PubMed Health⌕ Search

Biomedical subjects

S G Warren

Publications and source records attributed to S G Warren.

At least 19 recordsLinked to original sources
PubMed2002

Quantification of myocardial hypoperfusion with 99m Tc-sestamibi in patients undergoing prolonged coronary artery balloon occlusion.

Percutaneous transluminal coronary angioplasty provides an excellent opportunity to investigate the location and quantity of hypoperfusion during sudden complete occlusion of one of the major coronary arteries. Thirty-five patients referred for elective percutaneous transluminal coronary angioplasty were injected intravenously with 99mTc-sestamibi during balloon inflation. To visualize and quantify the hypoperfused region, a map of perfusion was constructed from that occlusion study and from the control study performed on the following day. Patients were divided into groups according to proximal or distal occlusion within each of the three coronary arteries. The region of myocardium supplied by each coronary artery varied in location and extended outside the typical borders for all arteries, but most prominently for the left circumflex coronary artery. The quantities of hypoperfusion varied within each artery group, but the average hypoperfusion was greater for the left anterior descending coronary artery than for either the right coronary artery or the left circumflex coronary artery. It is concluded that the quantities of hypoperfusion were highly variable within each artery group. Occlusion of the left anterior descending coronary artery was associated with the largest ischaemic region. The area of hypoperfusion extended outside the typical borders, most prominently for the left circumflex coronary artery.

Adult↗
PubMed2001

The absence of high-frequency QRS changes in the presence of standard electrocardiographic QRS changes of old myocardial infarction.

BACKGROUND: This study compares the high-frequency QRS components (HF-QRS) in patients with and without standard electrocardiogram (ECG) changes indicative of old myocardial infarction (MI). Previous studies have indicated that patients with an old MI differ in their HF-QRS compared with healthy subjects. The HF-QRS has been reported to be decreased during acute coronary occlusion and increased after reperfusion. However, there is controversy about the appearance of HF-QRS after the acute phase of MI. METHODS: A total of 154 patients were included, 57 with and 97 without QRS changes of old MI on the standard ECG. The patients with old MI were divided into subgroups on the basis of the MI location indicated by the standard ECG. Signal-averaged ECGs from the 12 standard leads were recorded. The root-mean-square values of the HF-QRS were determined within two frequency bands: 150 to 250 Hz and 80 to 300 Hz. RESULTS: There was a large interindividual variation in HF-QRS in patients without MI as well as in those with different MI locations. There were no significant differences between the groups in the summed HF-QRS of all 12 leads or in the pattern of lead distribution of the HF-QRS. Not even the patients with the greatest QRS changes of old MI could be differentiated from those without any changes of old MI on the standard ECG. The results were the same in both analyzed frequency bands. CONCLUSIONS: This study shows, contrary to previous studies, that analysis of HF-QRS cannot differentiate between patients with and without old MI.

Adult↗
PubMed2001

Impaired delay eyeblink classical conditioning in individuals with anterograde amnesia resulting from anterior communicating artery aneurysm rupture.

Anterior communicating artery (ACoA) aneurysm rupture can lead to an anterograde amnesia syndrome similar to that observed after damage to the hippocampus and medial temporal lobes (MT). It is currently believed that ACoA amnesia results from basal forebrain damage that disrupts hippocampal processing without direct hippocampal damage. Converging evidence from animal studies and computational modeling suggests that qualitative differences may exist in the pattern of memory impairment after basal forebrain or MT damage. For example, animals with basal forebrain but not hippocampal damage are impaired at delay eyeblink classical conditioning (EBCC). In this study, individuals with ACoA amnesia were shown to be impaired at delay EBCC compared with matched controls; this contrasts with the spared delay EBCC previously observed in MT amnesia. This finding suggests the beginning of a possible dissociation between the memory impairments in MT versus ACoA amnesia.

Adult↗
PubMed2000

Changes in high-frequency QRS components are more sensitive than ST-segment deviation for detecting acute coronary artery occlusion.

