Regional deficits of myocardial blood flow and function in left ventricular pacing-induced heart failure

Chronic high-rate pacing induces heart failure with preserved ejection fraction-like phenotype in Ossabaw swine

The lack of pre-clinical large animal models of heart failure with preserved ejection fraction (HFpEF) remains a growing, yet unmet obstacle to improving understanding of this complex condition. We examined whether chronic cardiometabolic stress in Ossabaw swine, which possess a genetic propensity for obesity and cardiovascular complications, produces an HFpEF-like phenotype. Swine were fed standard chow (lean; n = 13) or an excess calorie, high-fat, high-fructose diet (obese; n = 16) for ~ 18 weeks with lean (n = 5) and obese (n = 8) swine subjected to right ventricular pacing (180 beats/min for ~ 4 weeks) to induce heart failure (HF). Baseline blood pressure, heart rate, LV end-diastolic volume, and ejection fraction were similar between groups. High-rate pacing increased LV end-diastolic pressure from ~ 11 ± 1 mmHg in lean and obese swine to ~ 26 ± 2 mmHg in lean HF and obese HF swine. Regression analyses revealed an upward shift in LV diastolic pressure vs. diastolic volume in paced swine that was associated with an ~ twofold increase in myocardial fibrosis and an ~ 50% reduction in myocardial capillary density. Hemodynamic responses to graded hemorrhage revealed an ~ 40% decrease in the chronotropic response to reductions in blood pressure in lean HF and obese HF swine without appreciable changes in myocardial oxygen delivery or transmural perfusion. These findings support that high-rate ventricular pacing of lean and obese Ossabaw swine initiates underlying cardiac remodeling accompanied by elevated LV filling pressures with normal ejection fraction. This distinct pre-clinical tool provides a unique platform for further mechanistic and therapeutic studies of this highly complex syndrome.

Remodeling of left circumflex coronary arterial tree in pacing-induced heart failure

Congestive heart failure (CHF) is a very serious heart disease that manifests an imbalance between left ventricle supply and demand. Although the mechanical demand of the failing heart has been well characterized, the systematic remodeling of the entire coronary arterial tree that constitutes the supply of the myocardium is lacking. We hypothesize that the well-known increase in ventricle wall stress during CHF causes coronary vascular rarefaction to increase the vascular flow resistance, which in turn compromises the perfusion of the heart. Morphometric (diameters, length, and numbers) data of the swine left circumflex (LCx) arterial tree were measured in both CHF (n = 6) and control (n = 6) groups, from which a computer reconstruction of the entire LCx tree was implemented down to the capillary level to enable a hemodynamic analysis of coronary circulation. The vascular flow resistance was increased by ∼75% due to a significant decrease of vessel numbers (∼45%) and diameters in the first capillary segments (∼10%) of the LCx arterial tree after 3-4 wk of pacing. The structural remodeling significantly changed the wall shear stress in vessel segments of the entire LCx arterial tree of CHF animals. This study enhances our knowledge of coronary arterial tree remodeling in heart failure, which provides a deeper understanding of the deterioration of supply-demand relation in left ventricle.

Effect of pacing mode and pacing site on torsional and strain parameters and on coronary flow

BACKGROUND

Right ventricular apical pacing may induce detrimental effects on left ventricular function and coronary flow. In this study, the effects of pacing site and mode on cardiac mechanics and coronary blood flow were evaluated.

METHODS

This prospective study included 25 patients who received dual-chamber pacemakers with the ventricular lead placed in the right ventricular apex and presented in sinus rhythm (SR) at their regularly scheduled visits at the pacemaker clinic. Patients underwent complete transthoracic echocardiographic examinations while in SR, followed by noninvasive Doppler assessment of coronary flow in the left anterior descending coronary artery (LAD) and speckle-tracking echocardiography of short-axis planes in SR, atrial pacing (AAI-P), atrioventricular (dual-chamber) pacing (DDD-P), and ventricular pacing (VVI-P).

RESULTS

Rotation of the base was significantly decreased with VVI-P compared with AAI-P. Left ventricular twist decreased significantly with DDD-P compared with AAI-P. Circumferential strain of the base significantly decreased with DDD-P and VVI-P compared with SR. The velocity-time integral of diastolic flow in the LAD decreased significantly with DDD-P compared with SR (10.7 ± 2.2 vs 10.2 ± 2.2 vs 8.9 ± 1.6 vs 8.7 ± 2.6 cm in SR and with AAI-P, DDD-P, and VVI-P, respectively, P = .003). Basal rotation and time from onset of the QRS complex to peak basal rotation as a percentage of systole were independently associated with the velocity-time integral of diastolic flow in the LAD during SR and the three pacing modes.

