bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous recording of action potentials from endocardium and epicardium during ischemia in the isolated cat ventricle: relation of temporal electrophysiologic heterogeneities to arrhythmias.
Authors: Kimura S , Bassett A L , Kohya T , Kozlovskis P L , Myerburg R J
Published: June 2011

We studied the effects of ischemia on transmembrane action potentials, conduction time, and refractory periods of both endocardial and epicardial muscle cells of coronary-perfused cat left ventricles. Oxygenated Tyrode's solution was perfused through the left anterior descending coronary artery, while the preparation was superfused with Tyrode's solution gassed with 95% N2 and 5% CO2. Transmembrane action potentials recorded simultaneously from endocardial and epicardial cells were normal during coronary perfusion. When perfusion was discontinued ("ischemia"), rapid deterioration of action potentials and prolongation of conduction time were observed in both endocardial and epicardial cells. The magnitude of the reduction of action potential amplitude and action potential duration (APD), and of prolongation of conduction time, was greater in epicardial cells than in endocardial cells, although the change in resting membrane potential was almost the same. However, APD of endocardial cells decreased progressively during 30 min of ischemia, whereas APD of epicardial cells was reduced maximally at 10 min and then partially recovered. Shortening of refractory periods of endocardial cells paralleled APD shortening, whereas refractory periods of epicardial cells decreased for the first 10 min and then increased. At 10 min of ischemia, APD and refractory periods of epicardial cells were significantly shorter than those of endocardial cells. At 30 min of ischemia, refractory periods of epicardial cells exceeded those of endocardial cells because of development of greater postrepolarization refractoriness in epicardial cells. Accompanying these different changes in APD and refractory periods of endocardial and epicardial cells, spontaneous extrasystolic impulses increased and rapid runs of extrasystolic impulses could be induced by extrastimuli.(ABSTRACT TRUNCATED AT 250 WORDS)
The preexcitation index: an aid in determining the mechanism of supraventricular tachycardia and localizing accessory pathways.
Authors: Miles W M , Yee R , Klein G J , Zipes D P , Prystowsky E N
Published: June 2011

In this study we sought to determine whether characteristics of ventricular-induced atrial preexcitation during reciprocating tachycardia could help differentiate atrioventricular (AV) nodal reentry from orthodromic AV reentry using an accessory pathway and to identify the site of accessory pathways in patients with Wolff-Parkinson-White syndrome. Fifty-five patients with orthodromic AV reciprocating tachycardia and 22 patients with AV nodal reentrant tachycardia were studied with standard electrophysiologic techniques. There were 24 left free wall, 23 posterior septal, seven anterior septal, and one right free wall accessory pathways. Progressively premature right ventricular complexes (V2) were introduced during reciprocating tachycardia (V1V1). The V1V1 interval during tachycardia minus the longest V1V2 at which atrial preexcitation occurred defined a preexcitation index (PI). Atrial preexcitation occurred in 49 of 55 (89%) patients with AV reentry compared with only three of 22 (14%) patients with AV nodal reentry (p less than .001). In the three patients with AV nodal reentry who demonstrated atrial preexcitation, the PI was distinct from that of the septal pathways and was in the upper range of values for left free wall pathways. The percentage of tachycardias demonstrating atrial preexcitation was not different between the free wall and septal pathways, but His bundle activation was visible at the time of atrial preexcitation in only six of 17 (35%) left free wall compared with 13 of 16 (81%) posterior septal and seven of seven (100%) anterior septal pathways (p less than .05 free wall vs posterior or anterior septal).(ABSTRACT TRUNCATED AT 250 WORDS)
Vector mapping of myocardial activation.
Authors: Kadish A H , Spear J F , Levine J H , Hanich R F , Prood C , Moore E N
Published: June 2011

A custom-made probe, consisting of four electrodes arranged so that two orthogonal bipolar electrograms could be recorded from a single site, was used to record epicardial activity during atrial and ventricular pacing in five normal and five anesthetized open-chest mongrel dogs with myocardial infarction. Unfiltered bipolar electrograms recorded with a 2 mm interelectrode distance averaged 36 +/- 15 mV in amplitude and 16 +/- 5 msec in duration in normal areas and 14 +/- 11 mV and 23 +/- 12 msec in infarcted areas (p less than .01 infarct vs normal). The bipolar electrograms were vector summed so that a vector loop could be generated at each site. The direction of epicardial impulse propagation as determined by multipoint isochronal activation mapping was compared with that indicated by maximum x,y deflection of the vector loop. At 203 sites (141 normal and 62 infarcted) there was a median error of only 13 degrees and an excellent correlation by linear regression (r2 = .95). In normal myocardium vector loops were straight (60%), open (21%), or hooked (19%). In infarcted myocardium, notched and irregular loops were occasionally seen. However, a clear maximum x,y deflection was still obtained from 98% of infarcted sites. During ventricular pacing in normal dogs, uniform epicardial conduction was observed for up to 4 cm longitudinal to fiber orientation but only 1 cm transverse to it. At selected sites longitudinal to fiber orientation conduction velocity was 0.618 m/sec, electrogram duration 12 msec, and vector amplitude 76 mV compared with 0.304 m/sec, 18 msec, and 38 mV during conduction transverse to fiber orientation (p less than .05 for all comparisons). Vector mapping of epicardial activation was performed during ventricular tachycardia induced by programmed stimulation in two of five 2-week-old canine myocardial infarcts. Aside from minor irregularities caused by impulse spread around areas of block, vector loops indicated when impulses were spreading away from the area of early epicardial activity and thus directed mapping to the region of earliest activation. We conclude that vector loops generated by summing orthogonal local bipolar electrograms accurately represent the direction of epicardial activation in both normal and infarcted myocardium. Such loops may prove useful in mapping tachycardias and in clarifying details about cardiac activation processes.
Risk stratification for 1 year survival based on characteristics identified in the early hours of acute myocardial infarction. The Western Washington Intracoronary Streptokinase Trial.
Authors: Stadius M L , Davis K , Maynard C , Ritchie J L , Kennedy J W
Published: June 2011

