bluuebunny/crossref_metadata_2025 huggingface dataset:
Parasystole, reentry, and tachycardia: a canine preparation of cardiac arrhythmias occurring across inexcitable segments of tissue.
Authors: Antzelevitch C , Bernstein M J , Feldman H N , Moe G K
Published: June 2011

A protected ectopic focus created in tissue excised from one heart was allowed to interact with the activity of the intact heart of another animal. The protected focus consisted of a Purkinje fiber in which a narrow central zone was rendered inexcitable. The model permitted us to study parasystole, modulated parasystole, reentry, and tachycardia in the same preparation. At moderate levels of electrotonic influence across the region of block, frequency scans revealed wide zones of pacemaker entrainment. The incidence and pattern of premature ventricular contractions generated were always a sensitive function of heart rate. Parasystolic patterns could be converted to apparent reentrant patterns by simple alteration of the atrial driving rate or the level of block. Suppression of pacemaker automaticity converted a modulated parasystole model to one of pure reentry. Reciprocation of the impulse across the inexcitable tissue segment generated a ventricular tachycardia that could be initiated and terminated by a single properly timed event. Our observations suggest that ectopic activity that behaves like parasystole and activity characteristic of what is commonly diagnosed as reentry, including tachycardia and idioventricular rhythms, may be a manifestation of a common mechanism whose arrhythmic expression differs as a continuous function of heart rate, level of block, or level of automaticity.
Validation of a computerized edge detection algorithm for quantitative two-dimensional echocardiography.
Authors: Zwehl W , Levy R , Garcia E , Haendchen R V , Childs W , Corday S R , Meerbaum S , Corday E
Published: June 2011

An edge detection algorithm used in conjunction with digitized two-dimensional echocardiograms was applied to validate computerized two-dimensional echocardiographic (2DE) quantitation of cross-sectional areas of canine left ventricular chambers. Images were enhanced by space-time smoothing and dynamic range expansion, after which automatic edge detection was performed by convolving a Laplacian operator with the enhanced image. In an in vitro study of 29 myocardial slabs, computer-derived 2DE measurements of short-axis sections of the left ventricle were compared with manually derived 2DE data and validated against direct measurements of intraluminal areas of myocardial slabs. Correlations of both manually and computer-derived 2D echocardiograms vs direct measurements were equally satisfactory (r = .95 for both). Computer-derived measurements of perimeters tended to underestimate actual perimeters of the endocardial outlines of left ventricular sections. In 13 closed-chest anesthetized dogs, manually and computer-derived left ventricular short-axis areas measured by 2DE techniques showed a good correlation at both end-diastole (r = .91) and end-systole (r = .92). Left ventricular volumes reconstructed from 2DE images were compared with angiographically determined volumes. The computer-enhanced 2DE method correlated against angiography, with r = .93 for end-diastolic and r = .93 for end-systolic volumes. Left ventricular volume correlations between manually and computer-derived 2D echocardiograms were satisfactory, with r = .87 for end-diastole and r = .87 for end systole. We conclude that computerized enhancement and edge detection of 2D echocardiograms obtained in dogs provided accurate analysis of actual left ventricular cross-sectional areas and left ventricular volumes.
New indexes for assessing aortic regurgitation with two-dimensional Doppler echocardiographic measurement of the regurgitant aortic valvular area.
Authors: Veyrat C , Lessana A , Abitbol G , Ameur A , Benaim R , Kalmanson D
Published: June 2011

Direct examination of the aortic orifice at the level of the aortic valves (aortic valvular orifice area, AVOA) in the short-axis plane was performed with a 3 MHz two-dimensional pulsed Doppler echocardiographic apparatus. The AVOA was mapped with the Doppler gate to detect or rule out the presence of a regurgitant aortic valvular area (RAVA) established by recording of abnormal diastolic Doppler signals on a "yes or no" basis. A group of 12 normal subjects and 83 patients, including 40 patients with aortic regurgitation proven by aortography, were investigated with this procedure. In the 38 patients with aortic regurgitation diagnosed by Doppler echocardiography (diagnostic sensitivity 95%, specificity 100%), planimetric measurements of the RAVA and AVOA were performed with calculation of two indexes: the RAVA/square meter of body surface area and the RAVA/AVOA ratio. These indexes correlated well with independently performed angiographic grading on a three-point scale (r = .87 for the RAVA, .88 for the RAVA/AVOA; p less than .001), with highest significance of differences in mean values among each grade of severity found for the RAVA/AVOA (p less than .001). In addition, Doppler echocardiography identified the anatomic valvular site of the lesion, and we confirmed the site during surgery.
A life table and Cox regression analysis of patients with combined proximal left anterior descending and proximal left circumflex coronary artery disease: non-left main equivalent lesions (CASS).
Authors: Chaitman B R , Davis K , Fisher L D , Bourassa M G , Mock M B , Lespérance J , Rogers W J , Fray D , Tyras D H , Judkins M P
Published: June 2011

