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Biomedical subjects

G J Anderson

Publications and source records attributed to G J Anderson.

At least 127 records · Page 7Linked to original sources
PubMed1980

Differences in automaticity between Purkinje strands from right and left dog ventricle.

Previous in situ studies have implicated differences in the pacemaker rates between the left and right ventricular conduction system. Our studies were conducted to characterize automaticity in peripheral right and left canine Purkinje fibers in vitro. Standard microelectrode techniques were utilized. In paired right (RPF) and left (LPF) canine Purkinje fibers, control intrinsic rate (IR) was found to be higher in LPF (24.8 +/- 1.7 beats/min) than in RPF (11.5 +/- 1.5 beats/min, P less than 0.01). Following overdrive stimulation at various cycle lengths, LPF consistently showed earlier escape beats. In low K0+ (1.35 mM), IR increased comparably in both RPF and LPF. However, high K0+ (5.4 mM) resulted in a greater reducton of the IR in RPF (-78%) than in LPF (-58%). After epinephrine (10(-6) M) the IR of LPF > RPF although the chronotropic response was more pronounced in RPF. Adrenergic stimulation preceded by beta-adrenergic blockade did not produce significant differences in the intrinsic rate between RPF and LPF. These findings indicate that automaticity in right and left Purkinje strands is functionally dissimilar.

Action Potentials↗
PubMed1979

Electrophysiological effects of disopyramide phosphate during experimental myocardial ischemia.

In order to correlate the antiarrhythmic and electrophysiological effects of disopyramide phosphate during acute myocardial ischemia, we performed experiments in 17 mongrel dogs. Refractory periods obtained by the extrastimulus method and conduction times recorded from local electrograms were determined in potentially ischemic and nonischemic areas prior to, after left anterior descending coronary occlusion, and following intravenous administration of disopyramide phosphate 3 mg./Kg. Control refractory periods were similar in both nonischemic and ischemic areas. Following coronary ligation, a disparity of refractoriness of 28 msec. was induced between these two areas. After disopyramide administration, this disparity was reduced from 28 msec. to 5 msec. (p less than 0.001) after 5 to 15 minutes, and to 15 msec. (p less than 0.01) after 15 to 30 minutes. Coronary ligation prolonged conduction times by 8 msec. (p less than 0.005) in ischemic areas and disopyramide further prolonged conduction in these areas by an additional 9 msec. (p less than 0.001). A minimal and transient prolongation of conduction was present in nonischemic areas. We conclude that the differential effects exerted by disopyramide phosphate in ischemic areas may explain its suppressant action of arrhythmias of ventricular origin.

Animals↗
PubMed1979

The significance of exercise-induced Q waves.

The significance of transient exercise-induced Q waves present during treadmill testing was prospectively evaluated and correlated with the findings at cardiac catheterization. Exercise-induced Q waves were present in 14 of 560 patients (2.5 per cent) undergoing treadmill exercise testing. Thirteen patients had Q waves in leads V1 through V3 and one patient had Q waves in leads II, III and aVF. Ten patients underwent cardiac catheterization; six did not have coronary artery disease as determined by angiography. Two patients had a documented anterior myocardial infarction and did not undergo cardiac catheterization. Exercise myocardial perfusion imaging was performed in 10 patients. Six patients without coronary artery disease had no evidence of exercise perfusion defects. In the four patients with coronary artery disease, three patients had an abnormal resting perfusion study without change with exercise and one patient had a new exercise myocardial perfusion defect. We conclude that exercise-induced transient Q waves are not diagnostic of underlying coronary disease. In patients without coronary artery disease the mechanism of exercise-induced Q waves is as yet unclear. In patients with coronary artery disease, the mechanism may also be undefined or secondary to myocardial ischemia.

Adult↗
PubMed1978

The significance of hypotension developing during treadmill exercise testing.

The significance of hypotension developing during treadmill exercise testing was evaluated and correlated with the findings at cardiac catheterization in two groups of patients. Twenty-five patients (Group I) had a fall in systolic pressure during exercise and were compared to 50 consecutive unselected patients (Group II) with a normal blood pressure response. Clinical characteristics were similar in both groups. Females comprised 48 per cent of the patients in Group I and only 30 per cent in Group II. The incidence of significant coronary artery disease was not different when the two groups were compared as a whole, 56 per cent in Group I and 36 per cent in Group II (P = NS). When males and females were considered separately, it was noted that the incidence of coronary artery disease was higher in hypotensive males (77 per cent) when compared to control males (40 per cent) (p less than 0.01). Females in both groups had a lower but comparable incidence of coronary artery disease (25 per cent and 27 per cent, respectively). Resting hemodynamics and angiographic characteristics, such as contraction abnormalities, and the number and distribution of diseased coronary vessels, were similar in both groups of patients. These findings suggest that hypotension in females does not necessarily connote coronary artery disease. Males with hypotension have a higher incidence of coronary artery disease, but the extent and distribution of their disease is no different from that of patients with a normal blood pressure response to exercise.

