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Biomedical subjects

R E Kerber

Publications and source records attributed to R E Kerber.

At least 127 records · Page 7Linked to original sources
PubMed1986

Alterations in ventricular excitability in conscious dogs during development of chronic heart failure.

Arrhythmias in patients with heart failure may result from altered electrophysiological properties of the myocardium. To examine changes in ventricular excitability during cardiac failure and to relate these changes to ventricular structural and neurochemical abnormalities, right ventricular failure was produced in dogs by pulmonary artery banding and by creating tricuspid regurgitation. Right and left ventricular excitability thresholds were tested biweekly in heart failure (HF) and sham-operated conscious dogs by means of strength-duration curves (1-40 ms) at basic cycle lengths (BCL) of 300-500 ms until time of death (21-188 days). Marked increases in the excitability threshold of the right ventricle occurred in HF (mean maximum % increase, 205 +/- 42 at BCL 500 ms). Smaller, though significant increases in the left ventricular excitability threshold in HF were also seen (mean maximum % increase 103 +/- 36 at BCL 500 ms). Increases in the excitability threshold of the left as well as the right ventricles occurred, even though ventricular dilation (2-D Echo) was confined to the right ventricle. The time course of changes in the excitability threshold was variable (maximum occurrence at 21 +/- 3 days right ventricle, 23 +/- 11 days left ventricle). Tyrosine hydroxylase activity and norepinephrine content of the right ventricle were markedly depleted at death, when the excitability threshold was high. Similar though nonsignificant trends in reductions of these sympathetic neurochemicals were seen in the left ventricle. Levels of choline acetyltransferase and QNB binding in both ventricles were unaffected.

Animals↗
PubMed1986

Late effects of coronary reperfusion on regional left ventricular function. Can infarct size be estimated noninvasively?

The prognosis of patients with acute myocardial infarction is related to the infarction size. We evaluated the ability of a clinical technique, two-dimensional echocardiography, to assess infarct size based on the extent of regional contraction abnormalities. Conscious closed-chest dogs with preplaced coronary snares underwent permanent coronary occlusion. The animals were studied by two-dimensional echo 20 min and 2 days after occlusion. The extent of myocardial contraction abnormalities (systolic wall thinning instead of normal systolic thickening) was correlated with the infarct size determined pathologically. Some dogs had pressure-induced left ventricular hypertrophy. Extent of regional contraction abnormalities demonstrated by two-dimensional echo correlated well with infarct size both early (20 min) (r = 0.92) and late (2 days) (r = 0.94) after permanent coronary occlusion. Dyskinesis extent modestly overestimated the infarct size. The relationship between dyskinesis and infarct size were similar in both normal and left ventricular hypertrophied hearts. We then undertook a study to assess the effects of coronary reperfusion on dyskinesis-infarct size relationships. Conscious, closed-chest dogs underwent 1-2 h of coronary occlusion followed by 2-10 days of coronary reperfusion. Significant regional dyskinesis was present after 1-2 h of occlusion and decreased by 50-60% of the occlusion value after 2 days of reperfusion without further change in extent of dyskinesis between 2 and 10 days of reperfusion. Of importance, however, was that there was no significant correlation between infarct size and extent of regional dyskinesis by two-dimensional echo after reperfusion, either after 2 days (r = 0.09) or 10 days (r = 0.29) of reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Efficacy of an automated external defibrillator in the management of out-of-hospital cardiac arrest: validation of the diagnostic algorithm and initial clinical experience in a rural environment.

