bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic resonance imaging to evaluate patency of aortocoronary bypass grafts.
Authors: Rubinstein R I , Askenase A D , Thickman D , Feldman M S , Agarwal J B , Helfant R H
Published: June 2011

To assess the efficacy of magnetic resonance (MR) imaging in evaluating graft patency after coronary bypass surgery, 20 patients who had prior surgery (average 5.5 years, range 1.5 to 14) and recent cardiac catheterization because of chest pain were studied. No patient had surgical intervention or change in symptoms in the time interval between catheterization and MR imaging. These 20 patients had a total of 47 grafts, defined as proximal anastomoses: 20 to the left anterior descending or diagonal artery (LAD), 13 to the left circumflex artery marginal branches (LCX), and 14 to the right coronary artery or posterior descending artery (RCA). The patients underwent cardiac and respiratory gated MR scans in a 0.5 tesla magnet with an echo time of 22 msec and two repetitions in a 128 X 256 matrix. In-plane resolution was 2.7 mm. Every patient had a scan in the transaxial plane and some underwent scanning in the sagittal and coronal planes as well. A graft was considered patent by MR when a signal-free lumen was visualized in an anatomic position consistent with that of a bypass graft, had a lumen larger than the native vessels, was seen on more than one slice, and was seen at a level higher than that of the native vessels. If a known graft was not seen it was considered occluded. The scans were interpreted by consensus of two physicians aware of the operative but not the cardiac catheterization data.(ABSTRACT TRUNCATED AT 250 WORDS)
Electropharmacology of sotalol in patients with Wolff-Parkinson-White syndrome.
Authors: Mitchell L B , Wyse D G , Duff H J
Published: June 2011

The beta-adrenoceptor-blocking and class III effects of sotalol were assessed in 11 patients with inducible orthodromic reciprocating tachycardia. Serum sotalol concentration, maximum exercise heart rate, and electrophysiologic study data were obtained at control, at the beta-adrenoceptor-blocking dosage (407 +/- 149 mg/day, 1.4 +/- 0.5 micrograms/ml), and at the maximum well-tolerated dosage (924 +/- 337 mg/day, 3.2 +/- 1.3 micrograms/ml). Class III effects (increases in anterograde and retrograde accessory connection effective refractory periods, ventricular effective refractory period, and the QT interval during fixed-rate atrial pacing) were evident at the beta-adrenoceptor-blocking dosage of sotalol and became more marked at the maximum well-tolerated dosage. For example, the mean anterograde accessory connection effective refractory period was significantly increased over control (272 +/- 41 msec) by the beta-adrenoceptor blocker (324 +/- 52 msec) and was further significantly increased by the maximum well-tolerated dose (364 +/- 37 msec). Similarly, the minimum preexcited RR interval during atrial fibrillation was increased in all patients at each dosage tested. Antiarrhythmic efficacy, defined by the absence of inducible, sustained, orthodromic reciprocating tachycardia and a minimum preexcited RR interval during atrial fibrillation of 300 msec or greater, was achieved in four patients at the beta-adrenoceptor-blocking dosage and in another four patients at the maximum well-tolerated dosage. These eight patients received long-term sotalol therapy and none has had recurrent, sustained reciprocating tachycardia during 15 +/- 12 months of follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)
Development of coronary artery disease in cardiac transplant patients receiving immunosuppressive therapy with cyclosporine and prednisone.
Authors: Uretsky B F , Murali S , Reddy P S , Rabin B , Lee A , Griffith B P , Hardesty R L , Trento A , Bahnson H T
Published: June 2011

Coronary artery disease (CAD) has been shown in previous uncontrolled studies to be a limiting factor to long-term survival in patients undergoing cardiac transplantation and who were taking conventional immunosuppressive agents. To study the development of CAD after cardiac transplantation in patients taking the newer immunosuppressive agent cyclosporine, we prospectively performed yearly coronary arteriography on all eligible transplantation patients (first year, 57 patients; second year, 30 patients; third year, 14 patients). The prevalence of CAD by life table analysis was 18% at 1 year, 27% at 2 years, and 44% at 3 years. The occurrence of two or more major rejection episodes was associated (p less than .005) with the development of CAD. In two patients who died of CAD, coronary artery histology revealed subintimal inflammatory cellular infiltration in some lesions. These data demonstrate that the prevalence of CAD rises progressively over time and immunologic factors may be important in its development.
Alterations in endocardial activation of the canine papillary muscle early and late after myocardial infarction.
Authors: Kienzle M G , Tan R C , Ramza B M , Young M L , Joyner R W
Published: June 2011