CONCLUSIONS

Acute right ventricular apical pacing showed a detrimental effect on left ventricular twist and basal mechanics, with the latter being independently associated with decreased LAD diastolic flow velocity parameters.

C-type natriuretic peptide: a new cardiac mediator

Natriuretic peptides are endogenous hormones released by the heart in response to myocardial stretch and overload. While atrial and brain natriuretic peptides (ANP, BNP) were immediately considered cardiac hormones and their role was well-characterized and defined in predicting risk in cardiovascular disease, evidence indicating the role of C-type natriuretic peptide (CNP) in cardiovascular regulation was slow to emerge until about 8 years ago. Since then, considerable literature on CNP and the cardiovascular system has been published; the aim of this review is to examine current literature relating to CNP and cardiovascular disease, in particular its role in heart failure (HF) and myocardial infarction (MI). This review retraces the fundamental steps in research that led understanding the role of CNP in HF and MI; from increased CNP mRNA expression and plasmatic concentrations in humans and in animal models, to detection of CNP expression in cardiomyocytes, to its evaluation in human leukocytes. The traditional view of CNP as an endothelial peptide has been surpassed by the results of many studies published in recent years, and while its physiological role is still under investigation, information is now available regarding its contribution to cardiovascular function. Taken together, these observations suggest that CNP and its specific receptor, NPR-B, can play a very important role in regulating cardiac hypertrophy and remodeling, indicating NPR-B as a new potential drug target for the treatment of cardiovascular disease.

Selection of reference genes for normalization of real-time PCR data in minipig heart failure model and evaluation of TNF-α mRNA expression

Real-time PCR is the benchmark method for measuring mRNA expression levels, but the accuracy and reproducibility of its data greatly depend on appropriate normalization strategies. Though the minipig model is largely used to study cardiovascular disease, no specific reference genes have been identified in porcine myocardium. The aim of the study was to identify and validate reference gene to be used in RT-PCR studies of failing (HF) and non-failing pig hearts. Eight candidate reference genes (GAPDH, ACTB, B2M, TBP, HPRT-1, PPIA, TOP2B, YWHAZ) were selected to compare cardiac tissue of normal (n=4) and HF (n=5) minipigs. The most stable genes resulted: HPRT-1, TBP, PPIA (right and left atrium); PPIA, GAPDH, ACTB (right ventricle); HPRT-1, TBP, GAPDH (left ventricle). The normalization strategy was tested analyzing mRNA expression of TNF-α, which is known to be up-regulated in HF and whose variations resulted more significant when normalized with the appropriately selected reference genes. The findings obtained in this study underline the importance to provide a set of reference genes to normalize mRNA expression in HF and control minipigs. The use of unvalidated reference genes can generate biased results because also their expression could be altered by the experimental conditions.

Asymmetrical myocardial expression of natriuretic peptides in pacing-induced heart failure

High-frequency pacing of the left ventricle (LV) free wall causes a dyssynchronous pattern of contraction that leads to progressive heart failure (HF) with pronounced differences in regional contractility. Aim of this study was to evaluate possible changes in brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) mRNA expression in the anterior/anterior lateral region (pacing site, PS) as compared to the infero-septal region (opposite site, OS) and to explore possible association between the contractiling pattern and biomarker expression. Cardiac tissue was collected from minipigs with pacing-induced HF (n=8) and without (control, n=6). The samples were selectively harvested from the anterior left ventricular (LV) wall, PS, and from an area remote to the pacing-site, OS. BNP and CNP mRNA expression was evaluated by semi-quantitative polymerase chain reaction (PCR). A significant difference in BNP expression was found in the PS between HF animals and controls (BNP/GAPDH: 0.65+/-0.11 vs. 0.35+/-0.04, p=0.02), but not in the OS (BNP/GAPDH: 0.36+/-0.05, ns vs. controls). CNP expression was not different compared to controls, although higher levels were observed in the PS and in the OS with respect to the controls (CNP/GAPDH: controls 0.089+/-0.036, PS 0.289+/-0.23, OS 0.54+/-0.16). This finding was in tune with an increase of CNP tissue concentration (controls: 0.69+/-0.13; PS=1.56+/-0.19; OS=1.70+/-0.42 pg/mg protein; p=0.039 controls vs. OS). Higher BNP mRNA expression in the PS is consistent with a reduction in contractile function in this region, while higher CNP mRNA expression in the OS suggests the presence of concomitant endothelial dysfunction in the remote region.

