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Biomedical subjects

N Reichek

Publications and source records attributed to N Reichek.

At least 73 records · Page 4Linked to original sources
PubMed1990

Pulmonary vascular cine MR imaging: a noninvasive approach to dynamic imaging of the pulmonary circulation.

Cine gradient-recalled magnetic resonance (MR) imaging, which has flow sensitivity and high temporal resolution, may potentially yield both morphologic and dynamic flow-related information in the pulmonary vasculature. The authors used this modality to evaluate pulmonary vessels in 12 healthy subjects and in 14 patients with a variety of cardiopulmonary disorders. Normal pulmonary arteries and veins were characterized by distinctive signal intensity and diameter variations as well as motion of the vessels during the cardiac cycle. Patients with pulmonary arterial hypertension demonstrated loss of the normal pulsatile systolic increase and diastolic decline in velocity-related signal intensity and in diameter of the proximal pulmonary arteries. Disorders of pulmonary venous signal and diameter profiles during the cardiac cycle, which show a characteristic biphasic pattern in healthy subjects, were identified in five patients with mitral valvular disease. These initial results indicate that cine MR imaging techniques hold promise in the evaluation of pathophysiologic conditions in the pulmonary circulation.

Adult↗
PubMed1989

Prevalence of multivalvular regurgitation in athletes.

To assess the effects of exercise training on the prevalence of valvular regurgitation, 2-dimensional echocardiography and Doppler flow mapping were performed in 45 athletes and 26 sedentary control subjects of similar age and sex. Mitral, tricuspid, aortic and pulmonic regurgitations were sought in all possible views and mitral and tricuspid flow velocities were recorded. Mitral and tricuspid anulus diameters and the maximal areas of regurgitant flow were planimetered. Regurgitation of at least one of the cardiac valves was found in 91% of athletes but in only 38% of control subjects (p less than 0.001). Mitral and tricuspid regurgitation occurred more commonly in athletes than in control subjects (mitral 69 vs 27%; tricuspid 76 vs 15%). The prevalence of aortic and pulmonic regurgitation was similar. Although athletes and sedentary normal subjects differed with respect to heart rate, right and left ventricular filling patterns and tricuspid and mitral anulus diameters, none of these variables was related to the presence or severity of regurgitation. Thus, exercise training is associated with an increased prevalence of mitral and tricuspid regurgitation and altered ventricular inflow patterns. The mechanism of these findings is unclear. Multivalvular regurgitation is common in athletes and does not imply structural valvular abnormalities.

Adult↗
PubMed1989

Left ventricular shape, afterload and survival in idiopathic dilated cardiomyopathy.

Because idiopathic dilated cardiomyopathy is characterized by elevated wall stress and a more spherical left ventricle, the relations among shape, afterload and survival were examined. Thirty-six patients with cardiomyopathy were prospectively studied by two-dimensional echocardiography. Data included echocardiographic short- and long-axis cavity dimensions, their ratio and, with cuff systolic blood pressure, meridional and circumferential end-systolic stress and their ratios. Survivors (n = 16) were followed up for 52 months (range 40 to 76); nonsurvivors (n = 20) died an average of 11 months after study. Survivors had a smaller left ventricular end-diastolic short-axis dimension (6.4 versus 7.1 cm, p less than 0.03) but a similar long-axis length (8.6 versus 8.3 cm). However, overall cavity shape or the ratio of short- to long-axis end-diastolic dimensions was more spherical in those with poorer survival (ratio 0.76 versus 0.68, p less than 0.02). Meridional and circumferential end-systolic stresses were similar in the two groups, but stress was more evenly distributed in the long- and short-axis planes in nonsurvivors (meridional/circumferential stress ratio 0.57 versus 0.52 in survivors, p less than 0.05). Improved survival was associated with an end-diastolic short-axis dimension less than 7.63 cm, a short- to long-axis ratio less than 0.76 and a meridional to circumferential stress ratio less than 0.54. Life table analysis revealed a 28% mortality rate in patients with all three of these characteristics compared with 100% in patients with none. Survivors and nonsurvivors did not differ in systolic cavity dimension, wall thickness, relative wall thickness, cavity volume, percent posterior wall thickening or fractional shortening.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Alterations in diastolic function in response to progressive left ventricular hypertrophy.

