Pathophysiologie der Ventrikelkontraktion — Kontraktilität, Inotropie, Suffizienzgrad und Arbeitsökonomie des Herzens. In: Thauer R, Pleschka K, editors. Thema: Kontraktilität des Myokards. Heidelberg: Steinkopff; 1976. pp. 14-30. [DOI: 10.1007/978-3-642-87227-3_2]

An approach to ventricular efficiency by use of carbon 11-labeled acetate and positron emission tomography

BACKGROUND

Positron emission tomography-derived 11C-labeled acetate kinetics have been shown to reflect myocardial oxidative metabolism. The objective of the study was to use this metabolic imaging technique in combination with an evaluation of left ventricular work as an index of ventricular mechanical efficiency.

METHODS AND RESULTS

The effects of ventricular ejection fraction and loading on this index were studied quantitatively in a canine experimental model. There was a curvilinear relationship between efficiency and the end-diastolic volume per unit mass (r = 0.84), which appeared to integrate the main determinants of left ventricular mechanical performance successfully and allowed the detection of a decreased ventricular efficiency in acute experimental heart failure.

CONCLUSIONS

This approach appears to have the potential to assess the energetic working point of the ventricle in clinical heart disease and follow the effects of therapy. The data demonstrate the feasibility of an estimate of ventricular efficiency that relies on noninvasive data-acquisition techniques.

Myocardial energetics in dilated cardiomyopathy

To assess hemodynamic and energetic effects of different drug interventions on idiopathic dilated cardiomyopathy (IDCM), we determined hemodynamic variables of myocardial oxygen consumption (MVO2) in 37 patients with IDCM. Hemodynamics were measured during routine left and right heart catheterization. MVO2 was analyzed from myocardial blood flow (measured by the argon method) and aortocoronary sinus blood oxygen difference. The hemodynamic variable which correlated best with MVO2 was shown to be the systolic stress time integral (STI). Four different representative compounds were tested with respect to their acute effects on myocardial energetics (MVO2/STI) in patients with IDCM who were in compensated heart failure (NYHA class II-III). The drug interventions were performed at rest. Intravenous injection of the vasodilator nitroprusside yielded a 35% reduction in STI and a 30% reduction in MVO2; in other words, the ratio MVO2/STI was not altered. Injection of the calcium sensitizer and phosphodiesterase inhibitor pimobendan also did not alter this ratio, as both STI (36%) and MVO2 (33%) were lowered. The profound reduction in STI (60%) seen with the phosphodiesterase inhibitor enoximone was accompanied by a much smaller decrease in MVO2 (19%); therefore, the ratio of MVO2/STI increased significantly. An increase of this ratio was also seen with the partial beta-1 receptor agonist xamoterol. However, in this case STI did not change, whereas MVO2 increased by 26%. In summary, vasodilation has energy-saving effects, whereas positive inotropism is an energy-consuming process. We conclude that the overall effect on myocardial energetics of a drug which possesses both positive inotropic and vasodilating properties depends on the balance of the two properties.

Combined treatment with vitamins E and C in experimental myocardial infarction in pigs

The effect of two different combined treatments with vitamin E acetate and vitamin C on infarct size and recovery of regional myocardial function was investigated in ischemic, reperfused porcine hearts. The left anterior descending coronary artery was distally ligated in 30 thoracotomized pigs for 45 minutes followed by 3 days of reperfusion. Infarct size was determined as the ratio of infarcted (tetrazolium stain) to ischemic (dye technique) myocardium. Regional myocardial function was assessed by sonomicrometry. Ten pigs received vitamin E acetate (12 gm intravenously three times for 1 week) before ischemic and vitamin C (4.4 gm intravenously) before reperfusion (therapy A). Another 10 pigs were treated with vitamin E acetate (12 gm intraarterially) and vitamin C (4.4 gm intravenously) during ischemia (therapy B). An additional 10 pigs served as a control group. Global hemodynamics did not differ significantly among the groups before and during ischemia. Mean plasma concentrations of vitamin E amounted to 107 micrograms/ml in group A, 16 micrograms/ml in group B, and 0.9 micrograms/ml in the control group at the onset of reperfusion. Therapy A reduced the size of the infarct from 73 +/- 12% to 47 +/- 16% of the region at risk (p less than 0.005) and improved regional systolic shortening from 0 +/- 7% to 11 +/- 6% at 3 days after reperfusion (p less than 0.01). Therapy B decreased the size of the infarct to 64 +/- 9% of the region at risk (p = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment of reperfusion injury with intracoronary calcium channel antagonists and reduced coronary free calcium concentration in regionally ischemic, reperfused porcine hearts

