Abnormal cardiac and skeletal muscle mitochondrial function in pacing-induced cardiac failure

BACKGROUND

Previous studies have shown that marked changes in myocardial mitochondrial structure and function occur in human cardiac failure. To further understand the cellular events and to clarify their role in the pathology of cardiac failure, we have examined mitochondrial enzymatic function and peptide content, and mitochondrial DNA (mtDNA) integrity in a canine model of pacing-induced cardiac failure.

METHODS

Myocardium and skeletal muscle tissues were evaluated for levels of respiratory complex I-V and citrate synthase activities, large-scale mtDNA deletions as well as peptide content of specific mitochondrial enzyme subunits. Levels of circulating and cardiac tumor necrosis factor-alpha (TNF-alpha), and of total aldehyde content in left ventricle were also assessed.

RESULTS

Specific activity levels of complex III and V were significantly lower in both myocardial and skeletal muscle tissues of paced animals compared to controls. In contrast, activity levels of complex I, II, IV and citrate synthase were unchanged, as was the peptide content of specific mitochondrial enzyme subunits. Large-scale mtDNA deletions were found to be more likely present in myocardial tissue of paced as compared to control animals, albeit at a relatively low proportion of mtDNA molecules (<0.01% of wild-type). In addition, the reduction in complex III and V activities was correlated with elevated plasma and cardiac TNF-alpha levels. Significant increases in left ventricle aldehyde levels were also found.

CONCLUSIONS

Our data show reductions in specific mitochondrial respiratory enzyme activities in pacing-induced heart failure which is not likely due to overall decreases in mitochondrial number, or necrosis. Our findings suggest a role for mitochondrial dysfunction in the pathogenesis of cardiac failure and may indicate a commonality in the signaling for pacing-induced mitochondrial dysfunction in myocardial and skeletal muscle. Increased levels of TNF-alpha and oxidative stress appear to play a contributory role.

Specific and non-specific measurements of tissue angiotensin II cascade members

Although angiotensin II (ANG II) has been the focal regulatory peptide of the renin-angiotensin system, its proteolytic fragments have recently been demonstrated to have biological effects. Conventional measurement of angiotensins involves radioimmunoassay (RIA), which is a sensitive binding technique capable of measuring low physiological concentrations. However, ANG II antibody cross-reacts with ANG II and its fragments (ANG II cascade), rendering RIA measurement alone to be a non-specific measure of immunoreactive ANG II (ir-ANG II). On the other hand, high-performance liquid chromatography (HPLC) is capable of separating immunoreactive ANG II cascade members, but may not be sensitive enough to detect these low peptide concentrations often present in biological samples. Consequently, a reverse-phase HPLC method, with triethylammoniun formate as an ion-pair reagent, was developed to separate ANG II and its fragments, ANG III, ANG IV and ANG V. This HPLC separation was applied to extracts from normal canine hearts and ANG II cascade immunoreactive fractions were collected. Collected fractions were quantified by RIA, with the use of separate standard curves. The isocratic HPLC separation of ANG II, ANG III, ANG IV and ANG V was achieved in less than 5 min with adjacent peaks having baseline resolution. Measured cardiac left ventricle ANG III, ANG IV and ANG V concentrations (mean+/-SD) were 5.3+/-2.2,4.0+/-1.0 and 3.1+/-1.0 fmol/g (n=9), respectively. There was a significant difference (P=0.003, n=9) between left ventricular immunoreactive ANG II and 'true' ANG II, corrected for recovery rates of 86.2+/-22.5 and 53.5+/-16.2 fmol/g, respectively. We conclude that the combination of HPLC with RIA ensures the specific measurement of the ANG II cascade family members while non-chromatographic processing of tissue renders ANG II measurement non-specific. In addition, the use of triethylammonium formate as mobile phase additive is superior in the HPLC separation of the angiotensins.

Neurohormonal activation in severe heart failure: relations to patient death and the effect of treatment with flosequinan

BACKGROUND

Flosequinan is a direct-acting vasodilator that exerts beneficial hemodynamic effects and improves the exercise tolerance of patients with heart failure. However, a multicenter trial has demonstrated that long-term administration of flosequinan is associated with increased mortality rate. To explore a possible role of neurohormonal activation on this adverse outcome, we conducted a substudy to examine the plasma levels of 3 neurohormonal systems known to have prognostic implications in heart failure.

METHODS

At 20 participating Canadian centers, paired plasma samples at baseline and 1 month after randomization for the measurement of N-terminal atrial natriuretic peptide (N-ANP), angiotensin II, and norepinephrine were obtained in 234 patients (114 receiving flosequinan and 120 receiving placebo).

RESULTS

Treatment with flosequinan was associated with a decline in median plasma N-ANP levels (2139 pmol/L at baseline to 1625 pmol/L at 1 month [P =. 0001]), unchanged plasma angiotensin II levels (40 to 50 pmol/L [P =. 2700]), and a modest increase in plasma norepinephrine levels (391 to 439 pg/mL [P =.002]). These changes were not observed in the placebo group. Multivariate analysis of baseline variables revealed that plasma norepinephrine level predicted patients' death whereas analysis incorporating both baseline and 1-month variables indicated that plasma N-ANP level predicted patients' death. Furthermore, in the flosequinan group, a significant decline in plasma N-ANP level was observed in the survivors only. On multivariate analysis of baseline and 1-month data, the increase in plasma norepinephrine level did not predict the increase in heart rate associated with the use of flosequinan, suggesting that the 2 effects might be mediated by separate mechanisms.

CONCLUSIONS

Results of our study demonstrate that in patients with severe heart failure, baseline norepinephrine level predicts death. Flosequinan increases plasma norepinephrine level and heart rate in these patients through mechanisms that override its beneficial hemodynamic effects. Our study reinforces the concept that the direct actions of a pharmacologic agent may have a more profound impact on the prognosis of these patients than the hemodynamic effects.

Simultaneous separation of angiotensin and endothelin peptide families by high-performance liquid chromatography: application to the specific radioimmunoassay measurement of angiotensin II or endothelin-1 from tissue

Currently available measurements of endogenous angiotensin II (ANG II) and endothelin-1 (ET-1) concentrations by radioimmunoassay (RIA) lack specificity to ANG II or ET-1. ANG II and ET-1 antibodies cross-react with immuno-reactive angiotensin and endothelin family members, respectively. We have therefore developed an ion-pair reversed-phase high-performance liquid chromatography (HPLC) for simultaneously separating angiotensin and endothelin peptides and enhancing RIA specificity in the measurement of ANG II and ET-1. The developed HPLC separation was applied to canine myocardium extracts; ANG II or ET-1 fractions were collected and quantified by RIA. Elution times for both peptide families, ANG I, ANG II, ANG III, ANG IV, ANG II(4-8), bET-1, ET-1, ET-2 and ET-3 were within 25 min. In normal canine myocardium from the right atrium, right ventricle, left atrium and left ventricle, ANG II concentrations were 39+/-11, 28+/-21, 31+/-11 and 21+/-8 fmol/g and ET-1 concentrations were 43+/-16, 42+/-19, 55+/-21 and 57+/-34 fmol/g (mean+/-SD, N=7), respectively. The combination of HPLC with RIA renders the measurement of ANG II or ET-1 specific and convenient, and saves time. This HPLC separation may be applied to the specific measurement of other immuno-reactive angiotensin and endothelin peptides.

ARCTIC: assessment of haemodynamic response in patients with congestive heart failure to telmisartan: a multicentre dose-ranging study in Canada

BACKGROUND

The aim of this study was to examine the acute hemodynamic and neurohormonal effects of the angiotensin II antagonist telmisartan relative to placebo in patients with chronic symptomatic (New York Heart Association class II to III) congestive heart failure and to explore the dose-response relation for these effects.

METHODS AND RESULTS

After baseline hemodynamic and neurohormonal measurements made with the use of a pulmonary artery and radial arterial catheter, 82 patients were randomly assigned to placebo or 10, 20, 40, or 80 mg of telmisartan in a double-blind fashion. Hemodynamic and neurohormonal measurements were carried out over 24 hours. Telmisartan caused significant decreases in systemic arterial, pulmonary arterial, and pulmonary capillary wedge pressures with evidence of a dose-response relation for each of these parameters. The drug had no significant effects on heart rate, cardiac index, or systemic vascular resistance. Telmisartan did not have consistent effects on either plasma norepinephrine or plasma atrial natriuretic peptide levels, although it did cause significant increases in both plasma renin activity and angiotensin II levels at higher doses.

CONCLUSIONS

The acute administration of the angiotensin II antagonist telmisartan was associated with significant dose-dependent reductions in systemic arterial blood pressure and pulmonary pressures. Long-term follow-up studies are required to translate changes in hemodynamic parameters into a clinical benefit.