Permanent coronary occlusion produces time-dependent changes in surviving subendocardial cellular properties. We compared the functional alterations in Purkinje (P) and ventricular muscle (VM) activation early (24 hr) and late (4 weeks or greater) after permanent coronary occlusion in an in vitro preparation of canine papillary muscle. High-density extracellular (1 to 2 mm resolution) and selected intracellular recordings were made in five animals early and seven animals late during stimulation of a free-running P strand. Activation patterns of P and VM layers from ischemic and unaffected papillary muscles were compared in the same animal. Average P layer conduction velocity was determined in normal and ischemic regions with the use of a linear array of recording and stimulating electrodes. Purkinje activation was altered little in the early phase of infarction, while healing was associated with a generalized 25% reduction in P layer conduction velocity and localized block and fragmentation of P waveforms. Intracellular recordings at sites of nonsynchronous P activation revealed electrotonic interaction between cell groups. At 24 hr, small groups of VM were present but with abnormal activation patterns in regions of necrosis with fragmented and delayed extracellular waveforms produced by partially uncoupled groups of cells. Local delay and block could be modulated by rate and site of stimulation. After healing, VM activation abruptly stopped at the visual infarct border, marked by a characteristic "end potential." These studies demonstrate important differences in the functional attributes of the P and VM layers studied early and late after coronary occlusion. Alterations in cell-to-cell relationships are likely very important in determining abnormalities of activation in both settings.
The physiologic basis of dobutamine as compared with dipyridamole stress interventions in the assessment of critical coronary stenosis.
Authors: Fung A Y , Gallagher K P , Buda A J
Published: June 2011

Noninvasive cardiac imaging with echocardiography or thallium-201 scintigraphy utilizing pharmacologic agents as alternatives to exercise is gaining popularity. We investigated the physiologic rationale underlying the optimal choice of pharmacologic stress for functional versus perfusion imaging. With the use of an open-chest dog model, a critical stenosis of the left circumflex coronary artery was produced with total ablation of hyperemic response to a 15 sec period of complete occlusion. Regional left ventricular wall thickening was assessed by quantitative two-dimensional echocardiography. Regional myocardial blood flow was determined by microspheres in both the flow-restricted left circumflex area and the control area supplied by the left anterior descending artery. Eight dogs received 15 micrograms/kg/min dobutamine intravenously for 10 min, and nine dogs received 0.14 mg/kg/min dipyridamole intravenously for 4 min. Dobutamine induced wall thickening abnormalities in all dogs while dipyridamole induced dysfunction in only 55% of the animals studied (p less than .01). Subendocardial blood flow to the left circumflex area was unchanged after both dobutamine and dipyridamole when compared with baseline blood flow. However, subendocardial blood flow increased markedly after dipyridamole in the control area. Regional subendocardial blood flow ratio (left anterior descending/left circumflex) was 3.74 +/- 0.09 (mean +/- SEM) after dipyridamole versus 1.27 +/- 0.09 after dobutamine (p less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)
Skeletal muscle metabolism in patients with congestive heart failure: relation to clinical severity and blood flow.
Authors: Massie B , Conway M , Yonge R , Frostick S , Ledingham J , Sleight P , Radda G , Rajagopalan B
Published: June 2011

We and others have previously demonstrated excessive phosphocreatine (PCr) depletion and acidosis in skeletal muscle during exercise in patients with congestive heart failure (CHF). In the present study, we performed serial measurements of PCr and pH during gradually incremental flexor digitorum superficialis exercise in 22 patients with CHF and 11 age-matched controls to determine: (1) whether abnormalities were present at the same relative workloads (a comparison that would at least partially compensate for differences in muscle mass), (2) the temporable course of the metabolic changes, (3) the relationship of the metabolic findings to clinical variables, and (4) the relationship of the metabolic abnormalities to forearm blood flow. The patients with CHF had significantly lower [PCr] and pH at all submaximal levels of exercise, and these abnormalities were apparent from the onset of low-level exercise. There was considerable heterogeneity among the patients with CHF with respect to the metabolic findings, with 14 of 22 exhibiting either PCr or pH values more than 2 SDs below normal. Patients whose capacity was more limited during the protocol had lower [PCr], and especially pH, at low loads than did other patients with CHF or the control subjects. The more symptomatic patients and those with more limited bicycle exercise tolerance also had lower pH values. In contrast, there were no significant differences in forearm blood flow between the patients and controls and no relationship between forearm blood and either clinical variables or the metabolic findings. These results indicate that skeletal muscle metabolic abnormalities are present in many patients with CHF and that they are not primarily due to either muscle atrophy or impaired blood flow. These changes may explain in part the marked heterogeneity of symptom status and exercise capacity of patients with similar degrees of cardiac dysfunction.
Abnormal endothelial factor VIII associated with pulmonary hypertension and congenital heart defects.
Authors: Rabinovitch M , Andrew M , Thom H , Trusler G A , Williams W G , Rowe R D , Olley P M
Published: June 2011