The effect of intracoronary diltiazem, EGTA (ethylene-bis-(beta-aminomethylether)-N,N'-tetraacetic acid), nifedipine, verapamil and isotonic saline solution as placebo on reperfusion injury was investigated in regionally ischemic, reperfused porcine hearts. The left anterior descending coronary artery was distally occluded for 45 min and was reperfused for 3 days. Intracoronary infusion was started immediately before reperfusion and continued during 45 min of reperfusion. Infarct size was determined as the ratio of infarcted (tetrazolium stain) to ischemic myocardium (dye technique). Regional systolic shortening was assessed by sonomicrometry. Apart from left ventricular end-diastolic pressure before ischemia and during 45 min of reperfusion, global hemodynamic values in the five treatment groups did not differ; in particular, calculated left ventricular oxygen consumption before and during ischemia was equally low. Intracoronary EGTA decreased coronary venous free calcium concentration to about 70% of baseline value. Infarct size was reduced from 76 +/- 10% (control group, n = 8) to 60 +/- 10% (p less than 0.01) by intracoronary diltiazem (n = 8) and to 55 +/- 15% (p less than 0.01) by intracoronary EGTA (n = 8). Insignificant reductions in infarct size were found after treatment with intracoronary verapamil (63 +/- 18%, n = 8) and intracoronary nifedipine (68 +/- 9%, n = 7). Regional systolic shortening of the risk region, which did not differ among the groups before occlusion and during ischemia, recovered to the greatest extent in the EGTA-treated pigs (p less than 0.01 compared with values in the control group). Treatment with intracoronary calcium antagonists resulted in only marginal improvement of systolic shortening.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell death in ischemic, reperfused porcine hearts: a histochemical and functional study

The temporal development of infarcts was histochemically and functionally determined in porcine hearts. In one series of experiments (22 pigs), the distal third of the left anterior descending coronary artery (LAD) was transiently occluded for periods between 20 and 90 min and was reperfused for another 24 h. At the end of the experiments, the infarcted myocardium of four tissue slices was determined with a tetrazolium stain and related to the risk region which was delineated by a fluorescent dye. Infarcts started to develop in the ischemic septum and the subendocardial layer of the free anterior wall between 20 and 35 min of ischemia. Thereafter, infarctions progressed rapidly from the inner towards the outer layer at risk. The jeopardized anterior left ventricular wall became almost completely infarcted within 60 min of ischemia. In a second series of experiments (10 pigs) recovery of systolic shortening was studied with implanted ultrasonic crystals over 3 weeks of reperfusion. At the end of the experiments, systolic shortening was about 75% of baseline level when ischemia had lasted between 20 and 35 min. Almost no recovery was observed when the occlusion time lasted 45 to 60 min. This study suggests that the assessment of myocardial infarction with a tetrazolium stain after 24 h of reperfusion corresponds very well with functional recovery after 3 weeks of reperfusion. Furthermore, determination of regional myocardial function of the ischemic, reperfused segment in the chronic stage may be considered an additional tool to evaluate therapeutic effects on infarct size in this model.

Are isolated cardiomyocytes a suitable experimental model in all lines of investigation in basic cardiology?

