Kim Fox

Relation between the precordial projection of S-T segment changes after exercise and coronary angiographic findings

The recent introduction of electrocardiographic mapping permits measurement of the precordial area and severity of exercise-induced S-T segment changes. This study was designed to compare this technique with a modified 12 lead electrocardiogram in defining the degree and site of coronary artery disease. One hundred patients, who later had diagnostic coronary arteriography, underwent an exercise test using both 16 point precordial mapping and a modified 12 lead electrocardiogram. The sensitivity of electrocardiographic mapping (96 percent) for the diagnosis of coronary artery disease was significantly greater than that of the modified 12 lead electrocardiogram (80 percent). However, the specificity of the two lead systems was similar. Typical precordial projections of S-T segment change were found when the left main stem or proximal left anterior descending coronary artery were narrowed or when there was isolated disease of the left anterior descending or right coronary artery. Widespread precordial changes were found in patients with three vessel disease. Although there was no significant difference in the sensitivity (66 percent) and specificity (100 percent) of electrocardiographic mapping and of the 12 lead system in identifying three vessel disease, there was a significant difference in sensitivity (electrocardiographic mapping 74 percent, 12 lead system 42 percent) in identifying isolated single vessel disease. In addition, information regarding the presence of left main stem or proximal left anterior descending coronary arterial narrowing was obtained only with electrocardiographic mapping. The superiority of electrocardiographic mapping over the modified 12 lead electrocardiogram has been shown, and clinical application of this technique should be useful in the management of patients presenting with chest pain.

Precordial electrocardiographic mapping after exercise in the diagnosis of coronary artery disease

A technique is described for recording the precordial electrocardiographic body surface map before and after exercise. The technique provides an extra dimension to the conventional exercise electrocardiogram because a measurement can be made of the area and severity of S-T segment changes that are projected onto the front of the chest. Sixteen lead isopotential surface maps were recorded before and after exercise in 109 patients with angina who subsequently underwent coronary arteriography. In addition, exercise electrocardiograms were obtained in 53 of these patients using three orthogonal leads and in all patients using a single chest unipolar chest lead. Precordial surface mapping after exercise was found to have a greater sensitivity (95 percent) than electrocardiography using either the orthogonal leads (68 percent) or a single chest lead (64 percent) (P less than 0.01). The specificity of the three techniques did not differ significantly (P greater than 0.05). The technique of precordial surface mapping after exercise improves the ability to diagnose coronary artery disease and can easily be applied to clinical practice.

Inability of exercise-induced R wave changes to predict coronary artery disease.

To determine the value of exercise-induced R wave changes in diagnosing coronary disease 200 patients undergoing coronary angiography were studied with 16 lead precordial exercise mapping. R wave amplitude was calculated before and immediately after exercise as the sum of R in all 16 leads, the sum of the R waves in the left plus the S waves in the right precordial leads, as well as the sum of the R waves only in those leads that manifested S-T depression. Coronary artery disease was found in 154 patients, S-T depression developed in 122 (sensitivity 79 percent); the sum of R increased or remained unchanged in 61 and decreased in 93 (sensitivity 40 percent). Forty-six patients did not have coronary artery disease; S-T depression developed in 5 (specificity 89 percent); the sum of R increased or was unchanged in 30 and decreased in 16 (specificity 35 percent). Similar results were obtained using the other criteria for calculating R wave amplitude. Exercise-induced S-T depression was identified in 5. 1 +/- 2.6 (mean +/- standard deviation) of the 16 precordial leads and in 2.0 +/- 1. 1 of the chest leads of the standard electrocardiogram (p less than 0.01). Thus, electrocardiographic alterations found in the standard chest leads represent only a small variable proportion of the total projection. When the whole precordial area was analyzed, R wave changes were so unpredictable that they could not be used in the diagnosis of coronary disease.

Myocardial infarction in the dog: Effects of intravenous propranolol

The effects of propranolol on myocardial perfusion and metabolism during acute myocardial infarction were studied in 18 mongrel dogs. A reversible snare was placed on the left anterior descending coronary artery; regional myocardial perfusion was continuously measured using the short-lived isotope krypton-81m, and myocardial metabolism was assessed using the epicardial electrocardiogram and measurement of release of creatine kinase activity from the affected segment of myocardium. Six dogs with no arterial occlusion acted as sham operated dogs; six others in which the snare was occluded acted as a control group and a third group of six were given propranolol, 0.5 mg/kg, 30 minutes after coronary occlusion. All variables were recorded before and for 5 hours after coronary occlusion. Dogs treated with propranolol showed a significant improvement in regional myocardial perfusion to the affected segment, decreased loss of electrically active myocardium at the end of each experiment for any given degree of early S-T segment elevation and a delay in the local release of creatine kinase activity compared with that in the control dogs. These results suggest that propranolol exerts a beneficial effect on the progress of ischemic myocardial damage when given shortly after the onset of infarction.

Krypton-81m in the physiologic assessment of coronary arterial stenosis in man

Fifteen patients with frequent anginal chest pain underwent diagnostic cardiac catheterization. After coronary arteriography a specially designed cardiac catheter was seated in the aortic root, permitting the continuous infusion of krypton-81m into the right and left aortic sinuses. A gamma camera, areas of interest and a visual display unit were used to record images and the regional myocardial equilibrium of activity before, during and after a standarized atrial pacing test. The unique physical properties of krypton-81m allowed the continuous imaging and recording of moment to moment changes in regional myocardial perfusion. This investigation revealed that when the coronary arteriogram was normal or revealed lumonal stenosis of less than 50 percent, regional myocardial perfusion was uniform at rest and during stress. Two patients with a previous history of myocardial infarction had defects of regional perfusion at rest and during stress. Krypton scintigraphy demonstrated reversible regional defects in myocardial perfusion during stress in seven patients with greater than 70 percent stenosis of one or more coronary arteries. Alterations in regional myocardial perfusion occurred within 30 seconds of the start of atrial pacing in all the patients and preceded the onset of electrocardiographic signs of ischemia or chest pain.

