Norepinephrine release is increased in the hibernating heart, studied in a chronic canine model of myocardial hibernation

Correlation between activation of the sympathetic nervous system estimated by plasma concentrations of norepinephrine and Doppler echocardiographic variables in dogs with acquired heart disease

OBJECTIVE

To evaluate correlations between plasma concentrations of norepinephrine and Doppler echocardiographic variables for dogs with degenerative mitral valve disease (DMVD) or dilatative cardiomyopathy (DCM) to better understand the time course and magnitude of sympathetic activation in dogs with heart failure (HF).

ANIMALS

15 healthy dogs, 15 dogs with DMVD, and 15 dogs with DCM.

PROCEDURES

Dogs were positioned in lateral recumbency with minimal restraint for at least 20 minutes. Plasma samples were obtained and assayed by use of high-performance liquid chromatography. Concentrations were correlated with HF classification and with the main Doppler echocardiographic variables for each group.

RESULTS

Mean +/- SD norepinephrine concentration was significantly higher in dogs with DMVD (494.4 +/- 204.8 pg/mL) or DCM (655.7 +/- 652.5 pg/mL) than in healthy dogs (205.8 +/- 78.9 pg/mL), but concentrations did not differ significantly between the 2 groups with HF. Correlations were not detected between norepinephrine and heart rate or any M-mode echocardiographic variables evaluated, except for fractional shortening (FS) in DCM dogs. In that group, norepinephrine was inversely correlated with FS values. In DMVD dogs, no significant correlation was found between norepinephrine and the left atrium-to-aortic root ratio or mitral regurgitation.

CONCLUSIONS AND CLINICAL RELEVANCE

A proportional inverse correlation exists between norepinephrine and FS values in dogs with DCM. However, norepinephrine concentration was not correlated with the evaluated echocardiographic variables in dogs with DMVD. Sympathetic antagonists should be evaluated as a treatment option because of the increased plasma concentrations of norepinephrine detected in dogs with HF.

A porcine model of ischemic heart failure produced by chronic placement of a tube in a coronary artery

BACKGROUND AND AIMS

Animal models of heart failure (HF) are useful to clarify the mechanism and to develop therapeutic interventions. To produce an easy ischemic HF model, we induced myocardial infarction (MI) in pigs by placing a tube in the coronary artery.

METHODS

Twelve pigs underwent echocardiography and were randomly allocated to the myocardial infarction group (MI group) and the control group. In the MI pigs, a 4.2 F nylon tube was placed via the carotid artery in the left circumflex coronary (LCx) artery to induce MI. Three months thereafter, thoracotomy was performed in the both groups and left ventricular (LV) pressure-volume relation was evaluated.

RESULTS

Body weight, LV dimension and function did not differ in the baseline state between the two groups. Three months after the tube placement, LV diameter was larger (47+/-3 vs. 42+/-2 mm) and its fractional shortening was lower in the MI group than the control group. In addition, aortic flow was decreased, LV ejection fraction was decreased (25+/-5 vs. 52+/-6%) and LV diastolic pressure was elevated (14+/-3 vs. 8+/-2 mmHg) in the MI group compared with the control group. The extent of MI was 26+/-5% of the LV in the MI pigs.

CONCLUSION

The method of placing a tube in the coronary artery does not need thoracotomy or an additional procedure and enables the production of an ischemic HF model of pigs.

Dobutamine responsiveness, PET mismatch, and lack of necrosis in low-flow ischemia: is this hibernation in the isolated rat heart?