In patients with pulmonary hypertension associated with congenital heart defects, ultrastructural abnormalities are observed in endothelial cells, which suggest heightened metabolic function. If endothelial production of the von Willebrand factor (vWF) is increased, this may be associated with abnormal interactions with platelets leading to worsening of the pulmonary hypertension. We therefore evaluated vWF in 30 patients with pulmonary hypertension (25 with congenital heart defects) and in 30 individuals with normal pulmonary arterial pressure (12 with congenital heart defects). We measured the antigenic (vWF: Ag) and biologic (VWF: rist) activity of vWF in plasma and assessed endothelial vWF: Ag directly by an immunoperoxidase stain applied to lung biopsy tissue. Because of considerable variance and small size, the group of five patients with pulmonary hypertension and without congenital heart defects were excluded from statistical analyses. Patients with pulmonary hypertension and congenital heart defects had significant higher vWF: Ag levels than individuals with normal pulmonary arterial pressure without congenital heart defects (p less than .05), whereas values in those with normal pressure and congenital heart defects were intermediate. In lung biopsy tissue available from 29 patients in this study and from 11 others we previously reported, immunostain of pulmonary arterial endothelium for vWF was intense (suggesting increased production) in 29 of 32 with pulmonary hypertension and congenital heart defects and in only one of eight with normal pulmonary arterial pressure and congenital heart defects (p less than .01). Only three patients with congenital heart defects and pulmonary hypertension and increased vWF: Ag, however, had increased vWF: rist. Compatible with this discrepancy was a loss of vWF high-molecular weight forms as determined by both crossed immunoelectrophoresis and multimeric analysis. Our results suggest that increased vWF in most patients with congenital heart defects and pulmonary hypertension is associated with increased production of a biologically deficient molecule lacking high-molecular weight forms.
Chemically determined mineral content of explanted porcine aortic valve bioprostheses: correlation with radiographic assessment of calcification and clinical data.
Authors: Schoen F J , Kujovich J L , Webb C L , Levy R J
Published: June 2011

Bioprosthetic valve calcification is usually assessed pathologically by gross inspection, radiographic studies, and histologic examination. Quantitation of mineral content by chemical assay has not been reported for failed clinical valves removed from adults. In this study, calcium determination by atomic absorption spectroscopy was done on 52 removed porcine valves after routine pathologic examination, including specimen radiography done by a standard technique. Specimens included 31 valves with calcific primary tissue failure, two calcified (but not overtly dysfunctional) valves removed simultaneously with failed valves, 14 nondeteriorated valves obtained at reoperation or autopsy after long-term implantation, and five valves removed within 1 month after insertion. Chemically determined mineral content varied widely among patients and duration of function. Valves with calcific failure had 113 +/- 68 micrograms/mg calcium overall (mean +/- SD) after 36 to 156 months (mean 87) of function. Almost all dysfunctional porcine valves with radiographically demonstrated calcific deposits had greater than 34 and 67 micrograms/mg calcium for mitral and aortic valves, respectively. Nondeteriorated valves (implanted 8 to 145 months, mean 57) had 5 +/- 6 micrograms/mg calcium. Failed aortic valves had more calcium than failed mitral valves and valves with calcific stenosis more than valves with regurgitation caused by calcification with tearing. Correlation of semiquantitative radiographic grading with chemically determined valve mineral was good, indicating that radiographic assessment of calcification may be used reliably for clinical comparisons between valves.
Duplex scanning for diagnosis of aortoiliac and femoropopliteal disease: a prospective study.
Authors: Kohler T R , Nance D R , Cramer M M , Vandenburghe N , Strandness D E
Published: June 2011

We compared ultrasonic duplex scanning and angiography for the localization and classification of arterial stenoses and occlusions in 32 patients. The criteria for the detection of a greater than 50% diameter reducing stenosis was an increase in peak systolic velocity of greater than 100%, loss of reverse flow, and spectral broadening. Duplex studies and angiograms were evaluated in a blinded fashion. The agreement between duplex scanning and angiography for the 383 arterial segments studied was not significantly different than the previously reported agreement between two different radiologists reading the same angiograms (kappa of 0.55 vs 0.63). For detecting stenoses that were greater than 50% diameter reducing by angiography, duplex scanning had a sensitivity of 82%, a specificity of 92%, a positive predictive value of 80%, and a negative predictive value of 93%. These results are as good as previously reported comparisons between two different radiologists' readings of the same angiograms.
Validation of Doppler-derived pulmonary arterial pressure in patients with ductus arteriosus under different hemodynamic states.
Authors: Musewe N N , Smallhorn J F , Benson L N , Burrows P E , Freedom R M
Published: June 2011

Twenty-nine patients with a patent ductus arteriosus (PDA) in isolation (n = 17) or in combination with other lesions (n = 12) underwent simultaneous hemodynamic assessment and evaluation of PDA flow velocity by the Doppler method. The accuracy with which Doppler velocity across the PDA predicted pulmonary arterial pressure and the influence of PDA size and shape on the Doppler velocity-pressure relationship were examined. Seventy percent had a cone-shaped PDA (narrowest at the pulmonary artery end), and the remainder were tubular. Narrowest PDA diameter ranged from 1.5 to 9 mm (mean 3.5 mm). Peak systolic and mean pulmonary arterial pressure ranged from 10 to 116 and 8 to 72 mm Hg, respectively. Twenty-one patients (group 1) had left-to-right shunting only. The following variables showed significant correlation in this group: peak instantaneous systolic aortic-to-main pulmonary arterial (MPA) pressure gradient and maximum Doppler velocity across the PDA (slope = 1.03, SEE = 13 mm Hg, r = .94, p less than .001), mean aortic-to-MPA pressure gradient and mean Doppler velocity (slope = 1.06, SEE = 10 mm Hg, r = .95, p less than .001), and end diastolic aortic-to-MPA pressure gradient and minimum Doppler velocity (slope = 1.12, SEE = 8 mm Hg, r = .96, p less than .001). Eight patients (group 2) had bidirectional shunting. In this group peak instantaneous aortic-to-MPA pressure gradient significantly correlated with maximum Doppler velocity measured from the left-to-right shunt (slope = .70, SEE = 2 mm Hg, r = .92, p less than .002) and mean pressure gradient correlated with mean Doppler velocity (slope = .83, SEE = 3 mm Hg, r = .78, p less than .003). Right-to-left Doppler velocities showed no correlation with pressures. In six patients with pulmonary hypertension Doppler velocity changes accurately predicted the effect of pulmonary vasodilation on pulmonary arterial pressure. Doppler velocity of PDA flow reliably predicts pulmonary arterial pressure over a wide range of pressures and PDA shapes and sizes.
Analysis of flow characteristics in poststenotic regions of the human coronary artery during bypass graft surgery.
Authors: Kajiya F , Tsujioka K , Ogasawara Y , Wada Y , Matsuoka S , Kanazawa S , Hiramatsu O , Tadaoka S , Goto M , Fujiwara T
Published: June 2011

