of this study was to test the hypothesis that myocardial blood flow distal to a critical stenosis would increase during intraaortic balloon counterpulsation. Accordingly, 13 patients with severe coronary artery disease were studied at the time of elective preoperative insertion of an intraaortic balloon catheter. Hemodynamic measurements and measurements of myocardial blood flow were made before and during counterpulsation. Myocardial blood flow was measured with a xenon-133 washout technique. Compared with control measurements, the heart rate decreased from 87.8 +/- 18.8 to 82.8 +/- 13.4 beats/min (p = 0.02) and systolic arterial pressure decreased from 112.1 +/- 17.9 to 97.8 +/- 14.8 mm Hg (p = 0.004) during counterpulsation. Diastolic arterial pressure increased from 72.2 +/- 10.1 to 120.2 +/- 21.4 mm Hg (p = 0.00002) during counterpulsation. Myocardial blood flow for the entire group decreased from 48.8 +/- 14.1 to 42.6 +/- 11.0 ml/100 g per min (p = 0.008). Regional flows in the left anterior descending and circumflex distributions also decreased. Left anterior descending artery blood flow decreased insignificantly from 51.5 +/- 14.4 to 47.4 +/- 11.7 ml/100 g per min (p = not significant), while circumflex flow decreased from 50.7 +/- 12.2 to 41.1 +/- 8.9 ml/100 g per min (p = 0.008). When normalized for the rate-pressure product, myocardial blood flow was 53 +/- 16 X 10(-4) at rest and 55 +/- 12 X 10(-4) (p = not significant) during counterpulsation.(ABSTRACT TRUNCATED AT 250 WORDS)

Left ventricular function during exercise testing and training.

Left ventricular function (LVEF) deteriorates during incremental exercise (GXT) in patients with ischemia (+ISCH). Left ventricular (LV) functional response during steady-state exercise, typical of that used in exercise training, are unknown. We compared LVEF in patients with documented coronary heart disease (CHD) who either had (+) or did not have (-) ISCH, and in healthy volunteers (CONTROL) during GXT and steady state. First pass RNA was performed during upright cycle GXT at rest (R), at the ventilatory threshold (VT), and at maximal exercise (Max); and during steady state at the workload associated with VT after 10, 20, and 30 min of exercise. RNA allowed measurement of ejection fraction (EF) and wall motion (WM); ISCH was mild, angina being relieved by momentary reductions in workload during steady state. Although +ISCH demonstrated the expected deterioration in LV function during GXT (decreased EF, abnormal WM)(EF = 58 to 56 to 54%), there was no evidence for progressive deterioration of LV function during steady state despite the presence of mild ISCH (56 to 56 to 54 to 54%). In -ISCH and CONTROL there were normal responses of EF during GXT (43 to 51 to 51% and 59 to 65 to 61%) and steady state (43 to 51 to 53 to 51% and 59 to 65 to 68 to 69%). We conclude that mild ischemia may be tolerated during steady-state exercise at levels consistent with exercise training without progressive deterioration of LV function.

Left ventricular ejection fraction during incremental and steady state exercise

Despite extensive study of left ventricular (LV) function during incremental exercise (INC), there is little known about LV function during steady state exercise typical of that used during exercise training. In this study we evaluated LV ejection fraction (LVEF) during upright cycle ergometer exercise using first-pass radionuclide angiography (RNA). Healthy volunteers (N = 10) were studied during both INC and steady state. INC studies were performed at rest, at the ventilatory threshold (VT), and at maximal exercise. During steady state studies were performed after 10, 20, and 30 min of exercise at VT. During INC LVEF increased from rest (61% +/- 5%) to exercise at the VT (73% +/- 5%). There was no further change in LVEF at maximal exercise (73% +/- 5%). During steady state, LVEF increased from rest (61% +/- 5%), to exercise at VT (73% +/- 5%), with further increases after 20 (78% +/- 6%) and 30 (79% +/- 3%) min of exercise. The results suggest that LVEF is nearly maximal during submaximal exercise at VT. During steady state LVEF continues to increase with continuation of steady state exercise.

Characterization of 3D PET systems for accurate quantification of myocardial blood flow

Three-dimensional (3D) mode imaging is the current standard for PET/CT systems. Dynamic imaging for quantification of myocardial blood flow with short-lived tracers, such as 82Rb-chloride, requires accuracy to be maintained over a wide range of isotope activities and scanner counting rates. We proposed new performance standard measurements to characterize the dynamic range of PET systems for accurate quantitative imaging. Methods: 82Rb or 13N-ammonia (1,100–3,000 MBq) was injected into the heart wall insert of an anthropomorphic torso phantom. A decaying isotope scan was obtained over 5 half-lives on 9 different 3D PET/CT systems and 1 3D/2-dimensional PET-only system. Dynamic images (28 × 15 s) were reconstructed using iterative algorithms with all corrections enabled. Dynamic range was defined as the maximum activity in the myocardial wall with less than 10% bias, from which corresponding dead-time, counting rates, and/or injected activity limits were established for each scanner. Scatter correction residual bias was estimated as the maximum cavity blood–to–myocardium activity ratio. Image quality was assessed via the coefficient of variation measuring nonuniformity of the left ventricular myocardium activity distribution. Results: Maximum recommended injected activity/body weight, peak dead-time correction factor, counting rates, and residual scatter bias for accurate cardiac myocardial blood flow imaging were 3–14 MBq/kg, 1.5–4.0, 22–64 Mcps singles and 4–14 Mcps prompt coincidence counting rates, and 2%–10% on the investigated scanners. Nonuniformity of the myocardial activity distribution varied from 3% to 16%. Conclusion: Accurate dynamic imaging is possible on the 10 3D PET systems if the maximum injected MBq/kg values are respected to limit peak dead-time losses during the bolus first-pass transit.