Combined proximal left anterior descending and proximal left circumflex artery stenoses greater than or equal to 70% have been referred to as "left main equivalent" lesions. We compared the survival rates of medically treated patients who have this type of coronary anatomic characteristics with the survival rates of patients who have left main coronary artery stenoses greater than or equal to 70% by use of a stratified life table approach and a Cox regression model. Comparison of the patients with left main coronary artery stenoses with those who have left main equivalent lesions by use of life table analysis and three different calculations of patient exposure time revealed a poorer prognosis for the patients who had left main coronary artery disease (p less than or equal to .04 for all three methods). The stepwise Cox analysis also determined that patients who had left main artery stenoses had a significantly poorer prognosis than patients who had left main equivalent coronary disease (p = .002), even after consideration of important baseline variables known to affect survival rates. We then compared the patients who had combined proximal left anterior descending and proximal left circumflex artery disease with patients who had combined stenoses greater than or equal to 70% in the nonproximal left anterior descending stenosis influenced survival rates. The 5 year to determine if location of the left anterior descending stenosis influenced survival rates. The 5 year survival rate was not as high for the patients who had proximal left anterior descending artery disease (55% vs 70%, p = .001). In conclusion, combined proximal left anterior descending and proximal left circumflex artery disease identifies a high-risk (as determined by angiography) patient subset.(ABSTRACT TRUNCATED AT 250 WORDS)
The measurement of sinus node refractoriness in man.
Authors: Kerr C R , Strauss H C
Published: June 2011

We recently described a method for measuring sinus node refractoriness in the rabbit heart. Atrial premature beats either may result in reset return responses or may become interpolated because of encroachment on sinus node refractoriness. In previous studies with rabbits we defined the effective refractory period of the sinus node (SNERP) as the longest premature interval that is interpolated. This study presents results on the extension of this technique to the measurement of sinus node refractoriness in man. Out of 30 patients (12 with and 18 without sinus node dysfunction), SNERP could be measured in 26 at one or more basic cycle lengths. At a basic pacing cycle length of 600 msec, SNERP ranged from 250 to 380 msec (mean 325 +/- 39) in patients without sinus node dysfunction and from 500 to 550 msec (mean 522 +/- 20) in patients with sinus node dysfunction. This clear differentiation of patients with and without sinus node dysfunction by SNERP is in contrast to various results obtained by assessing sinus node function from sinus node recovery time and sinoatrial conduction time. Thus this study suggests the possible use of the measurement of SNERP in the assessment of sinus node function in man and its possible value in identifying patients with sinus node dysfunction.
Effects of short-term administration of verapamil on left ventricular relaxation and filling dynamics measured by a combined hemodynamic-ultrasonic technique in patients with hypertrophic cardiomyopathy.
Authors: TenCate F J , Serruys P W , Mey S , Roelandt J
Published: June 2011

The effects of short-term administration of verapamil on left ventricular isovolumetric relaxation and early and late diastolic filling dynamics were studied in 10 patients with hypertrophic cardiomyopathy by a combined hemodynamic-ultrasonic technique. Left ventricular pressures (recorded with high-fidelity micromanometers) were determined simultaneously with M mode echocardiography. After 10 mg of verapamil was given intravenously (2 mg/min), left ventricular contractility and systolic pressure dropped significantly (p less than .05). Left ventricular dP/dt fell from 1947 +/- 544 to 1489 +/- 334 mm Hg/sec, maximal velocity of the contractile element at zero load fell from 50 +/- 17 to 42 +/- 15 1/sec, peak velocity contraction of the contractile element fell from 37 +/- 10 1/sec to 29 +/- 10 1/sec (p less than .05), and left ventricular systolic pressure fell from 149 +/- 30 to 127 +/- 22 mm Hg. Left ventricular negative dP/dt increased from 1770 +/- 479 to 1477 +/- 377 mm Hg/sec (p less than .05), and the time constant of isovolumetric pressure decay was prolonged from 48 +/- 9 to 64 +/- 15 msec (p less than .05). Left ventricular end-diastolic pressure rose from 21 +/- 7 to 23 +/- 6 mm Hg (p less than .05). The time constant of isovolumetric pressure decay was calculated in three different ways, but none of these measurements was influenced by verapamil. Time of isovolumetric relaxation, duration of rapid ventricular filling, and peak rate of left ventricular lengthening were not significantly influenced by verapamil and remained highly abnormal. In contrast, peak rate of left ventricular posterior wall thinning declined further after verapamil from 2.9 +/- 1.2 to 2.4 +/- 1.4 1/sec (p less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)
A guide to the radiographic identification of prosthetic heart valves: an addendum.
Authors: Mehlman D J
Published: June 2011

Several years ago "A Guide to the Radiographic Identification of Prosthetic Heart Valves" (Circulation 57:613, 1978) described the radiographic silhouettes of 40 different cardiac prosthesis in clinical use. Since that time a number of prostheses have been developed and introduced to clinical practice. Ten of these newer prostheses manufactured by six domestic companies were photographed and radiographed as they would be expected to appear in standard chest radiographs. The radiographic silhouettes are described and distinguishing features are discussed.
Protective effect of early and late treatment with nifedipine during myocardial infarction in the conscious dog.
Authors: Melin J A , Becker L C , Hutchins G M
Published: June 2011

