Escherichia coli CspA stimulates translation in the cold of its own mRNA by promoting ribosome progression

Escherichia coli CspA is an RNA binding protein that accumulates during cold-shock and stimulates translation of several mRNAs-including its own. Translation in the cold of cspA mRNA involves a cis-acting thermosensor element, which enhances ribosome binding, and the trans-acting action of CspA. Using reconstituted translation systems and probing experiments we show that, at low temperature, CspA specifically promotes the translation of the cspA mRNA folded in the conformation less accessible to the ribosome, which is formed at 37°C but is retained upon cold shock. CspA interacts with its mRNA without inducing large structural rearrangements, but allowing the progression of the ribosomes during the transition from translation initiation to translation elongation. A similar structure-dependent mechanism may be responsible for the CspA-dependent translation stimulation observed with other probed mRNAs, for which the transition to the elongation phase is progressively facilitated during cold acclimation with the accumulation of CspA.

Perturbation of ribosomal subunit dynamics by inhibitors of tRNA translocation

Many antibiotics that bind to the ribosome inhibit translation by blocking the movement of tRNAs and mRNA or interfering with ribosome dynamics, which impairs the formation of essential translocation intermediates. Here we show how translocation inhibitors viomycin (Vio), neomycin (Neo), paromomycin (Par), kanamycin (Kan), spectinomycin (Spc), hygromycin B (HygB), and streptomycin (Str, an antibiotic that does not inhibit tRNA movement), affect principal motions of the small ribosomal subunits (SSU) during EF-G-promoted translocation. Using ensemble kinetics, we studied the SSU body domain rotation and SSU head domain swiveling in real time. We show that although antibiotics binding to the ribosome can favor a particular ribosome conformation in the absence of EF-G, their kinetic effect on the EF-G-induced transition to the rotated/swiveled state of the SSU is moderate. The antibiotics mostly inhibit backward movements of the SSU body and/or the head domains. Vio, Spc, and high concentrations of Neo completely inhibit the backward movements of the SSU body and head domain. Kan, Par, HygB, and low concentrations of Neo slow down both movements, but their sequence and coordination are retained. Finally, Str has very little effect on the backward rotation of the SSU body domain, but retards the SSU head movement. The data underscore the importance of ribosome dynamics for tRNA-mRNA translocation and provide new insights into the mechanism of antibiotic action.

Converting GTP hydrolysis into motion: versatile translational elongation factor G

Elongation factor G (EF-G) is a translational GTPase that acts at several stages of protein synthesis. Its canonical function is to catalyze tRNA movement during translation elongation, but it also acts at the last step of translation to promote ribosome recycling. Moreover, EF-G has additional functions, such as helping the ribosome to maintain the mRNA reading frame or to slide over non-coding stretches of the mRNA. EF-G has an unconventional GTPase cycle that couples the energy of GTP hydrolysis to movement. EF-G facilitates movement in the GDP-Pi form. To convert the energy of hydrolysis to movement, it requires various ligands in the A site, such as a tRNA in translocation, an mRNA secondary structure element in ribosome sliding, or ribosome recycling factor in post-termination complex disassembly. The ligand defines the direction and timing of EF-G-facilitated motion. In this review, we summarize recent advances in understanding the mechanism of EF-G action as a remarkable force-generating GTPase.

Translational recoding: canonical translation mechanisms reinterpreted

During canonical translation, the ribosome moves along an mRNA from the start to the stop codon in exact steps of one codon at a time. The collinearity of the mRNA and the protein sequence is essential for the quality of the cellular proteome. Spontaneous errors in decoding or translocation are rare and result in a deficient protein. However, dedicated recoding signals in the mRNA can reprogram the ribosome to read the message in alternative ways. This review summarizes the recent advances in understanding the mechanisms of three types of recoding events: stop-codon readthrough, –1 ribosome frameshifting and translational bypassing. Recoding events provide insights into alternative modes of ribosome dynamics that are potentially applicable to other non-canonical modes of prokaryotic and eukaryotic translation.

Active role of elongation factor G in maintaining the mRNA reading frame during translation

During translation, the ribosome moves along the mRNA one codon at a time with the help of elongation factor G (EF-G). Spontaneous changes in the translational reading frame are extremely rare, yet how the precise triplet-wise step is maintained is not clear. Here, we show that the ribosome is prone to spontaneous frameshifting on mRNA slippery sequences, whereas EF-G restricts frameshifting. EF-G helps to maintain the mRNA reading frame by guiding the A-site transfer RNA during translocation due to specific interactions with the tip of EF-G domain 4. Furthermore, EF-G accelerates ribosome rearrangements that restore the ribosome's control over the codon-anticodon interaction at the end of the movement. Our data explain how the mRNA reading frame is maintained during translation.

Non-canonical Binding Site for Bacterial Initiation Factor 3 on the Large Ribosomal Subunit

Canonical translation initiation in bacteria entails the assembly of the 30S initiation complex (IC), which binds the 50S subunit to form a 70S IC. IF3, a key initiation factor, is recruited to the 30S subunit at an early stage and is displaced from its primary binding site upon subunit joining. We employed four different FRET pairs to monitor IF3 relocation after 50S joining. IF3 moves away from the 30S subunit, IF1 and IF2, but can remain bound to the mature 70S IC. The secondary binding site is located on the 50S subunit in the vicinity of ribosomal protein L33. The interaction between IF3 and the 50S subunit is largely electrostatic with very high rates of IF3 binding and dissociation. The existence of the non-canonical binding site may help explain how IF3 participates in alternative initiation modes performed directly by the 70S ribosomes, such as initiation on leaderless mRNAs or re-initiation.