To examine the time course of the functional consequences of progressive left ventricular hypertrophy, diastolic left ventricular inflow and wall thinning variables were analyzed in 13 dogs before and 2, 4, 8 and 12 weeks after creation of perinephritic hypertension. Left ventricular echocardiograms were digitized for dimensions, mass and peak rates of wall thinning (-dh/dt/h) and cavity enlargement (dD/dt/D). Doppler recordings of left ventricular inflow were analyzed for peak early (E) and late (A) diastolic inflow velocities, their ratio and atrial filling fraction. At 2 weeks, systolic blood pressure increased from 151 to 233 mm Hg, wall stress from 52 to 80 kdynes/cm2 and posterior wall thickness from 0.68 to 0.84 cm (all p less than 0.05). Left ventricular mass increased from 90 to 115 g over 12 weeks (p less than 0.05). Heart rate, cavity size and systolic shortening were unchanged at all data points. Diastolic abnormalities accompanied the developing hypertrophy and included impairment of early function, as demonstrated by a peak rate of wall thinning, from -13.4 to -8.9 l/s at 2 weeks (p less than 0.05), increased dependence on atrial systolic filling, a decrease in E/A from 1.68 to 1.29 at 4 weeks (p less than 0.05) and an increase in atrial filling fraction from 30% to 43% at 8 weeks (p = NS). Thus, diastolic dysfunction is an early consequence of experimental left ventricular hypertrophy. Different aspects of diastolic impairment are sensitively reflected by echocardiographic Doppler recordings, suggesting that these methods should be useful for the detection of diastolic dysfunction in human patients.

Animals↗
PubMed1989

Intermittent nitrate therapy in angina pectoris.

The rationale for intermittent nitrate therapy is based on the pathophysiology of nitroglycerin tolerance and the diurnal pattern of symptoms encountered in patients with chronic stable angina. Nitrate tolerance was first observed as tolerance to headache in industrial toxicology. When long-acting nitrates for chronic stable angina became available, similar tolerance was observed but not thought to indicate tolerance to a haemodynamic or therapeutic effect. Subsequently, Needleman and coworkers (J Pharmacol Exp Ther 1973; 187: 324) defined in vitro the phenomenology of vascular smooth muscle tolerance to nitroglycerin-induced relaxation and reversibility was demonstrated. More recently, a potential molecular explanation for nitrate tolerance has been proposed: sulfhydryl group depletion in smooth muscle cells resulting in reduced formation of S-nitrosothiols on nitrate exposure with resultant reduced activation of cyclic GMP. In vivo, other mechanisms, including fluid retention and neurohumoral responses to vasodilation may also be important. The first demonstration that nitrate tolerance affected the therapeutic efficacy of long-acting nitrates was reported by Parker and coworkers in 1982 (Circulation 1987; 76: 572-6). This landmark study was not given much credence at the time because it appeared to be in conflict with earlier reports. However, in the past 6 years development of tolerance has been demonstrated with a variety of oral nitrates, transdermal nitroglycerin and intravenous nitroglycerin. When plasma concentrations are held constant, tolerance to antianginal effects is demonstrable within 24h, but varies markedly in severity from individual to individual.(ABSTRACT TRUNCATED AT 250 WORDS)

Angina Pectoris↗
PubMed1989

Two-dimensional and Doppler-echocardiographic and cardiac catheterization correlates of survival in primary pulmonary hypertension.