Expression of C-type natriuretic peptide and of its receptor NPR-B in normal and failing heart

C-type natriuretic peptide (CNP) was recently found in the myocardium, but possible insights into differences between atrium and ventricle production are so far lacking. Our aim was to evaluate, in an experimental model of pacing-induced heart failure (HF), plasma and tissue levels of CNP and mRNA expression of the peptide and of its specific receptor, NPR-B. Cardiac tissue was collected from male adult minipigs without (control, n=5) and with pacing-induced HF (n=5). Blood samples were collected at baseline and after pacing (10 min, 1, 2, 3 weeks). CNP in plasma and in cardiac extracts was determined by a radioimmunoassay, while the expression of mRNA by real time PCR. Compared to control, plasma CNP was increased after 1 week of pacing stress (36.9+/-10.4 pg/ml vs.16.7+/-1.1, p=0.013, mean+/-S.E.M.). As to myocardial extract, at baseline, CNP was found in all cardiac chambers and its content was 10-fold higher in atria than in ventricles (RA: 13.7+/-1.9 pg/mg protein; LA: 8.7+/-3.8; RV: 1.07+/-0.33; LV: 0.93+/-0.17). At 3 weeks of pacing, myocardial levels of CNP in left ventricle were higher than in controls (15.8+/-9.9 pg/mg protein vs. 0.9+/-0.17, p=0.01). CNP gene expression was observed in controls and at 3 weeks of pacing. NPR-B gene expression was found in all cardiac regions analyzed, and a down-regulation was observed in ventricles after HF. The co-localization of the CNP system and NPR-B suggests a possible role of CNP in HF and may prompt novel therapeutical strategies.

Alterations in vasomotor control of coronary resistance vessels in remodelled myocardium of swine with a recent myocardial infarction

The mechanism underlying the progressive deterioration of left ventricular (LV) dysfunction after myocardial infarction (MI) towards overt heart failure remains incompletely understood, but may involve impairments in coronary blood flow regulation within remodelled myocardium leading to intermittent myocardial ischemia. Blood flow to the remodelled myocardium is hampered as the coronary vasculature does not grow commensurate with the increase in LV mass and because extravascular compression of the coronary vasculature is increased. In addition to these factors, an increase in coronary vasomotor tone, secondary to neurohumoral activation and endothelial dysfunction, could also contribute to the impaired myocardial oxygen supply. Consequently, we explored, in a series of studies, the alterations in regulation of coronary resistance vessel tone in remodelled myocardium of swine with a 2 to 3-week-old MI. These studies indicate that myocardial oxygen balance is perturbed in remodelled myocardium, thereby forcing the myocardium to increase its oxygen extraction. These perturbations do not appear to be the result of blunted β-adrenergic or endothelial NO-mediated coronary vasodilator influences, and are opposed by an increased vasodilator influence through opening of K_ATP channels. Unexpectedly, we observed that despite increased circulating levels of noradrenaline, angiotensin II and endothelin-1, α-adrenergic tone remained negligible, while the coronary vasoconstrictor influences of endogenous endothelin and angiotensin II were virtually abolished. We conclude that, early after MI, perturbations in myocardial oxygen balance are observed in remodelled myocardium. However, adaptive alterations in coronary resistance vessel control, consisting of increased vasodilator influences in conjunction with blunted vasoconstrictor influences, act to minimize the impairments of myocardial oxygen balance.

Mismatch between uniform increase in cardiac glucose uptake and regional contractile dysfunction in pacing-induced heart failure

Increased glucose utilization and regional differences in contractile function are well-known alterations of the failing heart and play an important pathophysiological role. We tested whether, similar to functional derangement, changes in glucose uptake develop following a regional pattern. Heart failure was induced in 13 chronically instrumented minipigs by pacing the left ventricular (LV) free wall at 180 beats/min for 3 wk. Regional changes in contractile function and stress were assessed by magnetic resonance imaging, whereas regional flow and glucose uptake were measured by positron emission tomography utilizing, respectively, the radiotracers [(13)N]ammonia and (18)F-deoxyglucose. In heart failure, LV end-diastolic pressure was 20 +/- 4 mmHg, and ejection fraction was 35 +/- 4% (all P < 0.05 vs. control). Sustained pacing-induced dyssynchronous LV activation caused a more pronounced decrease in LV systolic thickening (7.45 +/- 3.42 vs. 30.62 +/- 8.73%, P < 0.05) and circumferential shortening (-4.62 +/- 1.0 vs. -7.33 +/- 1.2%, P < 0.05) in the anterior/anterior-lateral region (pacing site) compared with the inferoseptal region (opposite site). Conversely, flow was reduced significantly by approximately 32% compared with control and was lower in the opposite site region. Despite these nonhomogeneous alterations, regional end-systolic wall stress was uniformly increased by 60% in the failing LV. Similar to wall stress, glucose uptake markedly increased vs. control (0.24 +/- 0.004 vs. 0.07 +/- 0.01 micromol x min(-1) x g(-1), P < 0.05), with no significant regional differences. In conclusion, high-frequency pacing of the LV free wall causes a dyssynchronous pattern of contraction that leads to progressive cardiac failure with a marked mismatch between increased glucose uptake and regional contractile dysfunction.