Adult↗
PubMed1978

Detection of critical coronary lesions with treadmill exercise testing: fact or fiction?

This study was designed to determine whether treadmill exercise testing could identify patients with critical coronary lesions. Critical lesions were defined as obstruction of the left main coronary artery or concomitant narrowing of the left anterior descending and circumflex coronary arteries proximal to any major branches. The time of onset and degree of S-T segment depression were evaluated in 25 patients with critical lesions and in 50 patients with other types of lesions. S-T segment depression of 2 mm or more was present in 82 percent of patients with left main coronary disease and in 71 percent of patients with left main coronary equivalent lesions (both P less than 0.02 when compared with 36 percent of patients with other lesions). However, half of the 37 patients with this degree of S-T segment depression had noncritical lesions. Ischemic changes appearing in the first 3 minutes of exercise were seen in 63 percent of patients with left coronary disease and 35 percent of the patients with left main coronary disease equivalent lesions (P less than 0.001 and P less than 0.002, respectively, when compared with only 6 percent of patients with other lesions). The incidence of triple vessel disease was significantly greater in patients with critical lesions (55 percent in patients with left main coronary disease and 71 percent in those with the left main coronary equivalent lesions versus 10 percent in those with other lesions) (P less than 0.01). S-T segment depression of 2 mm or more is not a good indicator of critical coronary lesions because it has a low level of specificity. Consideration of the time of onset of ischemic changes adds to its usefulness, but it does not permit a definitive diagnosis in individual patients.

Adult↗
PubMed1978

Dissimilar atrial rhythms diagnosed by echocardiography.

A 27-year-old woman with ectopic atrial rhythm and apparent atrioventricular dissociation was found to have A waves on the mitral echocardiogram that bore no relation to the P wave on the surface electrocardiogram. The ECG did not reflect the presence of dissimilar atrial rhythms, and their presence became apparent only during the echocardiographic studies. The mechanism of this phenomenon and its clinical implications are discussed.

Adult↗
PubMed1976

Electrophysiological observations on the digitalis-potassium interaction in canine Purkinje fibers.

We studied the effects of elevating potassium concentration on the membrane potential of Purkinje cells exposed to toxic concentrations of acetylstrophanthidin or ouabain. Conventional intracellular microelectrode techniques were employed. Rapid elevation of [K+]o from 2.7 to 5.4 mEq/liter resulted in an initial increase (more negative) in membrane potential of cells demonstrating ouabain-induced phase 4 depolarization. The increase in maximal diastolic potential occurred initially without suppression of phase 4 depolarization. In cells rendered inexcitable by ouabain or acetylstrophanthidin, elevation of [K+]o consistently increased membrane potential and restored excitability. In four experiments automaticity was initiated within 2 minutes after the increase in [K]o. Although automaticity reappeared, as maximal diastolic potential increased, the automatic rate slowed and then pacemaker activity was suppressed. Studies with 3H-ouabain showed that the increase in membrane potential paralleled K+-induced release of 3H-ouabain from Purkinje cells. These studies suggest that elevation of [K+]o reverses digitalis toxic manifestations in canine Purkinje fibers by causing release of cardiac glycosides bound to the membrane. The observed increase in membrane potential of ouabain-treated Purkinje fibers that occurred after [K+]o elevation was considered to be mediated in part by restoration of the Na pump and by electrogenic pumping.

Action Potentials↗
PubMed1976

The efficacy of trapezoidal wave forms for ventricular defibrillation.

The purpose of this study was to evaluate the efficacy of a trapezoidal wave form for ventricular difibrillation. Overall efficacy showed the trapezoidal waveform to be effective for defibrillation, including patients weighing over 100 kg (220 lb). We concluded that (1) the trapezoidal waveform is an effective defibrillatory pulse and (2) the trapezoidal waveform offers pulse characteristics less deleterious than other established waveforms.

Biophysical Phenomena↗
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

The high frequency electrocardiogram in coronary artery disease.

The high-frequency ECG clearly contains information not available in the conventional ECG. Patients with angina pectoris could not be identified as statistically different from the normal group based on notching, although isolated examples existed. MI, on the other hand manifested abnormal notch counts in the presence of absence of abnormal Q-waves. We were unable to correlate the treadmill exercise test or the site of the arterial lesion with the high-frequency ECG. Pathophysiologic mechanisms are discussed.

Adult↗
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↗