Isolated cardiac myocytes of adult rats resemble the intact myocardium in many respects. Thus, use of isolated cells has been established in many lines of basic cardiological research. In electrophysiology, ionic channels can apparently be characterized more accurately than in intact tissue. The transport of metabolites across the sarcolemma can be studied independently of the influence of other types of cells and transport barriers. However, most reports about metabolism deal with quiescent cells, which obviously have a very low metabolic rate, provided they are intact, and their oxidative phosphorylation is not uncoupled. Thus, their application as a model of a working heart appears to be restricted. But using electrical stimulation, the metabolic activity of the cells can be gradually enhanced up to those values observed in beating hearts. In this case, the measurement of mechanical parameters as the myocytes respond to the electrical stimulation is of interest. The combination of the measurements of both metabolic and mechanical parameters in a physical model, led us to investigate the possibility of measuring inotropic effects as well as the relationship between mechanical changes and changes in oxygen consumption, e.g. as a result of the utilization of different substrates. This expands the application of the model to pharmacology, in which the influence of the mechanical action of the heart and its oxygen consumption is of major interest. If the model of isolated cardiomyocytes is employed in screening studies, a reduction in the number of experimental animals required for this line of research will inevitably result.

Intracoronary superoxide dismutase for the treatment of "reperfusion injury", A blind randomized placebo-controlled trial in ischemic, reperfused porcine hearts

The effect of recombinant human superoxide dismutase (rh-SOD) on infarct size was investigated in porcine hearts. The left anterior descending coronary artery was occluded in each of 24 anesthetized pigs for 45 min and reperfused for 24 h. The animals were randomly assigned to either rh-SOD (n = 12) or placebo treatment (n = 12). 2 min before reperfusion, an intracoronary (i.c.) infusion of rh-SOD (total dose: 2000 U/kg) or placebo was started which lasted for up to 45 min reperfusion. At the end of the experiment, the infarcted myocardium was assessed using a tetrazolium stain (NBT) and related to the risk region which was determined with a fluorescent dye. Two pigs of the SOD group and one of the control group died before the end of the experiments. Except for a lower calculated myocardial oxygen consumption and a lower dp/dtmax in the SOD group during ischemia, hemodynamic parameters of the two groups did not differ significantly. rh-SOD i.c. treatment during reperfusion did not reduce infarct size significantly. Infarct size amounted to 74 +/- 13% in the control group and to 66 +/- 19% in the treated group. The incidence of reperfusion arrhythmias was not affected by rh-SOD treatment. It is concluded that i.c. rh-SOD treatment at the beginning of reperfusion neither significantly reduces infarct size nor diminishes the incidence of reperfusion arrhythmias in this preparation.

A modified regionally ischemic porcine heart preparation with eligible residual blood flows

The left anterior descending coronary artery was occluded in each of 28 thoracotomized pigs around an intracoronary catheter for periods between 30 and 240 min followed by 90 min of reperfusion. The catheter was connected via an external pump with another arterial catheter. The pump rate was set to deliver 1.5 ml (group I), 3 ml (group II), or 6 ml blood/min (group III) respectively during ischemia. The distribution of the residual blood flow during ischemia was determined in group II with non-radioactive microspheres. We delineated the risk region by a fluorescent dye and the infarcted tissue with a tetrazolium stain. The higher residual blood flow in groups II and III reduced the incidence of ventricular fibrillation during ischemia from 70% (group I) to 28%, suggesting that the amount of residual blood flow is one important determinant for this rhythm disturbance. The subendocardial-subepicardial blood flow ratio in the risk region of the anterior wall was 41%. Infarcts started to develop after 30 min of ischemia (groups I and II). In all groups necrosis progressed most rapidly within the first 90 min of ischemia indicating that besides the beneficial effect of a high residual blood flow only early reperfusion is able to salvage a substantial amount of jeopardized myocardium. Compared to conventional regionally ischemic canine and porcine heart preparations the described model offers the following advantages: Accurate delineation of the risk region, eligible residual blood flow, reduction of ventricular fibrillation with higher residual blood flows, and the possibility to selectively test the metabolic influence of drugs on ischemic injury while avoiding systemic effects.