Poststenotic blood flow velocities were evaluated in nine patients with 75% to 99% stenosis of the left anterior descending coronary artery (LAD) during coronary artery bypass graft surgery. We used the 20 MHz 80-channel pulsed Doppler velocimeter developed in our laboratory. An operator placed a specially designed probe on the native LAD with his fingers. Before induction of extracorporeal circulation, LAD blood velocities were measured at several locations distal to the stenosis. The poststenotic flow velocities were rich in systolic flow component with reduced diastolic component. The velocity configuration in the poststenotic portions was characterized by the presence of reverse flow velocities and/or irregularity of the velocity pattern near the vessel wall, indicating the existence of flow separation and recirculation in the regions. The broadening of the velocity spectrum observed at central axial regions suggested the occurrence of flow disturbances. After grafting, the velocity waveform in the LAD beyond a vein bypass graft changed to a diastolic-predominant pattern with a relatively small systolic component. A transient bypass graft occlusion caused a marked reduction in diastolic flow velocity. The systolic-to-diastolic velocity ratio increased from 0.27 +/- 0.07 to 1.50 +/- 0.50 (p less than .01) by the graft occlusion.
Long-term prognosis of patients with variant angina.
Authors: Walling A , Waters D D , Miller D D , Roy D , Pelletier G B , Théroux P
Published: June 2011

The long-term prognosis of variant angina and the factors influencing it were assessed in 217 consecutive patients hospitalized in our coronary care unit and followed for a mean of 65 months (range 2 to 123). Cardiac death occurred in 30 patients and an additional 54 experienced a nonfatal myocardial infarction. Survival at 1 and 5 years was 95% and 89%, respectively; survival without infarction was 83% and 69%. Coronary disease and the degree of disease activity were strong predictors of survival by Cox analysis. Survival at 1 year was 99%, and that at 5 years was 95% and 94%, respectively, for patients with one-vessel disease (n = 81) and for those without stenoses of 70% or greater (n = 87). Survival at 1 and 5 years was only 87% and 77% for those with multivessel disease (n = 40). The Cox analysis selected left ventricular function, initial treatment, extent score, duration of angina at rest, and disease activity as multivariate predictors of survival without infarction. Coronary disease was a strong predictor (p less than .0001) of survival without infarction by univariate analysis. Treatment with nifedipine, diltiazem, or verapamil improved survival without infarction compared with other medical treatment (p = .002). Myocardial infarction occurred most commonly soon after diagnosis in patients with a short history of angina at rest. Late coronary events were almost never preceded by resting angina.
Effect of acute human cardiac allograft rejection on left ventricular systolic torsion and diastolic recoil measured by intramyocardial markers.
Authors: Hansen D E , Daughters G T , Alderman E L , Stinson E B , Baldwin J C , Miller D C
Published: June 2011

Left ventricular systolic torsion and diastolic recoil were quantified in 12 human cardiac transplant recipients with surgically implanted intramyocardial markers with the use of computer-aided analysis of biplane cineradiographic images. Measurements were performed between 6 and 16 weeks after surgery and related to the presence or absence of rejection as determined by cardiac biopsy. Torsional deformation, defined as twisting about the left ventricular long axis of the apical region with respect to the base, was characterized in terms of the rate and amplitude of systolic torsion and the rate of diastolic recoil by means of an internal reference system. Comparison of measurements before, during, and after recovery from 14 rejection episodes allowed assessment of the effects of acute reversible cardiomyopathy on left ventricular torsion and recoil. Compared with prerejection values, the amplitude of torsional deformation in the maximally deforming segment (theta max) decreased by 25% from 21.1 +/- 15.2 to 16.0 +/- 5.7 degrees (p less than .005) during acute rejection with myocyte necrosis; this was associated with significant (p less than .05) decreases in the peak systolic torsion rate (+d theta/dtmax), whereas the peak diastolic recoil rate (-d theta/dtmax) was unchanged. This suggests that the stiffness of elastic components of the myocardium may have increased, maintaining the rate of diastolic recoil when these elements are stretched less. With successful treatment of rejection episodes, the torsional deformation characteristics normalized. Heart rate, mean arterial pressure, left ventricular end-diastolic volume, stroke volume, ejection fraction, and peak left ventricular filling rate were unchanged with rejection episodes, whereas left ventricular end-systolic volume increased (p less than .05) during acute rejection and returned to normal with resolution of the rejection process. These data suggest that left ventricular torsional deformation amplitude and rate are sensitive to episodes of subclinical left ventricular dysfunction and that such intramyocardial marker techniques may provide new insights regarding the elastic properties of the ventricular myocardium and their impact on left ventricular mechanics.
A validation of derived epicardial potential distributions by prediction of the coronary artery involved in acute myocardial infarction in humans.
Authors: Kilpatrick D , Walker S J
Published: June 2011

