Kenneth E. Walter

Catecholamine Release After Spinal Cord Section

Summary Cervical spinal cord section causes an immediate rise in CF, MABP, and HR. The increase in these cardiovascular parameters is due to stimulation of the sympathetic nervous system, as indicated by the diminished response after treatment with sympatholytic agents, Hexameton and Guanethidine, and by the rise in blood catecholamines.

Preoperative evaulation of cardiac risk by means of atrial pacing and thallium 201 scintigraphy

Atrial pacing and thallium 201 scintigraphy were done in 61 patients with known or suspected coronary artery disease referred for evaluation of cardiac risk before elective vascular surgery. All patients had noncardiac limitations precluding performance of an adequate exercise stress test. Before atrial pacing all were considered to be at low risk of a postoperative cardiac event based on assessment of clinical parameters. Vascular surgery was subsequently performed in 47 patients. In these patients, pacing-induced ST segment depression greater than or equal to 1 mm occurred in 18, a fixed perfusion defect occurred in 11, and a reversible defect occurred in six. Two of the six patients with reversible perfusion defects had preoperative coronary angiography; both had significant coronary artery disease (one or more lesions greater than or equal to 50%). Two patients (one of whom had a reversible perfusion defect) underwent preoperative coronary revascularization and tolerated subsequent vascular surgery well. All other patients received only medical therapy. None of the 47 patients undergoing vascular surgery had a postoperative cardiac event (unstable angina, congestive heart failure, myocardial infarction, or cardiac death). Of the 14 patients in whom vascular surgery was deferred or canceled, surgery was canceled for noncardiac reasons in seven. Six of these seven patients had a normal perfusion scan; none had a reversible perfusion defect or marked (greater than or equal to 2 mm) ST segment depression. No cardiac event occurred during a 3-month period after atrial pacing in any of these patients. Six of the remaining seven patients had reversible perfusion defects.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial Pacing and Thallium 201 Scintigraphy: Combined Use for Diagnosis of Coronary Artery Disease

To evaluate the presence of coronary artery disease (CAD), atrial pacing and thallium 201 scintigraphy were performed in 36 patients with stable angina pectoris who were unable to perform an adequate exercise stress test. All patients underwent cardiac catheterization. Nine patients had previously undergone coronary artery bypass surgery. Significant CAD (one or more lesions ≥ 50%) was present in 33 patients. Atrial pacing produced ischemic ST segment depression (≥1 mm) in 18 (55%) patients with CAD, and angina in 20 patients (61%). As the number of vessels with CAD increased, there was no significant change in the sensitivities of pacing-induced angina or ST segment depression for detecting CAD. In the 3 patients without CAD, ST segment depression occurred in 1 patient and angina in none. Thallium 201 scintigraphy demonstrated perfusion defects in 27 (82%) patients with CAD, with fixed defects seen in 13 studies (39%) and reversible defects in 15 (45%). In the 3 patients without CAD, no perfusion defects were seen. The thallium 201 scan successfully predicted the presence of CAD in patients with single-vessel disease but usually underestimated the number of vessels involved in patients with multivessel disease. Combined sensitivity of pacing-induced ST segment depression and an abnormal thallium 201 scan finding for detecting CAD was 91%. The authors conclude that combined atrial pacing and thallium 201 scintigraphy is a useful test for detecting CAD in patients unable to perform an adequate exercise stress test.

Diagnosis of coronary artery disease with 201Tl. Computer analysis of myocardial perfusion images.

The diagnostic sensitivity of visually interpreted and computer-analyzed 201Tl myocardial perfusion images was compared to that of exercise electrocardiograms in 8 angiographically normal subjects and 24 patients with significant coronary artery disease. Visual interpretation was not significantly better than exercise ECGs. An index of perfusion homogeneity, derived from computer analysis of the 201Tl images, was more sensitive than visual interpretation (79% vs. 58%) and much more sensitive (p less than 0.05) than the exercise ECG (79% VS. 46%). The best overall sensitivity (88%) and specificity (75%) were achieved by combining computer analysis with exercise electrocardiography. The computer also permits enhanced detection of subtle perfusion changes which may not seem significant to the eye.

Assessment of percutaneous transluminal coronary angioplasty by atrial pacing and thallium-201 myocardial imaging: a case report

Combined atrial pacing and thallium-201 scintigraphy were performed in a man with multiple coronary artery lesions unable to perform exercise stress testing. Severe angina and ischemic ST depression in the inferior and anterior ECG leads occurred at a peak double product of 22,400 beats-mm Hg/min; thallium-201 scintigraphy showed reversible perfusion defects of the inferior, posterior, and septal segments. After angiographically successful angioplasty of a 95% right coronary artery lesion, repeat atrial pacing/thallium-201 scintig raphy (peak double product 27,750 beats-mm Hg/min) produced mild angina no ST depression in the inferior leads, and a normal thallium-201 scan. This case illustrates the value of the atrial pacing/thallium-201 stress test for evaluat ing the need for, and results of, coronary angioplasty in patients unable to per form exercise stress testing.

Torsades de Pointes: A Rare Complication of Temporary Pacing for Permanent Ventricular Pacemaker Failure

Torsades de pointes, a dislinctive type of polymorphous ventricular lachycardia, may be induced by critically timed ventricular stimulation during electrophysiologic studies or, rarely, in patients with temporary or permanent ventricular pacemakers. The following case illustrates how, when temporary ventricular pacing is instituted to maintain heart rate in a patient with a defective permanent ventricular pacemaker, this potentially fatal arrhythmia may occur as a complication of interaction between the two pacemakers.

Norepinephrine Content of Thoracic Duct Lymph During Tachycardia

Summary An increase in the NE content of TDL has been demonstrated during ventricular tachycardia in this canine preparation. This increase, under normal circumstances, may play a minor role in the venous washout phase. It is suggested that this lymphatic transport of biological active substances may play a more important role under various pathological states where pressure and/or flow of lymph are markedly altered.

EFFECT OF BILATERAL ADRENALECTOMY ON THE CARDIOVASCULAR RESPONSE TO INDUCED TACHYCARDIA.

Summary Relatively short bouts of electrically induced ventricular tachycardia of sufficiently high rate to result at least initially in a marked decrease in cardiac output and mean arterial blood pressure were induced in anesthetized dogs before and immediately after bilateral adrenalectomy. This study reveals that, although adrenalectomy affects the circulation under the experimental circumstances described, the degree of cardiovascular compensation in response to such bouts of tachycardia can remain relatively unaffected by bilateral adrenalectomy. Whether this remains true with bouts of higher rate tachycardia remains to be determined.

Modification of Norepinephrine Tachyphylaxis by Guanethidine.

Summary Pressor responses to repeated injections of norepinephrine were recorded in a control group of dogs and in dogs pre-treated with guanethidine. The results indicate that guanethidine maintains the pressor response of norepinephrine, i.e., delays tachyphylaxis to norepinephrine.