Contraction and metabolic activity of electrically stimulated cardiac myocytes from adult rats

An experimental setup has been developed, which allows electrical stimulation of cardiac myocytes and simultaneous measurement of oxygen consumption, lactate production, extent of shortening and of substrate uptake. In resting cells and in cells stimulated with 120 to 480/min the oxygen consumption ranged from 25 to 100 microliter/min X gww, with a linear relationship between rate of stimulation and oxygen consumption (VO2). When using 5 mM glucose plus 2 mM pyruvate or 10 mM lactate as substrates, isoproterenol (8 X 10(-8) M) augmented contraction and VO2 at all rates of stimulation. Assuming Hook's law for passive elastic behavior for the contracting myocytes over the length change observed, a good correlation exists between the degree of cell shortening calculated from VO2 per beat and the degree of contraction measured. This correlation can be used as a measure of the economy of O2 utilization.

Changes in myocardial substrate and energy metabolism by S-(4)-hydroxyphenylglycine and an N-(6)-derivative of adenosine

In 15 mongrel open chest dogs oxidative myocardial carbohydrate utilization was stimulated by activation of pyruvatedehydrogenase with S-(4)-hydroxyphenylglycine (HPG) or by inhibition of lipolysis with N(6)-allyl-N(6)-cyclohexyladenosine (PAA). HPG and PAA shifted cardiac respiratory quotients (RQ) from 0.83 to 0.89 and 0.99, respectively. Oxygen extraction ratio of lactate was significantly increased by both interventions. Arterial nonesterified fatty acids (NEFA) concentration decreased significantly only by PAA. The oxygen saving potency of both interventions was quantified over a wide hemodynamic range by comparing the directly measured myocardial oxygen consumption (MVO2) with the myocardial energy requirements calculated from its hemodynamic determinants according to the Bretschneider formula during base conditions and beta-stimulation. Inhibition of peripheral lipolysis with PAA reduced MVO2 by 14%, enzyme activation with HPG by 8%. The results show that the efficiency of the myocardial energy supply can be influenced by manipulation of the oxidative substrate metabolism.

Analysis of the efficacy of the new cardiotonic agent TA-064

TA-064 is a new cardiotonic agent which is also effective orally, according to investigations conducted in Japan. We analyzed computer-assisted alterations of pressure-volume relationships serially and of indirect myocardial oxygen consumption (MVO2) estimations on line during TA-064 influence in 16 patients with congestive cardiomyopathy: left ventricular function was moderately decreased in seven patients (group A) and drastically decreased in nine (group B). Results showed that TA-064, 8 micrograms/kg/min intravenously, exerted positive inotropic effects in both groups and induced mean maximal delta percentage changes at about 5 minutes of infusion as follows: left ventricular stroke work index +65% and +47%; dP/dtmax +61% and 59%; left ventricular efficiency +62% and 53%; MVO2 +31% and +11% (p less than 0.05). TA-064, 20 mg by mouth induced serum levels (group A = 23.8 +/- 12ng/ml and group B = 26.4 +/- 20 ng/ml) corresponding to the effects with dosages of 1 to 2 ng/kg/min intravenously (p greater than 0.05), thus implying that significant changes in left ventricular function require higher oral dosages. We conclude that TA-064 improves left ventricular function, primarily via a contractility increase, also in group B patients without toxic side effects. On-line indirect MVO2 assessment and analysis of serial pressure-volume relationships helped to provide a more complex definition of the mechanism and efficiency of the cardiotonic agent under study.