To determine correlates of survival in primary pulmonary hypertension, we compared 41 echocardiography-Doppler and nine catheterization parameters with outcome in 26 patients. Mean follow-up was 19.7 months in survivors; mean survival was 4.8 months in 16 nonsurvivors. Cox life-table univariate analysis correlated two echocardiographic, three Doppler, and three catheterization variables with poor survival (p less than or equal to 0.05), and chi 2 analysis ensured the best critical values: severity of pericardial effusion, heart rate of more than 87 beats/min, pulmonic flow acceleration time of less than 62 msec, tricuspid early flow deceleration (T-DEC) equal to or less than -300 cm2/sec, mitral early flow-to-atrial flow velocity ratio (M-E/A) equal to or less than 1.0, catheterization cardiac index (CI) equal to or less than 2.3 l/min/m2, mean pulmonary artery pressure of more than 61 mm Hg, and diastolic pulmonary artery pressure of more than 43 mm Hg. Multivariate life-table analysis of noninvasive variables revealed the severity of pericardial effusion to be independently significant (p = 0.006), whereas analysis of catheterization variables revealed cardiac index to be independently significant (p = 0.014). Combined multivariate analysis did not differ from the noninvasive results alone. Categorical modeling of the eight significant variables split at their critical values (present or absent) revealed M-E/A, T-DEC, and CI to be independently significant by multivariate analysis (p = 0.0014). Analysis of the five echocardiography-Doppler variables alone revealed M-E/A, T-DEC, and heart rate to be independently significant (p = 0.0016). In both cases, mortality increased with the number of critical values reached.(ABSTRACT TRUNCATED AT 250 WORDS)

Actuarial Analysis↗
PubMed1989

Noninvasive determination of coronary artery bypass graft patency by cine magnetic resonance imaging.

Cine magnetic resonance imaging (MRI) is a gradient-recalled, retrospectively gated, fast-scan technique that depicts laminar flowing blood as bright signal and has been proposed as a useful method for determination of coronary artery bypass graft (CABG) patency. Therefore, we performed a blinded prospective study to assess the value of cine MRI determination of CABG patency in 20 patients with 45 CABG proximal anastomoses who were undergoing repeat angiography. Ten normal subjects served as controls to define normal intrathoracic vascular patterns. There were 21 left anterior descending (LAD) grafts, of which four were left internal mammary (LIMA), 12 left circumflex (Cx), and 12 right coronary (RCA) grafts. After localizing spin-echo coronal images were obtained, multiple axial multislice interleaved cine MRI acquisitions, each consisting of two to four 5-10-mm-thick slices at eight to 24 frames per cardiac cycle, were obtained from the superior main pulmonary artery to the inferior left ventricle. Each acquisition took 5-8 minutes with a subsequent 5-10 minutes of computer image reconstruction. Total study time per patient was 50-75 minutes. Known to cine MRI interpreters were the original surgical CABG insertions but not the angiographic findings. A graft was called patent if a bright graft flow signal, not corresponding to a normal vessel, was identified on multiple frames at multiple levels abutting the great vessels or epicardial surface of the heart. Angiographically, there were 33 patent grafts, of which 29 were identified as patent by cine MRI (sensitivity, 88%).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1988

Electrocardiographic diagnosis of exercise-induced left ventricular hypertrophy.

To assess the prevalence of physiologic left ventricular hypertrophy and the usefulness of ECG criteria for its diagnosis, we compared ECGs and M-mode echocardiograms from 44 ultraendurance athletes and 20 similarly aged sedentary control subjects. Left ventricular mass was elevated in 25 of 44 (57%) athletes including 17 of 29 (59%) men greater than 134 gm/m2 and 8 of 15 (53%) women greater than 110 gm/m2. The sensitivity and specificity of the three ECG criteria used to diagnose left ventricular hypertrophy were: Sokolow-Lyon voltage (S-V1 + R-V5 greater than or equal to 3.5 mV), 65% and 61%; Romhilt-Estes score (greater than or equal to 4), 16% and 84%; and Cornell voltage (R-aVL + S-V3 greater than 2.8 mV in men and greater than 2.0 mV in women), 8% and 95%, respectively. Left ventricular mass, mass index, posterior wall thickness, chamber diameter, and relative wall thickness were not related to any measurement of QRS voltage. Nonvoltage ECG criteria for left ventricular hypertrophy were rare in athletes. Thus hypertrophy is a common but not universal adaptation to exercise. It is only moderately well detected by standard voltage criteria for left ventricular hypertrophy and is not reflected in nonvoltage criteria.