Translocation as continuous movement through the ribosome

In each round of translation elongation, tRNAs and mRNA move within the ribosome by one codon at a time. tRNA-mRNA translocation is promoted by elongation factor G (EF-G) at the cost of GTP hydrolysis. The key questions for understanding translocation are how and when the tRNAs move and how EF-G coordinates motions of the ribosomal subunits with tRNA movement. Here we present 2 recent papers which describe the choreography of movements over the whole trajectory of translocation. We present the view that EF-G accelerates translocation by promoting the steps that lead to GTPase-dependent ribosome unlocking. EF-G facilitates the formation of the rotated state of the ribosome and uncouples the backward motions of the ribosomal subunits, forming an open conformation in which the tRNAs can rapidly move. Ribosome dynamics are important not only in translocation, but also in recoding events, such as frameshifting and bypassing, and mediate sensitivity to antibiotics.

Kinetics of Spontaneous and EF-G-Accelerated Rotation of Ribosomal Subunits

Ribosome dynamics play an important role in translation. The rotation of the ribosomal subunits relative to one another is essential for tRNA-mRNA translocation. An important unresolved question is whether subunit rotation limits the rate of translocation. Here, we monitor subunit rotation relative to peptide bond formation and translocation using ensemble kinetics and single-molecule FRET. We observe that spontaneous forward subunit rotation occurs at a rate of 40 s(-1), independent of the rate of preceding peptide bond formation. Elongation factor G (EF-G) accelerates forward subunit rotation to 200 s(-1). tRNA-mRNA movement is much slower (10-40 s(-1)), suggesting that forward subunit rotation does not limit the rate of translocation. The transition back to the non-rotated state of the ribosome kinetically coincides with tRNA-mRNA movement. Thus, large-scale movements of the ribosome are intrinsically rapid and gated by its ligands such as EF-G and tRNA.

Directional transition from initiation to elongation in bacterial translation

The transition of the 30S initiation complex (IC) to the translating 70S ribosome after 50S subunit joining provides an important checkpoint for mRNA selection during translation in bacteria. Here, we study the timing and control of reactions that occur during 70S IC formation by rapid kinetic techniques, using a toolbox of fluorescence-labeled translation components. We present a kinetic model based on global fitting of time courses obtained with eight different reporters at increasing concentrations of 50S subunits. IF1 and IF3 together affect the kinetics of subunit joining, but do not alter the elemental rates of subsequent steps of 70S IC maturation. After 50S subunit joining, IF2-dependent reactions take place independent of the presence of IF1 or IF3. GTP hydrolysis triggers the efficient dissociation of fMet-tRNA(fMet) from IF2 and promotes the dissociation of IF2 and IF1 from the 70S IC, but does not affect IF3. The presence of non-hydrolyzable GTP analogs shifts the equilibrium towards a stable 70S-mRNA-IF1-IF2-fMet-tRNA(fMet) complex. Our kinetic analysis reveals the molecular choreography of the late stages in translation initiation.

Programmed -1 frameshifting by kinetic partitioning during impeded translocation

Programmed –1 ribosomal frameshifting (−1PRF) is an mRNA recoding event utilized by cells to enhance the information content of the genome and to regulate gene expression. The mechanism of –1PRF and its timing during translation elongation are unclear. Here, we identified the steps that govern –1PRF by following the stepwise movement of the ribosome through the frameshifting site of a model mRNA derived from the IBV 1a/1b gene in a reconstituted in vitro translation system from Escherichia coli. Frameshifting occurs at a late stage of translocation when the two tRNAs are bound to adjacent slippery sequence codons of the mRNA. The downstream pseudoknot in the mRNA impairs the closing movement of the 30S subunit head, the dissociation of EF-G, and the release of tRNA from the ribosome. The slippage of the ribosome into the –1 frame accelerates the completion of translocation, thereby further favoring translation in the new reading frame.

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Kinetics of –1 ribosomal frameshifting are monitored at single-codon resolution

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Frameshifting occurs when the backward movement of the 30S subunit head is impeded

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Two tRNAs at the XXXYYYZ mRNA sequence are stalled in chimeric POST states

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The shift to the –1 reading frame occurs prior to EF-G release from the ribosome

Dual use of GTP hydrolysis by elongation factor G on the ribosome

Elongation factor G (EF-G) is a GTPase that catalyzes tRNA and mRNA translocation during the elongation cycle of protein synthesis. The GTP-bound state of the factor on the ribosome has been studied mainly with non-hydrolyzable analogs of GTP, which led to controversial conclusions about the role of GTP hydrolysis in translocation. Here we describe a mutant of EF-G in which the catalytic His91 is replaced with Ala. The mutant EF-G does not hydrolyze GTP, but binds GTP with unchanged affinity, allowing us to study the function of the authentic GTP-bound form of EF-G in translocation. Utilizing fluorescent reporter groups attached to the tRNAs, mRNA, and the ribosome we compile the velocity map of translocation seen from different perspectives. The data suggest that GTP hydrolysis accelerates translocation up to 30-fold and facilitates conformational rearrangements of both 30S subunit (presumably the backward rotation of the 30S head) and EF-G that lead to the dissociation of the factor. Thus, EF-G combines the energy regime characteristic for motor proteins, accelerating movement by a conformational change induced by GTP hydrolysis, with that of a switch GTPase, which upon Pi release switches the conformations of EF-G and the ribosome to low affinity, allowing the dissociation of the factor.