Intracoronary hyperosmotic mannitol during reperfusion does not affect infarct size in ischemic, reperfused porcine hearts

We investigated the effect of reperfusion with hyperosmotic mannitol on the infarct size in porcine hearts. The distal half of the left anterior descending coronary artery was occluded in each of 21 anesthetized pigs for 75 min and was reperfused for 2 h. During reperfusion mannitol (1075 mosmol/kg) was intracoronarily infused at a dose of 0.5 ml/min in 6 pigs ("low" mannitol group), at a dose of 1.5 ml/min in another 6 pigs ("high" mannitol group), and at a dose of 5 ml/min in 3 pigs for the first 8 min of reperfusion ("very high" mannitol group). 6 pigs served as controls. Although mannitol infusion increased plasma osmolality in the ischemic, reperfused myocardium in all experiments, the infarct size expressed as the ratio of the infarcted tissue over the area at risk of necrosis was not significantly influenced. Infarct size amounted to 72 +/- 25% in the control group, to 75 +/- 14% in the "low" mannitol group, to 78 +/- 18% in the "high" mannitol group, and to 93 +/- 8% in the "very high" mannitol group. These results clearly indicate that reperfusion with hyperosmotic mannitol after 75 min of ischemia does not exert any beneficial effect on the infarct size.

Temporal and spatial development of infarcts in porcine hearts

We investigated the temporal and spatial development of infarcts in porcine hearts to evaluate the time-dependent beneficial effect of reperfusion on infarct size. The left anterior descending coronary artery (LAD) was occluded in 17 pigs for different periods of time followed by 4 hours of reperfusion. Transmural needle biopsies subdivided into subendocardial and subepicardial halves were taken from the ischemic apex after 60 min of ischemia to determine the tissue concentrations of ATP and NAD. The myocardium-at-risk was assessed with a fluorescent dye injected into the right atrium at the end of the experiments, just after the LAD had been reoccluded. The excised hearts were cut into slices parallel to the heart basis. The ischemic myocardium was measured by planimetry of the non-fluorescent areas whereas the infarcted tissue was determined with the NBT stain and related to the area-at-risk. Ischemic cell death started in the jeopardized left ventricular subendocardial septum after about 30 min of ischemia. The further progress involved the right subendocardial septum and the subendocardium of the left anterior free wall. Already after 75 min of ischemia most of the myocytes-at-risk were irreversibly injured. Infarctions reached their final extent after 90-120 min of ischemia. These results indicate that in hearts without a significant collateral blood flow reperfusion can only reduce infarct size if its initiated within 60-75 min of ischemia. Like in canine hearts infarctions progress from the ischemic subendocardium towards the outer layers.

Myocardial fatty acid oxidation: evidence for an albumin-receptor-mediated membrane transfer of fatty acids

Using a computer-assisted working rat heart preparation, which allows continuous registration of the respiratory quotient, it was tested which parameters determine fatty acid oxidation in the myocardium. Supplying albumin and palmitate in different concentrations the rate of fatty acid oxidation was measured. The UFA concentrations were calculated using stepwise equilibrium constants. When keeping constant the NEFA/albumin ratio and raising total NEFA concentration, an increase in fatty acid oxidation was found showing a saturation curve. Increasing NEFA at constant albumin concentration, however, results in a linear increase in fatty acid oxidation. Keeping constant the total NEFA concentration elevation of albumin shows an inhibitory effect. These results suggest the existence of a receptor for albumin on heart cell surface, which mediates uptake of albumin-bound NEFA. An additional supply of glucose and lactate does not show any effect on these relations. Acetate and dichloroacetate, an activator of the pyruvate dehydrogenase, are found to be competitive inhibitors of fatty acid oxidation.

A new method for continuous measuring of respiratory quotient in a computer-assisted working heart preparation

A method was developed for continuous monitoring of the respiratory quotient (RQ) and the ratio of O2-consumption to O2-demand (EQ) in an isolated working rat heart preparation. The RQ allows to get informations about substrates actually oxidized in the myocardium. The EQ is a parameter which behaves reciprocally to the ATP/O of the oxidized substrates during steady state and additionally it allows monitoring of a transitory oxygen debt. For registration of RQ the arterio-venous O2-difference and the CO2-release are measured. As the CO2-production is very small compared with arterial CO2- and HCO-3 -concentrations when using a bicarbonate buffer for perfusion, a bicarbonate-free perfusion-fluid is used. In a portion of coronary effluent the pH is lowered to shift the CO2/HCO-3 -equilibrium to the side of dissolved CO2. Then the pCO2 is measured with a CO2-Nelectrode. Additionally, ventricular pressure, cardiac input and coronary flow are continuously registrated. All data are fed via an AD-converter into an LSI 11-computer. Heart rate, maximum ventricular pressure, dP/dtmax, oxygen demand after Bretschneider's formula, RQ and EQ are calculated. The advantages of the system described are demonstrated with two examples.

