Biomedical subjects

S B Knoebel

Publications and source records attributed to S B Knoebel.

At least 55 records · Page 3Linked to original sources

PubMed1976

Computer detection of premature ventricular complexes: a modified approach.

The accuracy of a data reduction system for arrhythmia detection in identifying premature ventricular complexes was evaluated in continuous tape records of 30 patients in a coronary care unit. Computer analysis was performed with a Honeywell 316 digital computer. Threshold values for dominant complexes were automatically determined and recognition of premature ventricular complexes was based on differences in QRS configuration, timing and T wave configuration from the dominant complexes. Verification of the computer accuracy in detecting premature ventricular complexes was made with visual beat by beat inspection using a two channel strip chart recorder with simultaneous recording of the electrocardiogram and computer signal. This procedure allowed for exact beat to beat correlation and, thus, absolute determination of false positive and false negative identification. From 0.5 to 6 continuous hours of monitoring per patient (average 3.5 hours) were analyzed for a total of 105 monitoring hours. The basic cardiac rhythms noted were normal sinus rhythm, sinue arrhythmia, sinus tachycardia, demand pacemaker rhythm, atrial fibrillation and atrioventricular (A-V) dissociation with junctional rhythm. Premature ventricular complexes were evident in 28 tapes (93 percent) including 12 (43% with multifocal premature ventricular complexes and 3 (11 percent) with ventricular tachycardia. The visual count of premature ventricular complexes totaled 7,921. Of these, 7,542 (95 percent) were properly classified by the computer. The total computer count was 8.717, representing a 13 percent false positive and 5 percent false negative identification rate. The false positive identifications of premature ventricular complexes occurred during periods of 10 seconds or more of continuous noise artifact and in the presence of atrial premature complexes conducted aberrantly. When these sections of tape were excluded, the computer had a less than 2 percent false negative and 3 percent false positive rate of identification of premature ventricular complexes.

Arrhythmias, Cardiac↗

PubMed1976

Normalization of abnormal T waves in ischemia.

Inverted T waves due to coronary artery disease and previous myocardial infarction were observed to revert ot normal, upright position during ischemia in 38 patients. The normalization of inverted T waves was seen on the electroencephalograms of 19 patients during spontaneously occurring angina pectoris and of 11 patients when ischemia was provoked by treadmill exercise; for 8 patients, normalization occurred during the administration of isoproterenol hydrochloride and during the consequent episode of angina pectoris. The mechanism for normalization may be the algebraic sum of the extent of ST segment elevation and the amplitude of the T waves of acute ischemia plus the extent of preexisting ST segment depression and the degree of T wave inversion, to result in isoelectric ST segment and upright T wave. As with myocardial infarction, reciprocal changes may also be recorded. However, the reciprocal nature may be masked since either acute ST segment elevation of T wave inversion, or both, may not be recorded in the leads reflecting the ischemic area because of normalization.

Acute Disease↗

PubMed1975

Nonparoxysmal junctional tachycardia in acute myocardial infarction: computer-assisted detection.

Thirty consecutive patients with acture myocardial infarction had continuous magnetic tape recording of their stay in the coronary care unit. Analysis of the 24 hour tape recordings was implemented on a Honeywell model 316 digital computer. In the first 24 hours after admission to the coronary care unit, 12 of the 30 patients (40 percent) exhibited nonparoxysmal junctional tachycardia; in 5 the arrhythmia was not recognized by conventional monitoring techniques. For the subsequent 3 days, the incidence rate of the arrhythmia was 13 percent for the first 48 hours and 3 percent for 72 hours. Although the mortality rate in patients with nonparoxysmal junctional tachycardia was greater than in patients not demonstrating the arrhythmia (33 versus 6 percent), there was a greater percentage of patients with anterior infarction in the former group; therefore, mortality may have been related to site of infarction rather than being reflective of the arrhythmia or its associated pathophysiologic state. Of possible significance is the association of a greater degree of sinus arrhythmia with nonparoxysmal junctional tachycardia. The incidence of nonparoxysmal junctional tachycardia in this group of patients was greater than previously reported. It is possible that computer tape analysis may have provided more accurate recognition of the arrhythmia and, thus, more realistic incidence data. The association of nonparoxysmal junctional tachycardia with sinus arrhythmia could only have been recognized by computer technique. The computer system is not a diagnostic system but rather a tape review method.