We evaluated the relationship between baseline factors defined at 4.6 +/- 2.1 hr after onset of acute myocardial infarction and 1 year survival in 245 patients entered in the Western Washington Intracoronary Streptokinase Trial. Univariate statistics identified a significant relationship between 10 of these factors and survival. Multivariate analysis identified three factors as being most closely related to survival: (1) left ventricular ejection fraction (LVEF) (p less than .0001), (2) treatment with streptokinase (p = .03), and (3) location of infarction (p = .04). Mathematic models based on this analysis and applied to our patients identified high- and low-risk subgroups for 1 year mortality. Patients receiving standard, not interventional, therapy with anterior infarction and an LVEF of 50% or less and those with inferior infarction and an LVEF of 39% or less comprised the high-risk group. For patients receiving standard therapy, 1 year mortality was 41% in the high-risk group and 4% in the low-risk group. The models illustrated the magnitude of benefit of streptokinase treatment and achievement of complete reperfusion for those at low and high risk. We conclude that LVEF determined in the first hours of acute myocardial infarction is the most important of all baseline factors for prediction of 1 year survival. Mathematic models based on left ventricular function measured as ejection fraction are useful for risk stratification in this setting.
Myocardial infarction in young patients: an analysis by age subsets.
Authors: Hoit B D , Gilpin E A , Henning H , Maisel A A , Dittrich H , Carlisle J , Ross J
Published: June 2011

We examined, in age subsets, 2643 patients with acute myocardial infarction. Clinical features and 1 year morbidity and mortality were compared in 203 young patients (less than 45 years), 1671 patients 46 to 70 years old, and 769 elderly patients (greater than 70 years). Ninety-two percent of young patients were men, and a family history of premature coronary artery disease was more common in young patients (41% compared with 28% of middle-aged and 12% of elderly patients). More young patients were currently smoking cigarettes (82% compared with 56% of middle-aged and 24% of elderly patients), and only 8% of young patients had never smoked. Previous myocardial infarction and history of angina pectoris or congestive heart failure were less common (p less than .001) in the young patients than in middle-aged and elderly patients. In-hospital mortality was only 2.5% for young patients, compared with 9.0% in middle-aged and 21.4% in elderly patients (both p less than .001). Postdischarge 1 year mortality was also strikingly low in young patients, at 2.6% compared with 10.3% in middle-aged and 24.4% in elderly patients. The incidence of reinfarction during the 1 year of follow-up was similar in all subsets. The statistical significance of 65 variables as predictors of 1 year mortality and reinfarction was tested and the following found to be significant (p less than .05): hospital discharge on antiarrhythmic drugs, digoxin, or diuretics; history of previous myocardial infarction or congestive heart failure; chest x-ray findings of heart failure; low ejection fraction; and atrial fibrillation. Thus, young patients entering the hospital have an excellent 1 year prognosis, but those with prior infarction in whom there are selected abnormal findings at hospital discharge comprise a subgroup that may benefit from early aggressive management.
Resetting response patterns during sustained ventricular tachycardia: relationship to the excitable gap.
Authors: Almendral J M , Stamato N J , Rosenthal M E , Marchlinski F E , Miller J M , Josephson M E
Published: June 2011

We analyzed the resetting response (a noncompensatory pause after electrical stimulation) during 37 hemodynamically tolerated ventricular tachycardias (VTs) induced by programmed electrical stimulation in 32 patients with chronic coronary artery disease. The mean cycle length of VT was 369 +/- 59 msec. Single extrastimuli were delivered at the right ventricular apex during all 37 VTs, and double extrastimuli were delivered at the same site during 23 VTs. The resetting response pattern was considered increasing, decreasing, or flat if the return cycle increased, decreased, or remained constant in response to progressively shorter coupling intervals of the extrastimuli. Ten VTs had an increasing pattern and nine a flat pattern. In 11 VTs the pattern was mixed (flat at longer coupling intervals and increasing at shorter ones), and in the remaining seven the pattern could not be defined. No VT had a decreasing pattern. The mean duration of the resetting interval (range of coupling intervals resulting in resetting) was 66 +/- 45 msec, or 17% of the cycle length of VT. VT with a mixed pattern had longer resetting intervals than VT with an increasing pattern (102 +/- 34 vs 64 +/- 40 msec; p less than .035); however, cycle lengths of VT were similar (370 +/- 58 vs 386 +/- 86, p = NS). An excellent correlation was observed between the shortest return cycles in response to single and double extrastimuli (r = .99), with a mean difference of 5 msec. The cycle length of VT exceeded the return cycle (measured to the QRS onset) during 15 VTs (41%).(ABSTRACT TRUNCATED AT 250 WORDS)
Association of levels of lipoprotein Lp(a), plasma lipids, and other lipoproteins with coronary artery disease documented by angiography.
Authors: Dahlen G H , Guyton J R , Attar M , Farmer J A , Kautz J A , Gotto A M
Published: June 2011

