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Biomedical subjects

R E Kerber

Publications and source records attributed to R E Kerber.

At least 19 recordsLinked to original sources
PubMed1992

Variable morphology of coronary atherosclerosis: characterization of atherosclerotic plaque and residual arterial lumen size and shape by epicardial echocardiography.

The purpose of this study was to evaluate the in vivo characteristics of coronary atherosclerosis by using high frequency epicardial echocardiography. High frequency epicardial echocardiography was used to evaluate residual lumen and wall morphology at the sites of maximal coronary atherosclerosis in 26 patients undergoing coronary artery bypass grafting. The maximal/minimal wall thickness ratio was 3.1 +/- 0.2 (mean +/- SEM) with a large range (1.3 to 7.5). Portions of the wall were normal in 16 of 31 lesions; the percent normal circumference ranged from 9% to 85%. Maximal/minimal lumen diameter ratio was 1.5 +/- 0.1 (range 1.1 to 2.9). The shape of the residual coronary lumen was noncircular in 16 lesions: oval in 13 and complex in 3. The residual coronary lumen was eccentrically placed within six arteries. These data emphasize the variability of residual lumen and wall geometry in atherosclerosis.

Coronary Artery Bypass↗
PubMed1992

Transthoracic defibrillation: effect of sternotomy on chest impedance.

The purpose of this study was to determine the effect of sternotomy on transthoracic impedance, a major determinant of current flow and defibrillation success. Transthoracic impedance was determined by using a validated test-pulse technique that does not require actual shocks. Seventeen patients undergoing median sternotomy were studied prospectively. Transthoracic impedance was determined before operation, 3 to 5 days after operation and (in eight patients) greater than or equal to 1 month after operation. When measured using paddle electrodes placed in the standard apex-right parasternal defibrillating position, transthoracic impedance declined after sternotomy in all patients, from 77 +/- 18 to 59 +/- 17 omega (p less than 0.01); smaller declines were demonstrated by using other electrode positions. Transthoracic impedance remained below the preoperative level in the eight patients who underwent a second set of measurements at least 1 month after operation. Six normal subjects not undergoing sternotomy underwent serial transthoracic impedance measurements at least 5 days apart; mean transthoracic impedance did not change. It is concluded that transthoracic impedance declines after sternotomy. At any operator-selected energy level a higher current flow will result after sternotomy; this may facilitate postoperative defibrillation.

Cardiography, Impedance↗
PubMed1992

Ventricular tachycardia rate and morphology determine energy and current requirements for transthoracic cardioversion.

BACKGROUND: The electrical current and energy required to terminate ventricular tachyarrhythmias are known to vary by arrhythmia: Ventricular tachycardia (VT) is generally considered to require less energy than ventricular fibrillation (VF). The hypothesis of our study was that current requirements for transthoracic termination of VT are further determined by VT rate and QRS complex morphology. METHODS AND RESULTS: We prospectively studied 203 patients who received a total of 569 shocks for VT or VF by following a current-based protocol. This protocol recommended shocks for VT beginning at 18 A (70 +/- 22 J) and shocks for VF beginning at 25 or 30 A (137 +/- 52 J or 221 +/- 70 J). The ventricular tachyarrhythmias were subclassified as monomorphic VT (MVT): uniform QRS complex morphology on surface electrocardiogram and heart rate greater than 100 beats per minute; polymorphic VT (PVT): nonuniform QRS complex morphology and heart rate less than or equal to 300 beats per minute; or VF: nonuniform QRS complex morphology and heart rate greater than 300 beats per minute. We found that shocks of 18 A and 25 A for terminating MVT had success rates of 69% and 82%, respectively, whereas such low-current shocks were less successful for PVT (33% at 18 A) and for VF (19% at 18 A, 53% at 25 A). High-current shocks of 35 A and 40 A were equally successful for the three ventricular tachyarrhythmias. Subdividing MVT revealed that slower MVT (heart rate less than 200 beats per minute) had a significantly better success rate with low-current shocks of 18 A and 25 A than did faster MVT (greater than 200 beats per minute) (89% versus 72% success, p less than 0.01). Bundle branch block morphology, QRS axis, and duration of ventricular tachyarrhythmia did not alter current requirements. CONCLUSIONS: Heart rate and electrocardiographic degree of organization of ventricular tachycardia are important determinants of transthoracic energy and current requirements for cardioversion and defibrillation. Transthoracic termination of MVT requires relatively low current or energy, but PVT behaves more like VF and requires higher electrical current or energy.

Electric Countershock↗
PubMed1991

Effect of nisoldipine on hemodynamic responses to defibrillation.