Reduced pulmonary metabolism of endothelin-1 in canine tachycardia-induced heart failure

OBJECTIVES

Plasma endothelin-1 (ET-1) increases in congestive heart failure (CHF). The pulmonary vascular bed could contribute to this increase through a reduced clearance. We evaluated the effect of tachycardia-induced CHF on pulmonary ET-1 kinetics. To discern between changes due to variations in pulmonary hemodynamics from true alterations of endothelial cell functions, we quantified ET-1 kinetics in isolated rat lungs under variable pressure and flow-rate conditions.

METHODS AND RESULTS

Indicator-dilution studies were performed in anesthetized dogs (n = 14) before and 3 weeks after rapid ventricular pacing and in isolated lungs from healthy rats (n = 4). In isolated lungs, graded increases in perfusion rate from 5-25 ml/min caused gradual reductions in ET-1 extraction from 60 +/- 1.5% to 17 +/- 4.9% (mean +/- S.D.). The capacity to clear ET-1 from the circulation, as computed from the permeability-surface area product (PS), however did not vary over this range of flows. CHF increased plasma ET-1 (11.2 +/- 11.4 vs. 5.2 +/- 1.6 fmol/ml, p < 0.01), did not affect pulmonary ET-1 extraction (29.4 +/- 12.5% vs. 29.9 +/- 12.9%), but decreased the PS (8.3 +/- 5.4 cm3/s vs. 14.4 +/- 9.9 cm3/s, p = 0.038). Contrary to the invariability of the PS in normal isolated rat lungs, CHF was associated with a positive relationship between the PS and pulmonary plasma flow (r = 0.65, p < 0.01). ET-1 binding studies in lung tissues showed no significant variations in ETA and ETB receptors densities but revealed a threefold decrease in binding affinity (p < 0.01) that may explain the reduced clearance.

CONCLUSION

CHF causes a reduction of pulmonary ET-1 clearance that likely contributes to the increased circulating ET-1 levels and reflects pulmonary metabolic dysfunction associated with this condition.

Beneficial effects of long-term selective endothelin type A receptor blockade in canine experimental heart failure

OBJECTIVES

We examined the effects of chronic type A endothelin receptor (ETA) blockade in a dog model of pacing-induced cardiomyopathy.

METHODS

Eight dogs received an ETA antagonist, LU 135252 (50 mg/kg orally daily) and nine dogs received a matching placebo starting at day three of pacing and continued for the remainder of the three weeks of pacing.

RESULTS

In the placebo group, the mean pulmonary artery pressure and left ventricular end diastolic pressure increased from 16 +/- 3 and 8 +/- 2 mmHg, respectively, at baseline to 40 +/- 11 and 34 +/- 7 mmHg, respectively, at two weeks (both p < 0.001 versus baseline). Cardiac output declined from 3.5 +/- 0.7 to 1.9 +/- 0.6 l/min (p < 0.001). In the treatment group, LU 135252 attenuated the increase in mean pulmonary artery and left ventricular end diastolic pressure (16 +/- 3 and 9 +/- 1 mmHg at baseline to 29 +/- 3 and 27 +/- 3 mmHg, respectively, at two weeks (p < 0.001), and the decline in cardiac output (3.2 +/- 0.3 to 2.6 +/- 0.8 l/min, p < 0.01; p < 0.05 versus placebo for the three parameters). Systemic and pulmonary vascular resistance increased only in the placebo group. Left ventricular end-diastolic volume increased to a similar degree. However, LU 135252 attenuated the increase in plasma norepinephrine level (placebo, 1.2 +/- 0.5 to 3.7 +/- 1.9 pmol/l; treatment, 0.8 +/- 0.3 to 2.4 +/- 0.6 pmol/l; both p < 0.001 versus baseline; p < 0.05 versus placebo).

CONCLUSION

Our results suggest that endothelin-1 plays a role in the hemodynamic perturbations in canine pacing-induced cardiomyopathy. The favourable hemodynamic effects without concomitant aggravation of neurohormonal activation suggests that ETA receptor blockade may be beneficial in the treatment of heart failure.

Does a hypertonic saline load predict fluid retention in pacing induced heart failure?

OBJECTIVE

We examined the response to hypertonic saline challenge (SC) as a potential predictor of fluid retention during heart failure induced by rapid ventricular pacing.

METHODS

Twelve dogs (22 +/- 4 kg) were given an intra-arterial bolus of 30 ml of 20% saline after establishing baseline fluid intake and urine output (24 h). Dogs were classified according to whether they drank more (Group A) or less (Group B) than the amount required to dilute the s.c. to isotonicity. Fluid retention was then assessed during heart failure after rapid ventricular pacing according to a graded ordinal scale and correlated with the responses to s.c..

RESULTS

No difference was noted in baseline fluid intake (1112 +/- 236 ml in Group A vs. 809 +/- 129 ml in Group B). Five hours after s.c. cumulative water intake was significantly greater in Group A than in Group B (1018 +/- 136 vs. 591 +/- 17 ml) (P < 0.01). Urine sodium concentration was 113 +/- 11 and 124 +/- 28 mmol/l at baseline in Group A and B, respectively; increased to 190 +/- 21 and 295 +/- 59 mmol/l at 5 h and remained elevated 24 h after s.c., 177 +/- 60 and 274 +/- 55 mmol/l (both P < 0.01 for within-group comparisons vs. baseline). Urine sodium concentration was less in Group A than in Group B at 5 and 24 h (P < 0.05). The fluid retention score was greater in Group A (3.6 +/- 0.5) than in Group B (0.8 +/- 0.4) (P < 0.01). Fluid retention in heart failure correlated with water intake after the pre-pacing s.c. (r = 0.68, P < 0.025) and inversely with urine concentrating ability (r = -0.58, P < 0.05). Furthermore, water intake and urine concentrating ability following the s.c. were inversely related (r = -0.67, P < 0.02).

CONCLUSIONS

We conclude that normal dogs may be classified according to their fluid intake after s.c.. Those dogs that drank excessively and produced a dilute urine were more likely to retain fluid during pacing-induced heart failure. Hence, fluid intake and the ability to excrete a concentrated urine after a saline challenge may be useful variables to predict fluid retention in pacing-induced heart failure.

Biatrial appendage hypertrophy but not ventricular hypertrophy: a unique feature of canine pacing-induced heart failure

BACKGROUND

The canine model of pacing-induced heart failure is characterized by an absence of ventricular hypertrophy despite severe hemodynamic stress and neurohormonal activation. Given the mode of ventricular pacing, hypertrophy might occur in the atrial appendage.

METHODS AND RESULTS

Seventeen dogs underwent continuous right ventricular pacing for 3 weeks to severe heart failure. Twelve normal dogs served as control subjects. Pacing produced marked increases in both pulmonary capillary wedge pressure (7.6 +/- 1.8 mmHg at baseline to 32.6 +/- 7.5 mmHg at 3 weeks, P < .001) and right atrial pressure (6.5 +/- 1.8 to 15.1 +/- 2.4 mmHg, P < .001), marked increases in normalized left ventricular volume (3.0 +/- 0.5 to 4.6 +/- 0.5 mL/kg, P < .001) and left atrial volume (1.0 +/- 0.2 to 2.6 +/- 0.5 mL/kg, P < .001), but no change in left ventricular mass (2.3 +/- 0.4 to 2.6 +/- 0.5 g/kg, differences not significant), indicating no ventricular hypertrophy. Compared to the control dogs, total heart weight in the test animals was similar, but both the left appendage (0.18 +/- 0.04 vs 0.10 +/- 0.03 g/kg, P < .001) and right atrial appendage (0.15 +/- 0.03 vs 0.12 +/- 0.02 g/kg, P = .004) were much heavier than those of the control dogs.

CONCLUSIONS

Rapid right ventricular pacing in the dog induces severe heart failure associated with a dichotomous response in the atrial appendage versus the ventricle. Aside from being a useful heart failure model that simulates the human condition, this unique feature may have physiologic implications in terms of atrial mechanical and endocrine functions and have applications for future studies into the mechanisms of cardiac remodeling and hypertrophy.

Plasma and cardiac tissue atrial and brain natriuretic peptides in experimental heart failure

OBJECTIVES

This study evaluated the role of changes in heart rate, cardiac filling pressures and cardiac tissue atrial and brain natriuretic peptides in the modulation of their plasma levels in a model of heart failure.

BACKGROUND

Atrial and brain natriuretic peptides constitute a dual natriuretic peptide system that regulates circulatory homeostasis.

METHODS

The effects of 1) acute ventricular pacing, 2) acute volume expansion, and 3) volume expansion after 1 week of continuous pacing on plasma atrial and brain natriuretic peptide levels were compared in eight dogs. Atrial and ventricular tissue levels of the peptides were examined in 5 normal dogs (control group), 21 dogs paced for 1 week (group 1) and 10 dogs paced for 3 weeks (group 2).