In a study of 307 white patients who underwent coronary angiography, the relationship of coronary artery disease (CAD) to plasma levels of lipoprotein Lp(a) and other lipid-lipoprotein variables was examined. Lp(a) resembles low-density lipoprotein (LDL) in several ways, but can be distinguished and quantified by electroimmunoassay. CAD was rated as present or absent and was also represented by a quantitative lesion score derived from estimates of stenosis in four major coronary vessels. Coronary lesion scores significantly correlated with Lp(a), total cholesterol, triglycerides, LDL cholesterol, and high-density lipoprotein (HDL) cholesterol levels by univariate statistical analysis. By multivariate analysis levels of Lp(a) were associated significantly and independently with the presence of CAD (p less than .02), and tended to correlate with lesion scores (p = .06). Among subgroups Lp(a) level was associated with CAD in women of all ages and in men 55 years old or younger. An apparent threshold for coronary risk occurred at Lp(a) lipoprotein mass concentrations of 30 to 40 mg/dl, corresponding to Lp(a) cholesterol concentrations of approximately 10 to 13 mg/dl. Plasma Lp(a) in white patients appears to be a major coronary risk factor with an importance approaching that of the level of LDL or HDL cholesterol.
Validation of continuous-wave Doppler echocardiographic measurements of mitral and tricuspid prosthetic valve gradients: a simultaneous Doppler-catheter study.
Authors: Wilkins G T , Gillam L D , Kritzer G L , Levine R A , Palacios I F , Weyman A E
Published: June 2011

For patients with stenotic native valves, the modified Bernoulli equation (delta P = 4V2) may be applied to Doppler-measured transvalvular velocities to yield an accurate estimate of transvalvular gradients. Although it would be useful if the same approach could be used for those with stenotic prosthetic valves, no previous study has validated the Doppler technique in this setting. We therefore recorded simultaneous continuous-wave Doppler flow profiles and transvalvular manometric gradients in 12 catheterized patients in whom all atrial and ventricular pressures were directly measured (transseptal left atrial catheterization and transthoracic ventricular puncture were performed where necessary). A total of 13 prostheses were studied: 11 mitral (seven porcine, three Starr-Edwards, and one Björk-Shiley) and two tricuspid (one porcine and one Björk-Shiley). The Doppler-determined mean gradient was calculated as the mean of the instantaneous gradients (delta P = 4V2) at 10 msec intervals throughout diastole. The correlation of simultaneous Doppler (DMG) and manometric mean gradients (MG) for the whole group (n = 13) demonstrated a highly significant relationship (MG = 1.07 DMG + 0.28; r = .96, p = .0001). The correlation was equally good for porcine valves alone (n = 8) (MG = 1.06 DMG + 0.55; r = .96, p = .001) and for mechanical valves alone (n = 5) (MG = 1.06 DMG - 0.04; r = .93, p = .02). In a subset of patients without regurgitation (n = 8), prosthetic valve areas were estimated by two Doppler methods originally described by Holen and Hatle, as well as by the invasive Gorlin method. As expected from theoretical considerations, a close correlation was not demonstrated between results of the Gorlin method and those of either Hatle's Doppler method (r = .65, fp = NS) or Holen's method (r = .14, p = NS). Comparison of the results of the two Doppler methods yielded a somewhat closer correlation (r = .73, p less than or equal to .05). These results suggest that in patients with disk-occluder, ball-occluder, and porcine prosthetic valves, Doppler estimates of transvalvular gradients are virtually identical to those obtained invasively.
Amiodarone versus amiodarone and a type IA agent for treatment of patients with rapid ventricular tachycardia.
Authors: Marchlinski F E , Buxton A E , Miller J M , Vassallo J A , Flores B T , Josephson M E
Published: June 2011

Induction of rapid ventricular tachycardia or fibrillation during therapy with amiodarone is associated with an increased risk of sudden death. To determine whether the addition of a type IA antiarrhythmic agent to therapy would improve outcome, 37 patients in whom ventricular tachyarrhythmia of a cycle length less than 350 msec was induced after 14 +/- 2 days of amiodarone were randomly assigned to therapy with amiodarone alone (group 1, 20 patients) or amiodarone plus type IA agent (group 2, 17 patients). Type IA therapy consisted of procainamide in 13 patients and quinidine in four procainamide-intolerant patients. To assess the short-term effects of a type IA agent on inducibility of ventricular tachyarrhythmia, cycle length, and hemodynamic tolerance, 16 of 20 patients in group 1 and all patients in group 2 underwent repeat programmed stimulation after the intravenous administration of procainamide during amiodarone therapy (mean procainamide serum concentration 7.2 +/- 2.0 micrograms/ml). Procainamide prevented induction of sustained arrhythmia in only two of 33 patients. Procainamide increased the cycle length of induced ventricular tachycardia from 283 +/- 30 to 352 +/- 46 msec (p less than .001). After the addition of procainamide, 16 of 31 patients vs 10 of 37 patients on amiodarone alone had an induced arrhythmia that was tolerated hemodynamically (p less than .05). There were no differences between groups 1 and 2 with respect to patient or arrhythmia characteristics, response to short-term procainamide, or duration of follow-up. The mean follow-up for all patients was 14 +/- 10 months.(ABSTRACT TRUNCATED AT 250 WORDS)
The use of frequency histograms of ultrasonic backscatter amplitudes for detection of atherosclerosis in vitro.
Authors: Picano E , Landini L , Lattanzi F , Mazzarisi A , Sarnelli R , Distante A , Benassi A , L'Abbate A
Published: June 2011