Sequences of ventricular fibrillation-defibrillation cause transient hypertension; we hypothesized that this "adrenergic overshoot" might be blunted by the functional antiadrenergic effect of the calcium channel blocking drug nisoldipine, with a potentially beneficial reduction in myocardial oxygen requirements. However, other calcium channel blocking drugs have been shown to reduce shock success for defibrillation, a deleterious effect. Thus the purposes of this study were to assess the effect of nisoldipine on the hemodynamic responses to the sequences of ventricular fibrillation-defibrillation, and its effect on the energy requirements for defibrillation. In 16 dogs we administered intravenous nisoldipine (1 microgram/kg bolus followed by an infusion of 0.075 to 0.50 microgram/kg/min) to lower mean blood pressure 10% and 20% below baseline. Ventricular fibrillation was induced electrically, and shocks of varying energy levels (30, 50, and 100 joules) were administered to determine defibrillation energy requirements. Heart rates and blood pressures were recorded up to 3 minutes after each shock to determine hemodynamic responses. Measurements were made before nisoldipine administration and again at the two levels of drug-induced blood pressure decline. We found that the usual systolic blood pressure "overshoot" after defibrillation (typically maximum at 15 to 30 seconds after shocks) was significantly blunted after nisoldipine administration (p less than 0.05). Heart rate slowing after defibrillation (a cholinergic response) was not affected. Nisoldipine did not alter shock success rates, which varied from 12 +/- 7%SE at 30 joules to 68 +/- 12% at 100 joules. Thus nisoldipine blunted the "adrenergic overshoot" of systolic blood pressure following defibrillation, a potentially beneficial effect, without altering the energy requirements for transthoracic defibrillation.

Animals↗
PubMed1991

Coronary arterial remodeling studied by high-frequency epicardial echocardiography: an early compensatory mechanism in patients with obstructive coronary atherosclerosis.

Coronary arterial remodeling is a compensatory mechanism that may limit the adverse effects of coronary obstructive lesions by expansion of the entire vascular segment. To determine if this compensatory anatomic change occurs in patients, high-frequency epicardial echocardiography using a 12 MHz transducer was performed during open heart surgery in 33 patients (10 with normal coronary arteries undergoing valvular surgery and 23 with coronary atherosclerosis). From stop-frame videotape high-frequency epicardial echocardiographic images, cross-sectional measurements of luminal area and total arterial area (lumen, intima, media and dense adventitia) were made in the patients with atherosclerosis at the site of arterial lesions and from the most proximal portion of the same artery. Remodeling was defined as enlargement of the total arterial area. In normal arteries measurements were made from proximal and midarterial locations. In the patients with normal coronary arteries, total arterial area, as determined by high-frequency echocardiography, decreased from the proximal site to the midportion of the artery (from 10.4 +/- 0.9 to 8.4 +/- 1.0 mm2, p less than 0.05); luminal area also decreased (from 6.0 +/- 0.6 to 4.5 +/- 0.7 mm2, p less than 0.05). In patients with coronary arterial lesions, luminal area also decreased from the proximal site to the arterial lesion site (from 5.3 +/- 0.6 to 2.3 +/- 0.3 mm2, p less than 0.05), but total arterial area increased (from 11.6 +/- 1.0 to 13.0 +/- 1.0 mm2, p less than 0.05). Of the 25 coronary arteries evaluated, only 4 had angiographic evidence of coronary collateral formation. These data indicate that coronary arterial remodeling is an important compensatory mechanism in obstructive coronary disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Surgical Procedures↗
PubMed1991

Free radicals from plastic syringes.

We have found that disposable sterile plastic syringes can leach free radicals into the fluids they hold. The free radical we observe appears to be a nitroxide (aminoxyl radical) because in aqueous solution it produces a 1:1:1 three line spectrum with a hyperfine splitting constant of 16.9 G.

Electron Spin Resonance Spectroscopy↗
PubMed1991

Ischemic cerebrovascular complications and risk factors in idiopathic hypertrophic subaortic stenosis.

To determine the risk and time to cerebrovascular complications with idiopathic hypertrophic subaortic stenosis, we studied 119 patients (66 men and 53 women) with evidence of this disease based on strict echocardiographic criteria and followed them up for a mean +/- SEM of 6.5 +/- 0.6 years. Cerebral ischemic events occurred in 26 patients (22%), and in five patients stroke was the initial presenting event. Men had cardiac symptoms at a younger age than women, but there was no significant difference in age at the time of stroke. Cardioembolic cerebrovascular events were associated with atrial fibrillation and left atrial enlargement, whereas atheroembolic events were associated with hypertension. An increased risk of stroke was associated with female sex, mitral anulus calcification, hypertension, and atrioventricular conduction delay. Unlike most previous series, this study shows that patients with idiopathic hypertrophic subaortic stenosis may present with stroke.

Adult↗
PubMed1991

Echocardiographic assessment of atherosclerotic coronary lesions.