The effect of early and late nifedipine treatment on collateral blood flow and myocardial infarct size was investigated in 24 previously instrumented conscious dogs. Nifedipine was infused intravenously for 5 hr beginning 15 min (n = 9) and 3 hr (n = 6) after permanent occlusion of the midcircumflex coronary artery and compared with early and delayed vehicle treatment (controls; n = 9). Doses of nifedipine (90 to 168 micrograms/hr) were titrated to reduce mean arterial pressure by 5% to 10%. After animals died or were killed 2 to 7 days later, the anatomic risk region, or occluded coronary bed, was defined by postmortem coronary arteriography. The masses of infarct and risk region were measured by planimetry of weighed transverse sections of the left ventricle. Infarct size was smaller (p less than .05) with early and late nifedipine treatment compared with control, both as percent of left ventricle (15.6% and 14.6% vs 21.6%) and as percent of risk region (46.7% and 41.6% vs 65.7%). Collateral blood flow, measured with radioactive microspheres, increased 31% to 50% during 5 hr of nifedipine treatment, but the mean increase was not statistically greater than that seen in controls. Myocardial protection by nifedipine occurred consistently when epicardial collateral flow exceeded 0.40 ml/min/g and the increase after the drug was at least 0.1 ml/min/g. When flows were less than these amounts, however, only about half of the animals demonstrated reduced infarct size. The results suggest that an increase in collateral flow accounts for part of the beneficial effect of nifedipine but that direct mechanisms not mediated by flow may also contribute.
Assessment of left ventricular mechanics in patients with asymptomatic aortic regurgitation: a two-dimensional echocardiographic study.
Authors: St John Sutton M G , Plappert T A , Hirshfeld J W , Reichek N
Published: June 2011

We describe a noninvasive method for determining end-systolic meridional and circumferential wall stress and left ventricular architecture as the ratio of muscle to cavity area. With this technique, which uses two-dimensional echocardiography and cuff-determined values for systolic blood pressure, we assessed wall stress and left ventricular architecture in 15 normal subjects and 15 asymptomatic patients with severe chronic aortic regurgitation at rest and after load manipulations with sublingual nitroglycerin. Resting end-systolic meridional and circumferential stress were increased in patients with aortic regurgitation (113.9 +/- 29 and 260 +/- 50.7 X 10(3) dynes/cm2) compared with those in normal subjects (85.6 +/- 15.4 and 214.1 +/- 28.4 X 10(3) dynes/cm2) (both p less than .01) and remained significantly greater after nitroglycerin. Meridional stress values obtained from two-dimensional echocardiographic studies correlated closely (r = .89) with values calculated from simultaneously recorded M mode echocardiograms. Ejection fraction in patients with aortic regurgitation and normal subjects were similar at rest (55 +/- 10% vs 59 +/- 6%) and were unchanged by nitroglycerin. In spite of the increased left ventricular mass in patients with aortic regurgitation (227 +/- 60 g vs 130 +/- 22 g in normal subjects), the mass-to-volume ratio and the ratio of muscle to cavity area in diastole in patients with aortic regurgitation were significantly lower than normal (0.90 +/- 0.23 vs 1.30 +/- 0.21 and 0.91 +/- 0.23 vs 1.11 +/- 0.18 [p less than .005 and p less than .02]). These differences were exaggerated after nitroglycerin, while concomitant changes in relative wall thickness were virtually undetected by M mode echocardiography. Thus this technique can be used for early recognition of afterload excess and changes in left ventricular architecture in patients with aortic regurgitation. Furthermore, the mean slopes of the circumferential stress-diameter and meridional stress-length lines, which represent load-independent indexes of myocardial contractile state, could be assessed and were similar in the group of patients with asymptomatic aortic regurgitation and normal subjects, indicating that overall myocardial contractility was still normal. We conclude that circumferential and meridional wall stress, myocardial contractility, and left ventricular architecture can be determined noninvasively. These measurements may prove to be useful in assessing patients with primary myocardial or valvular heart disease and determining their long-term management.
The nonpharmacologic management of the permanent form of junctional reciprocating tachycardia.
Authors: Guarnieri T , Sealy W C , Kasell J H , German L D , Gallagher J J
Published: June 2011

The permanent or recurring form of junctional reciprocating tachycardia (PJRT) is an incessant tachycardia that has characteristic clinical and electrophysiologic features of PJRT. Each patient demonstrated near-incessant reciprocating tachycardia with a 1:1 atrioventricular (AV) relationship and with a retrograde P wave (P') occurring closer to the succeeding QRS complexes (i.e., long RP'). With initiation of the tachycardia, there was no prolongation of the PR or AH interval. All patients had evidence of early retrograde atrial activation in their posterior atrial septa and this retrograde limb had properties of decremental conduction. Eight of the nine patients underwent elective surgical ablation of the retrograde limb of tachycardia, and in seven it was successful. Epicardial and endocardial atrial maps recorded during PJRT demonstrated that the site of earliest retrograde activation was in the posterior atrial septum near the coronary sinus orifice. The seven patients in whom surgery was successful left the hospital in sinus rhythm with antegrade conduction, and all are free of tachycardia during the mean follow-up period of 31 months (range 1 to 70 months). In the two remaining patients PJRT was controlled by interruption of the antegrade limb of the tachycardia, the AV node-His bundle. In one patient this was done under direct vision at surgery after an unsuccessful attempt at pathway dissection.(ABSTRACT TRUNCATED AT 250 WORDS)
Long-term hemodynamic effects of prenalterol in patients with severe congestive heart failure.
Authors: Lambertz H , Meyer J , Erbel R
Published: June 2011

