S. E. Lewis

Alterations in left ventricular volumes and ejection fraction at rest and during exercise in patients with aortic regurgitation

This study was performed (1) to determine the changes in left ventricular volumes during exercise in patients with aortic regurgitation, and (2) to evaluate the importance of these alterations in characterizing left ventricular function in these patients. In 15 normal subjects (Group I) and in 17 patients with aortic regurgitation (Group II), left ventricular end-diastolic volume index, end-systolic volume index, ejection fraction and the ratio of peak systolic blood pressure to end-systolic volume index were measured at rest and during supine exercise. The patients with aortic regurgitation were classified into two groups on the basis of symptoms and chest radiographs: Group IIA, minimal or no symptoms, no cardiomegaly or pulmonary venous congestion; Group IIB, definite symptoms, with cardiomegaly and pulmonary venous congestion. Patients with aortic regurgitation had greater left ventricular end-diastolic and end-systolic volume indexes at rest and during exercise (p <0.05) than did normal subjects. During exercise, left ventricular end-diastolic volume index increased in normal subjects (53 ± 13 ml/m2 [mean ± standard deviation] at rest, 67 ± 18 ml/m2 during exercise, p <0.01), demonstrated a heterogeneous response in patients in Group IIA and increased in patients in Group IIB (180 ± 96 ml/m2 at rest, 209 ± 102 ml/m2 during exercise, p <0.05). During exercise, left ventricular end-systolic volume index decreased in normal subjects (18 ± 5 ml/m2 at rest, 15

Iodine-123 phenylpentadecanoic acid: detection of acute myocardial infarction and injury in dogs using an iodinated fatty acid and single-photon emission tomography

6 ml/m2 with exercise, p <0.01), increased in patients in Group IIB (82 ± 60 ml/m2 at rest, 118 ± 93 ml/m2 during exercise, p <0.05), and showed a variable response in those in Group IIA. At rest, left ventricular ejection fraction was similar in the three groups, but during exercise it increased in Group I (0.71 ± 0.07 at rest, 0.82 ± 0.07 with exercise, p <0.001), was unchanged in Group IIA and decreased in Group IIB (0.59 ± 0.15 at rest, 0.50 ± 0.16 during exercise, p <0.05). During exercise, there was an inverse relation between changes in left ventricular ejection fraction and endsystolic volume, but no relation between changes in end-diastolic volume and ejection fraction. Changes in the systolic pressure-volume ratio provided no more information than changes in end-systolic volume alone. Thus, abnormal alterations in left ventricular volumes occur during exercise in patients with aortic regurgitation and may be helpful in the further characterization of left ventricular performance in these patients.

Effect of oral propranolol on rest and exercise left ventricular ejection fraction, volumes, and segmental wall motion in patients with angina pectoris. Assessment with equilibrium gated blood pool imaging.

The ability of an iodinated fatty acid, iodine-123 phenylpentadecanoic acid (1-123 PPA), and single-photon emission computed tomography (SPECT) to detect myocardium injured by temporary or permanent coronary arterial occlusion was evaluated. In 5 control dogs, 11 dogs that underwent 90 to 120 minutes of fixed left anterior descending coronary artery (LAD) occlusion, and 8 dogs that underwent 90 minutes of temporary LAD occlusion and up to 90 minutes of reflow, 2 to 6 mCi of I-123 PPA were injected and the dogs were imaged with SPECT. Control dogs showed relatively uniform uptake and clearance of I-123 PPA in similar left ventricular (LV) regions. Dogs with permanent LAD occlusion were identified by computer algorithm as having regions of decreased I-123 PPA uptake in the infarct-related area and a reduced rate of I-123 PPA clearance (-9.4% in infarct sectors [washin], +3.7% in sectors adjacent to the area of infarction, and +15.4% in control LV sectors [p less than 0.01]). Dogs with temporary LAD occlusion and reperfusion had decreased clearance of I-123 PPA from the regions with infarction; I-123 PPA clearance was -5.2 +/- 16.4% in infarct sectors, 12.7 +/- 7.4% in periinfarct zones, and 30.4 +/- 12% in control LV regions. These data demonstrate that tomographic analysis of I-123 PPA uptake and clearance permits the relatively noninvasive detection of LV myocardium injured by permanent or temporary LAD occlusion and reperfusion.

