Robert W. Burt

Regional sympathetic denervation after myocardial infarction in humans detected noninvasively using I-123-metaiodobenzylguanidine.

Transmural myocardial infarction in dogs produces denervation of sympathetic nerves in viable myocardium apical to the infarct that may be arrhythmogenic. It is unknown whether sympathetic denervation occurs in humans. The purpose of this study was to use iodine-123-metaiodobenzylguanidine (MIBG), a radiolabeled guanethidine analog that is actively taken up by sympathetic nerve terminals, to image noninvasively the cardiac sympathetic nerves in patients with and without ventricular arrhythmias after myocardial infarction. Results showed that 10 of 12 patients with spontaneous ventricular tachyarrhythmias after myocardial infarction exhibited regions of thallium-201 uptake indicating viable perfused myocardium, with no MIBG uptake. Such a finding is consistent with sympathetic denervation. One patient had frequent episodes of nonsustained ventricular tachycardia induced at exercise testing that was eliminated by beta-adrenoceptor blockade. Eleven of the 12 patients had ventricular tachycardia induced at electrophysiologic study and metoprolol never prevented induction. Sympathetic denervation was also detected in two of seven postinfarction patients without ventricular arrhythmias. Normal control subjects had no regions lacking MIBG uptake. This study provides evidence that regional sympathetic denervation occurs in humans after myocardial infarction and can be detected noninvasively by comparing MIBG and thallium-201 images. Although the presence of sympathetic denervation may be related to the onset of spontaneous ventricular tachyarrhythmias in some patients, it does not appear to be related to sustained ventricular tachycardia induced at electrophysiologic study.

Acetazolamide enhanced single photon emission computed tomography (SPECT) evaluation of cerebral perfusion before and after carotid endarterectomy

Twenty-five patients were tested before and after carotid endarterectomy with resting and acetazolamide enhanced single photon emission computed tomography (SPECT) scans with hexamethyl propyleneamine oxine (HMPAO) or iofetamine hydrochloride I123 (123I labeled IMP), both widely available radiopharmaceuticals. Twenty preoperative SPECT studies were asymmetric, revealing focal or diffuse decreased perfusion reserve, and 13 also demonstrated infarcts. Five patients had symmetric (normal) studies. After carotid endarterectomy, 22 cases had changed flow distribution patterns. Usually improvement of reactivity ipsilateral occurred to the area operated on. In four, contralateral improvement was also found. Three of the patients who had preoperative symmetrical scans had increased ipsilateral reactivity after surgery indicating previous global loss of reactivity. Acetazolamide SPECT scans demonstrate a decreased perfusion reserve in 20 patients with carotid artery stenosis, indicating reduced perfusion and poor collateral circulation. Postoperative studies confirm improvement by demonstrating recovery of vascular reactivity in 84% of the patients. Acetazolamide enhanced SPECT scans may be helpful in providing objective evidence for selection of patients for carotid endarterectomy, especially in those who have an 80% carotid artery stenosis, but are asymptomatic.

Cerebral vascular reactivity assessed with acetazolamide single photon emission computer tomography scans before and after carotid endarterectomy

BACKGROUND AND METHODS In 64 patients, cerebral perfusion and vascular reactivity were assessed before and after carotid endarterectomy (CEA) using acetazolamide (ACZ)-enhanced single photon emission computer tomography (SPECT). Twenty-five patients were asymptomatic, whereas the remainder were symptomatic. Sixty-one patients had a > or = 70% ipsilateral internal carotid artery stenosis. RESULTS Fifty SPECT scans revealed decreased vascular reactivity. Twenty-three showed infarcts. Fourteen patients had normal studies. Twenty of the SPECT scans of asymptomatic patients demonstrated poor vascular reactivity. After CEA, 39 patients had improved ipsilateral vasoreactivity. In 12 patients, contralateral improvement was also found. CONCLUSION ACZ-enhanced SPECT scans, by assessing cerebral perfusion and vascular reactivity, may help to identify patients at risk of stroke should perfusion further diminish. Postoperative studies confirm improvement in vascular reactivity. ACZ-enhanced SPECT scans may provide objective evidence for the selection of patients with a high-grade asymptomatic carotid stenosis for CEA.