This study was designed to determine whether a quantitative analysis of integrated backscatter amplitude distribution is potentially useful in characterizing the atherosclerotic lesion. One hundred measurements (10 X 10 array) were made in fresh aortic regions (2 cm X 2 cm) of nine normal and 19 atherosclerotic arterial walls. A 10 MHz transducer was used. The integrated backscatter distinguished normal from atherosclerotic specimens (-56.7 +/- 4.3 vs -42.5 +/- 8.9 dB, p less than .01). The shape of the integrated backscatter amplitude distribution was analyzed by calculation of skewness and kurtosis of each arterial region. Both skewness values (0.134 +/- 0.325 vs -0.193 +/- 0.491 in normal and atherosclerotic segments, respectively, p = NS) and kurtosis values (0.055 +/- 0.765 vs -0.610 +/- 0.379, p less than .01) discriminated between the two groups. When only the six atherosclerotic specimens with mostly fatty and fibrofatty sites were considered, skewness and kurtosis still distinguished normal from atherosclerotic regions (0.134 +/- 0.325 vs -0.404 +/- 0.232, p less than .05 and 0.055 +/- 0.765 vs -0.558 +/- 0.337, p less than .05, respectively), while integrated backscatter values did not (-56.7 +/- 4.5 vs -52.3 +/- 6.1 dB, p = NS). In conclusion, atherosclerosis may be detected in vitro by the quantitative analysis of integrated backscatter distribution. This variable could also be of help in the identification of less obvious forms of atherosclerotic disease that are not distinguishable on the basis of integrated backscatter amplitude.
Quantitation of absolute area of a coronary arterial stenosis: experimental validation with a preparation in vivo.
Authors: Wiesel J , Grunwald A M , Tobiasz C , Robin B , Bodenheimer M M
Published: June 2011

The absolute cross-sectional area of a coronary stenosis measured by quantitative coronary angiography correlates well with its hemodynamic significance. We evaluated a combined approach using edge detection applied to the normal segment and videodensitometry applied to the stenosis to determine the absolute cross-sectional area of the stenosis (videodensity method). The results were then compared with those with the edge detection method applied directly to the stenosis. The area of the stenosis by the edge detection method was calculated by analyzing two orthogonal projections for irregular stenoses and with use of the formula for the area of an ellipse (ellipse method). The accuracy of both these techniques was assessed by analyzing digital angiograms acquired from closed-chest dogs in which 10 plastic cylinders with precisely machined circular and irregular lumina were inserted into the coronary arteries. Angiograms of irregular stenoses were acquired in two orthogonal views. The ellipse method applied to circular stenoses was very accurate, with r = .97, average absolute difference (AAD) = 0.21 mm2, and SEE = 0.30. For the videodensity method r = .97, AAD = 0.84 mm2, and SEE = 0.40. Irregular stenoses were better quantitated by the videodensity method applied in one view (AAD = 0.50 mm2, SEE = 0.47) than by the ellipse method applied in two orthogonal projections (AAD = 1.03 mm2, SEE = 0.87). Overall, the two methods were comparable in accuracy (for videodensity, AAD = 0.65 mm2, SEE = 0.71 vs AAD = 0.54 mm2, SEE = 0.79 for ellipse).(ABSTRACT TRUNCATED AT 250 WORDS)
The subendocardial border zone during acute ischemia of the rabbit heart: an electrophysiologic, metabolic, and morphologic correlative study.
Authors: Wilensky R L , Tranum-Jensen J , Coronel R , Wilde A A , Fiolet J W , Janse M J
Published: June 2011

Isolated preparations of rabbit interventricular septum were perfused through the coronary arteries with oxygenated Tyrode's solution and placed in a tissue bath where they were superfused as well. Transmembrane potentials were simultaneously recorded from the subendocardium with two flexibly mounted microelectrodes, one from a superficial cell, and the other from a deep cell. Ischemia was produced by stopping coronary flow while superfusion with oxygenated Tyrode's solution was maintained. After a 7 to 12 min ischemic period, the preparation was fixed by coronary perfusion with fixative while the microelectrodes remained in place. After fixation, the microelectrodes were withdrawn. Appropriate tissue blocks were cut in 4 micron serial sections and the microelectrode track was followed until the tip position was identified. Transmembrane potentials during ischemia were divided into two categories: "border zone" potentials (resting membrane potential [RMP] 73 +/- 3 mVe, action potential amplitude [APA] 81 +/- 13 mV, action potential duration [APD] 116 +/- 48 msec, n = 12) and "ischemic" potentials (RMP 53 +/- 4 mV, APA 44 +/- 11 mV, APD 102 +/- 42 msec, n = 8). Ischemic potentials were recorded from cells at depths greater than 560 micron below the endocardial surface and border zone potentials were recorded in a layer at between 130 and 650 micron below the surface. In a separate series of experiments, extracellular concentrations of K+ and pH were measured with ion-sensitive electrodes at different depths and, after a 10 min period of ischemia, part of the septum was placed in liquid nitrogen to allow determination of phosphocreatine (PC) levels in successive 50 to 100 micron layers. After 10 min of ischemia, extracellular K+ gradually increased from 4 to 9 mM in endocardium to a depth of 600 micron, pH fell from 7.4 to 6.6 over the same distance, and PC decreased to very low, stable levels at only 800 micron. It is concluded that in the first 10 min of acute ischemia, an endocardial border zone exists of 40 to 60 cell layers in which transmembrane potentials are affected relatively little by ischemia. Within this electrophysiologic border zone extracellular K+ was lower than 9 mM, pH was higher than 6.6, and tissue content of PC was not lower than 40% of normal. In layers deeper than 600 micron, with further development of a metabolic gradient, action potentials became markedly depressed. This electrophysiologic inhomogeneity within the ischemic subendocardium could be a factor in arrhythmogenesis during the first minutes of ischemia.
Assessment of the beta-adrenergic receptor pathway in the intact failing human heart: progressive receptor down-regulation and subsensitivity to agonist response.
Authors: Fowler M B , Laser J A , Hopkins G L , Minobe W , Bristow M R
Published: June 2011