RESULTS

Both acute pacing and volume expansion increased plasma atrial natriuretic peptide levels (from 53 +/- 41 to 263 +/- 143 pg/ml [mean +/- SD], p < 0.01, and from 38 +/- 23 to 405 +/- 221 pg/ml, p < 0.001, respectively). After 1 week, there was a marked increase in plasma levels of atrial natriuretic peptide, but the level did not increase further with volume expansion (from 535 +/- 144 to 448 +/- 140 pg/ml, p = 0.72). By contrast, plasma brain natriuretic peptide levels increased only modestly with acute pacing (from 12 +/- 4 to 20 +/- 8 pg/ml, p < 0.05) and after pacing for 1 week (from 13 +/- 4 to 48 +/- 20 pg/ml, p < 0.05) but did not change with acute or repeat volume expansion. In groups 1 and 2, atrial tissue levels of atrial natriuretic peptide (1.9 +/- 1.3 and 2.0 +/- 0.9 ng/mg, respectively) were lower than those in the control group (11.7 +/- 6.8 ng/mg, both p < 0.001), whereas ventricular levels were similar to those in the control group. Atrial tissue brain natriuretic peptide levels in groups 1 and 2 were similar to those in the control group. However, ventricular levels in group 2 (0.018 +/- 0.006 ng/mg) were increased compared with those in the control group (0.013 +/- 0.006 ng/mg, p < 0.05) and in group 1 (0.011 +/- 0.006 ng/mg, p < 0.05).

CONCLUSIONS

Atrial and brain natriuretic peptides respond differently to changes in heart rate and atrial pressures. Reduced atrial tissue atrial natriuretic peptide levels in heart failure may indicate reduced storage after enhanced cardiac release. However, the relatively modest change in cardiac tissue brain natriuretic peptide levels suggests that the elevated plasma levels may be mediated by mechanisms other than increased atrial pressures.

How does intermittent pacing modify the response to rapid ventricular pacing in experimental heart failure?

Rapid ventricular pacing is widely accepted as a useful model to produce heart failure. The heart failure is associated with reduced myocardial energy stores and absence of cardiac hypertrophy. In this study, it was hypothesized that a modification of the protocol to intermittent pacing would permit time for partial recovery of myocardial energetics leading to improved cardiac function and development of hypertrophy. Eight dogs underwent conventional continuous right ventricular pacing to a biologic endpoint of severe heart failure (group 1). Another eight dogs underwent an intermittent pacing protocol over 7 weeks, consisting of 48-hour pacing alternating with 24-hour sinus rhythm (group 2) so as to produce the same total exposure to continuous pacing as in group 1. Six additional normal dogs were used as control animals for tissue metabolic data. Although both paced groups had similar directional changes in hemodynamic, neurohormonal, and echocardiographic variables, the absolute increases in pulmonary capillary wedge and right atrial pressures in group 2 (13 +/- 8 and 3 +/- 4 mmHg, respectively) were less marked than in group 1 (29 +/- 5 and 12 +/- 4 mmHg, respectively; both P = .002). Group 2 also had a more modest rise in plasma atrial natriuretic peptide and norepinephrine concentrations. There was no significant increase, however, in left ventricular mass in either group, and myocardial adenosine 5'-triphosphate levels were reduced to a similar extent compared to the control animals. Intermittent pacing produces a less advanced syndrome of heart failure than continuous pacing. Furthermore, the data suggest that reduced energy stores are not the predominant mechanism for impaired cardiac function, although they may contribute to the failure to hypertrophy in this model.

Sarcoplasmic reticulum Ca-release channel and ATP-synthesis activities are early myocardial markers of heart failure produced by rapid ventricular pacing in dogs

The contraction-relaxation cycle of the heart is dependent on a cycle of ATP production and utilization and a cycle of Ca uptake and Ca release by the sarcoplasmic reticulum (SR). Heart failure (HF) is associated with abnormalities of myocardial Ca and ATP cycling, but the time course of their development is unknown. This study tested the hypothesis that, compared with ATP-utilizing and Ca-uptake activities, decreases in ATP-synthesis and Ca-release activities occurred earlier in the development of HF and persisted longer during recovery from HF. HF was induced by right ventricular pacing of dogs at 250 beats/min. Dogs were studied after 1 week of pacing (n = 8, early HF), at HF (n = 11, severe HF), and 4 weeks after cessation of pacing (n = 9) and were compared with dogs not subjected to pacing. At early HF, there were decreased activities (p < 0.05) of the SR Ca-release channel (rate constant from 199 +/- 36 x 10(-4) to 90 +/- 16 x 10(-4) s-1), mitochondrial ATP synthesis (from 11.2 +/- 2.4 to 7.0 +/- 2.2 international units (IU)/g), and creatine kinase (CK) from 2028 +/- 266 to 1811 +/- 79 IU/g). The decreased Ca-channel activity was due to a 32% decrease in maximal activity (rate constant from 249 +/- 50 x 10(-4) to 170 +/- 29 x 10(-4) s-1) and to a 2-fold increase (from 19.1 +/- 12.4 to 42.0 +/- 14.2%) in inhibition of maximal channel activity (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Recovery of attenuated baroreflex sensitivity in conscious dogs after reversal of pacing induced heart failure

OBJECTIVE

Rapid ventricular pacing reliably induces severe congestive heart failure in dogs, with an associated attenuation of baroreflex sensitivity. Unique to this model is the capacity for rapid recovery of haemodynamics and plasma noradrenaline following the cessation of pacing; however, whether baroreflex sensitivity will similarly recover is unknown. The aims of this study were (1) to assess baroreflex control of heart rate in response to acute hypertensive and hypotensive stimuli during the development of and recovery from severe heart failure, and (2) to correlate baroreflex sensitivity with haemodynamic and echocardiographic indices and with noradrenaline concentrations.

METHODS

Serial assessments were performed on six dogs paced to severe heart failure and then allow to recover for four weeks. R-R interval and systolic blood pressure were monitored during administrations of phenylephrine and nitroprusside and the slope (ms.mm Hg-1) of the resultant R-R interval-systolic blood pressure relationship was used to define baroreflex sensitivity.

RESULTS

Control phenylephrine and nitroprusside derived slopes were 27.05(SD 7.88) and 17.1(11.03) ms.mm Hg-1 respectively. After one week of pacing the phenylephrine derived slope was unchanged while the nitroprusside slope tended to be attenuated. In severe heart failure, both slopes were severely attenuated, at 1.88(6.45) ms.mm Hg-1 (phenylephrine) and 4.21(3.28) ms.mm Hg-1 (nitroprusside) (both p < 0.05). Intrinsic heart rate, noradrenaline concentrations and cardiac filling pressures were raised at severe heart failure while cardiac output and systolic blood pressure were significantly reduced. Recovery of baroreflex control of heart rate was evident as early as 48 h following pacing cessation and was maintained after four weeks recovery. Haemodynamics, cardiac output, and noradrenaline also returned to control while cardiac dilatation persisted. Nitroprusside and phenylephrine derived slopes were inversely correlated with intrinsic heart rate and pulmonary arterial/capillary wedge pressures respectively.

CONCLUSIONS

Despite marked attenuation of baroreflex control of heart rate at severe heart failure, rapid recovery was seen in response to both hypotensive and hypertensive stimuli. The speed with which recovery occurs suggests that attenuation of baroreflex sensitivity at severe heart failure is likely to be mediated by functional alterations rather than morphological damage.

Structural remodelling in heart failure: gelatinase induction

OBJECTIVE

Rapid ventricular pacing in the dog produces severe congestive cardiac failure in association with neurohumoral activation and marked depression of cardiac function. This syndrome is associated with left ventricular dilation, significant wall thinning, assumption of a more globular shape and disruption of the cardiac collagen infrastructure, given that the fibrillar collagen network is a major determinant of cardiac architecture. The purpose of the present study was to investigate whether there was evidence of increased activity of matrix metalloproteinases. The authors speculated that it could play an important permissive role in myocyte realignment, thereby resulting in the changes in cardiac size and shape.

DESIGN

Twenty-one male mongrel dogs underwent ventricular pacing and were allocated into one of three groups: early heart failure (n = 6), severe heart failure (n = 7) and recovered heart failure (n = 8). Measurements included echocardiographic and hemodynamic parameters, plasma noradrenaline levels, left ventricular noradrenaline levels and matrix metalloproteinase activity.