Echocardiographic techniques to visualize normal and atherosclerotic coronary arteries include transthoracic, transesophageal, epicardial (intraoperative), and intravascular approaches. All are capable of visualizing portions of the coronary arteries, especially proximal, and demonstrating atherosclerotic lesions. However, none of these methods are able, at present, to completely examine the coronary tree, and therefore none are ready to be used as a standard clinical technique for the diagnosis and management of coronary artery disease. Technological advances will enhance the future clinical value and applicability of these techniques.

Coronary Artery Disease↗
PubMed1990

Effect of age on diastolic left ventricular filling at rest and during inotropic stimulation and acute systemic hypertension: experimental studies in conscious beagles.

"Pharmacologic" stress testing with inotropic stimulation is useful in the detection of coronary artery disease when ventricular dysfunction is provoked. However, abnormal diastolic filling may be masked or mimicked because of the influence of aging, heart rate, and loading conditions. We evaluated age effects on left ventricular filling at rest in young (n = 5) and old (n = 6) purebred beagles that were free of occlusive coronary disease and left ventricular hypertrophy, and we also evaluated age-related differences in left ventricular filling velocities in response to dobutamine and phenylephrine. Pulsed Doppler echocardiography of left ventricular filling velocities was performed at baseline and then after the administration of dobutamine (10 to 20 micrograms/kg/min) infusion. Repeat baseline recordings were obtained and then phenylephrine was administered intravenously in doses of 5 to 25 micrograms/kg/min until systolic arterial pressure increased by at least 30 mm Hg above baseline. At baseline, Doppler echocardiography revealed that there were no significant differences in the early (E) velocity or velocity time interval (VTI), and atrial (A) velocity or the A/E velocity ratio between the young and old groups. However, the A VTI and the A/(A + E) VTI ratio were significantly increased in the old group. With dobutamine administration, the E velocity did not significantly increase from baseline in either group. The E VTI, A velocity and A VTI increased significantly in both groups, but the increases were not different between groups. With phenylephrine infusion there was a significant decrease in the E VTI in the old group but neither the A/E velocity or the A/(A + E) VTI ratio significantly changed from baseline.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1990

Tissue characterization of chronic myocardial infarction.

Determination of magnetic resonance (MR) relaxation times (T1 and T2) and ultrasound backscatter are potential methods of noninvasive myocardial tissue characterization. The authors postulated that infarct-related collagen deposition in a canine chronic myocardial infarction model would alter T1 and T2 relaxation times. Further, we sought to compare the changes in T1 and T2 with backscatter measurements. Eight animals were studied 4 to 6 weeks after occlusion of the left anterior descending coronary artery; standard echocardiography showed each to have left ventricular wall motion abnormalities. Time-averaged backscatter and cyclic backscatter variation (at 5 MHz) were measured in the open-chest animal with corresponding normal and infarcted areas undergoing in vitro T1 and T2 measurements (at 20 MHz) and water and hydroxyproline concentration analysis. Significant increases in T2, time-averaged ultrasound backscatter, and hydroxyproline concentration were found in the infarcted myocardium compared with normal muscle. Cyclic variation in backscatter and water content were not significantly different between the two groups. Although backscatter, T2, and tissue collagen content increased in the infarcted myocardium, a significant relationship was not found among these variables.

Animals↗
PubMed1990

Transthoracic defibrillation using sequential and simultaneous dual shock pathways: experimental studies.

Dual pathway sequential DC shocks reduce energy requirements for internal defibrillation. Our purpose was to determine if dual pathway shocks similarly reduce energy requirements or improve shock success in transthoracic (external) defibrillation. We studied 39 closed-chest anesthetized mongrel dogs. The dual pathways used were left chest to right chest and left chest to posterior. In eight dogs we also assessed dual shock pathways oriented orthogonally, left lower chest to right upper chest and left upper chest to right lower chest. Four different dual pathway groups were studied: group 1: simultaneous shocks, sinusoidal waveform; group 2: sequential shocks, sinusoidal waveform, 100-msec shock separation, orthogonal shock pathways; group 3: sequential shocks, sinusoidal waveform, 100 msec shock separation; and group 4: sequential shocks, rectangular waveform (sequential shocks: 2 pulses, 2.5 msec each, 0.1-msec separation; single shock: 1 pulse, 5 msec). Shocks were given at 50 (J) joules, 100 J and 150 J and curves of energy versus success compared for dual pathway shocks versus single shocks. We found that the highest mean success rates (96 +/- SD 9%) were achieved by simultaneous sinusoidal waveform dual pathway shocks at 100 J; this was identical to results achieved by the single pathway sinusoidal waveform comparison shocks at 100 J. Sequential dual pathway sinusoidal shocks separated by 100 msec achieved a mean success rate of 79 +/- 31% at 150 J; the comparison single pathway mean success rate was similar: 81 +/- 22% at 150 J. Thus, dual pathway sequential or simultaneous transthoracic shocks did not demonstrate clear superiority over single pathway shocks.

Animals↗