We developed methods for identifying beta-adrenergic receptors in human right ventricular endomyocardial biopsy tissue with the radioligand (-)[125I]iodocyanopindolol (ICYP). Specific ICYP binding in a crude, high-yield membrane preparation derived from endomyocardial biopsy tissue was high (specificity greater than 90%), of high affinity (KD around 20 pM), saturable and stereospecific for the (-) vs the (+) isomer of isoproterenol. Subjects with mild-moderate and severe biventricular dysfunction had respective decreases in beta-adrenergic receptor density of 38.2% and 57.7% when normalization methods were averaged, with no significant differences in ICYP dissociation constant. A subgroup of subjects was subdivided by left ventricular ejection fraction (LVEF) into those with mild cardiac dysfunction (LVEF less than 0.50 greater than 0.40) and severe heart failure (LVEF less than 0.20) and given graded sequential infusions of dobutamine and calcium gluconate. Those with severe cardiac dysfunction had marked impairment of the dobutamine dP/dt and stroke work index response, whereas these responses to calcium did not differ in the two groups. These data indicate that in the intact human heart endomyocardial biopsy may be used for direct analysis of beta-adrenergic receptors, heart failure-associated myocardial beta-adrenergic down-regulation begins with mild-moderate ventricular dysfunction, reduction in myocardial beta-receptor density is related to degree of heart failure, and beta-receptor down-regulation is associated with pharmacologically specific impairment of the beta-agonist-mediated contractile response.
Increased occurrence of left ventricular thrombi during early treatment with timolol in patients with acute myocardial infarction.
Authors: Johannessen K A , Nordrehaug J E , von der Lippe G
Published: June 2011

To examine whether early intervention with timolol influences the occurrence of left ventricular thrombi in acute anterior myocardial infarction, 40 patients with acute anterior myocardial infarction admitted to hospital within 6 hr of onset of symptoms were randomly assigned to receive intravenous followed by oral timolol maleate or placebo. Five (25%) of 20 patients in the placebo group and 14 (73.7%) of 19 patients with confirmed infarction in the timolol group developed a left ventricular apical thrombus as detected by two-dimensional echocardiography from 2 to 10 days after inclusion (p less than .005). Patients received anticoagulants only after a left ventricular thrombus had been diagnosed. Only one patient with thrombus suffered peripheral embolization (timolol group). The treatment groups were comparable with respect to location of regional left ventricular dysfunction, electrocardiographic changes, and infarct size estimated by creatine kinase release. However, computer-assisted regional wall motion analysis demonstrated significantly reduced apical wall motion in the timolol group compared with the placebo group (p less than .01). Also, the mean heart rate during the first 10 days after the acute infarction was reduced by 13% in the timolol group (p less than .001). The reduction in heart rate and left ventricular apical wall motion caused by timolol in patients with acute anterior myocardial infarction may increase the occurrence of left ventricular thrombi.
Single-chamber cardiac pacing with activity-initiated chronotropic response: evaluation by cardiopulmonary exercise testing.
Authors: Benditt D G , Mianulli M , Fetter J , Benson D W , Dunnigan A , Molina E , Gornick C C , Almquist A
Published: June 2011

In this study, sequential cardiopulmonary exercise testing was used to assess the physiologic benefits of a single-chamber ventricular pacing system that utilizes a piezoceramic sensor to adjust heart rate by detecting "physical activity." An initial exercise test was conducted with the pacemaker programmed (based on a randomization table) to either the fixed rate (VVI, 70 beats/min) or rate-variable (VVI-Act) mode, and the results were compared with those obtained during a second exercise test in which the pacemaker was programmed to the alternate pacing mode. A 1.5 to 2 hr rest period was permitted between exercise tests, each of which consisted of a symptom-limited constant speed (3.0 mph) Balke protocol with 2 min stages commencing at 0.0% grade with increments of 2.5% at end of each stage. Compared with findings during fixed-rate VVI pacing, VVI-Act pacing was associated with greater exercise-induced positive chronotropic response (mean maximum heart rate VVI-Act 128 +/- 15.3 beats/min vs VVI 90 +/- 28.4 beats/min; p less than .01), prolongation of exercise duration (VVI-Act 10.2 +/- 3.8 min vs VVI 7.7 +/- 2.5 min; p less than .01), increased peak oxygen consumption (VVI-Act 1617 +/- 656 ml O2/min vs VVI 1325 +/- 451 ml O2/min; p less than .01), and onset of anaerobic threshold at a higher oxygen consumption (VVI-Act 1208 +/- 343 ml O2/min vs VVI 1064 +/- 377 ml O2/min: p less than .01). Additionally, of 44 comparable exercise stages tested in the two pacing modes, perceived exertion (assessed by a numerical grading system) was lower in 38 of 44 instances during VVI-Act compared with VVI pacing.(ABSTRACT TRUNCATED AT 250 WORDS)
Left ventricular geometry and function in adults with Ebstein's anomaly of the tricuspid valve.
Authors: Benson L N , Child J S , Schwaiger M , Perloff J K , Schelbert H R
Published: June 2011

