bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rate-dependent effects of diltiazem on human atrioventricular nodal properties.
Authors: Talajic M , Lemery R , Roy D , Villemaire C , Cartier R , Coutu B , Nattel S 
Published: June 2012

BACKGROUND
Tachycardia enhances the channel-blocking effects of antiarrhythmic drugs. In contrast to the extensive data regarding the rate-dependent effects of sodium channel blockers in humans, little is known about the frequency-dependent effects of calcium channel blockers on human atrioventricular (AV) nodal properties. Accordingly, the purpose of this study was to evaluate the importance of heart rate in modulating the electrophysiological effects of diltiazem in humans.

METHODS AND RESULTS
Electrophysiological studies were performed in 25 patients. Sinus node, atrial, and AV nodal function were evaluated at multiple atrial rates under control conditions and after administration of one of three intravenous doses of diltiazem designed to produce low, intermediate, and high stable plasma concentrations (designated doses 1, 2, and 3, respectively). Results were analyzed in terms of the longest and shortest cycle lengths obtainable in each patient under control and drug conditions. Plasma concentrations of diltiazem were stable and averaged 43 +/- 4, 73 +/- 6, and 136 +/- 11 ng/ml for doses 1, 2, and 3, respectively. Sinus node recovery time, intra-atrial conduction time, atrial effective refractory period, and HV interval were unaffected by diltiazem infusion. Effects of diltiazem were limited to changes in AV nodal parameters. Stable, dose-dependent increases in Wenckebach cycle length were observed after all three doses of diltiazem (increases of 54 +/- 13, 84 +/- 18, and 174 +/- 33 msec for doses 1, 2, and 3, respectively). Small nonsignificant increases in AH interval and atrioventricular effective refractory period (AVERP) were observed after dose 1 of diltiazem. At long cycle lengths, diltiazem caused modest increases in AH interval (3 +/- 4 and 25 +/- 8 msec for doses 2 and 3, respectively) and AVERP (36 +/- 12 and 70 +/- 25 msec). Drug effects were far greater at short cycle lengths (45 +/- 17 msec, 58 +/- 12 msec for AH interval and 80 +/- 24 msec, 163 +/- 41 msec for AVERP; p less than 0.05 versus values at long cycle lengths). At rapid rates, effects of diltiazem on AVERP substantially exceeded those on AV conduction, a result that could account for the beneficial effects of diltiazem during paroxysmal AV reentrant tachycardia by decreasing the excitable gap.

CONCLUSIONS
Depressant effects of diltiazem on human AV nodal function are highly dependent on atrial rate; the rate-dependent actions on AV nodal refractoriness probably contribute to beneficial effects of diltiazem in patients with supraventricular arrhythmias.
Dipyridamole potentiates the myocardial infarct size-limiting effect of ischemic preconditioning.
Authors: Miura T , Ogawa T , Iwamoto T , Shimamoto K , Iimura O 
Published: June 2012

BACKGROUND
Recent studies implicated a key role for adenosine (ADO) receptor activation in the enhancement of ischemic tolerance by ischemic preconditioning. In this study, we aimed to test the hypothesis that dipyridamole, an ADO transport inhibitor, enhances the preconditioning effect.

METHODS AND RESULTS
Six groups of rabbits underwent 30-minute coronary occlusion and 72-hour reperfusion. Infarct size (IS) and the area-at-risk (AR) were determined by histology and by use of fluorescent particles, respectively. IS expressed as the percentage of AR (%IS/AR) was 46.5 +/- 3.4% (n = 13) in control rabbits. Preconditioning with 2-minute ischemia tended to limit %IS/AR (%IS/AR, 35.5 +/- 3.5%, n = 9), and that possible protection was abolished by pretreatment with 10 mg/kg 8-phenyltheophylline (8-PT), an ADO receptor antagonist (%IS/AR, 43.9 +/- 5.8%, n = 9). Administration of dipyridamole (0.25 mg/kg) before the 2-minute preconditioning markedly limited %IS/AR to 13.8 +/- 2.6% (n = 12), indicating the potentiation of the preconditioning effect by this agent. Furthermore, this enhancement of preconditioning effect by dipyridamole treatment was significantly attenuated by 8-PT (%IS/AR, 27.6 +/- 2.1%, n = 11). Dipyridamole given before the 30-minute ischemia, without preconditioning, did not reduce %IS/AR (55.3 +/- 5.2%, n = 7), and a previous study from this laboratory had demonstrated that the present dose of 8-PT alone did not modify IS in the rabbit.