In a controlled, randomized, double-blind study we investigated the long-term effects of the beta 1-adrenoceptor agonist prenalterol in 16 patients with severe congestive heart failure (NYHA class III or IV). Previous to and 1 week, 3 months, and 6 months after continuous oral intake of 40 to 120 mg prenalterol a day, catheterization of the right heart combined with an ergometer test was carried out; M mode and two dimensional echocardiograms as well as systolic time intervals were also recorded. With prenalterol the heart rate increased within 1 week from 81 +/- 7 to 90 +/- 7 beats/min (mean +/- SD) (p less than .05) and remained increased after 3 months (93 +/- 9 beats/min, p less than .01) and 6 months (91 +/- 6 beats/min, p less than .05). After 1 week the cardiac index rose from 2.7 +/- 0.7 to 3.3 +/- 0.7 l/min/m2 (p less than .01), and after 3 and 6 months it fell again to 3.0 +/- 0.9 l/min/m2 and 2.9 +/- 0.7 l/min/m2, respectively. In the ergometer test the improvement in performance was not significant. The mean velocity of circumferential fiber shortening initially increased from 0.58 +/- 0.20 to 0.79 +/- 0.28 circumferences/sec (p less than .01), but dropped after 3 months to 0.62 +/- 0.31 circumferences/sec. The ejection fraction determined from the two-dimensional echocardiogram rose after 1 week from 20 +/- 10 to 27 +/- 12% (p less than .05), but decreased again after 3 months (23 +/- 11%) and 6 months (20 +/- 10%).(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of three bradycardiac drugs on regional myocardial blood flow and function in areas distal to a total or partial coronary occlusion in dogs.
Authors: Gross G J , Lamping K G , Warltier D C , Hardman H F
Published: June 2011

The effectiveness of three bradycardiac drugs for increasing distal coronary perfusion pressure and decreasing stenosis resistance (SR) in partially occluded vessels, and thereby for increasing collateral blood flow and segmental function (%SS) in an occluded area dependent on the stenotic vessel, was studied in anesthetized dogs. Initially, the distal portion of the left anterior descending (LAD) coronary artery was occluded followed by subsequent stenosis of the left circumflex (LC) coronary artery that supplies collateral flow to the ischemic LAD area. A decrease in LC flow (35 +/- 3 to 24 +/- 3 ml/min) and distal coronary pressure (109 +/- 4 to 47 +/- 4 mm Hg) resulted in an increase in SR (0.03 +/- 0.02 to 2.97 +/- 0.53 U), and decreases in LC %SS (9.3 +/- 1.1% to 1.9 +/- 2.0%), subendocardial blood flow (1.11 +/- 0.06 to 0.43 +/- 0.05 ml/min/g), and LAD collateral flow (0.36 +/- 0.11 to 0.22 +/- 0.05 ml/min/g). Upon intravenous administration on the beta-receptor-blocking drug sotalol (0.3 mg/kg) or metoprolol (0.1 mg/kg) and the non-beta-blocking bradycardiac drug N-dimethyl-propranolol (5.0 mg/kg) in doses that produced similar decreases in heart rate (30 to 40 beats/min), distal coronary pressure, subendocardial blood flow, and %SS in the LC area were markedly improved. SR was significantly reduced (2.97 +/- 0.53 to 1.66 +/- 0.37 U). The improvement in %SS of the LC area was highly correlated (r = .93, p less than .001) with the increase in subendocardial blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)
Absence of a cumulative deterioration of regional function during three repeated 5 or 15 minute coronary occlusions.
Authors: Lange R , Ware J , Kloner R A
Published: June 2011

Recurrent myocardial ischemia is commonly seen in patients with coronary artery disease, in patients undergoing cardiac surgery with intermittent cross-clamping, and experimentally when multiple occlusion preparations are used to test drugs. Our study was designated to investigate whether myocardial injury is cumulative after three sequential ischemic episodes. Sixteen dogs were instrumented with ultrasonic crystals to assess percentage of segmental shortening and percentage of wall thickening in ischemic and nonischemic regions. The left anterior descending coronary artery was occluded three times for 5 min in one group (n = 8) and three times for 15 min in another group of dogs (n = 8) and each occlusion was followed by 30 min of reflow. Blood flow was determined with microspheres before coronary artery occlusion in the 5 min group and during occlusion in the 15 min group and in all dogs 25 min into the first and third reperfusion periods. During the three reperfusion periods mean segmental shortening in the ischemic zone recovered to only 60.5 +/- 8.7% (+/- SEM) of the preocclusion level (p less than .003) in the 5 min occlusion group and to 36.9 +/- 17.7% in the 15 min occlusion group (p less than .01). Mean wall thickening recovered to 61.3 +/- 16.6% (p less than .06) in the 5 min group and to 48.6 +/- 11.8% in the 15 min group (p less than .004). There were no significant differences during the reperfusion phase when mean values for the ischemic segment after the second and third occlusion were compared with the data obtained after the first occlusion in either group.(ABSTRACT TRUNCATED AT 250 WORDS)
Increased left ventricular emptying at maximal exercise after reduction in afterload.
Authors: Andersen K , Vik-Mo H
Published: June 2011