RESULTS

The study showed gelatinase activity present in normal left ventricular tissue predominantly attributable to a 72 kDa gelatinase (85%) and, to a much lesser extent, by a 92 kDa gelatinase (15%). Levels of 92 kDa gelatinase increased slightly within one week and reached maximal levels with severe heart failure, where it represented over one-half of the total gelatinase activity. In animals allowed to recover for four weeks, 92 kDa gelatinase decreased significantly to approximately 50% of the levels observed at severe heart failure. The levels of 72 kDa gelatinase did not change significantly during any experimental condition. Significant correlations between 92 kDa percentage activity and systolic and diastolic left ventricular areas across all time-points were evident (r = 0.59 and 0.63, respectively, P < 0.05 for both).

CONCLUSION

The association of 92 kDa gelatinase with changes in left ventricular area suggests a possible modulating role for this matrix metalloproteinase in disruption of the fibrillar components of the left ventricular extracellular matrix.

Left ventricular remodelling and disparate changes in contractility and relaxation during the development of and recovery from experimental heart failure

OBJECTIVES

Canine pacing induced heart failure is characterised by impaired left ventricular contractility and relaxation, and clinical recovery after cessation of pacing. It is unclear whether the impairment is responsive to adrenergic stimulation. The aim of this study was to assess left ventricular contractility and relaxation and their response to beta adrenergic stimulation during heart failure and after recovery.

METHODS

Eight dogs were paced (250 beats.min-1) for 3 weeks to severe heart failure and recovered for 4 weeks after cessation of pacing. During these periods, haemodynamic and echocardiographic measurements were made with and without beta adrenergic stimulation.

RESULTS

At heart failure, impaired left ventricular contractility was evidenced by reduced dP/dt [1412(SD 156) mm Hg.s-1 from 2437(382) mm Hg.s-1 at control, p < 0.01] and a downward displacement of the velocity of circumferential fibre shortening-end systolic wall stress relation. Impaired left ventricular relaxation was evidenced by raised end diastolic pressure [35(6) mm Hg from 7(4) mm Hg at control, p < 0.01] and prolonged relaxation time constant tau [28(4) ms from 17(6) ms, p < 0.01]. The ability of beta adrenergic stimulation to augment contractility was reduced: there was blunted dP/dt response to dobutamine. The ability of beta adrenergic stimulation to shorten relaxation was maintained: there was a similar degree of shortening of tau by dobutamine. At recovery, dP/dt returned to control and the shortening-stress relation moved upward, suggesting return of contractility. The response of dP/dt to dobutamine was restored. However, tau remained prolonged indicating persistent abnormal relaxation.

CONCLUSION

In pacing induced heart failure, there is a dissociation between the normal ability of beta adrenergic stimulation to augment contractility and shorten relaxation, and a differential capacity for recovery of contractility and relaxation.

Myocardial energetics and blood flow in acute rapid ventricular pacing

The mechanism whereby chronic rapid ventricular pacing induces severe heart failure is unclear, but the phenomenon is associated with a reduction in left ventricular ATP levels. Accordingly, the current study was undertaken to evaluate the acute effects of rapid ventricular pacing on hemodynamics, left ventricular adenine nucleotide levels, myocardial blood flow, and oxygen consumption. Anesthetized dogs (n = 7) were studied in sinus rhythm and during 30 min of pacing at 250 beats/min. Pacing caused a significant (means +/- SD, all p < 0.001) decrease in cardiac output (3.0 +/- 0.6 to 2.0 +/- 0.6 L/min) and peak left ventricular systolic pressure (133 +/- 14 to 82 +/- 10 mmHg (1 mmHg = 133.3 Pa)) and an increase in pulmonary wedge pressure (10 +/- 2 to 18 +/- 3 mmHg). Following pacing, the peak first derivative of left ventricular pressure and the relaxation time constant, tau, remained unchanged compared with baseline values. Myocardial blood flow and oxygen consumption both increased by 70% with pacing. The transmural distribution of myocardial blood flow and myocardial lactate consumption remained unchanged. There was no change in left ventricular ATP or ADP levels with the observed increase in myocardial oxygen consumption. Therefore, the hemodynamic deterioration associated with acute rapid ventricular pacing, in contrast to that of chronic pacing, is not associated with perturbed myocardial energetics.

Medical advances in the treatment of congestive heart failure

The increased incidence and prevalence of congestive heart failure place a high priority on novel treatment strategies. Left ventricular ejection fraction remains the single most valuable measurement providing both diagnostic and prognostic insights. The most systematic approach to heart failure involves an objective assessment of functional disability, to include exercise tests such as a 6-minute walk under standardized conditions. Left ventricular dysfunction incites a host of neurohumoral compensations that are of fundamental importance in the heart failure syndrome expression. Both vasoconstrictor and vasodilator neurohormones are stimulated and provide new therapeutic opportunities. The therapeutic approach to heart failure begins with a strong emphasis on prevention, patient education, and self-participation in therapy with respect to both its monitoring and adjustment. Diuretics remain a mainstay of therapy but, in the face of severe heart failure, may become ineffectual, requiring constant infusion of loop-active diuretics, combination diuretics, or diuretics in association with concomitant low-dose dopamine infusion. Vasodilator therapy has been an important advance: combination hydralazine and nitrate therapy was initially shown to be efficacious in improving survival, and more recently, angiotensin-converting enzyme (ACE) inhibitors, in the form of enalapril, have shown incremental benefit on survival over this combination. Interestingly, there is now evidence from both SOLVD and SAVE to demonstrate an unexpected and, as yet, unexplained reduction in the frequency of both unstable angina and myocardial infarction. Although, on balance, the weight of evidence concerning the long-term efficacy of inotropic agents has been disappointing, especially as it relates to their unfavorable effects on survival, recent information on vesnarinone, an agent with a complex and diversified mechanism of action, suggests that with appropriate doses, improved symptoms and survival are possible. A substantial amount of new information from randomized placebo-controlled trials attests to the symptomatic relief, hemodynamic improvement, and gain in exercise performance achieved by digoxin. A long-term survival study is ongoing to assess its effects on mortality. beta-Blockers, especially metoprolol, appear beneficial in some patients with heart failure, possibly related to their reduction in sympathetic nervous activity and restoration of beta-receptor population, with resultant improved contractile performance, enhanced myocardial relaxation, and overall increase in cardiac efficiency. Based on available evidence, the best contemporary approach to treatment involves the use of ACE inhibitors coupled with diuretic therapy, either continuous or intermittent, to relieve central or peripheral congestion. The addition of digoxin or a hydralazine nitrate combination is a logical next step, with commencement of low-dose beta-blocker a reasonable option.(ABSTRACT TRUNCATED AT 400 WORDS)

Dual natriuretic peptide system in experimental heart failure

OBJECTIVES

The objectives of this study were 1) to define in an experimental model of heart failure the time course of changes in plasma brain natriuretic peptide concentrations during the development of and recovery from heart failure, and 2) to relate the changes to changes in atrial natriuretic peptide concentration and hemodynamic status.

BACKGROUND

Brain natriuretic peptide is a circulating peptide with homology to atrial natriuretic peptide. However, unlike the latter, its changes during heart failure and its relation to cardiac filling pressures have not been studied.

METHODS

Eight male mongrel dogs underwent right ventricular pacing at 250 beats/min for 3 weeks until heart failure occurred and were followed up during recovery for 4 weeks after cessation of pacing.

RESULTS

Heart failure was characterized by an increase in both left ventricular and end-diastolic pressure (6.6 +/- 4.1 mm Hg at the control measurements to 35.1 +/- 5.9 mm Hg at 3 weeks, p < 0.01) and right atrial pressure (6.7 +/- 1.1 to 11.4 +/- 2.1 mm Hg, p < 0.01). Recovery was accompanied by a return of cardiac filling pressures to control level. The time course of change of arterial plasma brain natriuretic peptide concentration was similar to that of atrial natriuretic peptide. Plasma concentrations of both peptides increased after 1 week of pacing (16 +/- 4 pg/ml at the control measurement to 59 +/- 20 pg/ml at 1 week, p < 0.001 for brain natriuretic peptide and 84 +/- 55 to 856 +/- 295 pg/ml, p < 0.001 for atrial natriuretic peptide). The level of both peptides then stayed level with no further increase at 3 weeks and returned to the control value by 4 weeks of recovery. There was an excellent correlation between plasma concentrations of the two peptides (r = 0.86, p < 0.001) and between the two peptides and cardiac filling pressures. However, compared with atrial natriuretic peptide, plasma brain natriuretic peptide concentration had a smaller percent increase during evolving heart failure and a slower rate of decline at recovery.

CONCLUSIONS

Brain and atrial natriuretic peptide constitute a dual natriuretic system and are both responsive to changes in cardiac filling pressures in heart failure. However, brain natriuretic peptide appears to be less responsive than atrial natriuretic peptide.