Structural dynamics of bacterial translation initiation factor IF2

Bacterial translation initiation factor IF2 promotes ribosomal subunit association, recruitment, and binding of fMet-tRNA to the ribosomal P-site and initiation dipeptide formation. Here, we present the solution structures of GDP-bound and apo-IF2-G2 of Bacillus stearothermophilus and provide evidence that this isolated domain binds the 50 S ribosomal subunit and hydrolyzes GTP. Differences between the free and GDP-bound structures of IF2-G2 suggest that domain reorganization within the G2-G3-C1 regions underlies the different structural requirements of IF2 during the initiation process. However, these structural signals are unlikely forwarded from IF2-G2 to the C-terminal fMet-tRNA binding domain (IF2-C2) because the connected IF2-C1 and IF2-C2 modules show completely independent mobility, indicating that the bacterial interdomain connector lacks the rigidity that was found in the archaeal IF2 homolog aIF5B.

Modification of 16S ribosomal RNA by the KsgA methyltransferase restructures the 30S subunit to optimize ribosome function

All organisms incorporate post-transcriptional modifications into ribosomal RNA, influencing ribosome assembly and function in ways that are poorly understood. The most highly conserved modification is the dimethylation of two adenosines near the 3' end of the small subunit rRNA. Lack of these methylations due to deficiency in the KsgA methyltransferase stimulates translational errors during both the initiation and elongation phases of protein synthesis and confers resistance to the antibiotic kasugamycin. Here, we present the X-ray crystal structure of the Thermus thermophilus 30S ribosomal subunit lacking these dimethylations. Our data indicate that the KsgA-directed methylations facilitate structural rearrangements in order to establish a functionally optimum subunit conformation during the final stages of ribosome assembly.

Structural and functional studies of the Thermus thermophilus 16S rRNA methyltransferase RsmG

The RsmG methyltransferase is responsible for N(7) methylation of G527 of 16S rRNA in bacteria. Here, we report the identification of the Thermus thermophilus rsmG gene, the isolation of rsmG mutants, and the solution of RsmG X-ray crystal structures at up to 1.5 A resolution. Like their counterparts in other species, T. thermophilus rsmG mutants are weakly resistant to the aminoglycoside antibiotic streptomycin. Growth competition experiments indicate a physiological cost to loss of RsmG activity, consistent with the conservation of the modification site in the decoding region of the ribosome. In contrast to Escherichia coli RsmG, which has been reported to recognize only intact 30S subunits, T. thermophilus RsmG shows no in vitro methylation activity against native 30S subunits, only low activity with 30S subunits at low magnesium concentration, and maximum activity with deproteinized 16S rRNA. Cofactor-bound crystal structures of RsmG reveal a positively charged surface area remote from the active site that binds an adenosine monophosphate molecule. We conclude that an early assembly intermediate is the most likely candidate for the biological substrate of RsmG.

[Consensus Statement of Multisocietary Task Force--prescription of physical exercise in the cardiological environment (third part)]

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Adsorption of a multicomponent mixture of gases with multisite occupancy

In this paper, we present a study of the adsorption of multicomponent mixtures with multisite occupancy. The transfer-matrix technique is used to analyze the one-dimensional binary mixtures for interacting systems. A general expression for the characteristic polynomial is derived. Extension of the treatment to a higher dimension is also presented by using the mean-field Bragg-Williams approximation, transfer-matrix calculations, and Monte Carlo simulation. Partial and total isotherms are obtained for the dimer-trimer mixture where a different order appears.

Vasomotor reactivity evaluation in cardiac rehabilitation

Endothelial dysfunction is a generalized phenomenon detectable at various levels in the vasculature, and is evident very early in the atherosclerotic process. These peculiarities have stimulated the introduction of new non-invasive techniques dedicated to evaluate the vasomotor response of arteries or districts in favourable position in the body (forearm, hand) that may reflect the response of inner arteries otherwise requiring invasive procedures (i.e. coronary arteries). Moreover, these techniques can be theoretically used to detect abnormalities of vasomotor response before a clinical adverse event may occur in subjects prone to vascular accidents with risk factors for atherosclerosis. Of physical stimuli inducing e-NOS activation and subsequent nitric oxide synthesis, the shear stress produced by pulsatile blood flow is the most important. This property is actually used in clinical practice to study the flow-mediated vasodilation (FMD) of the brachial artery. Any condition that reduces the ability of endothelial cells to produce nitric oxide causes endothelial dysfunction, which is directly reflected into a depressed FMD. There is evidence that brachial artery flow-mediated dilation is improved after local as well as systemic exercise, suggesting that the improvement in endothelial function is generalized and documentable in different arterial districts with similar results. Aerobic exercise induces e-NOS expression and improves the endothelial-dependent relaxation in normal as well as cardiac patients. The endothelium-independent vasorelaxation is generally unchanged after chronic conditioning, but this result is not evident in all studies. The improved endothelial vasoreactivity is correlated with enhanced functional capacity after moderate aerobic exercise, suggesting an important pathophysiological role of oxygen transport in exercise tolerance. These beneficial effects has been described in patients with stable heart failure in II and III NYHA functional class and in patients with coronary artery disease with programs different for frequency, duration and intensity. The evaluation of vasomotor reactivity gives promising results in explaining the effects of medications and exercise training. The demonstration that flow-mediated dilation may quantify endothelial dysfunction in subjects with a variety of conditions can be used in clinical practice not only to assess the effects of interventions, but also to provide a preliminary screening in apparently healthy subjects who have an underlying silent coronary artery disease. In cardiac rehabilitation, there are promising results from FMD evaluation in selecting patients who take major benefits in terms of functional capacity and endothelium-dependent vasodilation.