Measurement of myocardial infarct size by technetium pyrophosphate single-photon tomography

The effect of oral propranolol on left ventricular ejection fraction, left ventricular volumes, cardiac output, and segmental wall motion was assessed with multigated blood pool imaging both at rest and during supine exercise in 15 patients with angina pectoris. Propranolol had no effect on resting left ventricular ejection fractions. Before propranolol, they did not change during exercise, whereas after propranolol the ejection fractions increased slightly. Exercise left ventricular ejection fractions increased with propranolol in three patients with resting left ventricular ejection fractions of less than 40 per cent. More specifically, left ventricular end-diastolic volume index, end-systolic volume index, stroke volume index, and cardiac index were not altered significantly at rest or during exercise by propranolol. Exercise left ventricular ejection fractions were increased in five and unchanged in eight patients by propranolol. Those patients with increases in left ventricular ejection fractions had a greater change in left ventricular end-diastolic volume indices and a greater change in left ventricular end-systolic volume indices during exercise while on propranolol. Left ventricular segmental wall motion was not altered significantly during exercise by propranolol. We conclude that: (1) Left ventricular functional responses to propranolol during exercise are heterogeneous and not easily predicted; (2) propranolol causes no consistent deterioration in exercise left ventricular ejection fraction even in patients with resting ventricular ejection fractions less than 40 per cent; (3) increased exercise left ventricular ejection fraction with propranolol is contributed to by significant increases in end-diastolic volume during exercise; and (4) gated blood pool imaging is a useful method for characterising rest and exercise left ventricular ejection fractions and left ventricular volumes during propranolol therapy.

Effects of verapamil and nifedipine on left ventricular function at rest and during exercise in patients with prinzmetal's variant angina pectoris

The primary determinant of prognosis after acute myocardial infarction (AMI) is the size of the acute infarct. The present study evaluates 46 patients with different infarct distributions and sizes to test the hypothesis that single photon emission computed tomography with technetium-99m pyrophosphate (Tc-99m-PPi) and blood pool overlay allows measurements of AMI size that provide insight into prognosis irrespective of infarct location. Identical Tc-99m-PPi and ungated blood pool projections were acquired over 180 degrees with a rotating gamma camera. Reconstructed sections were color-coded and superimposed for purposes of infarct localization. Areas of increased pyrophosphate uptake within myocardial infarcts were thresholded at 65% of peak activity. The blood pool was thresholded at 50% and subtracted so as to determine an endocardial border for the left ventricle. Using this method, myocardial infarcts weighed 2.5 to 81.2 g. The correlation of infarct mass with prognosis showed that patients without previous AMI and with acute infarcts that weighed more than 40 g had an increased frequency of death and congestive heart failure (p less than 0.001). The correlation of measured infarct mass with peak serum creatine kinase level was significant (r = 0.83, p less than 0.001; y = 0.015x + 13.20). The correlation coefficients for anterior, inferior and nontransmural AMI were not significantly different from those for the entire group. In conclusion, tomographically determined infarct mass data correlate with subsequent clinical prognosis, and Tc-99m-PPi tomography with blood pool overlay is a safe and effective means of sizing infarcts in patients with AMI.

Radionuclide Determination of Myocardial Blood Flow

To assess the effects of verapamil and nifedipine on left ventricular function at rest and during exercise in patients with Prinzmetals variant angina pectoris, 10 patients (6 men and 4 women with a mean age of 52 years) with variant angina were each treated for 2 months periods with placebo, verapamil (400 +/- 80 mg/day, mean +/- standard deviation [SD]) and nifedipine (82 +/- 31 mg/day). During the final week of each 2 month treatment period equilibrium gated blood pool scintigraphy was performed at rest and during exercise. At rest, heart rate during verapamil therapy was lower than during treatment with nifedipine; systolic blood pressure and left ventricular volumes and ejection fraction were similar for the three interventions. The maximal work load achieved was similar during placebo, verapamil and nifedipine therapy. At the maximal work load common to all three exercise studies, heart rate and systolic blood pressure were lower with verapamil than with placebo and nifedipine; ventricular volumes and ejection fraction were similar with the three agents. Thus, in patients with variant angina and a wide range of left ventricular function at rest, neither verapamil nor nifedipine significantly alters left ventricular volumes or ejection fraction at rest or during exercise.

Acute subendocardial myocardial infarction: its detection by Tc-99m stannous pyrophosphate myocardial scintigraphy.