Left ventricular myocardial blood flow, metabolism, and effects of treatment with enalapril: further insights into the mechanisms of canine experimental pacing-induced heart failure

Left ventricular myocardial blood flow and metabolic parameters were studied in dogs with severe heart failure induced by rapid ventricular pacing. The impact of early administration of enalapril was also evaluated. Seventeen dogs were randomly assigned in a blinded fashion to receive enalapril at a dose of 10 mg orally per day or a matching placebo commencing 1 week after initiation of pacing. Six dogs underwent sham operations and served as a control for the myocardial blood flow and metabolic studies. In general, there was no significant difference in myocardial blood flow among the control dogs, the placebo-treated, and the enalapril-treated, paced dogs. However, tissue adenosine triphosphate was markedly reduced in both the enalapril-treated, paced dogs (2.43 +/- 0.55 mumol/gm wet weight, mean +/- SD) and the placebo-treated, paced dogs (2.79 +/- 0.39 mumol/gm) compared with the level in control dogs (4.77 +/- 0.88 mumol/gm, both p < 0.01). Tissue glycogen and lactate levels were similar in the three groups. The time to development of severe heart failure tended to be longer in the enalapril-treated dogs (33 +/- 12 days) than in the placebo-treated dogs (24 +/- 10 days, p = 0.07). In pacing-induced heart failure, therefore, an imbalance between energy supply and demand may contribute to the left ventricular dysfunction, myocardial ischemia does not play a major role, and early treatment with enalapril may prolong the time to development of severe heart failure.

Myocardial myoglobin deficiency in various animal models of congestive heart failure

Myoglobin is known to protect the mechanical function of the heart from hypoxia by acting as a sarcoplasmic oxygen reservoir and shuttle. We postulated a role for myoglobin in the pathogenesis of congestive heart failure. Several models of congestive heart failure were employed to test the hypothesis, including spontaneous inherited dilated cardiomyopathy in Doberman Pinschers, and heart failure produced by rapid ventricular pacing in dogs, volume overload in chickens and furazolidone toxicity in turkeys. Myocardial myoglobin was decreased by approximately 50% for all models (P less than 0.05). In Doberman Pinschers dogs which are predisposed to the development of dilated cardiomyopathy and have mild subclinical depression of cardiac performance, myocardial myoglobin (1.05 +/- 0.22 mg/g) is approximately 50% decreased compared to healthy mongrel dogs (2.15 +/- 0.52 mg/g), approximately twice as much as dobermans with heart failure (0.47 +/- 0.25 mg/g) but similar to the concentration found in dogs paced to heart failure (1.09 +/- 0.34 mg/g). Myocardium from poultry had remarkably decreased myoglobin compared to mammals (34 +/- 4 micrograms/g) with heart failure produced either by furazolidone or salt toxicity causing a further 50% reduction. In the canine models of heart failure, myocardial myoglobin concentration was demonstrated to be correlated with biochemical and physiological indicators of myocardial performance, namely, mitochondrial and sarcoplasmic reticular ATPase activities, and cardiac output, systemic vascular resistance, pulmonary capillary wedge pressure and mean arterial pressure, respectively. Our data implicates a role for myoglobin deficiency in the pathogenesis of congestive heart failure and in the predisposition of doberman pinschers to dilated cardiomyopathy.

Atrial natriuretic factor: pharmacokinetics and cyclic GMP response in relation to biologic effects in severe heart failure

The pharmacokinetics of synthetic atrial natriuretic factor (ANF) and its effects on cyclic GMP, urinary sodium excretion, and hemodynamics were compared in 18 control subjects with normal hemodynamics and 12 patients with severe heart failure. Human 99-126 ANF was administered intravenously (0.2 micrograms/kg i.v. followed by 0.07 micrograms/kg/min for 30 min). As compared with controls, baseline plasma ANF concentration was higher in the heart failure group (329.2 +/- 166.1 vs. 33.6 +/- 17.3 pg/ml in controls, means +/- SD, p less than 0.01). Synthetic ANF increased plasma ANF concentration by similar amounts, but the elimination half-life (t 1/2) for synthetic ANF was longer in the heart failure group (6.5 +/- 2.6 vs. 3.8 +/- 0.8 min, p less than 0.05). Baseline plasma cyclic GMP concentration was higher in the heart failure group (13.8 +/- 6.8 vs. 4.2 +/- 2.2 pmol/ml, p less than 0.01) but ANF increased plasma cyclic GMP concentration to a lesser degree (14.4 +/- 7.6 pmol/ml, p less than 0.05 vs. 24.9 +/- 10.1 pmol/ml, p less than 0.001). Baseline urinary sodium excretion was less in the heart failure group (13.3 +/- 14.0 vs. 53.7 +/- 37.3 mumol/min, p less than 0.01) and ANF induced a smaller increase in urinary sodium excretion (22.1 +/- 32.3 mumol/min, p less than 0.05 vs. 305.7 +/- 242.9 mumol/min, p less than 0.001). Baseline plasma norepinephrine (NE), renin, and aldosterone were higher in the heart failure group. Synthetic ANF increased plasma NE only in the control group, had no effect on renin, and decreased aldosterone in both groups. Hemodynamic responses were similar in both groups except the decreased arterial blood pressure (BP) was accompanied by increased heart rate (HR) only in the controls. Therefore, in heart failure, the t 1/2 of ANF is prolonged and there appears to be a limit for further increase in cyclic GMP. These changes may explain in part the blunted renal response to ANF.

Evaluation of indices of left ventricular contractility and relaxation in evolving canine experimental heart failure

OBJECTIVE

The aim was to evaluate changes in indices of left ventricular contractility and relaxation in relation to changes in loading conditions in dogs with rapid pacing induced heart failure.

METHODS

14 conscious male mongrel dogs were paced at 250 beats.min-1 to severe heart failure, which occurred at 4.2(SD1.9) weeks. Six sham operated dogs served as controls. Right sided pressures were obtained by a thermodilution catheter. Left ventricular pressure and its derived variables were obtained by a high fidelity manometer tipped catheter. Rate corrected velocity of circumferential fibre shortening--end systolic wall stress relations were obtained by simultaneous haemodynamic and echocardiographic studies.

RESULTS

In the paced dogs, baseline right atrial pressure, 6.4(2.0) mm Hg, and pulmonary capillary wedge pressure, 7.1(2.5) mm Hg, increased to 13.3(3.1) mm Hg and 34.5(7.1) mm Hg respectively at severe heart failure (both p less than 0.0001). The peak first derivative of left ventricular pressure dP/dt decreased from 1515(274) mm Hg.s-1 at baseline to 975(321) mm Hg.s-1 at severe heart failure (p less than 0.05) while baseline left ventricular end diastolic pressure, 4.4(3.7) mm Hg, and relaxation time constant tau, 18.0(4.5) ms, increased to 37.2(6.6) mm Hg (p less than 0.01) and 51.9(21.4) ms (p less than 0.05) respectively. The shortening-wall stress relation was markedly displaced downward from baseline. Furthermore, weekly studies revealed a major downward displacement of this relation by one week of pacing with no significant further shift at severe heart failure, whereas both end diastolic diameter (preload) and end systolic wall stress (afterload) increased significantly further from one week. In the sham operated dogs, there was no change over time in any of these study variables.

CONCLUSIONS

In pacing induced heart failure, there is impairment of left ventricular contractility and relaxation. The major downward shift of the shortening-wall stress relation at one week suggests that left ventricular contractility is impaired early and may be the initiating mechanism of heart failure in this model.

Sequential echocardiographic-Doppler assessment of left ventricular remodelling and mitral regurgitation during evolving experimental heart failure

STUDY OBJECTIVE

The aim was to study the nature, magnitude, and time course of left ventricular structural adaptations to evolving heart failure.

DESIGN

17 male mongrel dogs, weight 24.9(SD 3.7) kg, underwent rapid ventricular pacing (250 beats.min-1) until severe heart failure developed. Two dimensional echocardiographic and Doppler studies were performed at control, then weekly to severe heart failure. Haemodynamic measurements were made at control and severe heart failure. All studies were performed with the animals conscious during temporary sinus rhythm.

MEASUREMENTS AND MAIN RESULTS

Left ventricular diastolic volume gradually increased and the left ventricle assumed a more globular shape associated with significant wall thinning. Both the change in diastolic volume after one week of pacing and at the time of severe heart failure correlated with the time to peak heart failure. Mitral regurgitation was mild after one week of pacing, became moderate in most animals at severe heart failure, and lagged temporarily behind the increase in cardiac dimensions. The percentage increase in mitral annular size was significantly less than the increase in left ventricular cross sectional area.

CONCLUSIONS

In pacing induced heart failure (1) marked left ventricular remodelling occurs, (2) the extent of left ventricular dilatation, both early and late, correlates directly with the time required for the development of severe heart failure, (3) mitral regurgitation is an epiphenomenon and is most likely to be caused by the increase in left ventricular cross sectional area.