We have developed computer algorithms that enable epicardial potential distributions to be calculated from electrocardiographic body surface data. To validate this inverse transformation we obtained body surface maps during the ST segment in 55 patients with acute infarction who subsequently underwent coronary arteriography and we constructed epicardial ST segment potential distributions for each patient. From the unlabeled epicardial maps one of us predicted the coronary artery that would be found to be involved in the infarction. These predictions were compared with the results of coronary arteriography and this showed that the analysis of the epicardial map correctly predicted the coronary artery involved in 40 of 55 patients (72.7%). In another eight patients the anatomy was partially predicted. In the 15 patients in whom the prediction was incorrect or partially correct (27.3%), 11 had critical disease or occlusions of the predicted coronary artery but the infarct-related artery was incorrectly identified. This verifies that sensible epicardial potential maps can be calculated from body surface electrocardiographic data, and that these data are sufficiently accurate to predict the vessel involved in acute infarction.
Blood flow distribution within skeletal muscle during exercise in the presence of chronic heart failure: effect of milrinone.
Authors: Drexler H , Faude F , Höing S , Just H
Published: June 2011

Recent studies suggest that, in the presence of heart failure, the capability of skeletal muscle to utilize delivered flow may be impaired due to maldistribution of blood flow within working muscle. Similarly, this mechanism could explain the failure of drugs to improve maximal oxygen consumption (VO2max) immediately. Accordingly, we assessed muscular blood flow distribution (ml/min/g, radioactive microspheres, 15 +/- 5 micron) among and within working muscle, VO2max, and arterial lactate in a rat preparation of myocardial infarction and heart failure (infarct size 36.0 +/- 3.3% of the left ventricle, n = 9), and in sham-operated animals (n = 11). Data were obtained at maximal treadmill exercise during alternate infusions of milrinone and saline. Total skeletal muscle blood flow during exercise was significantly lower in the infarction group (p less than .05 vs sham); reduced blood flow was primarily attributed to decreased flow to oxidative working muscle such as soleus and the red portion of gastrocnemius, whereas blood flow to glycolytic muscle portions (e.g., gastrocnemius white, vastus lateralis white) was similar in the infarction and sham-operated groups. Milrinone increased flow to the glycolytic working muscle portions in sham-operated animals (e.g., vastus lateralis white, 0.23 vs 0.29, p less than .05); by contrast, blood flow to the oxidative muscle fibers was increased in the infarction group (e.g., gastrocnemius red, 1.45 vs 1.87, p less than .05). Arterial lactate levels at similar workloads during exercise were higher in the infarction group (p less than .05). Neither lactate nor VO2max were significantly altered with milrinone in either group.(ABSTRACT TRUNCATED AT 250 WORDS)
Inhibition of coronary atherosclerosis by propranolol in behaviorally predisposed monkeys fed an atherogenic diet.
Authors: Kaplan J R , Manuck S B , Adams M R , Weingand K W , Clarkson T B
Published: June 2011

We studied the effect of propranolol on the diet-induced coronary artery atherosclerosis (CAA) in 30 adult male cynomolgus monkeys living in social groupings of five animals each. Animals in the "treated" segment (n = 15) consumed propranolol, which was mixed into an atherogenic diet. Animals in the "untreated" group (n = 15) consumed only the atherogenic diet. Finally, the social groupings were subjected to disruption through monthly redistribution of monkeys among the groups within each treatment segment. The experiment lasted 26 months, following which all animals underwent autopsy during which the coronary arteries were evaluated for atherosclerosis. Regarding atherosclerosis, we observed a significant interaction between social status and experimental condition (p less than .03). Socially dominant animals had (as in previous studies) significantly exacerbated CAA, but only in the untreated segment; the effect of social dominance on CAA was abolished by long-term administration of propranolol. The antiatherogenic effect of propranolol on dominant animals was independent of the influences of serum lipid concentrations, blood pressure, and resting heart rate. We conclude that treatment with beta-adrenergic-blocking agents may confer a degree of protection against CAA among individuals behaviorally predisposed to coronary heart disease.
Overdrive suppression of conduction at the canine Purkinje-muscle junction.
Authors: Gilmour R F , Davis J R , Zipes D P
Published: June 2011