OBJECTIVES: This study describes changes in high-frequency QRS components (HF-QRS) during percutaneous transluminal coronary angioplasty (PTCA) and compares the ability of these changes in HF-QRS and ST-segment deviation in the standard 12-lead electrocardiogram (ECG) to detect acute coronary artery occlusion. BACKGROUND: Previous studies have shown decreased HF-QRS in the frequency range of 150-250 Hz during acute myocardial ischemia. It would be important to know whether the high-frequency analysis could add information to that available from the ST segments in the standard ECG. METHODS: The study population consisted of 52 patients undergoing prolonged balloon occlusion during PTCA. Signal-averaged electrocardiograms (SAECG) were recorded prior to and during the balloon inflation. The HF-QRS were determined within a bandwidth of 150-250 Hz in the preinflation and inflation SAECGs. The ST-segment deviation during inflation was determined in the standard frequency range. RESULTS: The sensitivity for detecting acute coronary artery occlusion was 88% using the high-frequency method. In 71% of the patients there was ST elevation during inflation. If both ST elevation and depression were considered, the sensitivity was 79%. The sensitivity was significantly higher using the high-frequency method, p<0.002, compared with the assessment of ST elevation. CONCLUSIONS: Acute coronary artery occlusion is detected with higher sensitivity using high-frequency QRS analysis compared with conventional assessment of ST segments. This result suggests that analysis of HF-QRS could provide an adjunctive tool with high sensitivity for detecting acute myocardial ischemia.

Adult↗
PubMed2000

Cerebral arterial air embolism treated by a vertical head-down maneuver.

A case of cerebral arterial air embolism (CAAE) occurring from inadvertent injection of air during aortic root angiography is presented. Prompt treatment by suspending the patient briefly in a vertical head-down position beside the catheterization table appeared to be life-saving and resulted in complete neurological recovery. This approach may offer the first immediate therapy for CAAE. Cathet. Cardiovasc. Intervent. 49:185-187, 2000.

Cardiac Catheterization↗
PubMed2000

Sex differences and estropausal phase effects on water maze performance in aged rats.

An age-related decline in memory has been reported in male rats; however, there are few studies that have addressed these changes in aged female rats. In young female rats, hormonal cycles influence behavior. By the age of 22 months most female rats have not had regular hormonal cycles for at least 9 months. In the current study we examined how the hormonal status (persistent estrus and pseudo-pregnant) of the aged (22-24 months) female rat (Long Evans) influenced performance on a spatial version of the Morris water maze and compared this to aged male rats. Aged females in persistent estrus showed better performance on the water maze than both aged females that were pseudopregnant and aged males. Thus, postestropausal hormonal status may influence the course of aging in females.

Aging↗
PubMed2000

Spatial, individual, and temporal variation of the high-frequency QRS amplitudes in the 12 standard electrocardiographic leads.

BACKGROUND: Analysis of high-frequency QRS amplitudes (HF-QRS) may provide an additional diagnostic tool in patients with heart disease, but the basic properties of these waveforms have not been sufficiently investigated. This study describes the spatial, individual, and temporal variation at rest of HF-QRS recorded with the 12 standard electrocardiographic leads in patients with ischemic heart disease. METHODS AND RESULTS: Two consecutive electrocardiographic recordings from 67 patients were signal averaged and analyzed within a bandwidth of 150 to 250 Hz. The HF-QRS values were expressed as root mean square values. There was a spatial variation in HF-QRS among the 12 leads, with higher amplitudes in V(2) through V(4), II, aVF, and III. The individual variation among the patients was large for all leads. The sum of the HF-QRS for all 12 leads in each patient ranged from 20 to 75 microV (mean 36 +/- 11 microV). The mean of the temporal variation in HF-QRS for all 12 leads between the 2 recordings was only 0.10 +/- 0. 09 microV. CONCLUSIONS: Because of the large individual variation, analysis of HF-QRS is probably most applicable in monitoring situations when it is possible to track changes in a patient over time. The temporal variation in HF-QRS at rest is small, both in patients with and those without prior myocardial infarction.

Adult↗
PubMed2000

Stimulus exposure effects in human associative learning.

Learning that one cue (CS) predicts a second, salient cue (US) can often be slowed by prior exposure to one or both stimuli. In animals, CS-US learning is more strongly retarded following uncorrelated exposure to both CS and US than following exposure to the US alone. In this paper we present several studies showing a similar effect in humans, using a computer-based task. Experiments 1 and 2 used a between-groups design and demonstrated a strong CS/US exposure effect, whether or not the US was signalled by a neutral cue during exposure. Experiment 3 demonstrated similar effects using a within-subjects design. Overall, these results are consistent with several theoretical interpretations and suggest that uncorrelated CS/US exposure leads to a robust retardation of subsequent CS-US learning in humans.

Acoustic Stimulation↗
PubMed1999

Predictors of complications and learning curve using the Angio-Seal closure device following interventional and diagnostic catheterization.