Automatic external defibrillators (AEDs) may have advantages over manual defibrillation in managing prehospital cardiac arrest, particularly in rural communities. We conducted a two-part evaluation of a commercially available AED. We first established the diagnostic accuracy of the AED's rhythm recognition algorithm by challenging it with 205 cardiac arrest rhythms previously recorded from actual patients in the field. The AED demonstrated 100% specificity and 92% sensitivity for ventricular fibrillation (VF) in this nonclinical setting. We then compared the clinical efficacy of AEDs in 18 small communities (study group) with that of manual defibrillation in 18 additional communities (control group) of similar size. Ambulance technicians using manual defibrillators correctly diagnosed VF more frequently than the AEDs (98% vs 83%; p less than .025). Specificity for VF was similar in the two groups (100% for AEDs vs 94% for technicians; p greater than .10). AEDs were able to deliver shocks more quickly than was possible with the manual defibrillators (1.56 vs 2.77 min; p less than .001). The ability of the AEDs to terminate VF was excellent, converting VF in 28 of 29 (97%) patients to some other rhythm compared with only 37 of 53 (70%) patients in the control group (p less than .01). Hospital admission and discharge rates were similar for the two groups. Ten of the 35 (29%) patients managed with AEDs achieved admission and six (17%) were ultimately discharged. In the control group 17 of 53 (33%) patients with VF were admitted and seven (13%) were discharged (p less than .75). AEDs are an effective alternative to manual defibrillation in small communities.

Diagnosis, Computer-Assisted↗
PubMed1986

Ultrasound characterization of acute myocardial ischemia by quantitative texture analysis.

In this study we tested the efficacy of quantitative texture analysis in the identification of acute myocardial ischemia using an ultrasound data acquisition system that digitizes and stores echocardiographic data in polar format. In nine closed-chest dogs, data were acquired before and after coronary occlusion using a 2.4 MHz echocardiographic system. Regions of interest were analyzed at end-diastole and end-systole from the ischemic area and normal area at the same depth of field. Ultrasound data were evaluated using previously reported quantitative gray level texture measures. After occlusion, texture changes indicative of ischemia were found in systolic images. The directional component of the data analysis was important; analysis in the azimuthal direction was more accurate than in the axial direction. Six texture measures exhibited significant changes in the ischemic region from control to occlusion when analyzing data in the azimuthal direction. One false positive result occurred (significant texture change in the normal region from control to occlusion) in the azimuthal direction. Several false positive alterations in the normal regions from control to occlusion were found when the texture was evaluated in the axial direction. For accurate assessment of ischemic changes, preocclusion image data were required. We conclude that quantitative echocardiographic texture analysis using polar format data can identify subtle changes in myocardial texture such as that due to acute ischemia, using data acquired through the chest wall.

Acute Disease↗
PubMed1986

Paradoxical cerebral embolism: eight cases.

We evaluated eight patients with possible or probable paradoxical cerebral embolism. One patient had a hemispheric transient ischemic attack; the others had infarcts. Ischemic symptoms followed a Valsalva's maneuver in three cases. Others were linked to placement of a Swan-Ganz catheter, deep venous thrombosis and pulmonary embolism, right atrial myxoma, and use of oral contraceptives. Four had no known predisposing conditions. In six patients, contrast echocardiography showed right-to-left shunting. Cardiac catheterization showed a patent foramen ovale in three patients; one had an atrial septal defect. In the clinical setting of otherwise unexplained cerebral embolism in a young patient, paradoxical cerebral embolism should be considered. Contrast echocardiography is a useful screening test for this purpose.

Adolescent↗
PubMed1986

Application of Doppler technology to studies of the coronary circulation.

Presently available Doppler technology has allowed us to substantially increase our understanding of the regulation of the coronary circulation in humans. New technologic developments in this area promise to further enhance our understanding of the operational characteristics of the coronary circulation in patients in normal and pathologic states.

Angina Pectoris↗
PubMed1986

Effect of high-dose cyclophosphamide and total-body irradiation on left ventricular function in adult patients with leukemia undergoing allogeneic bone marrow transplantation.