Twelve healthy men were studied by M mode echocardiography during exercise to investigate the effect of afterload reduction on left ventricular function at maximal exertion. They performed two maximal exercise bicycle tests 4 hr apart while in the semisupine position and were given 20 mg nifedipine sublingually 30 min before the second test. During the first test end-systolic dimension decreased (p less than .01) and fractional shortening increased from rest to peak exercise (p less than .01), while end-diastolic dimension did not change significantly. At maximal exercise systolic blood pressure was lower after nifedipine than in the preceding control test (202 +/- 10 [mean +/- SD] vs 212 +/- 14 mm Hg; p less than .01), while heart rate was not significantly changed (168 +/- 15 vs 162 +/- 13 beats/min). End-systolic dimension was lower (25.6 +/- 3.3 vs 28.8 +/- 4.2 mm; p less than .01) and fractional shortening higher (50.7 +/- 6.0% vs 45.3 +/- 7.0%; p less than .01) while end-diastolic dimension was unchanged (52.3 +/- 1.9 vs 52.4 +/- 2.6 mm). Our data indicate increased left ventricular emptying at maximal exercise after nifedipine, most probably due to reduction in afterload.
Hemodynamic and clinical response to enalapril, a long-acting converting-enzyme inhibitor, in patients with congestive heart failure.
Authors: Levine T B , Olivari M T , Garberg V , Sharkey S W , Cohn J N
Published: June 2011

Enalapril, a new oral angiotensin converting-enzyme inhibitor, was administered to nine patients with severe congestive heart failure. Short-term hemodynamic response was noted within 2 hr and persisted for up to 24 hr. At peak effect mean arterial pressure fell from 83.4 +/- 10(SD) to 72.1 +/- 16.2 mm Hg (p less than .01), right atrial pressure from 13.6 +/- 6.0 to 10.4 +/- 7.5 mm Hg (p less than .01), pulmonary arterial pressure from 38.9 +/- 4.8 to 31.9 +/- 4.8 mm Hg (p less than .01), pulmonary capillary wedge pressure from 28.2 +/- 3.5 to 22.1 +/- 5.1 mm Hg (p less than .01), and total pulmonary resistance from 875 +/- 304 to 697 +/- 291 dynes-sec-cm-5 (p less than .05). Cardiac index was not changed, but there was a significant redistribution of regional blood flow with an increase of renal blood flow after enalapril. Plasma renin activity rose significantly from 6.2 to 28.6 ng/ml/hr, whereas plasma norepinephrine did not change after enalapril. Seven patients were treated with enalapril for 4 weeks. Five patients reported symptomatic improvement. Five of six patients tested had an increase in both exercise time (NS) and maximum oxygen consumption (NS). Repeat hemodynamic evaluation in six patients after long-term enalapril therapy showed a persistent effect with significant reductions in right atrial pressure from 13.8 +/- 7.2 to 7.1 +/- 4.7 mm Hg and in mean arterial pressure from 82.5 +/- 10.4 to 76.6 +/- 5.3 mm Hg and a significant increase in cardiac index from 2.1 +/- 0.5 to 2.5 +/- 0.5 l/min/m2 (all p less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)
Association between early graft patency and late outcome for patients undergoing artery bypass graft surgery.
Authors: Gould B L , Clayton P D , Jensen R L , Liddle H V
Published: June 2011

For a group of 658 patients who received coronary artery bypass graft surgery, we investigated the correlation between the degree of early (6 months) graft patency and recurrence of anginal symptoms, late myocardial infarction, and postoperative coronary-related death. The patients were grouped according to the number of surgically placed grafts, and each group was further subgrouped on the basis of the number of grafts functioning at the early postsurgical follow-up examination. The patients were observed over a period as long as 13 years. The frequency with which angina returned correlated significantly with the degree of patency within each of the groups (one, two, three, or four grafts); patients with a higher percentage of patent grafts experienced longer periods of freedom from angina. On the average, patients with all of their multiple grafts patent experienced at least 7 more years of symptomatic relief than their counterparts with all grafts occluded. Most surprisingly, the rate of the return of angina for those patients who had all grafts patent and were completely revascularized was independent of the number of diseased vessels or the number of grafts placed. The findings for coronary death and postoperative infarction showed similar trends.
Electrophysiologic testing in assessment of therapy with sotalol for sustained ventricular tachycardia.
Authors: Senges J , Lengfelder W , Jauernig R , Czygan E , Brachmann J , Rizos I , Cobbe S , Kübler W
Published: June 2011

Eighteen patients with sustained ventricular tachycardia underwent electrophysiologic studies to establish the therapeutic efficacy of sotalol. In each patient ventricular tachycardia could be reproducibly initiated by programmed stimulation during control studies. Sotalol prevented induction of sustained ventricular tachycardia in 12 of the 18 patients (67%). Prolongation of the QTC interval and of ventricular refractoriness was regularly observed after sotalol but did not reliably predict prophylactic efficacy. Severe adverse effects, including congestive heart failure and sinus node dysfunction, were noted early during sotalol therapy in three patients. Nine patients were placed on long-term oral treatment with sotalol and four patients on another effective agent. In these 13 patients, complete (12 patients) or partial (one patient) long-term prophylaxis against ventricular tachycardia was documented over a mean follow-up period of 16 months (range 8 to 24). The study suggests that sotalol can provide effective prophylaxis against sustained ventricular tachycardia; this prophylactic efficacy is not typical for pure beta-adrenergic antagonism but may at least partly result from experimentally observed prolongation of the ventricular action potential duration.
Localization of regional myocardial ischemia by recording of monophasic action potentials.
Authors: Franz M R , Flaherty J T , Platia E V , Bulkley B H , Weisfeldt M L
Published: June 2011