Myocardial oxygen consumption and regulation of coronary blood flow during stepped relief of the left ventricle

In 25 calves an atrio-ventriculo-aortic bypass was performed and the metabolism and the regulation of coronary blood flow during stepped assistance of the left ventricle was studied. With mean aortic blood pressure kept constant stepped decrease in left ventricular pressure from 120 to 0 mmHg diminished myocardial oxygen consumption from 7.7 to 1.9 ml O2/min X 100 g. Increasing right ventricular pressure by banding the pulmonary artery with left ventricular pressure and mean aortic pressure kept constant the oxygen uptake of the left ventricle increased about 20.7 +/- 32.% when measured by Fick's principle but remained unchanged when calculated from hemodynamic parameters of the left ventricle (-1.5 +/- 3.5%). At constant coronary perfusion pressure coronary blood flow decreased when left ventricular pressure was reduced from 120 to 100 mmHg. Further decrease in left ventricular pressure to 0 mmHg showed no effect on coronary blood flow. Increasing heart rate from 152 +/- 9 to 208 +/- 8 b.p.m. enhanced myocardial oxygen uptake of the assisted heart about 59.0 +/- 11.4% while resistance to flow decreased about 40.4 +/- 2.8%. These results show that the metabolic regulation of coronary blood flow is still acting even in the assisted left heart.

Systolic stress, coronary hemodynamics and metabolic reserve in experimental and clinical cardiac hypertrophy

The degree of LV hypertrophy may be determined by the relationships between mass-to-volume ratio and systolic wall stress. Systolic wall stress correlates directly with the MVO2 and inversely with LV function. In chronic hypertrophic heart disease (a) normal stress, (b) low stress and (c) high stress hypertrophy may occur. Low stress hypertrophy has normal LV function and normal or decreased MVO2, whereas high stress hypertrophy mostly has depressed function and an increased MVO2. The MVO2 is directly correlated to LV mass. This relationship is influenced by the variable degree of LV mass, by the mass-to-volume ratio and by inotropic interventions. Systolic stress reserve, the ratio of maximum to instantaneous systolic wall stress, averages 4.5. Similar reserves are present for the coronary (4.9) and for the metabolic reserve (4.6). It is concluded that systolic wall stress represents one of the major determinants of LV performance and of myocardial oxygen consumption.

Multifactorial determination of 201thallium uptake of the heart: an experimental study concerning the influence of ventricular mass, perfusion and oxygen consumption

Studies were performed in 42 cats in order to analyze the determinants of myocardial 201Thallium uptake. (1) Ventricular mass represents the major determinant of myocardial 201Thallium uptake. The inner (subendocardial) layer of the left ventricle storages 10-15 per cent more Thallium than the outer (subepicardial) layer, whereas the right ventricle has 201Thallium accumulation by 40 per cent less than the left ventricle. (2) Coronary perfusion increase as induced by intravenous injection of dipyridamole leads-at constant muscle mass-to considerable increase in myocardial 201Thallium uptake by 106 per cent. (3) Changes in myocardial oxygen consumption as induced by inotropic interventions are associated with considerable changes in the myocardial 201Thallium uptake. These results demonstrate that ventricular mass, myocardial flow and myocardial oxygen consumption are major determinants of myocardial 201Thallium uptake. Thus, by quantitiative determination of the myocardial 201Thallium uptake, a useful equivalent of the viability degree of the left ventricle, which itself is determined by mass, flow and metabolism, may be obtained.