We postulated that the abnormal shape, size, and function of the right heart and adjoining ventricular septum in adults with Ebstein's anomaly of the tricuspid valve might in turn alter the shape and function of the left ventricle. Seven adult patients with uncomplicated Ebstein's anomaly were studied. Left ventricular geometry was determined by two-dimensional echocardiography. Left ventricular function was assessed by treadmill exercise and radionuclide angiography at rest and with exercise. Paradoxic ventricular septal motion was consistently present. Left ventricular eccentricity (ratio of two minor axes in the short-axis view) was uniformly abnormal, averaging 1.35 +/- 0.23 (normal = 1.02 +/- 0.05). The ratio of right to left ventricular cavity size averaged 1.70 +/- 0.44 (normal 0.65 +/- 0.30), and tricuspid valve displacement into the right ventricular cavity averaged 52% (normal 8%). Functional right atrial size averaged 27.6 +/- 5.2 cm2 (normal right atrial area = 13.1 +/- 2.2 cm2). Resting left ventricular ejection fractions were below 50% in all but two patients. In response to Bruce protocol exercise stress, there were consistently appropriate increments in heart rate, blood pressure, and peak double product and, with one exception, radionuclide left ventricular ejection fraction. There were significant correlations between tricuspid valve displacement and functional right atrial size versus resting left ventricular ejection fraction and left ventricular eccentricity. These data support the hypothesis that derangements in right heart morphology and function in Ebstein's anomaly contribute to significant alterations in left ventricular geometry, but the geometric alterations are associated with tangible but less significant changes in left ventricular systolic function.
Long-term survival with open-chest cardiac massage after ineffective closed-chest compression in a canine preparation.
Authors: Kern K B , Sanders A B , Badylak S F , Janas W , Carter A B , Tacker W A , Ewy G A
Published: June 2011

The ultimate goal of cardiopulmonary resuscitation (CPR) is long-term, neurologically intact survival. This study examined whether open-chest cardiac massage could improve 7 day survival and neurologic function when instituted after the failure of standard closed-chest compression CPR. Twenty-nine mongrel dogs were anesthetized and then instrumented with catheters to monitor right atrial and ascending aortic pressures. Ventricular fibrillation was induced and after 3 min standard CPR was begun. Standard CPR was performed with a Thumper programmed for 2 inch chest compressions at 60/min with a 50% duty cycle. External defibrillation was attempted twice after 15 min of ventricular fibrillation. Unsuccessfully defibrillated animals were randomly assigned to either an additional 2 min of continued closed-chest compressions, or 2 min of open-chest cardiac massage. All animals underwent a period of advanced cardiac life support and were followed until they were resuscitated or died. Follow-up care, including scoring of neurologic deficit, was performed for 7 days. In dogs receiving open-chest cardiac massage there was significantly more immediate resuscitation success (14/14 vs 5/14; p less than .005), 24 hr survival (12/14 vs 4/14; p less than .005), and 7 day survival (11/14 vs 4/14; p less than .02) than in those receiving continued closed-chest compression. Open-chest cardiac massage significantly improved long-term outcome when instituted after 15 min of ineffective closed-chest compression.
Increased sensitivity of the denervated transplanted human heart to isoprenaline both before and after beta-adrenergic blockade.
Authors: Yusuf S , Theodoropoulos S , Mathias C J , Dhalla N , Wittes J , Mitchell A , Yacoub M
Published: June 2011

It is not known whether surgical denervation leads to increased beta-receptor sensitivity after human cardiac transplantation. We assessed cardiac beta-receptor sensitivity by studying the heart rate response to isoprenaline of the denervated donor heart as compared with the innervated recipient heart in eight patients who underwent heterotopic cardiac transplantation and in six patients with orthotopic transplantation. Changes in the donor and recipient hearts seen in these 14 patients were further compared with those seen in 10 normal volunteers. Incremental intravenous infusion of isoprenaline (5, 10, and 15 ng/kg/min) raised heart rate to a greater extent in the donor compared with the recipient hearts in the eight patients who had heterotopic grafts (slopes [beats/min/ng/kg]: donor = +2.26, recipient = +1.59; p less than .01). In addition, the donor hearts of the transplant patients were more sensitive than hearts of the normal volunteers (slopes: donor = +2.26, normal = +0.94; p less than .01). The changes in the two groups of donor hearts were similar (slopes: orthotopic = +2.24, heterotopic = +2.27; NS). The recipient hearts in the patients with heterotopic transplants were more sensitive than the hearts of the normal volunteers (p less than .05), suggesting that the observed differences in isoprenaline sensitivity in the patients with heterotopic grafts were not caused by a decreased sensitivity of the recipient heart. After beta-blockade, the heart rate responses to isoprenaline were attenuated to the same extent in denervated and innervated hearts.(ABSTRACT TRUNCATED AT 250 WORDS)
Spontaneous morphologic changes in left ventricular thrombi: a prospective two-dimensional echocardiographic study.
Authors: Domenicucci S , Bellotti P , Chiarella F , Lupi G , Vecchio C
Published: June 2011