Sequential changes in atrial pressures, dimensions, and plasma atrial natriuretic factor concentrations during volume loading in hemodynamically normal human subjects

The effects of volume loading on atrial pressures and dimensions, plasma levels of atrial natriuretic factor (ANF), and other neurohormonal variables were studied in 11 patients with normal hemodynamics with the patients in a supine -15 degree left decubitus posture by infusing 750 ml of normal saline solution over 30 minutes. Right and left atrial areas were measured by two-dimensional echocardiography. Plasma ANF level was sampled simultaneously from the pulmonary artery, aorta, and femoral artery and vein. At 30 minutes into the infusion, pulmonary capillary wedge pressure and right atrial pressure increased from 5.6 +/- 2.8 mm Hg (mean +/- SD) and 6.4 +/- 2.2 mm Hg to 10.2 +/- 3.2 and 9.5 +/- 2.2 mm Hg, respectively (both p less than 0.01). Left atrial area increased from 12.6 +/- 2.2 cm2 to 15.0 +/- 2.1 cm2 (p less than 0.05), whereas right atrial area did not change. Plasma ANF levels from all sampling sites increased significantly (e.g., 43 +/- 21 pg/ml to 71 +/- 62 pg/ml in the femoral artery, p less than 0.05). Plasma norepinephrine and renin levels were unchanged, whereas aldosterone level declined significantly. At 30 minutes after termination of the infusion, atrial pressures declined to baseline values in all patients. However, left atrial area remained significantly increased, and a trend for systemic arterial plasma ANF level to remain increased was seen. Plasma aldosterone level remained significantly suppressed.(ABSTRACT TRUNCATED AT 250 WORDS)

Response of atrial natriuretic factor to acute and chronic increases of atrial pressures in experimental heart failure in dogs. Role of changes in heart rate, atrial dimension, and cardiac tissue concentration

BACKGROUND

This study evaluated the role of changes in heart rate, atrial pressure, volume, and cardiac tissue atrial natriuretic factor (ANF) concentration in the modulation of plasma ANF concentration in a model of pacing-induced heart failure.

METHODS AND RESULTS

The effects of acute right ventricular pacing (250 beats/min), acute volume expansion (35 ml/min), and volume expansion after 1 week of right ventricular pacing on plasma ANF concentration were compared in eight dogs (group 1). As shown during right ventricular pacing previously, volume expansion produced significant increases in cardiac filling pressures and left atrial volume. Right ventricular pacing and volume expansion produced similar increments in plasma ANF concentration: from 32 +/- 12 to 168 +/- 153 pg/ml (p less than 0.05) and from 32 +/- 9 to 137 +/- 113 pg/ml (p less than 0.05), respectively. When pacing was initiated after volume expansion, plasma ANF concentration increased further to 462 +/- 295 pg/ml (p less than 0.05) despite little change in filling pressures and left atrial volume. With repeated volume expansion after 1 week of pacing, there were no significant further increases in left atrial volume and plasma ANF concentrations (from 332 +/- 121 to 407 +/- 113 pg/ml) despite significant increases in filling pressures. Atrial and ventricular tissue samples were also obtained from 21 dogs paced to severe heart failure (group 2) and from 14 normal dogs (controls). In all groups, atrial ANF was higher than ventricular ANF concentration. At 1 week (group 1), left atrial appendage ANF concentration (6.2 +/- 2.5 versus 16.1 +/- 10.3 ng/mg) was reduced, whereas left ventricular free wall ANF concentration (0.62 +/- 0.31 versus 0.24 +/- 0.16 pg/mg) was increased compared with that of controls (both p less than 0.001). At severe heart failure (group 2), atrial ANF remained low, whereas ventricular ANF concentration was similar to that of the controls.

CONCLUSIONS

These data indicate that in pacing-induced heart failure, changes in heart rate, atrial pressure, and volume all contribute to the increased plasma ANF concentration. However, by 1 week (early heart failure), ANF release is attenuated, perhaps because of the inability of the atria to be stretched further and because of reduced atrial ANF concentration. In addition, the ventricle may be an additional source of ANF.

Cardiac and muscle fatigue due to relative functional overload induced by excessive stimulation, hypersensitive excitation-contraction coupling, or diminished performance capacity correlates with sarcoplasmic reticulum failure

The development of muscle fatigue due to exhaustive exercise is associated with impaired sarcoplasmic reticulum (SR) Ca-transport activity. This study tested the hypothesis that SR failure is a consistent feature of cardiac and skeletal muscle fatigue owing to relative functional overload regardless of the method of induction: excessive stimulation, diminished performance capacity, or excessive excitation-contraction coupling. The Ca-transport activity was determined using three unique models of muscle fatigue: chronic and rapid ventricular pacing in dogs; metabolic inhibition caused by global cardiac ischemia in swine; and the hypermetabolic syndrome of porcine malignant hyperthermia (MH). Both pacing- and ischemia-induced fatigue resulted in reduction of SR Ca-transport ATPase activity: from 275 +/- 58 to 159 +/- 57 nmol.min-1.mg-1 (mU/mg) and from 577 +/- 82 to 177 +/- 133 mU/mg, respectively. Both pacing-induced fatigue and halothane-induced MH resulted in reduction of Ca-sequestration activity of muscle homogenates from 5.95 +/- 2.4 to 3.11 +/- 0.67 nM/s at 300 nM Ca and 38.7 +/- 10.5 to 16.3 +/- 8.0 nM/s at 1500 nM Ca, respectively (all p less than 0.01). The isolated SR Ca-ATPase activity correlated with Ca-sequestration activity of myocardial homogenates (r = 0.76; p less than 0.005). Different models were used to study the relationship of Ca-transport activity with relaxation function, degree of acidosis, and ionized Ca concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Fibrillar collagen and remodeling of dilated canine left ventricle

To test the hypothesis that in the failing volume-overloaded ventricle, the extracellular matrix and fibrillar collagen in particular are major determinants of the architectural remodeling of the myocardium, this histopathological study of the dilated, postmortem canine left ventricle secondary to rapid ventricular pacing or aortocaval fistula was undertaken. Using the picrosirius-polarization technique to enhance collagen birefringence, we sought to examine the structural integrity of the collagen matrix and interstitium. In the dilated failing ventricle secondary to rapid pacing, we found 1) interstitial edema and a disruption or disappearance of collagen fibers that were apparent within 6 hours of pacing, persisted for weeks, and subsequently were associated with muscle fiber disorganization within the endomyocardium, 2) interstitial fibrosis that was present in the midwall and epimyocardium with chronic pacing, and 3) an early remodeling of intramyocardial coronary arteries that included medial swelling with smooth muscle degeneration followed by proliferative lesions involving fibroblasts and a subsequent perivascular and medial fibrosis. Many of these findings were still evident 48 hours after pacing had been discontinued. In contrast, the collagen matrix and interstitium seen with ventricular dilatation secondary to the circulatory overload that accompanies an aortocaval fistula were indistinguishable from that in sham-operated controls. Thus, we conclude that unlike the chamber enlargement and preserved ventricular function that accompany an aortocaval fistula, ventricular dilatation and failure caused by rapid pacing are based on an architectural remodeling of the myocardium. This structural dilatation involves the extracellular matrix and interstitium and appears to be related to altered permeability of intramyocardial coronary arteries. The mechanism or mechanisms involved in the pathogenesis of myocardial remodeling with rapid ventricular pacing require further investigation.

Response of atrial natriuretic factor to postural change in patients with heart failure versus subjects with normal hemodynamics

The response of atrial natriuretic factor to an acute increase in atrial pressures produced by changing from a 45 degrees upright to a -15 degrees Trendelenburg tilt was examined in 21 patients with heart failure and 8 control subjects with normal hemodynamics. In the control subjects, baseline (45 degrees upright tilt) pulmonary capillary wedge and right atrial pressures increased from 3.1 +/- 0.9 (mean +/- SEM) and 4.4 +/- 0.3 mm Hg to 6.9 +/- 1.9 and 8.5 +/- 0.4 mm Hg, respectively (p less than 0.05 for both), 30 min after the -15 degrees tilt. Baseline arterial plasma atrial natriuretic factor concentration increased from 34 +/- 4 to 44 +/- 1 pg/ml (p less than 0.05) 30 min after the tilt, with an increase observed in every patient. In the group with heart failure, baseline pulmonary capillary wedge and right atrial pressures increased from 17.5 +/- 2.0 and 5.3 +/- 1.2 mm Hg to 24.6 +/- 1.8 and 9.7 +/- 1.3 mm Hg, respectively (p less than 0.01 for both), 30 min after the tilt. Plasma atrial natriuretic factor concentration was 326 +/- 38 pg/ml at baseline and 347 +/- 34 pg/ml (p = NS) 30 min after tilt. Compared with the 7 patients with heart failure who had increased atrial natriuretic factor concentrations after the tilt (responders), the 14 patients with unchanged or decreased atrial natriuretic factor concentrations after the tilt (nonresponders) had a higher baseline right atrial pressure and atrial natriuretic factor concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathophysiological role of changing atrial size and pressure in modulation of atrial natriuretic factor during evolving experimental heart failure

STUDY OBJECTIVE

The aim was to study the interactions between pulmonary capillary wedge pressure (an estimate of left atrial pressure), left atrial dimension, and atrial natriuretic factor during evolving heart failure.