Effects of trimetazidine on the contractile response of chronically dysfunctional myocardium to low-dose dobutamine in ischaemic cardiomyopathy

BACKGROUND

There is evidence that trimetazidine, an anti-ischaemic agent with a direct cytoprotective effect on the myocardium, is effective in stable angina. However, it is not clear whether trimetazidine can improve the mechanical efficiency of chronically dysfunctional myocardium, and whether this potentially beneficial effect can translate into improvements in left ventricular function as well as functional capacity.

METHODS

Thirty-eight patients (52.7 +/- 8 years) with post-necrotic left ventricular dysfunction (ejection fraction: 33 +/- 5%) and multivessel coronary artery disease were studied. Patients were randomized into two matched groups. Group A received trimetazidine (20 mg three times daily) for 2 months, while group B received a placebo during the same period. The usual antianginal medications were not altered during the study. At baseline and after 2 months, all patients underwent low-dose dobutamine echocardiography (5-20 microg x kg(-1) x min(-1)), and a symptom-limited cardiopulmonary exercise test.

RESULTS

On initial evaluation, systolic wall thickening score index, heart rate, systolic blood pressure and rate pressure product were similar at rest and peak dobutamine in both groups. However, at 2 months, group A patients had significant improvements in the rest and peak systolic wall thickening score index (13% and 20.7%, P<0.001) and ejection fraction (19.7% and 14.1%, P<0.001) without concomitant changes in heart rate and blood pressure. Peak VO2 was also significantly increased in patients taking trimetazidine (15%, P=0.001 vs controls).

CONCLUSIONS

In patients with ischaemic cardiomyopathy, trimetazidine improves the contractile response of chronically dysfunctional myocardium to dobutamine without haemodynamic changes. This effect was associated with improvements in left ventricular function and peak VO2.

Effects of dipyridamole on coronary collateralization and myocardial perfusion in patients with ischaemic cardiomyopathy

AIMS

There is evidence that oral dipyridamole, a nucleoside uptake blocker that increases myocardial adenosine levels, lessens myocardial ischaemia by inducing coronary collateral growth in animal models of ischaemic heart disease. However, whether dipyridamole can exert a similar effect in humans with coronary artery disease is controversial.

METHODS AND RESULTS

We studied 30 male patients (mean age 55+/-9 years) with coronary artery disease and left ventricular systolic dysfunction (ejection fraction >40%). Patients were randomized into three matched groups. Group A patients (n=10) received dipyridamole alone at a dose of 75 mg t.i.d. orally for 8 weeks. Group B patients (n=10) underwent exercise training at 60% of peak .VO(2)three times a week for 8 weeks, and received dipyridamole. Group C patients (n=10) had neither exercise testing nor dipyridamole. On study entry and after 8 weeks all patients underwent an exercise test with gas exchange analysis, dobutamine stress echocardiography, 201-thallium planar myocardial scintigraphy, and coronary angiography. Peak .VO(2)increased significantly only in trained patients. Thallium uptake of the collateral-dependent myocardium, coronary collateral score and wall thickening score increased significantly only in groups receiving dipyridamole, the greatest improvement being in group B patients. Plasma adenosine levels were also the highest in group B (P<0.001 vs A and C). Correlations were found between changes in adenosine levels and increases of both thallium uptake (r=-0.70;P=0.001) and collateralization (r=0.72;P=0.001).

CONCLUSION

Exercise training potentiates the effects of dipyridamole on coronary collateralization and myocardial perfusion in humans with ischaemic cardiomyopathy.

Exercise training intervention after coronary angioplasty: the ETICA trial

OBJECTIVES

The goal of this study was to determine the effects of exercise training (ET) on functional capacity and quality of life (QOL) in patients who received percutaneous transluminal coronary angioplasty (PTCA) or coronary stenting (CS), the effects on the restenosis rate and the outcome.

BACKGROUND

It is unknown whether ET induces beneficial effects after coronary angioplasty.

METHODS

We studied 118 consecutive patients with coronary artery disease (mean age 57+/-10 years) who underwent PTCA or CS on one (69%) or two (31%) native epicardial coronary arteries. Patients were randomized into two matched groups. Group T (n = 59) was exercised three times a week for six months at 60% of peak VO2. Group C (n = 59) was the control group.

RESULTS

Only trained patients had significant improvements in peak VO2 (26%, p < 0.001) and quality of life (26.8%, p = 0.001 vs. C). The angiographic restenosis rate was unaffected by ET (T: 29%; C: 33%, P = NS) and was not significantly different after PTCA or CS. However, residual diameter stenosis was lower in trained patients (-29.7%, p = 0.045). In patients with angiographic restenosis, thallium uptake improved only in group T (19%; p < 0.001). During the follow-up (33+/-7 months) trained patients had a significantly lower event rate than controls (11.9 vs. 32.2%, RR: 0.71, 95% confidence interval [CI]: 0.60 to 0.91, p = 0.008) and a lower rate of hospital readmission (18.6 vs. 46%, RR: 0.69, 95% CI: 0.55 to 0.93, p < 0.001).

CONCLUSIONS

Moderate ET improves functional capacity and QOL after PTCA or CS. During the follow-up, trained patients had fewer events and a lower hospital readmission rate than controls, despite an unchanged restenosis rate.

Oxidative stress and homocysteine in coronary artery disease

BACKGROUND

Oxidative stress is present in cardiovascular diseases (CVDs), and hyperhomocysteinemia, an independent risk factor for these diseases, may play a role by inducing production of oxygen free radicals.