Effect of hypoxemia on sodium and water excretion in chronic obstructive lung disease

To determine the role of hypoxemia in the pathogenesis of impaired sodium and water excretion in advanced chronic obstructive lung disease, 11 clinically stable, hypercapneic patients requiring long-term supplemental oxygen were studied. The renal, hormonal, and cardiovascular responses to sodium and water loading were determined during five-and-a-half-hour studies on a control day (arterial oxygen tension = 80 +/- 6 mm Hg) and on an experimental day under hypoxic conditions (arterial oxygen tension = 39 +/- 2 mm Hg). Hypoxemia produced a significant decrease in urinary sodium excretion but did not affect urinary water excretion. Hypoxemia also resulted in concomitant declines in mean blood pressure, glomerular filtration rate, and filtered sodium load. Renal plasma flow and filtration fraction were unchanged whereas cardiac index rose. On the control day, plasma renin activity and norepinephrine levels were elevated whereas aldosterone and arginine vasopressin levels were normal; none of these four hormones was affected by hypoxemia. Renal tubular function did not appear to be altered by hypoxemia as there was no significant change in fractional reabsorption of sodium. The concurrent decreases in glomerular filtration rate, filtered sodium load, and mean blood pressure at constant renal plasma flow suggest that the reduction in urinary sodium excretion was due to an effect of hypoxemia on glomerular function, possibly related to impaired renovascular autoregulation.

Symptom-limited arm exercise increases detection of ischemia during dipyridamole tomographic thallium stress testing in patients with coronary artery disease.

Exercise combined with dipyridamole during thallium stress testing in patients with coronary artery disease (CAD) increases the frequency of angina and ischemic ST changes in the electrocardiogram. Evidence for an increase in thallium abnormalities has been inconclusive. We prospectively examined 54 consecutive patients who underwent coronary angiography and tomographic thallium with dipyridamole (0.57 mg/kg) alone and combined with symptom-limited dynamic arm exercise. Most patients presented with a history of chest pain and 49 had angiographic evidence of significant coronary stenosis (50% diameter narrowing). Thallium abnormalities were scored blindly by consensus. The number of abnormal segments (total and ischemic) and indexes of left ventricular dysfunction, such as increased lung uptake or ischemic dilation, were compared in the 49 patients with CAD. During arm exercise more patients had evidence of ischemia (39 vs 30; p < 0.001), and the number of ischemic segments increased significantly from 1.3 +/- 1.5 to 2.5 +/- 2.2 (p < 0.001). There was also a significant increase in the indexes of left ventricular dysfunction, ischemic dilation (10 vs 4 patients; p < 0.03) and increased lung uptake (16 vs 5 patients; p < 0.001). Patients who exercised had increased thallium evidence of extent and severity of ischemia and more frequent indexes of left ventricular dysfunction. Thus, symptom-limited arm exercise improves detection of extent and severity of ischemia in patients with CAD undergoing dipyridamole thallium stress testing.

The value of acetazolamide single photon emission computed tomography scans in the preoperative evaluation of asymptomatic critical carotid stenosis

PURPOSE Acetazolamide (ACZ)-enhanced single photon emission computed tomography (SPECT) scans can assess both cerebral perfusion and vascular reactivity. Patients with asymptomatic critical carotid artery stenosis were evaluated for cerebral vascular reactivity to determine the effect of extracranial occlusive disease and the effect of carotid endarterectomy (CEA) on intracerebral reactivity. METHODS In 44 patients with asymptomatic critical carotid artery stenosis, cerebral perfusion and vascular reactivity were assessed before CEA with resting and ACZ-enhanced SPECT scans. All patients had a 70% or greater ipsilateral internal carotid artery stenosis. Preoperative ACZ-enhanced SPECT scans were obtained, usually 5 days before CEA. Postoperative ACZ-enhanced SPECT scans were obtained in 30 patients. RESULTS Preoperative SPECT scans were asymmetric, revealing focal (n = 19) or global (n = 15) decreased reactivity in 34 patients (77%). Ten patients had symmetric or normal reactivity. After CEA, 23 patients demonstrated an improvement in reactivity ipsilateral to the side of surgery. The remaining seven patients failed to improve after surgery. CONCLUSION Although all patients had a high-grade internal carotid stenosis, nearly a quarter of the patients had excellent intracerebral collateral flow. Only 71% of patients demonstrated improved intracerebral vasoreactivity after CEA. The lack of improvement in the other patients may have resulted from intracerebral pathology or lack of improvement in the extracranial carotid hemodynamics.