We have shown previously that overdrive suppression of conduction in depolarized His-Purkinje tissue requires conduction asymmetry. In this study we examined whether overdrive suppression of conduction can occur at the Purkinje-muscle junction, where natural asymmetry of conduction exists. Canine Purkinje-muscle preparations were superfused with hyperkalemic Tyrode's solution (KCl 8 to 12 mM), and action potentials were recorded from Purkinje, junctional, and muscle cells. Initially, the Purkinje fiber was paced at the shortest cycle length at which 1:1 anterograde Purkinje-muscle conduction occurred. The papillary muscle then was paced for 10 to 50 beats at shorter cycle lengths during which, because of conduction asymmetry at the Purkinje-muscle junction, 1:1 retrograde muscle-Purkinje conduction also occurred. After overdrive papillary muscle pacing, Purkinje fiber pacing at the same cycle length that previously resulted in 1:1 conduction now produced transient Purkinje-muscle conduction block (overdrive suppression of conduction). The degree and duration of overdrive suppression of conduction were proportional to the rate and duration of overdrive pacing. After overdrive pacing, Purkinje cell action potential amplitude and Vmax recovered within 300 msec, yet conduction block persisted for up to 7 sec. In contrast, excitability in papillary muscle cells near the Purkinje-muscle junction increased continuously after overdrive pacing. These data suggest that rapid activation of Purkinje cells during overdrive pacing was not required for overdrive suppression of conduction and that restoration of conduction after overdrive pacing was determined primarily by recovery of excitability in papillary muscle cells. Transient Purkinje-muscle conduction block after periods of rapid ventricular rates might account for overdrive-induced conduction disturbances normally attributed to bundle branch block.
Comparative influence of load versus inotropic states on indexes of ventricular contractility: experimental and theoretical analysis based on pressure-volume relationships.
Authors: Kass D A , Maughan W L , Guo Z M , Kono A , Sunagawa K , Sagawa K
Published: June 2011

We examined the quantitative influence of carefully controlled alterations in end-diastolic volume and afterload resistance on multiple simultaneously determined ejection and isovolumetric phase indexes of left ventricular contractile function in 23 isolated supported canine ventricles. The influence of load change on each index was compared with its sensitivity to inotropic stimulation, and this sensitivity was in turn contrasted to the response of the end-systolic pressure-volume relationship (ESPVR). Experimental data demonstrated various degrees of load sensitivity among the indexes, with a generally curvilinear relationship between load and index response for both preload and afterload alterations. The curvilinear nature of these relationships meant that over a select range of loading, many indexes demonstrated relative load independence. They also often displayed greater sensitivity to inotropic change than the ESPVR, and both factors help explain their enduring clinical utility. To further explore the influence of load and contractile state on several of the indexes, we developed a theoretical analysis, using variables common to pressure-volume relationships, in which these dependencies could be derived. The theoretical models fit very well with the experimental data, and reaffirmed the frequently curvilinear nature of the relationships. We conclude that while many clinical indexes of ventricular contractile function show significant load dependence, the information they provide can be reasonably interpreted within defined ranges of load and inotropic alteration. Any advantage of the ESPVR will derive not from the magnitude of its response to inotropic change, which is smaller than most other indexes, but from its relative insensitivity to load alteration over a wider range of load.
Marked platelet activation in vivo after intravenous streptokinase in patients with acute myocardial infarction.
Authors: Fitzgerald D J , Catella F , Roy L , FitzGerald G A
Published: June 2011

We assessed thromboxane biosynthesis as an index of platelet activation in 6 patients with acute myocardial infarction receiving intravenous streptokinase. Urinary 2,3-dinor-thromboxane B2 and plasma 11-dehydro-thromboxane B2, major enzymatic metabolites of thromboxane A2, were markedly increased after intravenous streptokinase (11,063 +/- 2758 pg/mg creatinine and 33 +/- 10 pg/ml, respectively) compared with levels in patients not receiving thrombolytic therapy (502 +/- 89 pg/mg creatinine and 3 +/- 0.7 pg/ml). Prostacyclin biosynthesis also increased markedly after streptokinase coincident with the increase in thromboxane A2 formation. Administration of aspirin between the time of onset of coronary thrombosis and reperfusion both in man and in a canine preparation demonstrated that this reflected thromboxane biosynthesis de novo and not metabolism of preformed inactive thromboxane B2 washed out from the coronary circulation. Since the platelet is the major source of thromboxane A2, these findings suggest that there is marked platelet activation after coronary thrombolysis with streptokinase. Studies in vitro demonstrated that streptokinase enhanced platelet activation in a dose-dependent manner, resulting in the secondary release of thromboxane A2. The increase in platelet activation and thromboxane A2 biosynthesis may limit the therapeutic effect of intravenous streptokinase in acute myocardial infarction.
Cardiorespiratory responses to exercise training after orthotopic cardiac transplantation.
Authors: Kavanagh T , Yacoub M H , Mertens D J , Kennedy J , Campbell R B , Sawyer P
Published: June 2011