Identification of regional myocardial ischemia by TQ-ST segment mapping, while commonly used, is relatively imprecise and nonspecific. In 41 open-chest dogs we examined whether monophasic action potentials (MAPs) recorded from the myocardial surface by means of a new contact-electrode technique could be used to more precisely and specifically index regional myocardial ischemia. After ligation of the left anterior descending coronary artery (LAD), epicardial and endocardial MAPs from the ischemic region demonstrated shortening of plateau duration followed by a progressive loss in amplitude to 48 +/- 8% and in maximum upstroke velocity (dV/dtmax) to 9 +/- 2% of control (n = 7). Regional hyperkalemia produced by intracoronary injection of potassium chloride also resulted in regional decreases in duration, amplitude, and dV/dtmax of the MAP. Similar to previously reported effects on transmembrane action potentials, ischemia- or hyperkalemia-induced loss in MAP amplitude was due to decreases in both diastolic (negative) and systolic (positive) potential and paralleled TQ segment depression and "true" ST segment elevation in unipolar direct current-coupled electrograms recorded from an adjacent site. In eight canine hearts we compared the abilities of MAP recordings and TQ-ST segment measurements in defining a region of myocardial ischemia. Transmural ischemia with a sharp flow border was produced by LAD ligation and distal embolization with dental rubber. One hour later simultaneous MAP and TQ-ST mapping was performed in each dog at 45 to 65 epicardial sites inside and outside the ischemic region. TQ-ST voltage was significantly increased 10 to 20 mm outside the visible cyanotic border, reaching a maximum just inside the border and decreasing progressively toward the center of the ischemic region to values not significantly different from those from sites 10 mm outside the ischemic border. In contrast, MAP amplitude and dV/dtmax were normal up to 5 to 10 mm outside the cyanotic border, decreased sharply across a lateral transition zone of only 8 mm to 8.7 +/- 2.3% and 4.3 +/- 0.9% of control, respectively, at sites 4 to 6 mm inside the border, and were uniformly abnormal across the entire ischemic region. Recordings made 3 hr after LAD ligation revealed an overall decline in the magnitude of TQ-ST, making definition of the ischemic border by TQ-ST even less precise, whereas the differences between MAPs from normal and ischemic myocardium had become even more pronounced than after 1 hr. Thus, unlike TQ-ST segment measurements, MAP recordings uniquely define ischemic and nonischemic sites and more precisely localize the border of an ischemic region.(ABSTRACT TRUNCATED AT 400 WORDS)
Drug-induced expansion of infarct: morphologic and functional correlations.
Authors: Hammerman H , Schoen F J , Braunwald E , Kloner R A
Published: June 2011

It has been established that glucocorticoids and several nonsteroidal antiinflammatory drugs, when administered early after coronary occlusion, interfere with myocardial scar formation. To determine whether this action is associated with expansion of myocardial infarct during the first week of coronary occlusion and whether expansion affects ventricular function, the effects of indomethacin on the left ventricle in the early phase of infarction were studied. In a blinded randomized study, experimental myocardial infarction was produced in 17 open-chest dogs by ligation of the proximal left anterior descending coronary artery; the treated group (n = 8) received 10 mg/kg iv indomethacin at 15 min and 3 hr after occlusion, and the control group (n = 9) received saline. After 7 days, regional function expressed as percent change of area (% delta A) of the left ventricular cavity was calculated from short-axis two-dimensional echocardiograms at the level of the infarct, the animals were killed, and their hearts were examined. The ratio of infarct thickness to noninfarcted wall thickness was 1.20 +/- 0.08 (mean +/- SEM) in the control group, and the ratio was lower in the indomethacin group, 0.96 +/- 0.04 (p less than .025). An expansion index of myocardial infarction was calculated as previously described and was 1.02 +/- 0.04 in the control group vs 1.29 +/- 0.06 in the indomethacin group (p less than .005). In eight dogs (six control and two treated) without expansion (expansion index less than 1.09), regional function expressed as % delta A was 46.8 +/- 2.6% (SEM), and in nine dogs (six treated and three control) with expansion, % delta A was significantly lower, 28.7 +/- 4.0% (p less than .005).(ABSTRACT TRUNCATED AT 250 WORDS)
The effect of two different diltiazem treatments on infarct size in ischemic, reperfused porcine hearts.
Authors: Klein H H , Schubothe M , Nebendahl K , Kreuzer H
Published: June 2011

The effect of diltiazem on the development of infarcts was investigated in porcine hearts. The left anterior descending coronary artery was occluded in each of 32 anesthetized pigs for 75 min and was reperfused for 4 hr. Diltiazem (15 micrograms/kg X min) was infused in 11 pigs for 30 min before occlusion (therapy A) and in another eight pigs before reperfusion (therapy B). Eleven pigs served as controls. Tissue concentrations of adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NAD) were determined in transmural needle biopsy samples taken from the ischemic apex after 70 min of ischemia. The infarct size, expressed as the ratio of the infarcted tissue over the area at risk of necrosis multiplied by 100, amounted to 79 +/- 20% in the control group. Although there was no significant difference between hemodynamics in the control and the treated groups, pretreatment with diltiazem significantly reduced infarct size (53 +/- 26%; p = .025). Reduction of infarct size by therapy B did not reach the required level of significance (66 +/- 33%). The ischemic loss of ATP and NAD was significantly lower in the pretreated group, which further indicates that the beneficial effect of diltiazem was exerted primarily during ischemia and not during reperfusion.
Mechanisms for atrial arrhythmias associated with cardiomyopathy: a study of feline hearts with primary myocardial disease.
Authors: Boyden P A , Tilley L P , Albala A , Liu S K , Fenoglio J J , Wit A L
Published: June 2011