CONCLUSIONS
Dipyridamole significantly potentiated the IS-limiting effect of preconditioning. This finding strongly supports the hypothesis that stimulation of ADO receptors by endogenous ADO, which builds up during preconditioning ischemia, mediates the increased ischemic tolerance afforded by preconditioning.
Long-term predictors of subsequent cardiovascular events with coronary artery disease and 'desirable' levels of plasma total cholesterol.
Authors: Miller M , Seidler A , Kwiterovich P O , Pearson T A 
Published: June 2012

BACKGROUND
Patients with coronary artery disease (CAD) are at considerable risk for subsequent cardiovascular events. Although hyperlipidemia accentuates the risk, predictors of subsequent events with CAD and desirable total cholesterol (TC) (less than 5.2 mmol/l) have not been assessed.

METHODS AND RESULTS
A survival analysis was performed in a subset of 740 consecutive patients who underwent diagnostic coronary arteriography between 1977 and 1978. Eight-three men and 24 women with angiographically documented CAD and desirable TC were followed for subsequent cardiovascular events, including myocardial infarction and cardiovascular death. Over a 13-year period, 75% of CAD subjects with reduced high density lipoprotein cholesterol (HDL-C) (less than 0.9 mmol/l) developed a subsequent cardiovascular event compared with 45% of those with HDL-C greater than or equal to 0.9 mmol/l (p = 0.002). A Kaplan-Meier analysis revealed significantly greater survival from cardiovascular end points in patients with baseline levels of HDL-C greater than or equal to 0.9 mmol/l (p = 0.005). After 11 variables were tested, an age-adjusted Cox proportional-hazards model identified two pairs of independent predictors of subsequent cardiovascular events: they were a left ventricular ejection fraction (LVEF) less than 35% (relative risk [RR], 6.5; 95% confidence interval [CI], 2.8, 15.3; p less than 0.001) and reduced HDL-C (RR, 2.0; 95% CI, 1.2, 3.3; p = 0.01) in the first model and LVEF less than 35% (RR, 6.5; 95% CI, 2.7, 15.6; p less than 0.001) and TC:HDL ratio greater than or equal to 5.5 (RR, 1.9; 95% CI, 1.1, 3.1; p = 0.02) in the second model.

CONCLUSIONS
Low HDL-C (or high TC:HDL-C) is strongly predictive of subsequent cardiovascular events in subjects with CAD, despite desirable TC. As such, identification of this potentially modifiable risk factor should be actively pursued in this high-risk subgroup.
Endogenous nitric oxide protects against platelet aggregation and cyclic flow variations in stenosed and endothelium-injured arteries.
Authors: Yao S K , Ober J C , Krishnaswami A , Ferguson J J , Anderson H V , Golino P , Buja L M , Willerson J T 
Published: June 2012

BACKGROUND
This study was designed to test the hypothesis that endogenously produced nitric oxide protects against platelet aggregation and cyclic flow variations in stenosed and endothelium-injured arteries of mongrel dogs.

METHODS AND RESULTS
NG-Monomethyl-L-arginine (L-NMMA), an inhibitor of nitric oxide formation, was administered at 5 mg/kg to 15 dogs after the left anterior descending coronary artery was mechanically injured and narrowed by external constrictors and to nine dogs before endothelial injury of the femoral artery and after injury and moderate arterial constriction. Treatment with L-NMMA resulted in cyclic flow variations (as detected by external Doppler flow probes) in the left anterior descending artery of seven of 15 dogs and in the femoral artery of four of nine dogs after endothelial injury. L-Arginine, the precursor for nitric oxide synthesis, was administered at 60 mg/kg and abolished cyclic flow variations in each of the 11 dogs. D-Arginine did not change the L-NMMA-induced cyclic flow variations. Saline infusion did not induce or change cyclic flow variations in any of the animals. Acetylcholine (1, 10, and 100 micrograms/min; n = 9) was administered in the femoral artery of nine additional dogs before and after endothelial injury in moderately stenosed femoral arteries. Acetylcholine did not induce cyclic flow variations in any animal; however, it did increase the severity of cyclic flow variations that developed in severely stenosed arteries. The diameter of the femoral artery was measured by intravascular ultrasound imaging. L-NMMA caused vasoconstriction of normal arteries, but no change was detected in endothelium-injured arteries. In contrast, L-arginine caused vasodilation of normal arteries, but, again, no change was noted in endothelium-injured arteries. Acetylcholine dilated normal femoral arteries but constricted arteries with endothelial injury. In both in vitro and ex vivo platelet studies, L-NMMA enhanced platelet aggregation, whereas L-arginine significantly reduced platelet aggregation. D-Arginine and acetylcholine showed no effect on platelet aggregation.