Adult↗
PubMed1988

Echocardiographic visualization of coronary artery anatomy in the adult.

In the light of technologic advances and the development of new imaging planes, the feasibility of two-dimensional echocardiographic visualization of coronary artery anatomy was reevaluated in the adult. Thirty-five subjects were studied using an ultrasonograph equipped with a 3.5 and 5.0 MHz annular array transducer, digital processing and cine loop review. There were 18 normal subjects and 17 patients with heart disease, including 9 patients with valvular, 5 patients with coronary, 2 patients with congenital and 1 patient with cardiomyopathic disease. The mean age was 47 +/- 18 years (range 17 to 79). Modifications of standard parasternal and apical views permitted high quality images of portions of each of the major epicardial vessels adequate for assessment of luminal diameter. The left main coronary artery was seen in 30 (86%) of the 35 subjects and its bifurcation was seen in 15. The left anterior descending coronary artery was seen in 30 subjects (mean length 3.9 +/- 2.3 cm, maximal length 7.5), the left circumflex artery in 11 (1.1 +/- 1.0, maximal 3.0) and the right coronary artery in 32 (5.6 +/- 2.6, maximal 12). Proximal and mid portions of the left anterior descending artery were seen in 23 and 11 subjects, respectively. The average proximal length visualized was 4.2 cm, and the average luminal diameter visualized was 4.9 mm. The average length of the mid left anterior descending coronary artery seen was 1.9 cm and the average luminal diameter seen was 4.6 mm. The proximal right coronary artery was seen in 17 subjects (average visualized length 2.7 cm and average diameter 3.1 mm).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1988

Antianginal effects of intravenous nitroglycerin over 24 hours.

To determine the constancy of hemodynamic and antianginal effects of the constant infusion of intravenous nitroglycerin (NTG) and their relationship to infusion rate and plasma NTG concentration, we administered maximal tolerated doses of intravenous NTG (range 10 to 120 micrograms/min, mean = 52 +/- 33 micrograms/min) and placebo to 10 patients with chronic stable angina for 25 hr each in a randomized, double-blind fashion. Sublingual NTG (0.4 mg) was given at 24.5 hr of infusion as a positive control. Bicycle exercise time (NIH protocol), blood pressure, heart rate, exercise ST response, and venous plasma NTG were determined before and at 1, 4, 8, 24, and 24.5 hr. Plasma NTG was linearly related to infusion rate, reached a steady state within 15 min and was unchanged over 24 hr (mean = 5.5 +/- 1.2 ng/ml). Mean plasma NTG clearance was 9.3 liters/min. However, during dose titration, patients demonstrated different relationships between plasma NTG and hemodynamic effects, with widely varying slopes and intercepts. Intravenous NTG produced a sustained reduction in blood pressure and a rise in heart rate at rest, and a reduction in blood pressure during submaximal exercise at as late as 24 hr, associated with reduced submaximal ST segment abnormality. In contrast, exercise tolerance to onset of angina showed a marked initial increase on intravenous NTG but fell progressively and did not differ from that with placebo at 24 hr. Increased exercise tolerance was associated with an increase in maximal heart rate and double product (heart rate X blood pressure), suggesting that direct coronary vasodilation and/or reduced left ventricular volume were the principal determinants of increased exercise tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Sublingual↗
PubMed1987

Nitroglycerin in chronic stable angina pectoris.