METHODS

To evaluate the possible role of homocysteine (Hcy) in inducing oxidative stress in coronary artery disease (CAD), plasma Hcy was measured in 68 consecutive cardiovascular patients, and plasma malondialdehyde (MDA), both free and total (free + bound), was measured in 40 patients with CAD (18 with chronic stable angina and 22 with unstable angina). As controls, we tested 70 healthy volunteers. Hcy was measured by an immunoenzymatic method and MDA, an index of lipid peroxidation, by gas chromatography-mass spectrometry.

RESULTS

Plasma Hcy concentrations were significantly higher in cardiovascular patients than in controls (10.2 vs 8.9 micromol/L; P <0.0002), with no significant difference between values in the stable and unstable angina subgroups. Similarly, total MDA was significantly higher in the CAD group than in the controls (2.6 vs 1.3 micromol/L; P <0.00001), again with no significant difference between stable and unstable angina patients. By contrast, free MDA, which was significantly higher in the CAD patients than the controls (0.4 vs 0.2 micromol/L; P < 0.00001), was also significantly higher in the unstable than in the stable angina group (0.5 vs 0.3 micromol/L; P <0.03). However, no correlation was observed among Hcy and free and total MDA.

CONCLUSIONS

Our findings show that a moderate increase of Hcy is associated with CVD but that Hcy at the detected values cannot be considered completely responsible for oxidative damage. That lipid peroxidation is involved in CAD is shown by our observation of significantly increased plasma free and total MDA concentrations compared with controls. Moreover, free MDA values discriminated between unstable and chronic stable angina, and could thus represent a new diagnostic tool.

Cost-effectiveness analysis of long-term moderate exercise training in chronic heart failure

The purpose of this study is to perform a cost-effectiveness analysis of long-term moderate exercise training (ET) in patients with stable chronic heart failure. In particular, the study focuses on the survival analysis and cost savings from the reduction in the hospitalization rate in the exercise group. In the past 10 years, ET has been shown to be beneficial for patients with stable class II and III heart failure in many randomized clinical trials. However, the cost-effectiveness of a long-term ET program has not been addressed for outcomes related to morbidity/mortality end points or health care utilization. We examined the cost-effectiveness of a 14-month long-term training in patients with stable chronic heart failure. The estimated increment cost for the training group, $3,227/patient, was calculated by subtracting the averted hospitalization cost, $1,336/patient, from the cost of ET and wage lost due to ET, estimated at $4,563/patient. For patients receiving ET, the estimated increment in life expectancy was 1.82 years/person in a time period of 15.5 years, compared with patients in the control group. The cost-effectiveness ratio for long-term ET in patients with stable heart failure was thus determined at $1,773/life-year saved, at a 3% discount rate. Long-term ET in patients with stable chronic heart failure is cost-effective and prolongs survival by an additional 1.82 years at a low cost of $1,773 per/life-year saved.

Trimetazidine and the contractile response of dysfunctional myocardium in ischaemic cardiomyopathy

BACKGROUND

The therapeutic effect of anti-ischemic compounds is related to their ability to improve the oxygen supply-demand balance of the ischemic myocardium by increasing myocardial blood flow (calcium-antagonists), by reducing regional myocardial oxygen consumption (verapamil, betablockers) and increasing peripheral pooling of blood (nitrates, nifedipine). All these actions are also accompanied by hemodynamic changes, as evidenced by a lower double product, reduced wall stress, lower pulmonary wedge pressure, and lower systemic arterial pressure. In general, it was found that the combination of a betablocker with nifedipine improved the antianginal effect by further reducing the number and duration of ischemic events. The combination of a nitrate with a beta-blocker is particularly useful because it reduces the risk of heart failure by lowering left ventricular end-diastolic pressure and volume and by attenuating the negative inotropic effect of the betablocker. Although a combination therapy demonstrated benefits in comparison with drug treatment alone, it is associated with a higher incidence of untoward events. Trimetazidine (2, 3, 4 trimethoxybenzyl-piperazine dihydrochloride) is a novel anti-ischemic compound with a peculiar mechanism of action. Its anti-ischemic properties are unrelated to changes in myocardial oxygen supply-to-demand ratio, as shown by no significant effects on heart rate, blood pressure or rate-pressure product both at rest and during dynamic exercise. There are several possible mechanisms of action by which trimetazidine promotes preservation of membrane structures and cellular function: limitation of intracellular acidosis, correction of disturbances of transmembrane ion exchange leading to calcium overload, prevention of an excessive production of free radicals, inhibition of the inflammatory reaction and an antiplatelet effect. These documented actions cooperate to increase the rate of resynthesis of high-energy phosphates within myocardial cells after episodes of ischemia. In several trials, trimetazidine has been tested as an antianginal agent, both as monotherapy and combined with "classical" anti-ischemic compounds. In comparison with nifedipine, trimetazidine had similar efficacy in reducing the number of weekly anginal attacks and in increasing the ischemic threshold in a group of 39 patients with stable angina. However, the incidence of side effects was significantly higher with nifedipine (5 vs 20), and affected 5 patients with trimetazidine and 13 patients with nifedipine (p = 0.03). In a relatively large European study involving 149 patients (Trimetazidine European Multicenter Study, TEMS), trimetazidine (20 mg t.i.d.) was compared with propranolol (40 mg t.i.d.) in patients with stable angina pectoris and documented significant coronary artery stenoses. The number of anginal attacks was reduced equally by both drugs and exercise duration was increased by both treatments. However, in contrast with propranolol trimetazidine did not alter the rate pressure product. In patients already treated with nifedipine or beta-blockers, the addition of trimetazidine (20 mg t.i.d.) was able to reduce the number and the duration of anginal attacks and improved also the exercise capacity. Trimetazidine is generally well tolerated and only minor side effects have been reported (drowsiness, sedation, diarrhea). The improvement in cardiac energy metabolism should theoretically translate into enhancement in mechanical efficiency. This hypothesis has been object of recent investigations in patients with ischemic heart disease with and without left ventricular dysfunction. Brottier, et al. demonstrated that patients with ischemic cardiomyopathy treated with trimetazidine had a higher ejection fraction (measured by radionuclide angiography) than control patients who received a placebo after 6 months of therapy (p < 0.018). The group of Chierchia demonstrated that trimetazidine improved ischemic regional myocardial dysfunction at rest and during stress-induced ischemia in 15 patients with chronic coronary artery disease without affecting the hemodynamic determinants of myocardial oxygen consumption. There is recent demonstration that trimetazidine improves the contractile response of left ventricular hibernating myocardium in patients with ischemic heart disease. Belardinelli et al. showed that trimetazidine improved the contractile response of dysfunctional myocardial to low-dose dobutamine in patients with ischemic heart disease and left ventricular function. Twenty-two patients with prior anterior myocardial infarction and injection fraction < 35% (33 +/- 7%) were randomized into 2 groups. A group (= 11) received trimetazidine (20 mg tid) for 2 months, while another group (= 11) received a placebo. The usual medications were not altered during the study. (ABSTRACT TRUNCATED)