Sequencing and cardiac expression of natriuretic peptide receptor 2 (NPR-B) in Sus Scrofa

The cardiovascular actions of the C-type natriuretic peptide (CNP) are mainly mediated by the interaction with natriuretic peptide receptor-B (NPR-B). The aim of this study was to identify the sequence of NPR-B in Sus Scrofa, which is not present in GenBank, to verify the expression of NPR-B in the different cardiac chambers of normal pigs and evaluate its homology with murine and human species. Using the guanidinium thyocyanate-phenol-chloroform method, we extracted total RNA from samples obtained from heart of mouse and from the atrium, ventricle, and septum of normal pigs. Pig NPR-B mRNA was sequenced using polymerase chain reaction primers designed from mouse consensus sequences. Sus Scrofa natriuretic peptide receptor 2 mRNA, 1-396 bp, was submitted to GenBank (accession number DQ487044). The presence of NPR-B at mRNA level was detected in all the cardiac chambers; moreover, the bands obtained from pig cardiac tissue shared a 93% sequence homology with a region of the mouse NPR-B and a 95% sequence homology with Homo sapiens. Therefore, NPR-B sequencing provides a new tool to investigate the role of CNP under physiological and pathological conditions in the experimental and clinical setting.

Myocardial protection in the failing heart: II. Effect of pulsatile cardioplegic perfusion under simulated left ventricular restoration

OBJECTIVE

The open ventricle was studied in pacing-induced experimental heart failure to determine the extent of coronary perfusion and distribution during either continuous or pulsatile cardioplegic perfusion compared with whole blood in the beating heart.

METHODS

In 5 animals that underwent pacing-induced heart failure and in 6 control swine, regional coronary blood flows were measured on bypass in the open left ventricle (simulating exposure for left ventricle restoration) during (1) beating, (2) nonpulsatile cardioplegia, and (3) pulsatile cardioplegia modalities. Mean perfusion pressure was maintained at 80 mm Hg.

RESULTS

Flow magnitude and distribution differed in control and failing hearts in the open left ventricle. In control hearts, transmural and endocardial cardioplegic flow of nonpulsatile and pulsatile flow (which were similar to each other) exceeded beating flow by 63% and 70%, respectively, in the open left ventricle condition. Transmural and subendocardial vascular resistance increased in failing hearts during cardioplegic delivery, resulting in lower subendocardial flow under nonpulsatile conditions for the same perfusion pressure. In failing hearts, subendocardial perfusion conditions did not change in the beating state (0.89 vs 0.78 mL/min/g in control and failing open beating states, respectively), but nonpulsatile cardioplegic flow was significantly reduced by 154%, and became lower than beating flow by 32.2% (0.78 vs 0.59 mL/min/g). Conversely, pulsatile cardioplegic delivery improved endocardial flow in the open failing hearts, as cardioplegic perfusion with pulsatility exceeded beating flow by 41%. In heart failure, pulsatility from either the beating heart, which causes extrinsic compression of coronary vessels, or intrinsic vessel distension during pulsatile cardioplegic perfusion preserved endocardial perfusion better than nonpulsatile cardioplegia at the same perfusion pressure.

CONCLUSION

In the failing open ventricle (simulated geometry during ventricular restoration), subendocardial blood flow was maintained in the beating state, but decreased significantly from control values during nonpulsatile cardioplegic perfusion. Conversely, pulsatile cardioplegic delivery improved subendocardial perfusion of the open failing ventricle. These findings of improved subendocardial perfusion during pulsatile delivery (either during beating or cardioplegic perfusion) compared with nonpulsatile cardioplegic delivery may have important implications for myocardial protection in failing hearts.

Myocardial substrate metabolism in the normal and failing heart

The alterations in myocardial energy substrate metabolism that occur in heart failure, and the causes and consequences of these abnormalities, are poorly understood. There is evidence to suggest that impaired substrate metabolism contributes to contractile dysfunction and to the progressive left ventricular remodeling that are characteristic of the heart failure state. The general concept that has recently emerged is that myocardial substrate selection is relatively normal during the early stages of heart failure; however, in the advanced stages there is a downregulation in fatty acid oxidation, increased glycolysis and glucose oxidation, reduced respiratory chain activity, and an impaired reserve for mitochondrial oxidative flux. This review discusses 1) the metabolic changes that occur in chronic heart failure, with emphasis on the mechanisms that regulate the changes in the expression of metabolic genes and the function of metabolic pathways; 2) the consequences of these metabolic changes on cardiac function; 3) the role of changes in myocardial substrate metabolism on ventricular remodeling and disease progression; and 4) the therapeutic potential of acute and long-term manipulation of cardiac substrate metabolism in heart failure.