Protocols used to prepare patients with leukemia for bone marrow transplantation have the potential for cardiac toxicity due to high-dose cyclophosphamide and total-body irradiation. We have reported one regimen, combining cytarabine (5 mg/kg), cyclophosphamide (90 mg/kg), and total-body irradiation (900 cGy), which is relatively effective in the treatment of leukemia. To assess cardiac effects of this treatment regimen, we performed serial echocardiography and radionuclide ventriculography in 28 patients with leukemia (age range, 18-48 years; mean, 31; 21 males) undergoing allogeneic bone marrow transplantation. No significant change in left ventricular fractional minor axis shortening or increase in left ventricular diastolic dimension was seen with weekly echocardiography. At an average of 77 days (range, 28-358) after transplant, repeat radionuclide ventriculography in 17 patients revealed no significant change in resting left ventricular ejection fraction compared to that on admission to the hospital (58% +/- 6.8% vs 56% +/- 8.0% SD; P = not significant). In seven of these 17 patients (41%), resting ejection fraction fell between baseline and discharge (from mean of 60% to 50%). Resting ejection fraction in four of these patients (23% of the entire group) fell into the abnormal range (from mean of 56% to 44%; lowest, 41%). Ten patients also had exercise radionuclide ventriculography and all had normal responses (greater than 5% increase with exercise) pre- and post-transplant. We conclude that this effective bone marrow transplantation regimen has little apparent short-term cardiac toxicity in the majority of patients; since a few patients do exhibit a deterioration in left ventricular function, continued cardiac surveillance is probably indicated in posttransplant patients.

Adolescent↗
PubMed1986

Energy requirements for defibrillation.

Available clinical data indicate that an initial shock energy of 200 J will defibrillate the majority of patients. There is no advantage in starting at a higher energy, and lower energy shocks may be safer. Measurements of transthoracic impedance may permit the use of even lower energy levels for initial shocks. If the initial shock fails to defibrillate it should be repeated immediately, at the same energy level, and then increased if defibrillation is still not achieved. If the initial shock defibrillates but refibrillation occurs later there is no reason to increase the energy; it should be repeated at 200 J. We suggest the following energy selection algorithm for defibrillation (VF = ventricular fibrillation): (Formula: see text).

Electric Countershock↗
PubMed1986

Transient myocardial ischemia: experimental echocardiographic demonstration and evaluation of myocardial contraction abnormalities.

A continuing theme in our laboratory has been the use of echocardiographically-measured systolic myocardial wall thickening to demonstrate and evaluate the consequences of regional myocardial ischemia. This presentation focuses on two areas: the immediate mechanical consequences of induced myocardial ischemia in two experimental models: canine and human; the correlation between persistent regional myocardial dysfunction and morphologic infarction after sequences of coronary artery occlusion and reperfusion. Many experiments using animal models have demonstrated that acute myocardial ischemia produces almost immediate replacement of normal systolic myocardial wall thickening by systolic thinning. Less is known about the immediate mechanical response of human myocardium to acute ischemia. This was studied in 5 open-chest humans undergoing various cardiac operations. Wall thickening was continuously displayed by a 7 MHz M-mode echocardiographic transducer coupled to the epicardium by suction to maintain constant position. Coronary flow velocity was displayed by a pulsed Doppler device coupled to an epicardial coronary artery by suction. Ischemia was induced by the surgeon who manually occluded the coronary artery with a soft-tipped Kitner dissector or vascular forceps for 30 seconds. It was found that cessation of coronary flow was accompanied by reductions in normal systolic thickening but systolic thinning or expansion only rarely occurred. In contrast, when the identical techniques were used in 5 dogs, systolic thinning always occurred immediately after coronary arterial occlusion. This suggests that there are important species differences between canine and human myocardium in the immediate mechanical response to myocardial ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Myocardial infarct size threshold for two-dimensional echocardiographic detection: sensitivity of systolic wall thickening and endocardial motion abnormalities in small versus large infarcts.