Quantitative analysis of changes occurring in muscle vastus lateralis in patients with heart failure after low-intensity training

OBJECTIVE

To quantitate the changes occurring in muscle vastus lateralis after exercise training of low intensity adopted for the rehabilitation of patients with chronic heart failure.

STUDY DESIGN

Nine consecutive males with a clinical diagnosis of idiopathic dilated and ischemic cardiomyopathy underwent an eight-week period of training. The intensity of the work was calculated as 40% of peak VO2. The program consisted of 30 minutes of cycling three times per week. A cardiopulmonary exercise test, hemodynamic measurements and echocardiographic studies were carried out. Needle biopsies were taken from muscle vastus lateralis before starting and after completing training. Quantitative analysis was carried out on sections stained with ATPase at pH 9.5 for measurement of the lesser diameter of type 1 and 2 fibers (by using an image analyzer) and on UEA 1-stained sections for capillary density and capillary/fiber ratio (by using a frame in the eyepiece of the microscope). The Wilcoxon test was applied to identify significant differences before and after training. Spearman's rank correlation coefficient was also calculated to highlight any correlation between the morphologic data and results of clinical tests.

RESULTS

After completing the training program, all the patients experienced an improvement in exercise tolerance and a significant increase (P < .004) in the VO2 and VCO2 peak. Skeletal muscle showed a significant (P < .02) increase in the capillary/fiber ratio. The changes were not significantly correlated with any of the clinical findings.

CONCLUSION

Low-intensity training can improve the functional capacity of patients with heart failure while producing only mild morphologic changes in their muscles.

Monitoring skeletal muscle oxygenation during exercise by near infrared spectroscopy in chronic heart failure

Patients with chronic heart failure (HF) have a reduced skeletal muscle blood flow which can in part explain reduced exercise tolerance and increased ventilation. All the techniques commonly employed to measure skeletal muscle blood flow have limitations that reduce their accuracy and clinical application. Near infrared spectroscopy (NIRS) is a noninvasive, inexpensive, and reproducible technique able to monitor muscle oxygenation both at rest and during exercise, providing information about tissue perfusion. The principle of NIRS is based on the observation that the light absorption characteristics of hemoglobin (Hb) and myoglobin (Mb) in the near infrared region (700-1000 nm) change depending on their relative saturations. In humans, NIRS has been employed to monitor skeletal muscle oxygenation during exercise and/or after cuff-induced limb ischemia in normal subjects as well as patients with chronic HF. Patients with chronic HF have a reduced Hb/Mb oxygenation at any matched work rate and a more rapid deoxygenation above the anaerobic threshold than normal subjects. More recently, NIRS has been used to determine the kinetics of muscle oxygenation in recovery after constant work rate exercise, providing evidence of an inverse relation with cardiac function as assessed by peak oxygen uptake. In conclusion, NIRS appears to be a new promising noninvasive technique for studying muscle oxygenation in a variety of experimental models. (c)1999 by CHF, Inc.

Randomized, controlled trial of long-term moderate exercise training in chronic heart failure: effects on functional capacity, quality of life, and clinical outcome

BACKGROUND

It is still a matter of debate whether exercise training (ET) is a beneficial treatment in chronic heart failure (CHF).

METHODS AND RESULTS

To determine whether long-term moderate ET improves functional capacity and quality of life in patients with CHF and whether these effects translate into a favorable outcome, 110 patients with stable CHF were initially recruited, and 99 (59+/-14 years of age; 88 men and 11 women) were randomized into 2 groups. One group (group T, n=50) underwent ET at 60% of peak &f1;O2, initially 3 times a week for 8 weeks, then twice a week for 1 year. Another group (group NT, n=49) did not exercise. At baseline and at months 2 and 14, all patients underwent a cardiopulmonary exercise test, while 74 patients (37 in group T and 37 in group NT) with ischemic heart disease underwent myocardial scintigraphy. Quality of life was assessed by questionnaire. Ninety-four patients completed the protocol (48 in group T and 46 in group NT). Changes were observed only in patients in group T. Both peak &f1;O2 and thallium activity score improved at 2 months (18% and 24%, respectively; P<0. 001 for both) and did not change further after 1 year. Quality of life also improved and paralleled peak VO2. Exercise training was associated both with lower mortality (n=9 versus n=20 for those with training versus those without; relative risk (RR)=0.37; 95% CI, 0.17 to 0.84; P=0.01) and hospital readmission for heart failure (5 versus 14; RR=0.29; 95% CI, 0.11 to 0.88; P=0.02). Independent predictors of events were ventilatory threshold at baseline (beta-coefficient=0.378) and posttraining thallium activity score (beta-coefficient -0.165).