Giant Flow Reversal in Pulmonary Venous Flow as a Possible Mechanism for Asynchronous Pacing-induced Heart Failure

BACKGROUND

Mechanistic roles of the immediate increase in left atrial (LA) pressure in pacing-induced congestive heart failure have not been clearly understood. We evaluated the impact of asynchronous rapid ventricular pacing on LA hemodynamics in this model.

METHODS

Transthoracic and transesophageal echocardiography and hemodynamic assessment were performed in 23 healthy mongrel dogs. Data were acquired before and 5 minutes after initiation of rapid right ventricular pacing (200/min).

RESULTS

At 5 minutes after initiation of the pacing, giant pulmonary venous (PV) flow reversal (-76 cm/s) was observed in association with 1:1 ventriculoatrial conduction or complete atrioventricular dissociation. This giant PV flow reversal corresponded to an inappropriately timed atrial contraction, especially during systole. Cardiac output (3.21 vs 2.00 L/min, P < .001) was decreased corresponding to the decrease in the forward blood volumes as described by decrease in the Doppler left ventricular (LV) outflow (8.99 vs 4.73 cm, P < .0001), mitral inflow (6.89 vs 3.19 cm, P < .0001), and PV flow (14.15 vs 7.22 cm, P < .0001) velocity integrals. As a result, there was a marked elevation of the mean pulmonary capillary wedge (9.1 vs 17.1 mm Hg, P < .001) and LV end-diastolic (8.2 vs 17.4 mm Hg, P < .01) pressures leading to congestive heart failure.

CONCLUSIONS

The giant PV flow reversal seen during asynchronous rapid right ventricular pacing corresponds to an inappropriate atrial contraction, immediately elevates LA pressure, and may initially promote congestive heart failure. The increase in LV end-diastolic pressure associated with decreased LV ejection fraction caused decrease in the LV filling volume leading to further increase in the LA pressure. This sustained marked elevation in the LA pressure and LV end-diastolic pressure could contribute to the heart failure process.

Control of coronary blood flow during exercise

Under normal physiological conditions, coronary blood flow is closely matched with the rate of myocardial oxygen consumption. This matching of flow and metabolism is physiologically important due to the limited oxygen extraction reserve of the heart. Thus, when myocardial oxygen consumption is increased, as during exercise, coronary vasodilation and increased oxygen delivery are critical to preventing myocardial underperfusion and ischemia. Exercise coronary vasodilation is thought to be mediated primarily by the production of local metabolic vasodilators released from cardiomyocytes secondary to an increase in myocardial oxygen consumption. However, despite various investigations into this mechanism, the mediator(s) of metabolic coronary vasodilation remain unknown. As will be seen in this review, the adenosine, K(+)(ATP) channel and nitric oxide hypotheses have been found to be inadequate, either alone or in combination as multiple redundant compensatory mechanisms. Prostaglandins and potassium are also not important in steady-state coronary flow regulation. Other factors such as ATP and endothelium-derived hyperpolarizing factors have been proposed as potential local metabolic factors, but have not been examined during exercise coronary vasodilation. In contrast, norepinephrine released from sympathetic nerve endings mediates a feed-forward betaadrenoceptor coronary vasodilation that accounts for approximately 25% of coronary vasodilation observed during exercise. There is also a feed-forward alpha-adrenoceptor-mediated vasoconstriction that helps maintain blood flow to the vulnerable subendocardium when heart rate, myocardial contractility, and oxygen consumption are elevated during exercise. Control of coronary blood flow during pathophysiological conditions such as hypertension, diabetes mellitus, and heart failure is also addressed.

Optimizing ventricular shape in anterior restoration

Ishemic dilated cardiomyopathy results from altered muscle mechanics. Ventricular restoration is aimed at altering the volume and shape changes that follow myocardial infarction. Optimal surgical methods to achieve this goal are not well defined, but it has been shown that sphericity is an important determinant of long-term outcome. We present the rationale and techniques for returning the globular remodeled ventricle to a more elliptical shape. Clinical data from our RESTORE registry does not suggest an improvement in early or late mortality with such methods but opens the way for late evaluation of functional and exercise capacity.