This study evaluated the ability of 2-dimensional echocardiography to detect myocardial infarcts of varying sizes. Echocardiography was performed in 29 closed-chest, conscious dogs 2 days after circumflex coronary artery occlusion, and the ultrasonic recordings were analyzed for regional abnormalities in either wall thickening or endocardial motion. Acute myocardial infarct (AMI) size and extent were assessed by morphologic examination. In 5 dogs, coronary occlusion failed to produce AMI; in these dogs wall thickening analysis showed no abnormalities (100% specificity), and endocardial motion analysis yielded 1 false-positive result (80% specificity). In 24 dogs an AMI developed; infarcts larger than 18% of left ventricular mass uniformly resulted in echocardiographically detectable contraction abnormalities. When the AMI was small (1 to 6% of left ventricular mass) and primarily subendocardial, the sensitivity of echocardiography was poor: Only 3 of 10 of the dogs with a small AMI had abnormalities by wall thickening, and only 1 of 10 by endocardial motion. Thus, in this canine model of AMI, 2-dimensional echocardiography was insensitive to small, subendocardial AMI. If this is so in humans as well, it is a potential limitation of the clinical use of echocardiography in the detection of AMI.

Animals↗
PubMed1985

Experimental evaluation and initial clinical application of new self-adhesive defibrillation electrodes.

We evaluated the efficacy of self-adhesive electrode pads for defibrillation and cardioversion in animals and patients. In 11 anesthetized dogs, the success rate of shocks given to terminate electrically-induced ventricular fibrillation was similar for both self-adhesive electrode pads and hand-held electrode paddles; success rate approached 100% at energies of 125-150 joules. Eighty patients undergoing defibrillation or elective cardioversion received shocks from self-adhesive pads. In all but 2 patients defibrillation or cardioversion was achieved at least once using these pads. The pads were equally effective from either apex-anterior or apex-posterior positions. The transthoracic impedance using self-adhesive pads was 75 +/- 21 ohms, similar to transthoracic impedance we previously reported when using standard hand-held paddles. No complications occurred with the use of the pads. We conclude that self-adhesive electrode pads are effective for defibrillation and cardioversion.

Animals↗
PubMed1985

Defibrillator electrode-chest wall coupling agents: influence on transthoracic impedance and shock success.

The purpose of this study was to determine if the difference in transthoracic impedance produced by different coupling agents affects the success of shocks for defibrillation. Three different coupling agents, Harco pads (Hewlett-Packard), Littman pads (3M) and Redux paste (Hewlett-Packard), were assessed in 10 anesthetized dogs in which ventricular fibrillation was induced by electrical stimulation of the right ventricle. Defibrillation was attempted 15 seconds later, using 50, 100 and 150 joules (selected energy). Actual delivered energy, current, impedance and the percent of the shocks that achieved defibrillation were determined for the three coupling agents. Redux paste gave significantly lower impedance and higher current than the two disposable performed coupling pads tested. Despite this, there were no significant differences in shock success among the three coupling agents. Thus, in this experimental model, over a three-fold energy range, disposable coupling pads were as effective as electrode paste for defibrillation despite the slightly higher impedance of the disposable pads.

Alcohols↗
PubMed1985

Artifactual regional gray level variability in contrast-enhanced two-dimensional echocardiographic images: effect on measurement of the coronary perfusion bed.

The purpose of this study was to determine the extent of regional variability of image echocardiographic amplitude (expressed as gray level variability) in contrast-enhanced two-dimensional echocardiographic images, and to assess the effect of such baseline gray level variability on quantitation of the coronary perfusion bed. In 10 anesthetized closed chest dogs, short-axis papillary muscle echocardiographic images were obtained during control preinjection conditions and during injection of three contrast agents into the left main coronary artery with and without circumflex artery occlusion. Regional echocardiographic amplitude variation was measured by computer-based videodensitometric analysis of mean gray levels in four myocardial regions after cavity (background) gray level subtraction. To determine the effect of regional gray level variability on quantitation of the coronary perfusion bed, the contrast-enhanced left anterior descending artery perfusion bed was measured by two methods. The circumferential method ignored myocardial contrast inhomogeneity by measuring the circumferential extent of contrast enhancement, whether or not the enhancement by contrast medium extended transmurally. The exact method measured only the area of myocardium actually enhanced by contrast medium, which often did not extend transmurally. The perfusion beds determined by the two echocardiographic methods were compared with the anatomic perfusion bed determined by postmortem barium-gelatin coronary arteriography. Regional gray levels varied qualitatively and quantitatively in the control state (before contrast injection), with lateral regions being less bright than axial regions. After injection of contrast medium, brightness increased in all regions, the axial regions brightening most.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Extreme intracardiac coiling of a transvenous pacemaker: a case report.