Previous retrospective echocardiographic studies have reported a higher embolic potential of left ventricular thrombi with protruding configuration and patterns of mobility. The present study was performed to prospectively assess the shape and mobility patterns of left ventricular thrombi and their spontaneous changes with time. Two-dimensional echocardiograms were obtained in 109 consecutive patients with acute anterior myocardial infarction within 24 hr of the onset of symptoms, every 24 hr until day 5, every 48 hr until day 15, and then every month for a follow-up of 1 to 29 (mean 14 +/- 8) months in the survivors. None of the patients were treated with anticoagulants or platelet inhibitors during the study period. Left ventricular thrombi, detected in 59 patients (54%), appeared from 1 to 362 (mean 12 +/- 47) days after myocardial infarction. At first detection, the shape was mural in 21 patients and protruding in 38; patterns of mobility were present in eight patients. During follow-up, changes in the shape of the thrombi were noted in 24 patients (41%; from mural to protruding in nine, from protruding to mural in 15). These variations were encountered between 2 and 490 (mean 64 +/- 117) days after the first observation of the thrombus. Patterns of mobility, previously detected in eight patients, disappeared in five of eight within 2 to 28 (mean 14 +/- 11) days.(ABSTRACT TRUNCATED AT 250 WORDS)
Direct assessment of right ventricular transmural pressure.
Authors: Santamore W P , Constantinescu M , Little W C
Published: June 2011

Although the measurement of transmural pressure is important, calculation of transmural pressure is complicated by the difficulties in measuring pericardial pressure. Recently, flat balloons have been proposed to measure pericardial pressure. Over a wide range of volumes, right ventricular diastolic pressure and pericardial balloon pressure were similar in diastole, suggesting that the right ventricle is unstressed at physiologic volumes and that right atrial pressure can be used to estimate pericardial pressure. To evaluate these concepts and to assess indirectly the accuracy of measuring pericardial pressure using flat balloons, six canine hearts were examined postmortem. The pericardium was removed and the hearts were submerged in cold cardioplegic solution. Balloons were inserted into the right and left ventricles, and right and left ventricular pressure-volume curves were obtained. Right ventricular transmural pressures of 2.6 +/- 0.5, 3.9 +/- 0.9, 5.9 +/- 1.4, and 8.9 +/- 2.4 mm Hg were required to distend the right ventricle to 10, 20, 30, and 40 ml, respectively. For the left ventricle, transmural pressures of 3.4 +/- 0.7, 5.4 +/- 1.2, 8.6 +/- 2.1, and 14.1 +/- 3.8 mm Hg were recorded at volumes of 10, 20, 30, and 40 ml, respectively. Although the right ventricular transmural pressures were less than the left ventricular transmural pressures over the physiologic range, right ventricular transmural pressures were always positive and increased with increments in ventricular volume. Thus the right ventricle is not unstressed over the entire range of physiologic volumes, suggesting that pericardial balloon pressures may overestimate pericardial pressure and that right atrial pressure cannot be used to estimate pericardial pressure.
Color Doppler evaluation of aortic dissection.
Authors: Iliceto S , Nanda N C , Rizzon P , Hsuing M C , Goyal R G , Amico A , Sorino M
Published: June 2011

Color Doppler studies were performed in 16 adult patients with proven DeBakey type I and III aortic dissection. Simultaneous opacification of both aortic lumina with oppositely directed flow was noted by color Doppler in at least one aortic segment in 14 of 16 patients (12 type I, two type III). In two patients (one type I, one type III), flow was seen in one lumen only, with clot demonstrated in the other lumen in one of them. Of 12 patients in whom communication between two aortic dissection channels was shown by angiography/surgery, color Doppler correctly identified them in nine patients (four ascending aorta, two aortic arch, and three descending aorta), either by direct visualization of flow moving from one lumen into the other (six patients) or indirectly by analyzing differences in timing of opacification of the two lumina and flow direction (three patients). Also, color Doppler correctly diagnosed aortic regurgitation as severe (aortic regurgitation jet occupying more than 75% of left ventricular outflow) in three patients and moderate in four patients. Color Doppler provides comprehensive evaluation of flow dynamics in aortic dissection.
Long-term follow-up of patients with the antibiotic-sterilized aortic homograft valve inserted freehand in the aortic position.
Authors: Barratt-Boyes B G , Roche A H , Subramanyan R , Pemberton J R , Whitlock R M
Published: June 2011

A series of 252 isolated aortic homograft valves in 248 patients have been followed for 9 to 16.5 years (mean 10.8). The valves were sterilized in antibiotic solution and stored in a nutrient medium at 4 degrees C and were nonvital. There were 15 in-hospital deaths (6%) and a mortality of 2.7% in patients undergoing an elective first operation. Actuarial survival with the study valve in situ was 57% at 10 years and 38% at 14 years. Only 8.4% of the patients died late from homograft valve failure, chiefly because of failure to refer patients with endocarditis for reoperation or because reoperation was refused in elderly, frail subjects. Incompetence was the sole cause of valve failure and was due either to valve wear or endocarditis. Significant incompetence required reoperation. On actuarial analysis, freedom from significant incompetence for the entire group was 95% at 5 years, 78% at 10 years, and 42% at 14 years. Factors increasing the risk of significant incompetence due to valve wear on multivariate analysis were increasing donor valve age (greater than or equal to 55 years), recipient age (less than 15 years), and an aortic root diameter over 30 mm. Analysis of the patient group that excluded each of these variables (low-risk group), which comprised 61% of the study population, indicated freedom from significant incompetence due to valve wear of 98% at 5 years, 94% at 9 years, and 56% at 13 years.
The effect of intravenous thrombolytic therapy on left ventricular function: a report on tissue-type plasminogen activator and streptokinase from the Thrombolysis in Myocardial Infarction (TIMI Phase I) trial.
Authors: Sheehan F H , Braunwald E , Canner P , Dodge H T , Gore J , Van Natta P , Passamani E R , Williams D O , Zaret B
Published: June 2011