Regional myocardial mechanics: integrative computational models of flow-function relations

Many cardiac disorders result in regionally altered myocardial mechanics. Although myocardial strain distributions can be measured experimentally and clinically, regional wall stresses must be computed from computational models. Combining these approaches can provide insight into the structural basis of regional dysfunction under conditions such as acute myocardial infarction and ischemia-reperfusion. Recently, 3-dimensional computational models have helped to elucidate the structural basis of the functional border zone adjacent to acutely ischemic myocardium. They have also shown that heterogeneous dysfunction in ischemic-reperfused stunned myocardium does not necessarily imply heterogeneous myofilament injury. Now that computational models are able to reproduce many complex features of the 3-dimensional patterns of regional myocardial deformation observed experimentally, we suggest possible roles for such integrative models in clinical diagnosis.

Increased coronary artery blood flow with aortomyoplasty in chronic heart failure

BACKGROUND

We hypothesized that diastolic counter-pulsation using aortomyoplasty will increase coronary blood flow.

METHODS

In dogs (n = 6, 20 to 25 kg), the left latissimus dorsi muscle was isolated, wrapped around the descending thoracic aorta, and conditioned by chronic electrical stimulation. Heart failure was induced by rapid ventricular pacing. In a terminal study, left ventricular and aortic pressures, and blood flow in the left anterior descending coronary artery and descending aorta were measured. The endocardial-viability ratio was calculated.

RESULTS

Aortomyoplasty increased mean diastolic aortic pressure (70 +/- 5 to 75 +/- 5 mm Hg, p < 0.05) and reduced peak left ventricular pressure (86 +/- 4 to 84 +/- 4 mm Hg, p < 0.05), leading to a 16% increase in endocardial-viability ratio (1.29 +/- 0.05 to 1.49 +/- 0.05, p < 0.05). Coronary blood flow was increased by 15% (8.2 +/- 1.5 to 9.4 +/- 1.6 mL/min, p < 0.05). During muscle contraction, 2.7 +/- 0.5 mL was ejected from the wrapped aortic segment.

CONCLUSIONS

These data demonstrate that aortomyoplasty provides successful diastolic counterpulsation after muscle conditioning and heart failure.

The role of coenzyme Q10 in the pathophysiology and therapy of experimental congestive heart failure in the dog

BACKGROUND

Coenzyme Q10 (CoQ10) is essential for ATP generation and has antioxidant properties. Decreased CoQ10 levels have been reported in human heart failure (CHF), but it remains unclear if this is a conserved feature of CHF. The objective of the study was to determine if tachycardia-induced CHF in the dog is associated with reduced CoQ10 levels. Furthermore, it was hypothesized that CoQ10 supplementation may improve CHF severity by preventing CoQ10 deficiency (if present) or via antioxidant effects.

METHODS AND RESULTS

Serum and myocardial levels of CoQ10 were examined in normal dogs (n = 6), dogs with CHF (control, n = 5), and dogs with CHF treated with CoQ10 (CoQ10; 10 mg/kg/day, n = 5). Serum CoQ10 levels did not change with CHF in control dogs, and myocardial levels were similar to those of normal dogs. CoQ10 therapy increased serum but not myocardial levels of CoQ10. In early CHF, CoQ10-treated dogs had lower filling pressures, and, in severe CHF, CoQ10-treated dogs had less hypertrophy as compared with untreated dogs. Other indices of CHF severity were similar in control and CoQ10-treated dogs.

CONCLUSION

These data indicate that CoQ10 deficiency is not present in this model of CHF. Although dramatic effects on hemodynamics were not observed, CoQ10 supplementation did appear to attenuate the hypertrophic response associated with CHF. Key words: enzymes, cardiomyopathy, hormones, antioxidant.

Augmented basal nitric oxide production contributes to maintenance of coronary blood flow in dogs with pacing-induced heart failure