DESIGN

Sequential simultaneous measurements of haemodynamic variables, left atrial dimension, and plasma atrial natriuretic factor concentrations were obtained during evolving experimental pacing induced heart failure.

EXPERIMENTAL MATERIAL

Eight male mongrel dogs were paced (250 beats.min-1) to severe heart failure over 4.9(SD 1.8) weeks.

MEASUREMENTS AND RESULTS

The development of heart failure was characterised by a progressive increase in pulmonary capillary wedge pressure and left atrial cross sectional area, from 5.6(1.3) mm Hg and 7.9(1.2) cm2 respectively at control, to 25.3(4.9) mm Hg and 14.2(2.5) cm2 respectively (both p less than 0.01) at severe heart failure. In contrast to the progressive increase in pulmonary capillary wedge pressure and left atrial area, plasma atrial natriuretic factor concentration increased from 98(51) ng.litre-1 at control to a peak of 422(110) ng.litre-1 (p less than 0.01) at 1 week, then plateaued and reached 354(108) ng.litre-1 at severe heart failure (p less than 0.05 v control). Plasma atrial natriuretic factor correlated with pulmonary capillary wedge pressure and left atrial area at 1 week (r = 0.73, r = 0.71 respectively, both p less than 0.01), but not at the time of severe heart failure.

CONCLUSION

The divergent time course of the changes in plasma atrial natriuretic factor concentration, pulmonary capillary wedge pressure, and left atrial dimension suggests that in this model, the release of atrial natriuretic factor becomes attenuated as severe heart failure develops.

Pharmacokinetics, hemodynamic, renal, and neurohormonal effects of atrial natriuretic factor in experimental heart failure

The hemodynamic, renal, neurohormonal effects and pharmacokinetics of synthetic atrial natriuretic factor (ANF) were studied in six conscious dogs with severe heart failure induced by right ventricular pacing at 250 beats/min for 5.0 +/- 0.6 weeks. Severe heart failure was characterized by a low cardiac output (2.1 +/- 0.1 L/min, elevated pulmonary capillary wedge pressure (26.8 +/- 2.8 mmHg) and right atrial pressure (14.5 +/- 2.2 mmHg). Synthetic ANF (human 99ser-126tyr ANF) was administered intravenously as 2 consecutive 30 min infusions (0.02 and 0.10 microgram/kg.min respectively); and each infusion was preceded by a priming dose of 1 microgram/kg. In contrast to the potent vasorelaxant, natriuretic and renin-lowering effects previously reported in normal dogs, these effects were not observed in the dogs with heart failure with either dose of ANF. The plasma half-life was 10.0 +/- 2.6 min, significantly longer than that reported previously in normal dogs. These data suggest that in this model of heart failure, the pharmacokinetics of ANF are altered and there is generalized target organ resistance to the actions of ANF.

A new method for hemodynamic and echocardiographic assessment of conscious dogs: comparison with thiopental-morphine anaesthesia

A method allowing assessment of cardiac structure and function in the conscious dog using readily available instrumentation is desirable and should provide physiologic advantages when compared to anaesthesia. Accordingly, we studied 19 dogs (22 +/- 2.5 kg), using two-dimensional echocardiographic and Swan-Ganz and femoral artery catheterization; ten were conditioned to permit conscious studies and nine received anaesthesia. Dogs receiving anaesthesia were induced with intravenous thiopental (16 +/- 4 mg/kg), followed by a maintenance dose (7 +/- 1 mg/kg/h) plus morphine sulphate (213 +/- 5 micrograms/kg/h). Cardiac index, mean blood pressure, and systemic vascular resistance were similar between groups. However, anaesthesia as compared to conscious studies resulted in a marked tachycardia (147 +/- 30 bpm, vs 98 +/- 19 bpm, p less than 0.0005), significantly lower right atrial pressure (5 +/- 2 mmHg vs 8 +/- 2 mmHg, p less than 0.05), and a trend towards a lower pulmonary capillary wedge pressure (6 +/- 5 mmHg vs 9 +/- 3 mmHg). Simultaneous echocardiography showed left ventricular diastolic cross sectional area to be smaller in the anaesthesia group (8.5 +/- 1.7 cm2 vs 10.4 +/- 1.5 cm2, p less than 0.05); however, ejection fraction in the two groups was similar. Velocity of circumferential fiber shortening (Vcf), normalized for heart rate and preload, was significantly lower in the anaesthetised dogs (0.63 +/- 0.22 circ/sec vs 0.89 +/- 0.26 circ/sec, p less than 0.05); this decline in Vcf, in association with a lower systolic wall stress (85 +/- 29 10(3) dynes/cm2 vs 119 +/- 23 10(3) dynes/cm2, p less than 0.05) indicates that thiopental-morphine anaesthesia depresses contractility.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid ventricular pacing of dogs to heart failure: biochemical and physiological studies

Chronic, rapid ventricular pacing produces congestive heart failure in dogs. The objectives of this study were to determine whether or not (i) in vitro myocardial biochemical alterations reported for heart failure by volume or pressure overload also occurred with heart failure due to rate overload, and (ii) these biochemical alterations were related to relevant in vivo cardiac physiologic alterations. We compared 27 dogs that were paced to advanced heart failure with 21 sham-operated dogs. Dogs with heart failure had 55% lower left ventricular ejection fraction (22.5 +/- 7.6 vs. 50.5 +/- 5.1%) and cardiac index (81 +/- 22 vs. 178 +/- 48 mL.min-1.kg-1), 287% higher pulmonary capillary wedge pressure (27.5 +/- 6.8 vs. 7.1 +/- 3.4 mmHg; 1 mmHg = 133.3 Pa), and 64% greater left ventricular diastolic area (18.4 +/- 3.7 vs. 11.2 +/- 1.3 cm2) (all p less than 0.05). Dogs with heart failure also had (i) 69% lower norepinephrine (232 +/- 139 vs. 747 +/- 220 ng/g protein), (ii) 25-50% lower activities of myofibrillar Ca ATPase (0.188 +/- 0.026 vs. 0.253 +/- 0.051 U/mg myofibrils), sarcoplasmic reticulum Ca-transport ATPase (0.155 +/- 0.074 vs. 0.288 +/- 0.043 U/mg membrane), and the glycolytic enzyme phosphofructokinase (33.4 +/- 10.0 and 47.7 +/- 15.8 U/g), (iii) 32% higher activity of the beta-oxidation enzyme hydroxyacyl-CoA dehydrogenase (11.43 +/- 1.48 vs. 8.67 +/- 1.70 U/g), and (iv) 60% higher activity of Krebs cycle oxoglutarate dehydrogenase (2.89 +/- 0.77 vs. 1.81 +/- 0.95 U/g) (all p less than 0.05). No differences between groups were observed for isozyme patterns and ATPase activity of myosin.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in serum sodium in relation to atrial natriuretic factor and other neuroendocrine variables in experimental pacing-induced heart failure

The pathophysiologic role of atrial natriuretic factor and other neuroendocrine variables in relation to serum sodium and renal function was evaluated in 15 conscious dogs with severe chronic ventricular pacing-induced heart failure (250 beats/min for 5.1 +/- 0.4 weeks). Six sham-operated dogs observed over an 8 week period served as controls. Development of heart failure was characterized by a progressive increase in plasma norepinephrine, renin activity and aldosterone from control values of 293 +/- 15 pg/ml, 1.4 +/- 0.4 ng/ml per h and 124 +/- 42 pg/ml, respectively, to 1,066 +/- 96 pg/ml, 10.2 +/- 2.4 ng/ml per h and 577 +/- 151 pg/ml (all p less than 0.01), respectively, at severe heart failure. In contrast to other neuroendocrine variables, plasma atrial natriuretic factor increased from a control level of 243 +/- 74 pg/ml to a peak concentration of 724 +/- 149 pg/ml (p less than 0.01) at 2 weeks, then declined and plateaued at twice the level of the control value as severe heart failure developed. At severe heart failure, serum sodium decreased from 147 +/- 0.6 to 141.8 +/- 2.1 mmol/liter (p less than 0.05), whereas urea increased from 6.0 +/- 0.5 to 7.8 +/- 0.6 mmol/liter (p less than 0.05). The change in serum sodium concentration correlated with plasma renin activity and aldosterone (r = -0.77, -0.88, respectively, both p less than 0.01), but not with norepinephrine or atrial natriuretic factor. When sinus rhythm was restored, 14 dogs were observed for 48 to 72 h and 8 dogs were followed up for another 4 weeks after cessation of pacing.(ABSTRACT TRUNCATED AT 250 WORDS)