In Phase I of the NHLBI trial of Thrombolysis in Myocardial Infarction (TIMI), 290 patients admitted within 7 hr after onset of acute infarction were randomly assigned to intravenous treatment with either streptokinase (SK) or recombinant tissue-type plasminogen activator (rt-PA). Left ventricular function was measured from contrast ventriculograms in 145 patients with both pretreatment and predischarge studies analyzable. Regional wall motion in the infarct site was measured by the centerline method and expressed in units of standard deviations (SDs) from the mean motion in 52 normal subjects. Patients treated with rt-PA (n = 77) achieved a significantly higher reperfusion rate after 90 min of treatment. Perfusion of the infarct-related artery improved from visual grade 0 or 1 (total occlusion or penetration without perfusion) to grade 2 or 3 (partial or full reperfusion) in 62% receiving rt-PA vs 31% receiving SK (n = 68) (p less than .001). However, the ejection fraction did not change significantly from before treatment to before discharge in either treatment group (+0.7 +/- 6.7% vs +1.0 +/- 8.3%, respectively). A small but significant increase in regional wall motion was observed in each of the two groups (+0.4 +/- 0.8 vs +0.3 +/- 0.8 SD/chord, respectively; each p less than .001 compared with baseline). This was countered by declines in the hyperkinesis of the noninfarct region (-0.3 +/- 1.0 SD/chord [p = .01] compared with baseline and -0.2 +/- 1.0 SD/chord [p = .23], respectively). Analysis of the combined groups revealed that the ejection fraction increased only in patients who achieved reperfusion by 90 min after onset of therapy or who had subtotal occlusions initially. There was greater recovery of left ventricular function in patients who achieved reperfusion earlier vs later than 4 hr after symptom onset and in patients with vs without some collateral circulation to the infarct-related artery.
Calibration of color Doppler flow mapping during extreme hemodynamic conditions in vitro: a foundation for a reliable quantitative grading system for aortic incompetence.
Authors: Switzer D F , Yoganathan A P , Nanda N C , Woo Y R , Ridgway A J
Published: June 2011

If color Doppler imaging is to continue to evolve into a reliable clinical method to noninvasively evaluate regurgitant lesions, then its grading methods must be quantitated and calibrated under extreme hemodynamic conditions. A left heart pulse duplicator was used to provide a completely controllable system to study aortic incompetence jet morphologies as a function of hemodynamic extremes. The system was first used to calibrate the limits of resolution of color Doppler imaging. Next, to define which jet features reliably predict the defect size or the regurgitant fraction and which are primarily influenced by instantaneous hemodynamic variables, we measured the jets' maximal length, width, proximal width, and temporal pattern of color variance during independent variations in the heart rate, cardiac output, and pressure gradient across the incompetent valve. The proximal jet width (immediately below the valve plane) was the only reliable independent predictor of both the defect size and the regurgitant fraction. Jet depth accurately predicted peak velocity (quantitated by laser Doppler velocimetry); it reliably predicted the severity of incompetence only at a known pressure gradient across the valve. Large defects (5 mm) produced jets with maximal color variance in early diastole, whereas small defects produced pandiastolic variance.
Prospective evaluation of ultrafast cardiac computed tomography for determination of coronary bypass graft patency.
Authors: Bateman T M , Gray R J , Whiting J S , Sethna D H , Berman D S , Matloff J M , Swan H J , Forrester J S
Published: June 2011

Twenty-five consecutive patients with 68 independent (single distal anastomosis) saphenous vein aortocoronary and 12 internal mammary bypass grafts (27 to left anterior descending, 10 to diagonal, 23 to left circumflex, 20 to right coronary artery) entered a reader-blinded, prospective, standardized study to establish the accuracy of ultrafast (cine) cardiac computed tomography (CT) for determining graft patency compared with invasive angiography. All patients underwent imaging after injection of 35 to 45 ml of meglumine diatrizoate (Renografin-76; 7 to 9 ml/sec for 5 sec) into an arm vein. Electrocardiographically triggered images were acquired over eight to 16 tomographic levels at 1 cm intervals from aortic arch to mid left ventricle. Criteria for graft patency were contrast opacification on at least two noncontinguous levels and contrast density-time curves morphologically similar to that of the aorta. Ultrafast CT correctly determined that 46 of 48 bypass grafts were patent and 31 of 32 were occluded (sensitivity, specificity, and accuracy 96%, 97%, and 96%); there were no interpretation errors in 23 (92%) of the 25 patients. Accuracy was independent of vessel bypassed and not different for saphenous veins (96%) compared with internal mammary bypasses (100%). This study establishes a 20 min outpatient intravenous injection technique that is highly accurate for determining patency of coronary artery bypass grafts.