It remains controversial whether basal nitric oxide (NO) production in coronary resistance vessels in heart failure is enhanced or not. A transonic Doppler flow probe was placed around the left anterior descending coronary artery, and complete atrioventricular block was produced in fifteen dogs. The coronary pressure-flow relationships during long diastole were analyzed without and with pacing-induced heart failure. Three weeks after pacing at 240/min, plasma norepinephrine and renin activity significantly rose. Right atrial pressure and left ventricular end-diastolic pressure increased, and cardiac output and coronary perfusion pressure decreased; however, mean coronary blood flow did not change after pacing (55 +/- 5 to 52 +/- 5 ml/min/100 g, mean +/- SEM). The slope of the diastolic coronary pressure-flow relationship became steeper (1.22 +/- 0.13 to 1.62 +/- 0.09 ml/min/100 g/mmHg, p < 0.05) with a slight increase in the measured zero-flow pressure (29.5 +/- 1.1 to 32.8 +/- 1.5 mmHg, p < 0.05) after pacing. After pretreatment with indomethacin, administration of NG-nitro-L-arginine methyl ester caused an equal increase in the zero-flow pressure before (31.4 +/- 1.7 to 39.2 +/- 2.2 mmHg, p < 0.05) and after heart failure (33.9 +/- 2.5 to 41.6 +/- 2.2 mmHg, p < 0.05), and more decline of the slope of the coronary pressure-flow relationship in heart failure (1.86 +/- 0.22 to 1.20 +/- 0.05 ml/min/100 g/mmHg, p < 0.05) than before heart failure (1.11 +/- 0.12 to 1.05 +/- 0.11 ml/min/100 g/mmHg, N.S.). This indicates that in failing hearts the vasodilatory action of NO in small vessels predominates despite the presence of several vasoconstricting factors. These results suggest that coronary blood flow is maintained despite detrimental hemodynamic and activated neurohumoral factors in the initial stage of heart failure, and that increased basal NO production plays a central role in the maintenance of basal coronary blood flow.

Changes in myocardial protein expression in pacing-induced canine heart failure

Canine rapid ventricular pacing produces a low output cardiomyopathic state which is similar to dilated cardiomyopathy. In this study dogs were paced at 245 beats per minute (bpm) for 3-4 weeks until signs of heart failure were apparent. Unpaced dogs were used as controls. A previous study identified myocardial protein changes in the pH region 4-7 following ventricular pacing by using two-dimensional electrophoresis (2-DE) (Heinke et al., Electrophoresis 1998 19, 2021-2030). Many of these proteins were associated with mitochondria, energy metabolism within the cardiomyocyte, the cytoskeleton and calcium cycling. The present study aimed to examine the proteins migrating in the more basic region of the 2-DE pattern using immobilised pH gradient 3-10 strips to separate myocardial proteins. The expression of 31 proteins was altered in the paced myocardium: 21 were decreased and 10 increased. Following the identification of 23 of these spots by either amino acid compositional analysis or peptide mass fingerprinting or a combination of both, we confirm that many of the proteins whose expression is altered following ventricular pacing are associated with the mitochondria and energy production within the cardiomyocyte, including creatine kinase M, triosephosphate isomerase, phosphoglycerate mutase, cytochrome c oxidase, cytochrome b5, hydroxymethyl glutaryl CoA synthase, myoglobin, and 3,2-trans-enoyl-CoA transferase. Additionally, the cytoskeletal protein actin was increased in the paced hearts. These results strongly support the notion that energy production is impaired and mitochondrial dysfunction is involved in the development of heart failure in the paced dog.

Mapping of regional myocardial strain and work during ventricular pacing: experimental study using magnetic resonance imaging tagging

OBJECTIVES

The purpose of this study was to determine the spatial distribution of myocardial function (myofiber shortening and work) within the left ventricular (LV) wall during ventricular pacing.

BACKGROUND

Asynchronous electrical activation, as induced by ventricular pacing, causes various abnormalities in LV function, perfusion and structure. These derangements may be caused by abnormalities in regional contraction patterns. However, insight into these patterns during pacing is as yet limited.

METHODS

In seven anesthetized dogs, high spatial and temporal resolution magnetic resonance-tagged images were acquired in three orthogonal planes. Three-dimensional deformation data and LV cavity pressure and volume were used to determine midwall circumferential strain and external and total mechanical work at 192 sites around the left ventricle.

RESULTS

During ventricular pacing, systolic fiber strain and external work were approximately zero in regions near the pacing site, and gradually increased to more than twice the normal value in the most remote regions. Total mechanical work, normalized to the value during right atrial pacing, was 38 +/- 13% (right ventricular apex [RVapex] pacing) and 61 +/- 23% (left ventricular base [LVbase] pacing) close to the pacing site, and 125 +/- 48% and 171 +/- 60% in remote regions, respectively (p < 0.05 between RVapex and LVbase pacing). The number of regions with reduced work was significantly larger during RVapex than during LVbase pacing. This was associated with a reduction of global LV pump function during RVapex pacing.

CONCLUSIONS

Ventricular pacing causes a threefold difference in myofiber work within the LV wall. This difference appears large enough to regard local myocardial function as an important determinant for abnormalities in perfusion, metabolism, structure and pump function during asynchronous electrical activation. Pacing at sites that cause more synchronous activation may limit the occurrence of such derangements.