CONCLUSIONS

Long-term moderate ET determines a sustained improvement in functional capacity and quality of life in patients with CHF. This benefit seems to translate into a favorable outcome.

Muscle oxygenation kinetics measured by near-infrared spectroscopy during recovery from exercise in chronic heart failure

The aim of the present study was to determine the kinetics of recovery of muscle oxygenation (MO) from comparable levels of exercise in chronic heart failure (CHF) patients and normal subjects and to relate MO kinetics to the level of exercise intolerance. The rationale is based on the observation that the O2 debt is increased in patients with heart failure and repayment of the debt is relatively slow. Ten patients with stable CHF (mean age 47 +/- 10 years) and nine healthy control subjects (47 +/- 6 years) were studied. All patients had ischemic cardiomyopathy (ejection fraction 33 +/- 7%). On different days, all subjects performed an upright incremental cycle ergometer exercise test with gas-exchange analysis to determine peak VO2, and a 6-minute constant work-rate (CWR) protocol at 60% of peak VO2. Oxygenation of the vastus lateralis muscle was continuously monitored during exercise and recovery using near-infrared spectroscopy (NIRS). Both MO and VO2 responses to recovery were described by a monoexponential model with a time delay. The time constant and time delay were combined to calculate a mean response time (MRT). Recovery VO2 and MO MRTs for the incremental and constant work rate exercise test were longer in CHF patients than in control subjects (p < 0.05). Both VO2 and MO MRTs were inversely related to peak VO2 (r = -0.73 and -0.52, respectively; p < 0.05 for both). However, both kinetics were not significantly different within each group between the two exercise intensities. In conclusion, the greater the cardiac dysfunction, as assessed by peak VO2, the more the recovery of muscle and total body oxygenation from both maximal and submaximal exercise is delayed.

A four-minute submaximal constant work rate exercise test to assess cardiovascular functional class in chronic heart failure

To develop a submaximal constant work rate exercise test able to grade cardiovascular dysfunction in patients with chronic heart failure, 80 patients and 59 control subjects performed a symptom-limited incremental exercise test and a constant work rate exercise test at a fixed work rate (50 W for 4 minutes). The time constant of VO2 at the start of constant work rate exercise and time for gas exchange ratio (respiratory exchange ratio) to equal 1 were independent predictors of cardiovascular functional class and correctly classified the functional class in 89 +/- 9% and 83 +/- 11% of patients, respectively.

Low dose dobutamine echocardiography predicts improvement in functional capacity after exercise training in patients with ischemic cardiomyopathy: prognostic implication

OBJECTIVES

This study sought to investigate whether the identification of hibernating myocardium by low dose dobutamine stress echocardiography (LDSE) may predict an improvement in functional capacity after moderate exercise training in patients with ischemic cardiomyopathy. Another objective was to assess whether exercise training may affect the outcome.

BACKGROUND

There is evidence that exercise training improves left ventricular (LV) function as well as functional capacity in patients with a previous myocardial infarction and LV dysfunction. We hypothesized that the magnitude of these improvements might be related to the extent of hibernating myocardium.

METHODS

We studied 71 consecutive patients 56+/-9 years old (mean +/- SD) with chronic heart failure secondary to ischemic cardiomyopathy (LV ejection fraction [LVEF] <40%). All patients were in sinus rhythm and were clinically stable during the previous 3 months. Patients were randomized into two matched groups. Group T (n = 36) underwent exercise training at 60% of peak oxygen uptake (Vo2) three times a week for 10 weeks. Group C (n = 35) did not exercise. At study entry and end, all patients underwent an exercise test with gas exchange analysis and LDSE (5 to 20 microg/kg body weight per min).

RESULTS

At baseline, a positive contractile response (CS+) to LDSE was observed in 317 of 576 segments in group T and 291 of 560 segments in group C. After 10 weeks, peak Vo2 and peak work rate increased only in trained patients (peak Vo2: from 16.2+/-3 to 20.8+/-4 ml/kg per min; work capacity: from 108+/-20 to 131+/-25 W, p < 0.001 vs. group C for both). The presence of CS+ at baseline was associated with a sensitivity of 70% and a specificity of 77% for predicting an increase in the functional capacity after exercise training. Positive and negative predictive values of LDSE were 84% and 59%, respectively. Independent predictors of cardiac events were a pre-to-posttraining difference in LVEF at peak dobutamine infusion and the presence of a viable response at baseline (p = 0.004 and 0.008, respectively). The log-rank test demonstrated that trained patients had a significantly lower probability of cardiac events during follow-up than sedentary control patients (p < 0.001).

CONCLUSIONS

The presence of hibernating myocardium as assessed by LDSE predicts the magnitude of improvement in functional capacity after moderate exercise training in patients with chronic heart failure. A significant increase in functional capacity after exercise training is associated with a lower incidence of cardiac events during follow-up.

Effects of moderate exercise training on thallium uptake and contractile response to low-dose dobutamine of dysfunctional myocardium in patients with ischemic cardiomyopathy

BACKGROUND

There is evidence that exercise training can induce myocardial and coronary adaptations in both animals and humans. However, the significance of these potentially important changes remains to be determined in patients with ischemic heart disease and left ventricular (LV) systolic dysfunction.