Recent evidence suggests that traditional approaches to the use of nitroglycerin (NTG) in patients with chronic stable angina should be reconsidered. Studies of the time to onset of hemodynamic effects of sublingual NTG suggest that the first detectable effect, on left ventricular end-diastolic pressure, occurs at a mean of 90 seconds after administration. By timing the duration of exertional angina after formal exercise testing, one can show that, on average, chest pain is gone within 2 minutes. Thus, in many patients, it is unlikely that sublingual NTG can further shorten episodes of exertional angina. The value of sublingual NTG is greater when patients exercise beyond the onset of pain, when patients have more protracted episodes of exertional pain and when there is a need to resume immediately the activity that brought on the angina. With respect to angina prophylaxis, the pioneering studies of Parker and co-workers have now been amply confirmed. Continuous nitrate administration by oral, transdermal or intravenous routes results in substantial, albeit incomplete, tolerance. Tolerance occurs even when high plasma concentrations are achieved and persist over time. Tolerance can eliminate responsiveness to sublingual NTG. Preliminary evidence suggests that tolerance to the antianginal effects of NTG at maximal exercise may be more marked than tolerance to the effects of NTG on silent ischemia at submaximal activity levels. The significance of this dissociation in time course and its implications are unclear at this time. Three potential strategies exist for avoiding NTG tolerance in patients with chronic stable angina. Administration of a thiol donor has been shown to reverse some hemodynamic manifestations of tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Sublingual↗
PubMed1987

Variable responses of mitral valve motion and flow in systemic hypertension and in idiopathic dilated cardiomyopathy.

The relation between transmitral flow and diastolic mitral valve motion were examined in 17 normal persons, 14 patients with hypertension and 12 patients with idiopathic dilated cardiomyopathy. M-mode echograms were analyzed for early and late diastolic mitral leaflet separations, their ratio and E-F slope. Pulsed Doppler transmitral flow was analyzed for early and late velocities, their ratio and early flow deceleration. Early diastolic mitral valve leaflet separation was reduced in patients with hypertension (at 28 +/- 5 mm [p less than 0.05] ) and in patients with cardiomyopathy (at 22 +/- 3 mm [p less than 0.01] ). Flow velocity was also reduced in patients with hypertension (at 52 +/- 11 cm/s [p less than 0.05] ) and in patients with cardiomyopathy (at 48 +/- 15 cm/s [p less than 0.01] ). However, early leaflet separation and flow velocity were not related (r = 0.26). Late diastolic leaflet separation was similar (at 25 +/- 5 mm) in normal subjects and in those with hypertension (at 23 +/- 6 mm), but was reduced in patients with cardiomyopathy (at 18 +/- 3 mm [p less than 0.01] ). In contrast, late flow velocity was increased in patients with hypertension (at 52 +/- 12 cm/s [p less than 0.05] ) but unchanged in patients with cardiomyopathy (at 42 +/- 16 cm/s). The ratio of early to late leaflet separation was similar in all groups, whereas the ratio of flow velocities was reduced in hypertensive patients. Neither the E-F slope not early flow deceleration was altered in either pathologic group. Thus, hypertension and cardiomyopathy had similar effects in early rather than late diastole.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Contribution of afterload, hypertrophy and geometry to left ventricular ejection fraction in aortic valve stenosis, pure aortic regurgitation and idiopathic dilated cardiomyopathy.

To investigate the relation of left ventricular (LV) afterload, hypertrophy, geometry and systolic pump function, 17 normal persons, 24 patients with aortic stenosis (AS), 20 with aortic regurgitation (AR) and 15 with idiopathic dilated cardiomyopathy (DC) were studied. Two-dimensional echograms were used to assess end-systolic meridional and circumferential stresses and their ratio, LV mass, relative wall thickness (h/R ratio) and the ratio of LV minor axis to length, used as an index of shape. Independently obtained ejection fraction (EF) was used to determine which patients had normal (EF greater than or equal to 55%) and which had depressed (EF less than 55%) pump function. Patients with AS and low EF had similar LV mass (228 vs 215 g) but larger LV cavity (5.6 vs 4.5 cm), lower h/R ratio (0.53 vs 0.73, p less than 0.01), and therefore higher circumferential stress (336 vs 268 kdyne/cm2, p less than 0.05). Compared with normal persons, patients with DC had a lower h/R ratio (0.28 vs 0.38, p less than 0.01), higher circumferential stress (362 vs 215 kdyne/cm2, p less than 0.01) and more uniform stress distribution (meridional to circumferential stress ratio 0.57 vs 0.39, p less than 0.01), implying that meridional stress overestimates effective afterload. Afterload excess and LV shape change may be important to pump function in patients with AS or DC. In contrast, in those with AR, no significant shape differences were noted, although LV mass was higher in those with low EF (279 vs 211 g, p less than 0.05). Depressed pump function may result from impaired myocardial performance in AR without afterload excess.