An experimental study of cardiac natriuretic peptides as markers of development of congestive heart failure

The use of cardiac peptide measurements as possible diagnostic tools in congestive heart failure has been extensively discussed in the recent literature. Therefore, the aim of this study was to establish a model of experimental chronic heart failure, and thereby perform a comparative study of secretion and circulating levels of the cardiac peptides atrial natriuretic peptide (ANP), N-terminal proatrial natriuretic peptide (N-terminal proANP) and brain natriuretic peptide (BNP) during evolving heart failure. Chronic heart failure was induced in seven pigs by rapid left atrial pacing for three weeks. The effects of failure induction were documented 24 h after pacemaker deactivation. Hemodynamic indices of cardiac preload, like pulmonary capillary wedge pressure (PCWP) and right atrial pressure (RAP), were all considerably increased compared to sham operated controls. Likewise, plasma endothelin-L, noradrenaline, renin activity, aldosterone and angiotensin II were all markedly increased. Heart failure was accompanied by significant increases in both estimated cardiac secretory rate and plasma concentrations of all three cardiac peptides, significantly correlated to the PCWP. The directional changes during evolving heart failure were similar, although the percentage increase in plasma BNP was much larger than for ANP and N-terminal proANP. In absolute molar terms, however, the BNP concentration changes were minor compared to those of the other two peptides. The larger percentage increase of BNP might indicate its superiority as a marker of heart failure development, provided a functional assay suitable for clinical use can be designed for a peptide circulating in this low concentration range.

Restoring the remodeled enlarged left ventricle: experimental benefits of in vivo porcine cardioreduction in the beating open heart

Conceptual models have been used to assess the efficacy of cardioreduction (i.e., Batista procedure) because in vivo models were not available. This study reproduces an experimental angiographic model of heart failure by placing a large pericardial patch to sphericalize the left ventricle. Patch removal restored an elliptical normal cardiac shape. Cardioreduction was evaluated in 20 mini-pigs on cardiopulmonary bypass. Myocardial protection with a beating open method was used and cardioplegia was not used. Studies were made after an LV incision (i.e., circumflex marginal artery occlusion with the Batista incision). A large pericardial patch sphericalized the left ventricle, and LV closure by patch removal restored normal cardiac shape (ellipse). Ventricular function was evaluated by inscribing Starling curves to fill the heart systolic elastance (Ees, conductance catheter), and surface echocardiogram for fiber shortening. After defining LV function in normal hearts on bypass only, an LV incision to divide the median ramus circumflex artery was made. This ventriculotomy reduced stoke work (SW) 37% +/- 4%, but did not change elastance (Ees) or SW/end-diastolic volume (EDV) significantly. Using the LV incision function as control, patch placement reduced SW 33% +/- 4%, Ees 40% +/- 3%, and SW/EDV 44% +/- 7% and decreased fiber shortening 43% +/- 5% by echocardiogram. Patch removal restored stroke work, SW/EDV, and Ees, and echocardiograms returned to normal values after LV incision. Ventricular function after patch removal was unchanged when the beating open cardioprotective technique was used. We conclude that sphericalization of left ventricular dimensions by pericardial patch placement causes cardiac failure that is relieved by restoring the ellipsoid shape by patch removal. These findings support the value of restoration of an elliptical shape by surgical cardioreduction, when the beating open ventricle is used for myocardial protection.

Dissociation between regional dysfunction and beta-adrenergic receptor signaling in heart failure

We have previously shown that left ventricular (LV) pacing-induced heart failure is associated with preserved wall thickening in the interventricular septum (IVS) compared with the posterolateral wall (PLW). The current study focuses on the relationship between regional myocardial function and altered beta-adrenergic receptor (beta-AR) signaling. We studied 15 pigs: 6 controls and 9 paced from the left ventricle (225 beats/min, 26 +/- 3 days). Heart failure was documented by decreased LV fractional shortening (P < 0.0001) and increased left atrial pressure (P < 0.0001). In heart failure, despite marked differences in basal regional function (percent wall thickening: IVS, 33 +/- 10% vs. PLW, 13 +/- 7%; P = 0.0003), there were no differences between the two regions in beta-AR responsiveness, measured by regional wall thickening in response to dobutamine infusion and any measurement of adrenergic signaling. Adenylyl cyclase activity, beta-AR number, and beta-AR/Gs coupling were markedly reduced in failing LV without regional differences. In animals with heart failure, LV G protein receptor kinase (GRK) isoform 2 content was unchanged and GRK5, the other major GRK isoform, was increased more than threefold (IVS, 0.51 +/- 0.20 vs. 0. 12 +/- 0.12 arbitrary densitometric units, P = 0.01; PLW, 0.47 +/- 0. 15 vs. 0.13 +/- 0.09 arbitrary densitometric units, P = 0.03), but again, there were no regional differences. These data indicate that systemic rather than regional factors govern LV adrenergic signaling and that regional adrenergic signaling abnormalities poorly predict wall thickening in the same regions.