Acetazolamide SPECT Scans in the Evaluation of Symptomatic and Asymptomatic Patients with Carotid Occlusive Disease

Acetazolamide (ACZ)-enhanced Single Photon Emission Computer Tomography (SPECT) scans can assess both cerebral perfusion and vascular reactivity. Patients with poor reactivity lack perfusion reserve, and are at risk for stroke should perfusion diminish further. This study compared the preoperative ACZ-enhanced SPECT scans of 60 symptomatic to 40 asymptomatic patients with internal carotid artery stenosis (ICAS) in an effort to better define the cause of their symptoms and effects of carotid endarterectomy (CEA) on cerebral perfusion and reactivity in these two groups of patients. Symptomatic patients had at least a 60% (x=84%) ICAS. Asymptomatic patients had at least an 80% (x=90%) ICAS. Preoperative ACZ SPECT scans were obtained usually one week before CEA. All patients underwent CEA. Postoperative ACZ SPECT scans were obtained in 78 of the patients, usually at the first postoperative (-30 days) visit. PRE-OP SPECT SCAN PRE-OP SPECT SCAN Ipsilateral Perfusion Ipsilateral Reactivity Ipsilateral Reactivity n decreased nl decreased nl n improved Symptomatic 60 30(50%) 30(50%) 51(85%) 9(15%) 50 40(91%) Asymptomatic 40 29(72.5%) 11(27.5%) 31(77.5%) 9(22.5%) 28 19(73%) Total 100 59 41 82 18 78 59 *These percentages are based on a denominator of 44 symptomtic and 26 asymptomatic patients. These are the patients who had decreased preoperative reactivity and underwent a postoperative ACZ scan. Asymptomatic patients demonstrated poorer perfusion than symptomatic patients, which tends to support the premise that most strokes and carotid symptoms are secondary to emboli rather than hypoperfusion. Interestingly, cerebral reactivity was poor in both symptomatic and asymptomatic patients before CEA, suggesting inadequate collaterals and dependency on the ipsilateral carotid. Carotid endarterectomy improved vasoreactivity in 84% of the patients. ACZ SPECT scans provided evidence of the return of cerebral perfusion and reactivity following endarterectomy.

Application of SPECT scanning with I-123 HIPDM to forensic medicine.

The use of I-123 HIPDM, a cerebral perfusion agent, in the demonstration of an intracranial bullet track is described. Visualization of the bullet track was dependent on the use of single photon emission CT.

In-111 granulocyte response to intervening surgery. Evidence of sustained in vivo viability

A patient with chronic osteomyelitis had surgery performed between the early and delayed images of an ln-111 granulocyte scan. The early images showed no uptake, while the delayed images demonstrated marked soft tissue uptake, which was felt to be secondary to the inflammation of the intervening surgery. It was concluded that granulocytes, when labeled with ln-111, remain viable and can respond to inflammation that occurs after their injection.

Comparison of CVA imaging with 99mTc phosphates, 99mTc pertechnetate, and computed tomography.

SummaryA retrospective study was made of 111 patients who underwent computed tomography (CT) and nuclear brain scans, with both pertechnetate and phosphate bone agents (PHOS), within 7 days of each other. Specifically, 78 patients who had a recent cerebral vascular accident (CVA) were compared. There were no significant sensitivity differences between the methods. While these studies appear complementary, the most important criterion is the time after onset when the studies were performed. The axiom “if the intensity of the phosphate scan exceeds that of the pertechnetate, the lesion must be a CVA” is true, only if the study is performed within 4 weeks of onset. The most economical method for optimum detection of CVA, with avoidance of frequent errors, is an early CT followed by a PHOS brain scan about 14 days after ictus in those that have an initial negative CT.