The clinical hallmarks of hibernating myocardium include hypocontractility while retaining an inotropic reserve (using dobutamine echocardiography), having normal or increased [18F]fluoro-2-deoxyglucose-6-phosphate (18FDG6P) accumulation associated with decreased coronary flow [flow-metabolism mismatch by positron emission tomography (PET)], and recovering completely postrevascularization. In this study, we investigated an isolated rat heart model of hibernation using experimental equivalents of these clinical techniques. Rat hearts (n = 5 hearts/group) were perfused with Krebs-Henseleit buffer for 40 min at 100% flow and 3 h at 10% flow and reperfused at 100% flow for 30 min (paced at 300 beats/min throughout). Left ventricular developed pressure fell to 30 +/- 8% during 10% flow and recovered to 90 +/- 7% after reperfusion. In an additional group, this recovery of function was found to be preserved over 2 h of reperfusion. Electron microscopic examination of hearts fixed at the end of the hibernation period demonstrated a lack of ischemic injury and an accumulation of glycogen granules, a phenomenon observed clinically. In a further group, hearts were challenged with dobutamine during the low-flow period. Hearts demonstrated an inotropic reserve at the expense of increased lactate leakage, with no appreciable creatine kinase release. PET studies used the same basic protocol in both dual- and globally perfused hearts (with 250MBq 18FDG in Krebs buffer +/- 0.4 mmol/l oleate). PET data showed flow-metabolism "mismatch;" whether regional or global, 18FDG6P accumulation in ischemic tissue was the same as (glucose only) or significantly higher than (glucose + oleate) control tissue (0.023 +/- 0.002 vs. 0.011 +/- 0.002 normalized counts. s-1x g-1x min-1, P < 0.05) despite receiving 10% of the flow. This isolated rat heart model of acute hibernation exhibits many of the same characteristics demonstrated clinically in hibernating myocardium.

Retrograde cardioplegia

OBJECTIVE

This study was undertaken to compare the efficacy of retrograde cardioplegia for myocardial perfusion with that of antegrade cardioplegia at the same flow rate.

METHODS

Colored microspheres were used in rat hearts to assess the capillary flow of cardioplegia solution. Myocardial perfusion was evaluated with magnetic resonance imaging in pig hearts. Phosphorus 31 magnetic resonance spectroscopy was used to determine the efficacies of the cardioplegic techniques in sustaining myocardial energy metabolism.

RESULTS

At the same flow rate, the number of colored microspheres delivered to the capillaries by retrograde cardioplegia (15 +/- 1 microspheres/mm2) was significantly lower than that delivered by antegrade cardioplegia (29 +/- 2 microspheres/mm2). Furthermore, only 19% +/- 3% of the colored microspheres delivered to the capillaries by retrograde cardioplegia were found in the arteriolar portions of the capillaries, whereas most (80% +/- 3%) remained in the venular portions. Moreover, magnetic resonance images showed that contrast-enhanced signal-time courses obtained from different regions of the myocardium during retrograde cardioplegia varied significantly. Localized phosphorus 31 spectra showed that retrograde cardioplegia required a higher flow rate than did antegrade cardioplegia to sustain normal myocardial energy metabolism.

CONCLUSIONS

We conclude that retrograde cardioplegia provides significantly less capillary flow than does antegrade cardioplegia. Its microvascular perfusion varies significantly among the various small areas of the myocardium. As a result, its efficacy in sustaining normal myocardial energy metabolism is lower than that of antegrade cardioplegia.

Increased myocardial gene expression of tumor necrosis factor-alpha and nitric oxide synthase-2: a potential mechanism for depressed myocardial function in hibernating myocardium in humans

BACKGROUND

Whether cardioinhibitory cytokines are elevated in regions of hibernating myocardium and account in part for the depression in resting function is currently not known. Methods and Results- Thirteen patients with stable ischemic ventricular dysfunction scheduled for bypass surgery underwent preoperative dobutamine echocardiography (DE) and intraoperative myocardial biopsies. The numbers of copies of mRNA for the negatively inotropic cytokines tumor necrosis factor-alpha (TNF-alpha) and inducible nitric oxide synthase (NOS2) were quantified by reverse transcription-polymerase chain reaction. In normal segments, myocardial TNF-alpha was barely detectable (1.2+/-0.4 copies per 10(6) copies of beta-actin). A 13.7-fold increase in myocardial TNF-alpha was observed in dysfunctional segments with a biphasic response to DE (contractile reserve and ischemia) and was highest (45.5-fold) in segments with ischemia and without contractile reserve (P<0.001). A similar graded increase was seen for NOS2. Cytokine results were also similar if analysis was performed using recovery of function at 3 months as the index of viability. The change in serum TNF-alpha and nitrite levels from baseline to 3 months after surgery correlated inversely with both the change in ejection fraction and the number of DE viable segments (r=-0.92 to -0.93; P<0.001).

CONCLUSIONS

TNF-alpha and NOS2 gene expression is regionally upregulated in hibernating myocardium to a level intermediate between that of normal regions and ischemic regions without contractile reserve. This, along with a decline in serum cytokine levels after revascularization proportional to the extent of myocardial viability, suggests a contributing role for cardioinhibitory cytokines in the observed depression of function seen in hibernating myocardium.