Variable susceptibility to dynamic coronary obstruction: An elusive link between coronary atherosclerosis and angina pectoris

Growing evidence suggests that dynamic coronary obstructions play an important but elusive role in the genesis of ischemic events. Dynamic coronary obstructions can develop during certain phases of coronary disease as a result of a variable combination of vasoconstriction, arterial wall lesions, and increased thrombotic tendency. In a certain phase of their disease some patients develop dynamic coronary obstruction, while others with a similar degree of fixed atherosclerotic obstruction do not.

Interaction between cigarettes and propranolol in treatment of angina pectoris.

To determine whether cigarette smoking interferes with the medical management of angina pectoris, 10 patients with angina pectoris who smoked at least 10 cigarettes a day were studied before, during, and after a standardised maximal exercise test. This was done at the end of four randomly allocated one-week treatment periods during which the patients took glyceryl trinitrate while not smoking, took glyceryl trinitrate while smoking, took glycerly trinitrate and propranolol (380 mg/day) while not smoking, and took glyceryl trinitrate and propranolol while smoking. Carboxyhaemoglobin was measured to ensure compliance. Smoking was associated with a significantly higher heart rate, blood pressure, number of positions with ST-segment depression, and total ST-segment depression after exercise than non-smoking (p < 0.01) whether or not the patients were taking propranolol. These results suggest that smoking aggravates the simple haemodynamic variables used to assess myocardial oxygen requirements and the exercise-induced precordial electrocardiographic signs of myocardial ischaemia. These effects were still evident after treatment with propranolol and represent a hindrance to the effective medical treatment of angina pectoris.

Electrocardiographic mapping after exercise for evaluation of coronary bypass graft surgery

Abstract Electrocardiographic mapping after exercise adds an extra dimension to the routine exercise test because a measure can be made of the area and severity of electrocardiographic changes that occur after exercise. The value of this technique in assessing coronary bypass graft surgery was investigated in 50 patients who had postoperative coronary angiography after undergoing such surgery. The patients were classified into three groups: The 35 patients in Group 1 were free of pain at follow-up and had no new precordial Q waves. Among these, 24 patients had patent grafts and no precordial area of S-T segment change after exercise. The remaining 11 patients had areas of exercise-induced S-T segment change postoperatively; 10 of the 11 had at least one blocked graft and 1 had a patent although poorly functioning graft. The 10 patients in Group 2 continued to have chest pain after operation. Eight of the 10 had an area of S-T segment change that persisted after exercise and at least one blocked graft; the 2 patients without precordial S-T segment changes after exercise had patent grafts. The five patients in Group 3 were in poorer condition after operation; three had greater areas of S-T segment change after exercise, and the remaining two had new areas of Q waves. All patients had at least one occluded graft. In 8 (16 percent) of the 50 patients studied before operation precordial areas of S-T segment change after exercise that were identified with electrocardiographic mapping were not identified using a modified 12 lead system. After operation, mapping revealed precordial areas of ischemia in 24 patients; In 4 (17 percent). These areas were not detected with the modified 12 lead electrocardiogram. Electrocardiographic mapping after exercise is a simple noninvasive test that objectively describes the effects of coronary bypass surgery on myocardial ischemia and aids in interpretation of a patients report of a change in the frequency of angina. Because it provides more information than a modified 12 lead system it may reduce the need for postoperative angiocardiography.

Precordial electrocardiographic mapping in the identification of patients with left main stem narrowing

This study was designed to determine if exercise testing using 16-lead precordial mapping can be used to identify patients with left main stem narrowing. In a group of 235 consecutive patients undergoing coronary angiography there were 35 patients with left main stem narrowing. The patients with left main stem disease differed from the others in that not only did they develop extensive S-T segment depression, but more specifically these changes occupied a characteristic position high on the precordium above the usual site of the precordial leads of the 12-lead electrocardiogram. This finding was then tested prospectively in a second group of 100 patients. Fourteen of the 100 patients had left main stem narrowing; the sensitivity and specificity of S- T segment changes high on the precordium in identifying patients with left main stem disease were 82 and 84% respectively. Thus precordial mapping and exercise testing is valuable in the diagnosis of patients with left main stem narrowing. The technique is simple and inexpensive and provides data not available using the conventional precordial leads of the 12-lead electrocardiogram.

Assessment of coronary venous bypass graft function using krypton-81m.

Fifteen patients with intractable angina pectoris underwent coronary angiography and coronary arterial bypass graft surgery. After the operation, a continuous infusion of krypton-81m was delivered into each graft. A gamma camera and multichannel analyzer were used to record the regional myocardial distribution of perfusion provided by each graft. The disappearance of myocardial activity at the end of each infusion was used to calculate the flow per unit volume in the myocardial distribution provided by each vessel. Myocardial perfusion provided by the grafts to all the major coronary arteries were recorded individually as high spatial resolution images. Myocardial flow rates in the distribution of each graft were measured using the washout of krypton-81m. The rates were 0.5 to 2.0 ml/g per min in the 13 patients with no evidence of previous myocardial infarction. Krypton-81m was infused into grafts to the left anterior descending coronary artery in two patients with a history and electrocardiographic evidence of previous anterior myocardial infarction. The grafts provided poor perfusion to the anterior and apical portions of the ventricles. An experimental model of myocardial perfusion was used to demonstrate that the washout of krypton-81m can be used to measure flow per unit volume within or above the physiologic range.