The cellular electrophysiologic and structural characteristics of arrhythmic and non-arrhythmic atria isolated from feline hearts with spontaneously occurring cardiomyopathy were studied. The animals were divided into three groups according to the degree of left atrial enlargement: mild (group I), moderate (group II), and severe (group III). The right atria were of relatively normal size. Microelectrode recordings showed that inexcitable cells were present in both left and right atria of all groups but were most numerous in the left atria of group III animals. Most inexcitable cells had low resting membrane potentials. There was also a significant reduction in resting membrane potentials, maximum rate of phase 0 depolarization, and action potential amplitude of excitable cells in left atria of animals in groups II and III, whereas action potentials of excitable cells in the right atria were normal. Acetylcholine or norepinephrine often restored excitability to cells that originally did not generate action potentials. Norepinephrine also caused slow-response action potentials as well as abnormal automaticity and triggered activity due to delayed afterpotentials. The diseased atria showed marked structural abnormalities, which were most pronounced in group III cats, including large amounts of interstitial fibrosis, cellular hypertrophy and degeneration, and thickened basement membranes. Therefore electrophysiologic abnormalities and concurrent changes in cell structure may be involved in the genesis of atrial tachyarrhythmias caused by cardiomyopathy.
Contrasting effects of nifedipine and adenosine on regional myocardial flow distribution and metabolism distal to a severe coronary arterial stenosis: observations in sedated, closed-chest, domestic swine.
Authors: Gewirtz H , Gross S L , Williams D O , Most A S
Published: June 2011

This study tested the hypothesis that intrinsic negative inotropic effects of a drug used to induce coronary vasodilation distal to a severe coronary arterial stenosis may influence the extent of redistribution of transmural flow and its metabolic consequences. To test this hypothesis, studies were conducted in eight closed-chest, sedated swine with severe (82% reduction in luminal diameter) coronary arterial stenoses. Measurement of hemodynamic parameters, regional myocardial blood flow (microsphere technique), lactate metabolism, and oxygen consumption were made (1) under control conditions, (2) after 10 min of intracoronary infusion of a vasodilator distal to the stenosis, and (3) under repeat control conditions. Each animal received both intracoronary adenosine (400 micrograms/min) and nifedipine (50 micrograms/min). The order of drug infusion was chosen at random and a control period separated administration of each. In response to nifedipine there was no significant change in the group mean (+/- SD) value of endocardial flow (1.21 +/- 0.34 to 1.29 +/- 0.61 ml/min X g-1) distal to the stenosis. In contrast, epicardial flow increased in comparison with control in response to nifedipine (1.30 +/- 0.58 to 1.79 +/- 0.74 ml/min X g-1; p less than .05). Regional myocardial oxygen consumption (MVO2) declined in comparison with control in response to nifedipine (14.0 +/- 4.2 to 11.1 +/- 5.0 ml/min X 100 g-1; p less than .05). Regional lactate extraction did not change in comparison with control during infusion of nifedipine (18.2 +/- 22.4 vs 11.7 +/- 16.8). In response to adenosine, endocardial blood flow distal to the stenosis declined in comparison with control (1.25 +/- 0.53 to 1.07 +/- 0.38 ml/min X g-1; p less than .05), while epicardial flow increased (1.31 +/- 0.55 to 2.26 +/- 0.59 ml/min X g-1; p less than .01). Regional MVO2 also tended to decline in comparison with control in response to adenosine (13.4 +/- 4.9 to 11.7 +/- 2.9 ml/min X 100 g-1) and was significantly (p less than .05) reduced in comparison with postintervention control (14.6 +/- 4.2 ml/min X 100 g-1). In contrast to nifedipine, adenosine caused a significant decline in regional lactate extraction in comparison with control (12.7 +/- 23.2% to -40.6 +/- 55.0%; p less than .01). Thus, administration of nifedipine, a negative inotropic agent, resulted in (1) a decline in regional MVO2, (2) increased epicardial blood flow with variable effects on endocardial flow distal to the stenosis, and (3) no evidence of de novo or worsening ischemia, even in animals in which endocardial flow decreased.(ABSTRACT TRUNCATED AT 400 WORDS)
Beta-adrenergic stimulation of the failing ventricle: a double-blind, randomized trial of sustained oral therapy with prenalterol.
Authors: Roubin G S , Choong C Y , Devenish-Meares S , Sadick N N , Fletcher P J , Kelly D T , Harris P J
Published: June 2011