A retrospective study was conducted to determine the frequency and nature of groin complications when the Angio-Seal device was used on 252 occasions by one operator immediately following interventional (66%) and diagnostic (34%) procedures. Sixty-nine percent of the 238 successfully deployed cases received ticlopidine or clopidogrel, 16% received abciximab, and 15% received heparin postprocedure. Complications included vascular surgery for collagen plug perforation into the femoral artery (0.8%), failure to deploy (5.6%), pseudoaneurysm (0.4%), brisk, visible bleeding (9%), persistent ooze (14%), hematoma > 6 cm (0.8%), hematoma </= 6 cm (2.4%), and ecchymosis > 1 cm(2) (10%). Multivariate analysis identified diagnostic cases (6 Fr sheaths) to be associated with a reduced risk of complications [odds ratio (OR) 0.1] while interventional procedures (8 Fr sheaths), postprocedure heparin, and body mass index (BMI) < 28 (OR 10.1, 3.2, and 2.8, respectively) were associated with increased risk. Gender, age, ticlopidine, clopidogrel, and abciximab were not independent predictors of complications. A learning curve for device deployment was observed in the first 50 cases (14% nondeployment vs. 3.5% for the subsequent 202 procedures, P = 0.009) and failure to deploy was independent of sheath size used. Angio-Seal can be used with reasonable safety and efficacy immediately after diagnostic and interventional procedures. Cathet. Cardiovasc. Intervent. 48:162-166, 1999.

Adult↗
PubMed1998

Electrocardiographic changes during prolonged coronary artery occlusion in man: comparison of standard and high-frequency recordings.

Detection of acute myocardial ischaemia using electrocardiographic methods is generally based on assessment of the ST segments in the standard 12-lead electrocardiogram (ECG). Several studies have also shown changes in high-frequency QRS components during acute ischaemia. The purpose of the present study was to determine the changes in high-frequency QRS components during prolonged percutaneous transluminal coronary angioplasty (PTCA) and to compare these changes with ST-segment deviations in the standard 12-lead ECG. The study population consisted of 19 patients receiving prolonged PTCA. Standard and high-resolution signal-averaged ECGs were recorded before and during balloon inflation. The high-resolution recordings were performed using bipolar X, Y and Z leads. The QRS complexes in the high-resolution signal-averaged ECGs were analysed within a bandwidth of 150-250 Hz. During inflation, significant reductions in high-frequency QRS components were observed (12-72%). Changes in the high-frequency QRS components were seen in four of the patients without ST-segments deviation in the standard ECG. The correlation between the ST-segment deviation and the reduction in high-frequency QRS components was weak (r = 0.27). Acute coronary artery occlusion produces changes in high-frequency QRS components, even in the absence of ST-segment deviation in the standard ECG. Further studies need to be carried out to evaluate whether analysis of high-frequency QRS components could provide a method for detecting myocardial ischaemia and give additional information to that available in the ST segment in the standard ECG.

Adult↗
PubMed1997

Spatial and nonspatial learning across the rat estrous cycle.

Recent evidence has demonstrated that there are fluctuations in both the anatomy and physiology of the hippocampus across the estrous cycle of the female rat. In the present study we examined the behavioral implications of these changes by testing females on either a hippocampal or nonhippocampal version of the Morris water maze during the various phases of the estrous cycle. Males were also tested on these tasks. Although there was little variance on the nonhippocampal cue task, females in proestrus performed significantly better than those in estrus. Optimal female performance on the spatial version of the task occurred during the phase of estrus, whereas the least efficient performance occurred during proestrus. These results do not support the traditional view that hippocampal long-term potentiation is positively correlated with spatial learning.

Animals↗
PubMed1995

LTP varies across the estrous cycle: enhanced synaptic plasticity in proestrus rats.

Previous studies have shown that the number of dendritic spines and synapses in hippocampal CA1 stratum radiatum decreases more than 30% between the proestrus (high estrogen) and estrus (low estrogen) phases of the rat estrous cycle [10,27]. In the present study, we investigated whether hippocampal synaptic plasticity, as measured by long-term potentiation (LTP), might also vary across the estrous cycle of the female rat. Male rats, and female rats at each phase of the estrous cycle were tested in either the morning or afternoon. There were no significant group differences in the pre-LTP I/O curves. However, females examined during the afternoon of proestrus, the phase during which prior studies indicate synapse number to be highest, demonstrated the greatest degree of potentiation. Diestrus, proestrus and estrus females tested in the morning demonstrated similar amounts of potentiation. There were also significant differences in post-LTP I/O curves between the afternoon proestrus females and males tested in the afternoon. These results suggest that gonadal hormones, interacting with the time of day, may regulate neural processes underlying learning and memory.