We report an unusual complication of transvenous pacing: extreme coiling of a pacemaker catheter, which formed a redundant, twisted loop protruding into the right ventricular outflow tract. This may be a result of "twiddling" (rotation) of the pacemaker generator by the patient and/or inadequate fixation of the catheter at the venous entry site. Careful fixation of the generator to the venous entry site within the subcutaneous pocket may prevent such a complication.

Adult↗
PubMed1985

Automated impedance-based energy adjustment for defibrillation: experimental studies.

In defibrillation, current flow depends on the energy selected and the transthoracic impedance. If transthoracic impedance is high, current flow may be inadequate to defibrillate. We developed a method by which high transthoracic impedance is automatically compensated for by an increase in operator-selected energy when impedance is high. Transthoracic impedance was predicted in advance of the first shock by passing a low-level current between the defibrillator electrodes during the defibrillator charge cycle; a microprocessor monitored current flow and determined impedance. In 28 mongrel dogs we manipulated transthoracic impedance by placing glycerin-soaked gauze pads between the paddle electrodes and the chest. If the predicted impedance exceeded a preset value, the delivered energy was automatically increased by 40% or 100%. Using this impedance-based energy adjustment technique, we found significant improvements in current flow and success rate of shocks when energy was automatically increased to compensate for high transthoracic impedance. The use of transthoracic impedance as a basis for energy adjustment appears a promising technique to minimize the hazards of high electrical energy; it allows low-energy shocks in most patients while avoiding inappropriate low energies in patients with high impedance. Clinical trials are justified.

Animals↗
PubMed1985

The effect of cardiac hypertrophy on the coronary collateral circulation.

We have previously shown that dogs with renal hypertension and left ventricular hypertrophy have larger infarcts (per risk area size) than do control animals. A potential explanation for this is that collateral resistance is higher in these dogs. Paradoxically, previous postmortem studies in human hearts with left ventricular hypertrophy have suggested that coronary collaterals are actually increased in this condition. To test the hypothesis that left ventricular hypertrophy is associated with alterations in coronary collateral resistance, studies were performed in dogs with renal hypertension and left ventricular hypertrophy and in patients with aortic valvular disease at the time of cardiac surgery. With an isolated, adenosine-vasodilated, blood-perfused cardiac preparation, collateral and normal zone pressure-flow relationships were established by means of radioactive microspheres in nine dogs with renal hypertension and left ventricular hypertrophy and in 17 controls. Collateral resistance calculated from these pressure-flow relationships were similar in both groups (4.0 +/- 0.7 in dogs with renal hypertension and left ventricular hypertrophy and 3.9 +/- 0.4 mm Hg/ml/min/100 g in controls). In addition, normal zone resistance was not different between groups (transmural resistances 0.17 +/- 0.01 in controls and 0.18 +/- 0.02 in dogs with renal hypertension and left ventricular hypertrophy. In five patients with aortic valve disease, left ventricular hypertrophy, and normal coronary arteries and in six patients without left ventricular hypertrophy who had normal left anterior descending coronary arteries, a 7 MHz suction-mounted echo transducer was used to monitor systolic wall thickening during transient occlusions of the left anterior descending artery at the time of cardiac surgery. Because noncollateralized myocardium ceases to contract promptly after coronary occlusion, this approach provides an indirect index of collateral perfusion. Twenty seconds after the onset of coronary occlusion, systolic thickening had markedly decreased in both groups (15 +/- 10% of control values in nonhypertrophied hearts and 10 +/- 10% in hearts with left ventricular hypertrophy; p = NS between groups). Thus the severity of contraction abnormality induced during transient coronary occlusion in these two groups of patients was similar, suggesting that the degree of severity of ischemia was comparable between the two groups. We conclude that collateral resistance is not altered by hypertension and left ventricular hypertrophy and that left ventricular hypertrophy in patients is not associated with functional evidence of an enhanced collateral circulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