Adult↗
PubMed1987

Unreliability of hemodynamic indexes of left ventricular size during cardiac surgery.

Pulmonary artery diastolic (PADP) and wedge pressures (PAWP) and left ventricular end-diastolic pressure (LVEDP) are commonly used to estimate left ventricular (LV) preload. To assess the ability of hemodynamic indexes of preload to estimate anatomical preload, or LV volume, we studied 45 patients during a coronary (18 patients) or aortic valve (27 patients) procedure and compared epicardial two-dimensional echocardiographic LV cavity area with simultaneous measurements of PADP, PAWP, and high-fidelity LVEDP. Pulmonary artery diastolic pressure, PAWP, and their percent change after bypass did not correlate with absolute values (before or after bypass) or percent change in LVEDP. Percent change in LV area correlated weakly with percent change in PADP (r = .34, p less than .03) but not with changes in PAWP or LVEDP. Changes were opposite in direction in 45% (PADP), 50% (PAWP), and 67% (LVEDP) of patients. In conclusion, both PADP and PAWP were poor guides to LVEDP and neither reflected changes in LV size. Thus, hemodynamic indexes of preload should be used with caution during cardiac operations.

Adult↗
PubMed1987

Comparison of echocardiographic methods for assessment of left ventricular shortening and wall stress.

M-mode echocardiographic measurement of left ventricular fractional shortening and meridional wall stress has been used extensively alone and in combination to describe left ventricular systolic function. To determine whether the improved dimensional information afforded by two-dimensional echocardiography might result in shortening and stress calculations yielding a different view of left ventricular function, we compared two-dimensional and M-mode echocardiograms in 69 subjects (19 normal, 13 with aortic stenosis, 22 with aortic regurgitation and 15 with congestive cardiomyopathy). Fractional shortening was greater with M-mode than with two-dimensional echocardiography in all subjects, especially in those with cardiomyopathy (p less than 0.05). In aortic stenosis, two-dimensional shortening, at 24 +/- 5%, was reduced (p less than 0.05 versus normal), but M-mode shortening, at 34 +/- 5%, was not. M-mode estimates of meridional stress were higher than two-dimensional values, again especially in cardiomyopathy. Two-dimensional echocardiography enabled determination of long- and short-axis ratios, circumferential stress and the ratio of circumferential to meridional stresses. Circumferential stress was elevated in aortic stenosis at 302 +/- 65 X 10(3) dynes/cm2, suggesting afterload excess as the cause for the observed reduction in two-dimensional shortening. The more spherical cardiomyopathic hearts had a meridional to circumferential stress ratio closer to 1, such that use of meridional stress alone would overestimate effective afterload. It is concluded that M-mode and two-dimensional echocardiographic analyses of left ventricular shortening and stress produce different results. Two-dimensional echocardiographic methods may enhance the assessment of ventricular function, especially in patients with aortic stenosis and cardiomyopathy.

Adult↗
PubMed1987

Experimental myocardial cryoinjury: local electromechanical changes, arrhythmogenicity, and methods for determining depth of injury.