Analysis of Variance↗
PubMed1995

Continued benefit of lovastatin in the treatment of hypercholesterolemia in 36 patients.

After one year of treatment, low-dose (20 mg/d) lovastatin achieved continued efficacy without tachyphylaxis in 36 patients with Type IIa or IIb hyperlipoproteinemia. Six week and one year reductions in low density lipoprotein (LDL) cholesterol were significant at 33% and 31% in these patients respectively; reductions in total cholesterol were also significant at 25% and 22% respectively. Increases in high density lipoprotein cholesterol (HDL) were 6% at six weeks and 10% at one year; triglycerides were reduced 16% and 11% respectively. The cholesterol lowering effects were similar for males and females (23% and 21% respectively). Low-dose lovastatin (20 mg/d) is a good choice for reducing cholesterol in patients with primary Type IIa or IIb hyperlipoproteinemia refractory to diet therapy because it is effective in lowering LDL-cholesterol, while raising HDL-cholesterol with few side effects and without tachyphylaxis.

Aged↗
PubMed1994

New guiding catheter configuration for aortocoronary vein graft angioplasty.

A new family of four guiding catheters (8 French and 9 French) has been developed for angioplasty of aortocoronary vein grafts and native coronary arteries beyond vein graft insertions. In 67 consecutive grafts and native vessels dilated through the grafts in 54 patients, the procedural success rate was 97%. The G-1 standard catheter was employed for the majority of the procedures (66%), but the G-3 catheter was better for high anterior grafts and the G-4 catheter was better for high left grafts. The G-2 catheter was better for lower right grafts, especially in dilated aortas. Balloon angioplasty alone using 8 French catheters was performed in 60 procedures, and excimer laser with adjunctive balloon angioplasty using 9 French catheters was performed in 7 procedures. These unique guiding catheters provide an attractive alternative to existing vein graft guides by their improved seating and backup support. They may be the primary choice for vein graft angioplasty and may have future application in stent deployment and transluminal extraction catheter (TEC) atherectomy.

Adult↗
PubMed1990

Guiding catheter exchange during coronary angioplasty.

A new technique to exchange one angioplasty guiding catheter for another with the guide wire in place and across a coronary artery stenosis has been developed to decrease the dangers of having to recross the stenosis with a guide wire. This technique utilizes a regular extended angioplasty guide wire and enables the exchange of guiding catheters during the angioplasty procedure. In 683 consecutive angioplasty procedures by one operator, this technique has been attempted 57 times in 43 patients (6.3%) and has been successful 51 times (90%). The only failures were when the second catheter had a large or open curve (left Amplatz II, 5/22 unsuccessful or multipurpose, 1/3 unsuccessful). There have been no complications. We conclude that exchange of a guiding catheter over a guide wire by the method described is safe and helpful in cases where different guiding catheters are needed for back-up power once the lesion has been crossed with a guide wire.

Angiography↗
PubMed1990

Effectiveness of low-dose lovastatin in lowering serum cholesterol. Experience with 56 patients.

This study reviews the progress of 56 consecutive patients with type IIa and IIb hyperlipoproteinemia following treatment with lovastatin. Lovastatin, a potent inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, has been shown to have a cholesterol-lowering effect in doses ranging from 10 to 80 mg/d. Thus far, however, no large study has been performed to show the effectiveness of low-dose lovastatin (20 mg/d) for more than a 6-week duration. Fifty-six patients with known coronary artery disease were prospectively studied, with fasting lipid values being measured at baseline and after 6, 12, 18, and 24 weeks of 20-mg/d lovastatin therapy given as a single evening dose. The total cholesterol level fell 26% from a mean baseline of 8.12 mmol/L (314 mg/dL) and triglyceride levels fell by 12% from a mean baseline of 2.46 mmol/L. The high-density lipoprotein levels increased 7.6%. One patient with known preexisting liver disease was withdrawn from the study owing to an asymptomatic significant rise in liver function test results; one subject complaining of proximal muscle weakness was also withdrawn. The maximal decrease in total cholesterol level occurred within 6 weeks of initiation of therapy. We conclude that low-dose (20-mg/d) lovastatin was effective in lowering serum cholesterol levels in patients with primary type IIa or IIb hyperlipoproteinemia with minimal short-term side effects. Further studies are needed to establish the long-term safety and effectiveness of this drug.

Cholesterol↗