We have tested the feasibility and effectiveness of a 2 year (average 16 +/- 7 months) walk/jog exercise program on 36 male orthotopic cardiac transplant patients (21 to 57 years old) seen initially 2 to 23 months after surgery. Comparison of initial exercise test results with those in 45 age-matched normal men showed the patients to have a lesser lean body mass (56 +/- 7 vs 63 +/- 8 kg, p less than .001), with a higher resting heart rate (104 +/- 12 vs 77 +/- 14 beats/min, p less than .001) and systolic (138 +/- 16 vs 129 +/- 17 mm Hg, p less than .001) and diastolic (95 +/- 14 vs 84 +/- 10 mm Hg, p less than .001) blood pressures. Peak power output was less than normal (101 +/- 27 vs 219 +/- 41 W, p less than .001), as was peak heart rate (136 +/- 15 vs 176 +/- 13 beats/min, p less than .001), peak oxygen intake (VO2max) (22 +/- 5 vs 34 +/- 6 ml.kg.min-1, p less than .001), and absolute anaerobic threshold (1.18 +/- 0.40 vs 2.04 +/- 0.40 liters.min-1, p less than .001). Peak ventilatory equivalent was higher (48 +/- 9 vs 37 +/- 61.1-1, p less than .001). Cardiac output (Q), as estimated by the CO2 rebreathing method, was slightly above normal at rest (p less than .01), but below normal at two submaximal work rates. The group's average weekly training distance was 24 km, with eight highly compliant patients progressing to 32 km or more weekly. After training, lean tissue increased (+2.4 +/- 3.1 kg, p less than .001), and resting values were reduced for heart rate (-4 +/- 11 beats/min, p less than .05), systolic (-13 +/- 20 mm Hg, p less than .001), and diastolic (-9 +/- 17 mm Hg, p less than .001) blood pressures. There were significant reductions in submaximal values for minute ventilation (VE), ratings of perceived exertion, and diastolic blood pressure at equivalent workloads. Peak values increased for power output (+49 +/- 34 W, p less than .001), VO2max (+4.0 +/- 6.0 ml.kg.min-1, p less than .001), VE (+20 +/- 20 l.min-1, p less than .001), and heart rate (+13 +/- 17 beats/min, p less than .001), and decreased for diastolic blood pressure (-8 +/- 15 mm Hg, p less than .001).(ABSTRACT TRUNCATED AT 400 WORDS)
Influence of compression rate on initial success of resuscitation and 24 hour survival after prolonged manual cardiopulmonary resuscitation in dogs.
Authors: Feneley M P , Maier G W , Kern K B , Gaynor J W , Gall S A , Sanders A B , Raessler K , Muhlbaier L H , Rankin J S , Ewy G A
Published: June 2011

The influence of chest compression rate on initial resuscitation success and 24 hr survival after prolonged manual cardiopulmonary resuscitation (CPR) was investigated in 26 morphine-anesthetized dogs (17 to 30 kg). After placement of aortic and right atrial micromanometers and induction of ventricular fibrillation, manual CPR was commenced immediately and continued for 30 min. One group of 13 dogs underwent manual CPR at a compression rate of 60/min, and the other group at a rate of 120/min. The compression durations in the two groups were not significantly different (51.7 +/- 1.8% at 60/min vs 51.6 +/- 1.9% at 120/min). No drugs other than sodium bicarbonate were administered during CPR. A maximum of three attempts was permitted to defibrillate the heart. Successfully defibrillated animals were followed for 24 hr, during which time no treatment, other than naloxone, was given to reverse the effects of morphine. Arterial blood pH, PCO2, and PO2 were not significantly different in the two groups throughout the CPR period. When compared with the compression rate of 60/min, the compression rate of 120/min produced more successfully defibrillated animals (12/13 at 120/min vs 2/13 at 60/min, p less than .002) and more 24 hr survivors (8/13 at 120/min vs 2/13 at 60/min, p less than .03). All 24 hr survivors were conscious and able to sit, stand, and drink normally. One 24 hr survivor in each group had difficulty walking. Improved survival with the high-rate compression technique was consistent with the significantly higher mean aortic (systolic and diastolic) and coronary perfusion pressures attained with high-rate compressions (all p less than .002). Although the clinical applicability of these findings has yet to be demonstrated, they provide empirical support for the recent decision to increase the chest compression rate for manual CPR recommended by the American Heart Association, and indicate that the hemodynamic and survival benefits of faster compression rates in this experimental preparation were not dependent on covariant alterations in compression duration.
Circadian occurrence of symptomatic paroxysmal supraventricular tachycardia in untreated patients.
Authors: Irwin J M , McCarthy E A , Wilkinson W E , Pritchett E L
Published: June 2011

Fifty-two patients with paroxysmal supraventricular tachycardia were studied to determine whether there was a circadian pattern to the occurrence of this arrhythmia. Antiarrhythmic therapy was discontinued, and patients were followed until they had one recurrence of tachycardia documented by telephone transmission of the electrocardiogram. By least-squares analysis, the times of day that the 52 attacks (one from each patient) occurred were fit to a sinusoidal density function with a period of 24 hr. The highest relative incidence of tachycardia was at 4 P.M.; tachycardia was five times more likely to occur at 4 P.M. than at 4 A.M., the time of the lowest relative incidence. A second attack of tachycardia was recorded from 35 of the 52 patients. The times of the two attacks in individual patients were found to be independent; thus the times of day at which the second attacks occurred were used as a test set for the distribution estimated from the first. The empirical distribution for the times from the 35 second attacks was compared with the distribution function estimated from the 52 first attacks, and there was no significant departure; this finding confirmed the circadian pattern. Since the relative incidence of attacks of paroxysmal supraventricular tachycardia is higher in the afternoon, it may be helpful to target antiarrhythmic therapy to that time of day.
New diagnostic evidence on the T wave map indicating involved coronary artery in patients with angina pectoris.
Authors: Ishikawa T , Watabe S , Yamada Y , Miyachi K , Sakai Y , Ito A , Sotobata I
Published: June 2011