Analog-Digital Conversion↗

PubMed1975

Echocardiography in acute myocardial infarction.

Sixty-four patient with acute transmural myocardial infarction had daily echocardiograms while in the coronary care unit. Patients with previous infarction were excluded. The electrocardiographic site of infarction was anterior wall in 28, inferior wall in 33 and both anterior and inferior wall in 3 patients. Echocardiograms satisfactory for interpretation were obtained in 92 percent of cases. Abnormal left ventricular wall motion corresponding to the electrocardiographic site of infarction was seen in the echocardiogram in 84 percent of cases. Exaggerated normal motion in noninfarcted areas was seen in 30 percent. The left ventricular internal dimension correlated with clinical heart failure (P less than 0.005) and was increased in 50 percent. Abnormal mitral valve closure, which reflects increased left ventricular end-diastolic pressure, was present in 33 percent. This finding did not correlate significantly with clinical heart failure. By combining the measurements of left ventricular internal dimension and mitral valve closure, it was possible to predict hospital mortality from the echocardiograms. The results indicate that echocardiography is a useful technique in the study and management of patients with acute myocardial infarction.

Acute Disease↗

PubMed1975

Nitroglycerin and premature ventricular complexes in myocardial infarction.

Because of clinical observations suggesting that nitroglycerin may suppress premature ventricular complexes during acute ischaemia, a study was undertaken to assess the effect of nitroglycerin on the incidence of premature ventricular complexes in patients with acute myocardial infarction. Forty patients with acute myocardial infarction were studied. Twenty-six patients received 0.4 mg nitroglycerin sublingually every 4 hours for the first 24 hours after admission to the coronary care unit. The total premature ventricular complex count for the 26 patients for 15 minutes before nitroglycerin was 592, and 276 for the 15 minutes after the drug (P less than 0.005). In the remaining 14 patients on the same nitroglycerin schedule, a single electrocardiographic lead was continuously recorded on tape. During the first hour after nitroglycerin, the premature ventricular complex count decreased by 58 per cent, and the second and third hours showed a decrease from control count of 71 and 65 per cent respectively. By the end of 4 hours the ectopic count was back to control level. The data indicate that nitroglycerin may decrease the number of premature ventricular complexes for up to 3 hours in patients with acute myocardial infarction. The mechanism of action of nitroglycerin is not elucidated by this study, but the observation may be of value in further studies of specific antiarrhythmic therapy and prevention of arrhythmias in patients with coronary artery disease.

Administration, Oral↗

PubMed1975

Myocardial blood flow response to isometric (handgrip) and treadmill exercise in coronary artery disease.

Thirty patients undergoing coronary cineangiography for diagnosis or evaluation of coronary artery disease had myocardial blood flow studies pre and post handgrip (isometric) exercise just prior to cineangiography. The handgrip was maintained at one-third maximum effort for three minutes. The patients also had treadmill exercise testing a day or two prior to the study. Treadmill testing was carried out until angina or positive ST-segment changes occurred or the patient attained 90% of predicted maximal heart rate. Of the 30 patients, seven had no coronary artery disease and 23 had significant disease, i.e., greater than 75% occlusion of at least one major coronary artery. Six of the 23 patients (26%) with disease had angina with handgrip and demonstrated a decreased myocardial blood flow, a significantly different response from the patients without agina (P less than 0.001). For the group without angina, the blood flow response was not significantly different from the normal group. Treadmill tests were positive in 19 of the 23 patients with coronary disease (83%). The arterial systolic and diastolic pressure rise was almost identical with the two stresses. The heart rate response, however, was significantly different (P less than 0.001), the rate increase being greater with treadmill exercise. The myocardial blood flow data demonstrate the relative insensitivity of handgrip exercise for the diagnosis of coronary artery disease. In terms of the supply demand ratio (diastolic pressure time/systolic pressure time) concept for subendocardial perfusion, it is possible that the difference between handgrip and treadmill stress may be due to the different heart rate response, more rapid heart rates having a relatively greater effect on diastolic than on systolic time indices, all other factors being equal.

Angina Pectoris↗

PubMed1974