Eleven patients with severe left ventricular impairment (mean ejection fraction 24%) and moderate impairment of exercise tolerance underwent a double-blind, placebo-controlled, cross-over trial of the orally administered beta-agonist prenalterol. Exercise hemodynamics and tolerance were measured during bicycle and treadmill exercise after 2 weeks of therapy with placebo or prenalterol. Cardiac index, ejection fraction, and stroke work index were not improved and exercise duration and peak oxygen consumption were not significantly different during the two treatments. During prenalterol treatment heart rate during exercise was consistently reduced. These results show that prolonged therapy with prenalterol does not improve hemodynamics or exercise tolerance and is associated with a diminished heart rate response to exercise.
Enhanced atrioventricular nodal conduction in man: electrophysiologic effects of pharmacologic autonomic blockade.
Authors: Benditt D G , Klein G J , Kriett J M , Dunnigan A , Benson D W
Published: June 2011

Enhanced atrioventricular nodal conduction (EAVC) comprises a portion of the spectrum of atrioventricular node electrophysiology in which physiologic slowing of atrioventricular conduction is diminished. To evaluate the basis of EAVC in humans, we compared the effect of pharmacologic autonomic blockade on electrophysiologic characteristics of atrioventricular nodal conduction and refractoriness in 10 patients with EAVC and 12 patients without EAVC (non-EAVC). The effects of autonomic blockade (0.2 mg/kg iv propranolol and 0.04 mg/kg iv atropine) on sinus cycle length and atrial refractory period were similar in both EAVC and non-EAVC patients. After autonomic blockade, minimum atrial paced cycle length with 1:1 atrioventricular conduction lengthened in EAVC patients (control, 268 +/- 25 msec; blockade, 307 +/- 34 msec; p less than .01), but remained unchanged in non-EAVC patients (control, 392 +/- 69 msec; blockade, 382 +/- 49 msec; p = NS). Similarly, atrioventricular nodal functional refractory periods tended to lengthen in EAVC patients, while remaining unchanged or shortening in non-EAVC patients. Furthermore, although autonomic blockade reduced differences between EAVC and non-EAVC patients, both minimum cycle length with 1:1 atrioventricular conduction and atrioventricular functional refractory period remained shorter in EAVC than in non-EAVC patients (p less than .02). Thus, baseline differences in autonomic atrioventricular nodal control differ in EAVC and non-EAVC patients, but do not fully account for differences in atrioventricular nodal electrophysiologic properties in these patients. Consequently, underlying structural functional factors may play an important role in determining the range of atrioventricular nodal electrophysiologic characteristics in man.
99mTc-pyrophosphate imaging in patients with acute myocardial infarction: comparison of planar imaging with single-photon tomography with and without blood pool overlay.
Authors: Corbett J R , Lewis M , Willerson J T , Nicod P H , Huxley R L , Simon T , Rude R E , Henderson E , Parkey R , Rellas J S
Published: June 2011

To test the hypothesis that single-photon emission computed tomography (SPECT) of 99mTc-pyrophosphate (99mTc-PPi) with and without the overlay of tomographic blood pool scintigrams might detect small infarcts not identified by planar imaging, 52 patients were studied 3.2 +/- 2.0(SD) days after hospital admission for suspected acute myocardial infarction. Patients were chosen prospectively for tomographic study primarily, but not exclusively, because planar four-view imaging with 99mTc-PPi was either negative or equivocal. SPECT was performed with a commercial rotating detector system immediately after planar imaging on one occasion. Corresponding 99mTc-PPi and blood pool sections were mapped into opposite halves of a bichromic color table and displayed as an overlay. Planar images, SPECT and SPECT with blood pool overlay were interpreted separately and in random order without knowledge of clinical data. Seventeen patients had transmural infarcts (four anterior, 13 inferior), 19 had nontransmural infarcts, and 16 patients did not have acute myocardial infarction. The sensitivity of SPECT with blood pool overlay was significantly better than planar imaging for the entire group with myocardial infarction (97% vs 78%; p less than .025); this was primarily due to increased sensitivity in the detection of nontransmural myocardial infarction (95% vs 67%; p less than .05), although in one additional patient inferior transmural myocardial infarction was also detected by the SPECT overlay technique. The specificities of the SPECT overlay technique and planar imaging were not significantly different; however, receiver operating characteristic analysis showed enhanced observer confidence with the tomographic method. SPECT without overlay was intermediate in sensitivity and specificity.(ABSTRACT TRUNCATED AT 250 WORDS)
Ventricular arrhythmias during the first year after acute myocardial infarction: influence of long-term treatment with metoprolol.
Authors: Olsson G , Rehnqvist N
Published: June 2011

Three hundred and one patients who had been hospitalized for acute myocardial infarction, were less than 70 years old, were in sinus rhythm, and did not have complete bundle branch block were stratified before discharge according to age, size of infarction, and type of ventricular arrhythmias as determined on a 6 hr electrocardiogram (ECG). They were thereafter randomly assigned to double-blind treatment with 100 mg bid metoprolol or placebo. Repeat 6 hr ECGs were recorded 3 days and 1, 6, and 12 months after treatment had begun. In the placebo group there was a significant increase in the proportion of patients with complex premature ventricular complexes (PVCs) (i.e., multiform, paired and R-on-T PVCs, or ventricular tachycardia) as well as increased numbers of PVCs in the patients during the follow-up. In contrast, an initial decrease in the number of PVCs (p less than .001) was found in the metoprolol group, whereas the complexity of PVCs was constant in those patients who continued on metoprolol therapy throughout the follow-up period. We conclude that the increase in complexity and number of PVCs that is part of the natural clinical course after myocardial infarction is counteracted by long-term treatment with metoprolol.