CONCLUSIONS
Promotion of nitric oxide production decreases platelet aggregation and may eliminate cyclic flow variations, whereas a reduction in nitric oxide formation enhances platelet aggregation and may induce cyclic flow variations. Acetylcholine causes vasoconstriction at the femoral arterial site of endothelial injury and may increase the severity of cyclic flow variations.
Positron emission tomography detects metabolic viability in myocardium with persistent 24-hour single-photon emission computed tomography 201Tl defects.
Authors: Brunken R C , Mody F V , Hawkins R A , Nienaber C , Phelps M E , Schelbert H R 
Published: June 2012

BACKGROUND
Four-hour 201Tl redistribution images underestimate myocardial viability in patients with coronary artery disease (CAD). Because 4-hour defects often redistribute late, delayed imaging may enhance assessment of tissue viability. Myocardial metabolic activity was therefore assessed with positron emission tomography (PET) in 26 CAD patients with impaired ventricular function (ejection fraction, 32.1 +/- 13.9%) and 24-hour single-photon emission computed tomography (SPECT) 201Tl defects.

METHODS AND RESULTS
On circumferential profile analysis, PET ischemia was defined by preserved glucose metabolism in hypoperfused myocardium, and PET infarction was defined by concordant reductions in perfusion and metabolism. On 19 stress-redistribution and seven rest-redistribution SPECT studies, four observers visually scored 201Tl activity in eight segments on a scale from 0 (normal) to 3 (complete defect). Using an improvement in visual score > or = 0.75 to define redistribution, there were 100 fixed, 17 partially reversible, and 12 completely reversible defects. PET identified tissue metabolic activity in 51 (51%) segments with fixed defects (21 PET ischemia, 30 PET normal) and nine (53%) segments with partially reversible defects (five PET ischemia, four PET normal). When grouped by 24-hour score, the proportion of fixed defects with metabolic activity varied from 84% (scores < or = 1.4) to 15% (scores > 2.6). For partially reversible defects, only 53% with scores < 2.0 and one of two with scores > or = 2.0 were considered metabolically viable on PET. Of 12 completely reversible defects, six (50%) were normal, five (42%) had PET ischemia, and one (8%) had PET infarction. The proportion of fixed defects with metabolic activity did not depend on whether a rest or stress study was performed or on the change in visual score used to define 201Tl redistribution (0.25, 0.50, 0.75, and 1.00).

CONCLUSIONS
In CAD patients, PET identifies glucose metabolic activity in the majority of fixed 24-hour 201Tl defects. However, very severe (near-complete) 24-hour 201Tl defects are less likely to exhibit metabolic activity on PET imaging than are defects with less-pronounced reductions in segmental 201Tl activity.
QT intervals at heart rates from 50 to 120 beats per minute during 24-hour electrocardiographic recordings in 100 healthy men. Effects of atenolol.
Authors: Viitasalo M , Karjalainen J 
Published: June 2012

BACKGROUND
Conflicting reports about changes in QT intervals suggest that QT values should be compared at similar heart rates.

METHODS AND RESULTS
Relations between QT and RR intervals were determined after measurement of QT values by Holter recording at heart rates of 50, 60, 70, 80, 90, 100, 110, and 120 beats per minute in 100 healthy young men. Fifteen men underwent a second recording during acute treatment with the beta-blocking agent atenolol. At heart rates between 80 and 120 beats per minute, the QT interval was significantly longer (from 9 to 16 msec), and at a heart rate of 50 beats per minute significantly shorter (26 msec), than values calculated from Bazett's formula. Sleep prolonged QT values by 18 msec at a heart rate of 60 beats per minute and by 21 msec at a heart rate of 50 beats per minute compared with the waking state. Atenolol lengthened QT intervals significantly (by 11-14 msec) at heart rates between 90 and 110 beats per minute and shortened them (by 12 msec) at a heart rate of 60 beats per minute. During sleep, QT intervals were the same before and after atenolol.