To define the clinical significance of T wave map changes in patients with angina at rest, body surface isopotential T distributions were obtained in 48 patients with single-vessel disease (left anterior descending artery, 34; right coronary artery, eight; left circumflex artery, six) documented angiographically and were compared with those in 120 healthy subjects and those in 19 patients with left ventricular overload whose electrocardiograms showed negative T waves accompanied by an increase in R wave amplitude in left precordial leads. The T wave map abnormalities were observed in 24 of 48 patients (50%) with angina and were classified into three types: (1) type I (18 patients, 37.5%) was characterized by a segmental negative potential in the positive area located at the left thorax and the minimum at the peak of T wave positioned in the upper portion of the left anterior chest, (2) type II (three patients, 6.3%) was characterized by a negative potential with a minimum in the inferior thorax and an indentation of negative potential at the lower margin of the positive potential located over the upper thorax, and (3) type III (three patients, 6.3%) was characterized by a negative potential with a minimum at the back throughout the period of T wave. All patients showing T wave map abnormalities of type I had a significant stenosis of the left anterior descending artery. Likewise, all patients with type II or III had single-vessel disease of the right coronary or left circumflex artery, respectively. All types of T wave map changes observed in patients with angina were different from those in patients with left ventricular overload, whose maps showed the generalized negative potential at the inferior thorax and the left back and the minima clustered at the precordium. In seven patients with lesions of the left anterior descending artery, T wave map abnormalities of type I recovered to normal after successful percutaneous transluminal coronary angioplasty. The behavior of the negative potential and its extrema on the T wave map, which was not available from routine electrocardiography, was indicative of the involved coronary artery and probably of its associated ischemic area in one-half of our patients with angina pectoris.
Doppler mapping of postoperative left atrioventricular valve regurgitation.
Authors: Meijboom E J , Wyse R K , Ebels T , Deanfield J E , Quaegebeur J M , Anderson R H , Brenner J I
Published: June 2011

Left atrioventricular valve regurgitation often occurs as a postoperative hemodynamic complication from repair of an atrioventricular septal defect. In this study, cross-sectional two-dimensional Doppler flow mapping of the left atrium was used to quantify postoperative regurgitant flow in 29 patients. Its severity and location was related to the shape of the three leaflets of the left component of the atrioventricular valve, especially to the size of the mural leaflet. To identify which leaflet configuration was likely to cause regurgitation, the position of the leaflets was obtained from the parasternal short-axis view and the angular size of the mural leaflet expressed in degrees of an arc. Doppler mapping was performed in the apical four-chamber and the parasternal long-axis views, dividing the left atrium in nine squares in each. Regurgitation was defined as a jetlike systolic downstroke of the Doppler frequency shift in early systole. The angular size of the mural leaflet varied from 38 to 144 degrees (mean 86 +/- 36 SD). Massive regurgitation (six to nine sites) was encountered in seven patients, five with a mural leaflet size of over 110 degrees, one with mural leaflet size between 70 and 110 degrees, and one with a mural leaflet size of under 70 degrees. No or minimal regurgitation was encountered in 10 patients, three having a mural leaflet size of 70 to 110 degrees and seven with a mural leaflet size of less than 70 degrees. These data suggest that massive regurgitation is encountered in patients with large mural leaflets, whereas patients with smaller mural leaflets tend to have no or mild regurgitation.(ABSTRACT TRUNCATED AT 250 WORDS)
Quantitative rotational thallium-201 tomography for identifying and localizing coronary artery disease.
Authors: DePasquale E E , Nody A C , DePuey E G , Garcia E V , Pilcher G , Bredlau C , Roubin G , Gober A , Gruentzig A , D'Amato P
Published: June 2011

The purpose of this study was to develop and validate a method for quantifying the uptake, redistribution, and washout of thallium-201 (201Tl) obtained with rotational tomography. This method generates maximum count circumferential profiles of the short-axis slices of the left ventricle, translates them into polar coordinate profiles, and displays them as a bullseye plot, which consists of a series of concentric circles with the apex at the center and the base at the periphery. Normal limits were established for the distribution of 201Tl in 36 patients with a low (less than 5%) probability of coronary artery disease (CAD). Forty-five patients who had undergone coronary angiography were used as a pilot group to define criteria for the identification and localization of perfusion defects. The best agreement with the results of angiography was found when abnormal regions of the bullseye were defined as contiguous defects over 2.5 SDs below normal. These criteria were applied prospectively to 210 points (179 points with greater than 50% diameter stenosis and 31 with less than 50%). Visual, quantitative, and combined visual and quantitative analysis were compared for overall detection of disease and for detection of individual vessel involvement. The overall sensitivity for detection of disease by these methods was 97%, 95%, and 95%, respectively. The specificities were 68%, 74%, and 71% respectively. The sensitivity for detection of individual vessel involvement with the bullseye alone was 78% for the left anterior descending artery (LAD), 89% for the right coronary artery (RCA), and 65% for the left circumflex (LCx). For visual analysis, the results were 70%, 88%, and 50%, respectively, while the use of visual and quantitative analysis combined identified 75% of LAD, 87% of RCA, and 55% of LCx lesions. We conclude that quantitative analysis of rotational 201Tl tomographic images is a highly accurate technique for determining the presence and location of CAD.