Recovery from heart failure: structural and functional analysis in a canine model

Chronic, rapid ventricular pacing produces congestive heart failure in the dog. Using echocardiography, the features of developing heart failure were analysed and the capacity of this model for recovery was assessed once pacing had been discontinued. Fifteen dogs were studied; nine were paced at 250 beats/min (bpm) to severe heart failure (5.0 +/- 1.8 weeks) and six served as sham controls. In the paced animals at severe heart failure, two-dimensional echocardiography demonstrated a significant increase in diastolic cross-sectional cardiac area (from 11 +/- 3 to 16 +/- 2 cm2, p less than 0.05), associated with a marked fall n area ejection fraction (54 +/- 8 to 21 +/- 8%, p less than 0.05), and significant left ventricular wall thinning (from 6.0 +/- 0.7 to 4.7 +/- 0.9 mm, p less than 0.05). In addition, significant increases in heart rate (77 +/- 7 to 126 +/- 13 bpm, sinus rhythm; p less than 0.05), respiratory rate (41 +/- 13 to 80 +/- 20 cycles/min, p less than 0.05), and body weight (21 +/- 1 to 24 +/- 3 kg, p less than 0.05) were noted. Serum sodium fell (146 +/- 3 to 140 +/- 8 mmol/L, p less than 0.05), while blood urea nitrogen (6 +/- 2 to 10 +/- 2 mmol/L, p less than 0.05) and creatinine (86 +/- 12 to 101 +/- 15 mmol/d, p less than 0.05) increased. Recovery was characterized by rapid improvement such that all measured parameters normalized by 1 week, except for cross-sectional cardiac area which remained dilated up to 4 weeks (14 +/- 3 cm2, p less than 0.05 versus control).(ABSTRACT TRUNCATED AT 250 WORDS)

Physiological effects of synthetic atrial natriuretic factor in normal conscious dogs

The objective of this study was to examine the integrative physiologic effects of atrial natriuretic factor (ANF). Synthetic 99-126 ANF was administered to 6 normal conscious dogs as two consecutive infusions (0.02 and 0.1 microgram/kg/min respectively) each over 30 min: each infusion was preceded by a priming dose of 1 microgram/kg. With the first infusion, mean arterial pressure declined from 113 +/- 2 to 103 +/- 4 mmHg, pulmonary capillary wedge pressure declined from 9.6 +/- 0.5 to 7.2 +/- 0.7 mmHg and right atrial pressure declined from 9.8 +/- 0.4 to 8.0 +/- 0.7 mmHg (all p less than 0.05). No change in heart rate was seen. Despite very high plasma ANF concentrations, no further decline in arterial or central filling pressures were seen in the second infusion. In contrast, cardiac output declined progressively from 3.8 +/- 0.2 to 2.8 +/- 0.21/min (p less than 0.01) by the end of second infusion. Plasma renin activity declined from 2.2 +/- 0.7 to 0.9 +/- 0.3 ng/ml/hr (p less than 0.05) while plasma norepinephrine remained unchanged. Urine output and sodium excretion increased in a dose dependent manner. The diverse time course of the hemodynamic, renal and neuroendocrine effects suggests these effects of ANF are mediated by different mechanisms. Furthermore, the failure of heart rate and plasma norepinephrine to increase despite a significant decline in blood pressure and cardiac output suggests ANF may have a depressant effect on the sympathetic nervous system.

Early recovery from heart failure: insights into the pathogenesis of experimental chronic pacing-induced heart failure

Chronic rapid ventricular pacing (250 beats/min) induces severe heart failure in a canine model. To assess the potential for recovery after cessation of pacing, simultaneous hemodynamic and two-dimensional echocardiographic studies were conducted in nine conscious dogs paced to severe heart failure (4.3 +/- 1.7 weeks). Heart failure was characterized by elevated left and right ventricular filling pressures from 9 +/- 3 and 7 +/- 2 mm Hg to 25 +/- 6 and 15 +/- 3 mm Hg (both p less than 0.01), respectively. Left ventricular cross-sectional area (an estimate of preload) and systolic wall stress (an estimate of afterload) increased from 12 +/- 2 cm2 and 119 +/- 23 10(3) dynes/cm2 to 17 +/- 3 cm2 and 210 +/- 46 10(3) dynes/cm2 (both p less than 0.01), respectively. Left ventricular ejection fraction decreased from 54% +/- 7% to 13% +/- 5% (p less than 0.01). When pacing was discontinued to allow resumption of sinus rhythm, left and right ventricular filling pressures declined rapidly at 48 hours after resumption of sinus rhythm, by 36% and 53%, respectively. Ejection fraction doubled, although left ventricular cross-sectional area and wall stress remained elevated at 48 hours. The recovery of systolic function in the absence of major changes in loading conditions suggests that pacing-induced heart failure is mediated by a decrease in left ventricular contractility. Moreover, the persistent dilation of the left ventricle after cessation of pacing suggests that structural remodeling of the left ventricle occurs during the development of pacing-induced heart failure.

Intravenous nisoldipine in severe congestive heart failure

The acute hemodynamic effects of intravenous nisoldipine were studied in 10 patients with severe congestive heart failure. Nisoldipine was administered in three consecutive doses (1.5, 3.0, and 6.0 micrograms/kg) at least 150 min apart. Following the first dose, mean arterial pressure declined from 96 +/- 17 to 87 +/- 16 mm Hg (p less than 0.01), cardiac index increased from 2.1 +/- 0.7 to 2.4 +/- 0.7 L/min/m2 (p less than 0.025), and systemic vascular resistance fell from 27 +/- 10 to 19 +/- 6 units (p less than 0.01). Maximal hemodynamic effects occurred by 2 to 5 min and gradually waned over the next 120 min. There were no significant changes in heart rate or filling pressures. The time course for the hemodynamic effects were similar with subsequent doses but the magnitude of change was significantly greater. There was a dose-dependent increase in peak arterial nisoldipine concentration. Baseline plasma norepinephrine and renin were high but did not change with nisoldipine administration. No significant changes were seen after nisoldipine administration. No major side effects were observed. These data suggest that nisoldipine is a potent arterial vasodilator that can be of benefit in patients with low output cardiac failure.

Congestive heart failure

Congestive heart failure (CHF) is a condition that is increasing in incidence and is associated with significant morbidity and mortality rates. The main abnormality that underlies CHF is depressed myocardial function. The resulting decrease in cardiac output activates several peripheral compensatory mechanisms, which may further impair ventricular function and worsen the prognosis. Although systolic dysfunction is the traditional descriptor of CHF, diastolic dysfunction is increasingly recognized as a distinct entity. In prescribing therapy the predominant type of ventricular dysfunction and the peripheral components of the heart failure should be identified. The ultimate aim is to alleviate symptoms, minimize complications and prolong survival. Recent data from two multicentre trials have suggested that vasodilators can achieve these goals. Trials are under way to assess the impact of early vasodilator therapy on CHF.

A comparative evaluation of hemodynamic and neurohumoral effects of nitroglycerin and nifedipine in congestive heart failure

Nitroglycerin and nifedipine have been suggested as useful agents in the therapy of congestive heart failure. Because of the rapid action and feasability for sublingual administration of both drugs, their comparative hemodynamic and neurohumoral effects were studied in 12 patients with congestive heart failure. After sublingual nitroglycerin, there was a significant decrease in mean arterial pressure (96 +/- 17 to 90 +/- 15 mm Hg, p less than 0.01), left ventricular (LV) filling pressure (30 +/- 12 to 22 +/- 10 mm Hg, p less than 0.01), right atrial pressure (15 +/- 6 to 10 +/- 5 mm Hg, p less than 0.01) and systemic vascular resistance (21.5 +/- 7.7 to 19.3 +/- 6.2 units, p less than 0.05) and an increase in cardiac index (2.2 +/- 0.6 to 2.4 +/- 0.7 liters/min/m2, p less than 0.05) and LV stroke work index (20.4 +/- 7.0 to 24.5 +/- 8.6 gm-m/m2, p less than 0.01). After sublingual nifedipine, there was also a significant decrease in mean arterial pressure (96 +/- 16 to 89 +/- 14 mm Hg, p less than 0.01) and systemic vascular resistance (22.1 +/- 7.1 to 18.0 +/- 6.1 units, p less than 0.01) and an increase in cardiac index (2.1 +/- 0.6 to 2.4 +/- 0.6 liters/min/m2, p less than 0.01); in contrast to nitroglycerin, this was unaccompanied by significant changes in right- or left-sided filling pressures or LV stroke work index.(ABSTRACT TRUNCATED AT 250 WORDS)