CONCLUSIONS
The method of plotting QT against RR intervals after measurement of QT values at similar stable spontaneous heart rates before and after intervention allows changes in autonomic state and heart rate to be taken into account. By this method, QT values can be compared without distortion effects caused by correction formulas.
Abnormal neuroendocrine responses during exercise in heart transplant recipients.
Authors: Braith R W , Wood C E , Limacher M C , Pollock M L , Lowenthal D T , Phillips M I , Staples E D 
Published: June 2012

BACKGROUND
Osmotic and neural factors stimulate neuroendocrine activity during exercise. In contrast to excitatory mechanisms, afferent information from cardiac mechanoreceptors inhibits integrative centers in the hypothalamus and medula oblongata, which serves to buffer neuroendocrine activity. Orthotopic cardiac transplantation results in the loss of afferent information from cardiac mechanoreceptors. Thus, transplantation possibly results in exaggerated neuroendocrine responses when patients are physically active.

METHODS AND RESULTS
We measured the neuroendocrine response to moderate and strenuous exercise performed at the same relative intensity in 11 heart transplant recipients (50 +/- 14 years old) 18 +/- 12 months after transplantation and 11 control subjects matched with respect to sex, age, and body size. Plasma levels of norepinephrine, vasopressin, renin activity, atrial natriuretic peptide, angiotensin II, and aldosterone were measured at rest, during a maximal graded exercise test, and during submaximal exercise at 40% and 70% of peak power output on a cycle ergometer (W). Plasma renin activity and atrial natriuretic peptide were elevated at rest in heart transplant recipients (p < or = 0.05). Heart rate (%HRmax reserve), rating of perceived exertion, and reductions in plasma volume (% delta from rest) at the conclusion of the three exercise conditions did not differ between heart transplant recipients and control (p > or = 0.05). Relative changes in neuroendocrine hormones were similar (p > or = 0.05) in heart transplant recipients and control during exercise at 40% of peak power output. Relative changes in plasma norepinephrine, vasopressin, atrial natriuretic peptide, and plasma renin activity were greater (p < or = 0.05) in heart transplant recipients during exercise at 70% of peak power output and the graded exercise test.

CONCLUSIONS
We interpret these data as a possible indication of ablation of cardiac mechanoreceptor afferents and unopposed neuroendocrine stimulation in heart transplant recipients. Furthermore, chronic neuroendocrine hyperactivity is likely in ambulatory heart transplant recipients. Although cyclosporine nephrotoxicity is implicated in the development of hypertension, our data suggest that chronic neuroendocrine hyperactivity, which alters renal volume regulation, also contributes to the incidence and severity of hypertension in heart transplant recipients.
A prospective study of nutritional factors and hypertension among US men.
Authors: Ascherio A , Rimm E B , Giovannucci E L , Colditz G A , Rosner B , Willett W C , Sacks F , Stampfer M J 
Published: June 2012

BACKGROUND
An effect of diet in determining blood pressure is suggested by epidemiological studies, but the role of specific nutrients is still unsettled.

METHODS AND RESULTS
The relation of various nutritional factors with hypertension was examined prospectively among 30,681 predominantly white US male health professionals, 40-75 years old, without diagnosed hypertension. During 4 years of follow-up, 1,248 men reported a diagnosis of hypertension. Age, relative weight, and alcohol consumption were the strongest predictors for the development of hypertension. Dietary fiber, potassium, and magnesium were each significantly associated with lower risk of hypertension when considered individually and after adjustment for age, relative weight, alcohol consumption, and energy intake. When these nutrients were considered simultaneously, only dietary fiber had an independent inverse association with hypertension. For men with a fiber intake of < 12 g/day, the relative risk of hypertension was 1.57 (95% confidence interval, 1.20-2.05) compared with an intake of > 24 g/day. Calcium was significantly associated with lower risk of hypertension only in lean men. Dietary fiber, potassium, and magnesium were also inversely related to baseline systolic and diastolic blood pressure and to change in blood pressure during the follow-up among men who did not develop hypertension. Calcium was inversely associated with baseline blood pressure but not with change in blood pressure. No significant associations with hypertension were observed for sodium, total fat, or saturated, transunsaturated, and polyunsaturated fatty acids. Fruit fiber but not vegetable or cereal fiber was inversely associated with incidence of hypertension.