Nonperfusion applications in nuclear cardiology: Report of a task force of the American society of nuclear cardiology

ConclusionsIn conclusion, there seems to be a combination of factors that have contributed to the underutilization of nonperfusion applications of nuclear cardiology. For some procedures (i.e., infarct-avid imaging, probe radiocardiography, and functional evaluation with mental stress) there is a perceived lack of clinical application. For these, further clinical validation and education of referring physicians is necessary. Other nonperfusion studies (i.e., equilibrium RNV) have not kept pace technologically with competing modalities. For these, camera and computer manufacturers should be encouraged to develop and implement appropriate new hardware and software. For others (i.e., 123I MIBG “nerve” imaging and fatty acid analog metabolic imaging) radiopharmaceutical availability, particularly in the United States, is severely limited. For these, radiopharmaceutical companies should be encouraged to sponsor clinical trials validating clinical efficacy and cost-effectiveness, and if justified, appropriate applications should be filed with federal agencies. Last, and perhaps most important, physicians practicing nuclear cardiology must be motivated to embrace these nonperfusion radionuclide applications when appropriate, target patient populations in their institutions who will most benefit, and convince referring physicians of the clinical efficacy and cost effectiveness.For these and so many other facets of nuclear cardiology, the old cliché applies: “Nothing ventured, nothing gained.”

First-pass radionuclide angiography during bicycle and treadmill exercise

BackgroundTreadmill testing is usually preferred over cycle ergometry because of the greater sensitivity in diagnosing coronary artery disease. Treadmill testing has only recently been used with radionuclide angiography (RNA) because patient motion makes RNA imaging difficult. In this study we evaluate the comparability of treadmill and cycle exercise RNA with a dual isotope motion correction technique.Methods and ResultsVolunteer patients (n=27) performed first-pass RNA during maximal exercise using both cycle ergometer and treadmill. Exercise capacity was greater during treadmill exercise (8.1±2.4 vs 7.5±2.2 METs). Twenty-three of 27 treadmill and all cycle ergometer exercise studies were technically adequate. Maximal heart rate was greater during treadmill exercise (150±24 vs 143±25 beats *min −1), however, systolic blood pressure was greater during cycle ergometry (174±23 vs 188±25 mmHg), resulting in no difference in heart rate times systolic blood pressure (25.7±7.2 vs 26.9±6.0). There were no differences between treadmill and cycle ergometer for peak exercise left ventricular ejection fraction (56%±13% vs 57%±14%) (r=0.89). Calculated left ventricular end-diastolic volume was not different at rest (183±42 ml vs 176±44 ml) but differed significantly at peak exercise (282±75 ml vs 231±60 ml). The clinical impression, based on wall motion and left ventricular ejection fraction was very similar between treadmill and cycle ergometer.ConclusionTreadmill exercise RNA is feasible, with about 85% of studies likely to be technically adequate. The overall clinical results are very similar to cycle exercise RNA, although the ordinarily expected advantages of treadmill exercise were largely absent.

Technically suboptimal first-pass radionuclide angiographic studies

First-pass radionuclide angiography (FPRNA) has proven to correctly assess left ventricular function, however, technical difficulties do occur. One hundred and thirty one patients had contrast angiography and resting radionuclide angiography within 24 h. Of the 131 patients, 86 (66%) had adequate studies and 45 (34%) were technically suboptimal studies. In the latter group, low counts affected the quality of the images but did not change the left ventricular ejection fraction (LVEF) or regional wall motion (RWM) scores. Patients with high background activity showed overestimation of LVEF, however, by using a formula that was derived from the linear regression the LVEF could be calculated accurately in most cases. Multiple technical problems were noted in 14 patients in whom the best correlation was between contrast LVEF and backgrounduncorrected LVEF from FPRNA (r=0.87). In the latter group, FPRNA showed overestimation of RWM in 8 patients (57%), mainly in the inferior wall. We conclude that for most technically compromised first-pass radionuclide angiographic data, accurate LVEF values can be achieved but errors in regional wall motion interpretation will occur, especially when multiple technical problems exist.

CORRELATION OF CORONARY ARTERY CALCIUM SCORING ON UNGATED COMPUTED TOMOGRAPHY COMPARED TO GATED CARDIAC COMPUTED TOMOGRAPHY SCANS FROM THE MULTI-ETHNIC STUDY OF ATHEROSCLEROSIS

Coronary Artery Calcium (CAC) obtained from ECG-gated cardiac CT predicts cardiovascular (CVD) events. This is an ancillary study from Multi Ethnic Study of Atherosclerosis (MESA) using both gated and ungated chest CT obtained at one scanning visit. The purpose of this study is to correlate the