The diffusible-indicator method of determining tissue blood flow was devised by Kety and his associates, 1–3 who observed the washout of an intraarterially injected tracer from the tissue of interest, and found that it was proportional to tissue blood flow. Ketys original tracer was nitrous oxide, but he soon adapted his method to the use of 24 Na. Other investigators developed Ketys method further, substituting 85 Kr, and ultimately, 133 Xe as diffusible indicators. It has been found that if 133 Xe is injected directly into a coronary artery and its washout from myocardium is observed with a scintillation probe over the precordium, the resulting determination, mean myocardial blood flow, is of limited application. Since coronary artery disease is a regional process, the most useful determination is one that yields regional myocardial blood flow. This may be determined by one of the original Kety methods, 3 i.e., observing the washout of tracer injected directly into the myocardium, but since it requires thoracotomy this method is not widely applicable. Several groups have assembled instrument systems based on the use of scintillation camera-computer combinations with which they can enter the image of the passage of a bolus of intracornoary arterially injected tracer, and by means of image data quantification derive regional myocardial blood flow values by Ketys method. The authors have studied more than 130 dogs before and after experimental coronary embolization and have described a complete method of deriving regional myocardial blood flows with an Anger camera-small computer system. Analysis of flow curves thus generated has suggested the existence of more than one compartment within myocardial blood flow. These compartments might be related to primary/collateral flow or to the volume of perfused tissue incorporated in the region of interest. Cannon et al. 25–27 have employed a multicrystal camera of the autofluoroscope type and an IBM 360/91 computer, in which the camera functions as 294 isolated detectors for the purpose of identifying as many regions of myocardial blood flow. Cannon et al. have studied both normal human subjects and patients with radiographically demonstrable coronary artery disease and have found regional flow to be a valid method both for identifying the myocardial flow inhomogeneities expected with coronary artery disease and for evaluating the results of reparative surgery.

Doughnut technetium pyrophosphate myocardial scintigrams. A marker of severe left ventricular dysfunction

Sixty-two patients hospitalized because of prolonged chest pain and initial electrocardiographic (ECG) changes of ST depression and T-wave inversion suggestive of acute subendocardial myocardial infarction were evaluated to determine the ability of Tc-99m-stannous pyrophosphate myocardial scintigraphy to detect the presence or absence of acute subendocardial myocardial necrosis. Three groups of patients were designated. Group A consisted of eight patients (13%) who developed reduction of R-waves of more than 25% or new Q-waves broader than 0.03 seconds; of these patients with acute transmural myocardial infarction, all had well-localized, abnormal scintigrams. Group B consisted of 30 patients with ECG changes and subsequent enzymatic documentation, including elevated serum creatine kinase-B levels as determined by radioimmunoassay, of the presence of acute subendocardial myocardial infarction. Of these, 27 had abnormal scintigrams, including 18 with well-localized patterns and nine with “poorly localized” patterns. Group C consisted of 24 patients (39%) with chest pain, but without enzymatic documentation of the presence of acute myocardial infarction (acute coronary insufficiency). Eight of these had abnormal scintigrams, including one with a well-localized pattern and seven with “poorly localized” patterns. In four of the latter, the scintigrams were “persistently positive” several weeks to months after a previous myocardial infarct. Serial myocardial imaging will be necessary to identify such patients.

Recent advances in nuclear cardiology. 1. "Hot-spot" and "cold-spot" myocardial scintigraphy.

The “doughnut” pattern on Tc-99m pyrophosphate (PPi) myocardial scintigraphy is characterized by a border of tracer uptake surrounding a central zone of relatively decreased activity. This pattern is generally associated with large transmural anterior myocardial infarcts (Ml) caused by occlusion or critical stenosis of the left anterior descending coronary artery. Such infarcts typically involve a significant portion of the anterior wall and are associated with a complicated clinical course and poor prognosis. In order to evaluate the relationship between the presence of the doughnut pattern and left ventricular (LV) function, radionuclide ventriculography was performed within 15 days after infarction in 58 patients with transmural anterior Ml. In patients without previous Ml, 15/38 (39.5%) had doughnut scintigrams. These patients demonstrated significant reductions in LV ejection fraction (EF) (28 ± 10% versus 45 ± 12%, P < 0.001) and normalized LV wall motion scores (29 ± 11% versus 61 ± 10%, P < 0.001) when compared with patients with “nondoughnut” scintigrams. Patients with doughnut scintigrams had a significantly greater incidence of severe septal hypokinesis (P<0.001) and apical dyskinesis (P<0.03). LV end-systolic volumes were also larger in the patients with doughnut scintigrams (73 ± 32 ml versus 40 ± 17 ml/M2, P < 0.005). In contrast, there was no significant difference in LVEF, normalized LV wall motion score, or LV volumes between doughnut and nondoughnut groups in patients with previous Ml.

Nongeometric determination of right ventricular volumes from equilibrium blood pool scans

Nuclear cardiology is a comparatively new field of cardiovascular medicine in which technologic advances have provided relatively noninvasive means of evaluating cardiovascular abnormalities. The purpose of this two-part review is to emphasize some important recent advances and to place in perspective the advantages and disadvantages of those new techniques that are particularly useful clinically.