CONCLUSIONS
These results support hypotheses that an increased intake of fiber and magnesium may contribute to the prevention of hypertension.
Percutaneous polymeric stents in porcine coronary arteries. Initial experience with polyethylene terephthalate stents.
Authors: Murphy J G , Schwartz R S , Edwards W D , Camrud A R , Vlietstra R E , Holmes D R 
Published: June 2012

BACKGROUND
To test the feasibility of percutaneous deployment of intracoronary polymeric stents, a prototype polyethylene terephthalate (PET) stent and a catheter-based delivery system were developed.

METHODS AND RESULTS
Polymeric stents were deployed in the coronary arteries of 11 Yucatan swine: six stents were placed in the left anterior descending coronary artery, four stents were placed in the circumflex artery, and one stent was placed in the right coronary artery. Stent deployment was achieved by withdrawal of an outer delivery sheath, thus allowing the PET stent to self-expand to a preformed configuration. Two animals died during surgery, one during stent placement and the other several hours after implantation due to intracoronary thrombus formation. Two animals were electively sacrificed within 24 hours of stent implant to examine the adequacy of stent deployment within the coronary vessel. The remaining seven animals survived until the termination of the study 4-6 weeks later. Light microscopic examination of the stented vessels showed an extensive neointimal proliferative response with vessel occlusion in all animals who survived initial stent placement. There were two distinct types of histological responses to the PET stent--a chronic foreign body inflammatory response around the stent tines and a neointimal proliferative response in the center of the occluded vessel lumen. The histological response seen in the central area of the vessel was morphologically similar to that seen in patients with restenosis after successful percutaneous transluminal coronary angioplasty, whereas the morphological response seen at the periphery of the stent tine was similar to that exhibited by a chronic foreign body reaction and was not typical of that seen in a restenosis lesion. A ventricular aneurysm also developed in the area of myocardium that was previously supplied by the occluded vessel.

CONCLUSIONS
This study demonstrates that percutaneous deployment of polymeric stents in the coronary arteries is technically feasible. The use of PET polymer was associated with an intense proliferative neointimal response that resulted in complete vessel occlusion. Histological examination of the stented segments of the vessel revealed no evidence that dissection of the vessel wall had occurred at the time of initial stent deployment. Although the PET polymer was of similar quality to that used in the manufacture of balloon angioplasty catheters, a toxic chemical or contaminant effect cannot be completely excluded as the stimulus to intimal proliferation. This finding may have relevance to the selection of materials for use as intravascular devices.
Evaluation of colestipol/niacin therapy with computer-derived coronary end point measures. A comparison of different measures of treatment effect.
Authors: Blankenhorn D H , Selzer R H , Mack W J , Crawford D W , Pogoda J , Lee P L , Shircore A M , Azen S P 
Published: June 2012

BACKGROUND
The Cholesterol Lowering Atherosclerosis Study has demonstrated beneficial effect of colestipol/niacin on coronary atherosclerosis using a panel-determined global coronary change score. We now report treatment group comparisons using quantitative coronary angiographic (QCA) measures from all processable segments in 85 of 162 randomly selected baseline/2-year film pairs.

METHODS AND RESULTS
Treatment benefit was established for percent stenosis for either continuous or categorical analyses with regression established regardless of the per-patient scoring procedure. In addition, treatment benefit favoring regression was established in some cases for roughness and for percent involvement, a longitudinal estimate of the percent of coronary surface involved by raised lesions. Benefit on minimum diameter was directly related to whether the segment was proximal to a graft insertion and hemodynamically related to the bypass graft. QCA correlates of panel-determined progression were increases in percent stenosis and numbers of occluded lesions in native arteries and the number of progressing lesions in bypass grafts.

CONCLUSIONS
These results demonstrate that a variety of computer measures can be used as end points in coronary angiographic therapy trials, but change in percent stenosis correlates best with visual panel assessments and best reflects the treatment benefit; when treatment effect sizes are moderate to large, the required sample size of coronary angiographic trials can be reduced when QCA is used.