To characterize the electromechanical effects of acute and 2-week-old cryoinjury, programmed stimulation and epicardial M-mode echo mapping (7.5 mHz) were performed prior to, at 15 minutes and 15 +/- 2 days after cryoinjury in 10 dogs. Epicardial and intramural bipolar and unipolar electrograms were recorded in five of the dogs. Cryoinjury was produced with a 5 mm in diameter flat cryoprobe at -60 degrees C applied to the left ventricular epicardium for 10 minutes at each of six contiguous sites. Cryoinjury, acutely and at 2 weeks, was characterized by a loss of normal intramural systolic thickening and a decrease in echo density. The maximum depth of cryoinjury determined by echo ranged from .55 to .85 cm acutely, and .50 to .80 cm chronically and it correlated acutely and chronically (r = .80; r = .85) with pathologically documented depth of cryoinjury at 2 weeks. Acutely, the presence of either an abnormal intramural unipolar or bipolar electrogram also defined the depth of cryoinjury within .16 cm. In contrast, epicardial electrograms were not useful for judging depth of cryoinjury. A QS complex on the epicardial unipolar electrogram was recorded over the cryoinjury acutely and at 2 weeks in four of five dogs despite preserved subendocardial systolic wall thickening and normal histology extending 40 to 65% of the wall thickness. Epicardial bipolar electrograms uniformly showed a marked decrease in amplitude and slope of the intrinsic deflection, a small but insignificant increase in width and no multicomponent activity. Ventricular fibrillation was reproducibly initiated with three ventricular extrastimuli in five of 10 dogs at 2 weeks. No ventricular tachycardia was initiated.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Experimental congestive heart failure produced by rapid ventricular pacing in the dog: cardiac effects.

Chronic rapid ventricular pacing in the dog reportedly produces a useful preparation of low-output heart failure. However, little information is available regarding cardiac changes in this preparation. Accordingly, we evaluated the effects of both short-term (3 weeks) and prolonged (2 months) rapid ventricular pacing on cardiac hemodynamics, mass, and chamber size. The effects of short-term pacing on left ventricular wall thickening, blood flow, and metabolism were also examined. Compared with 16 control dogs, dogs paced for either 3 weeks (n = 8) or 2 months (n = 13) exhibited reduced cardiac outputs (control 130 +/- 20 ml/min/kg, 3 week pacing 112 +/- 19 ml/min/kg, 2 month pacing 116 +/- 14 ml/min/kg) and elevated pulmonary wedge pressures (control 10 +/- 3 mm Hg, 3 week pacing 26 +/- 5 mm Hg, 2 month pacing 26 +/- 8 mm Hg) and right atrial pressures (control 4 +/- 1 mm Hg, 3 week pacing 13 +/- 3 mm Hg, 2 month pacing 9 +/- 3 mm Hg) (all p less than .01 vs control). At the postmortem examination, both groups of paced dogs also exhibited increased left ventricular volumes (control 13 +/- 6 ml, 3 week pacing 27 +/- 6 ml, 2 month pacing 26 +/- 8 ml), right ventricular volumes (control 13 +/- 5 ml, 3 week pacing 27 +/- 9, 2 month pacing 24 +/- 7 ml), and right ventricular mass (control 27 +/- 5 g, 3 week pacing 32 +/- 6 g, 2 month pacing 34 +/- 6 g) (all p less than .03 vs control) but had normal left ventricular mass. Three weeks of pacing also decreased percent left ventricular shortening (34 +/- 6% to 17 +/- 7%) associated with a disproportionate deterioration of posterior wall thickening (58 +/- 16% to 17 +/- 18%) (both p less than .01), as assessed by echocardiography. This left ventricular dysfunction was associated with no change in myocardial lactate extraction (prepacing 40 +/- 10%, 3 week pacing 36 +/- 10%), myocardial arteriovenous O2 difference, or myocardial histology, suggesting that it was not due to myocardial ischemia. These data indicate that rapid ventricular pacing in the dog produces a useful experimental preparation of low-output heart failure characterized by biventricular pump dysfunction, biventricular cardiac dilation, and nonischemic impairment of left ventricular contractility.

Animals↗