METHODS AND RESULTS

To investigate whether exercise training can improve thallium uptake and the contractile response to low-dose dobutamine of dysfunctional myocardium, 46 patients (42 men, 4 women; mean age, 57+/-9 years) with chronic coronary artery disease and impaired LV systolic function (ejection fraction < 40%) were randomly assigned to two groups. The exercise group (n = 26) underwent exercise training at 60% of peak oxygen uptake for 8 weeks. The control group (n = 20) was not exercised. At baseline and after 8 weeks all patients underwent an exercise test with gas exchange analysis and stress echocardiography using low-dose dobutamine (5 to 10 microg/kg per minute) followed by thallium myocardial scintigraphy. Coronary angiography was performed in 23 patients at baseline and after 8 weeks. After 8 weeks, peak oxygen uptake increased significantly only in trained patients (24%). Significant improvements in the contractile response to dobutamine and thallium activity were observed in trained patients (28% and 31%, respectively; trained versus control: P<.001 for both). In a subgroup of trained patients, both improvements were correlated with an increase in the coronary collateral score (P<.005 and P<.001, respectively).

CONCLUSIONS

Moderate exercise training improves both thallium activity and the contractile response of dysfunctional myocardium to low doses of dobutamine in patients with ischemic cardiomyopathy. The implication of this study is that even a short-term exercise training may improve quality of life by improvement of LV systolic function during mild-to-moderate physical activity in patients with ischemic cardiomyopathy.

Skeletal muscle oxygenation and oxygen uptake kinetics following constant work rate exercise in chronic congestive heart failure

The aim of the present study was to determine the kinetics of recovery of muscle oxygenation (MO) from comparable levels of exercise in patients with chronic congestive heart failure (CHF) and in normal subjects, and to relate MO kinetics to the level of exercise intolerance. Ten patients with stable CHF secondary to ischemic cardiomyopathy (ejection fraction 34 +/- 6%) (mean age 47 +/- 10 years) and 8 healthy matched control subjects underwent an upright incremental cycle ergometer exercise test with gas exchange analysis and a 6-minute constant work rate protocol at 60% of peak oxygen consumption (VO2). Oxygenation of the vastus lateralis muscle was continuously monitored during exercise and recovery using near infrared spectroscopy. Recovery VO2 and MO mean response times for the constant work rate exercise test were longer in patients with CHF than in control subjects (p <0.05). Both VO2 and MO mean response times were inversely related to peak VO2 (r = -0.73 and -0.52, respectively; p <0.05 for both). Thus recovery of muscle and total body oxygenation from submaximal exercise is more delayed the greater the cardiac dysfunction, as assessed by peak VO2. This suggests that regeneration of phosphocreatine and/or resaturation of venous oxyhemoglobin take place more slowly the worse the cardiac function.

Lung function and exercise gas exchange in chronic heart failure

BACKGROUND

The ventilatory response to exercise in patients with chronic heart failure (HF) is greater than normal for a given metabolic rate. The objective of the present study was to determine the mechanism(s) for the high ventilatory output in patients with chronic HF.

METHODS AND RESULTS

Centers in Germany, Italy, Japan, and the United States participated in this study. Each center contributed studies on patients and normal subjects of similar age and sex. One hundred thirty patients with chronic HF and 52 healthy subjects participated. Spirometric and breath-by-breath gas exchange measurements were made during rest and increasing cycle exercise. Arterial blood was sampled for measurement of pH, PaCO2, PaO2, and lactate during exercise in 85 patients. Resting forced expiratory volume in 1 second (FEV1) and vital capacity (VC) were proportionately reduced at all levels of impairment. Patients with more severe HF had greater tachypnea and a smaller tidal volume (VT) at a given exercise expired volume per unit time (VE). This was associated with an expiratory flow pattern characteristic of lung restriction. VE and VCO2 as a function of VO2 were increased during exercise in HF patients. The increases were greater the lower the peak VO2 per kilogram of body weight. The ratio of VD (physiological dead space) to VT and the difference between arterial and end tidal PCO2 at peak VO2 also increased inversely with peak VO2/kg. In contrast, the difference between alveolar and arterial PO2 and PaCO2 were both normal, on average, at peak VO2 regardless of the level of impairment. The more severe the exercise limitation, the higher the lactate and the lower the HCO3- at a given VO2, although pH was tightly regulated.

CONCLUSIONS

The increase in VE in chronic HF patients is caused by an increase in VD/VT due to high ventilation/perfusion mismatching, an increase in VCO2 relative to VO2 resulting from HCO3- buffering of lactic acid, and a decrease in PaCO2 due to tight regulation of arterial pH. With regard to the excessive VE in HF patients, the increases in VD/VT and VCO2 relative to VO2 are more important as the patient becomes more exercise limited. Regional hypoperfusion but not hypoventilation typifies lung gas exchange in HF. This and other mechanisms might account for the restrictive changes leading to exercise tachypnea in HF patients.

Diagnostic criteria and management of subacute ventricular free wall rupture complicating acute myocardial infarction

In this prospective study we evaluated the value of the main diagnostic criteria for postinfarction subacute rupture of the ventricular free wall. Two-dimensional echocardiograms and recordings of right atrial pressure and waveform were immediately obtained in every patient exhibiting rapid clinical and/or hemodynamic compromise in the acute infarction setting. The same protocol was applied to patients referred from other hospitals for suspected myocardial rupture. In 28 cases a subacute free wall rupture was identified. In most of the patients the diagnosis was based on the demonstration of hemopericardium and cardiac tamponade by echocardiography, cardiac catheterization and, occasionally, by pericardiocentesis. In 2 instances, the identification of intrapericardial echo densities suggesting clots, in the absence of cardiac tamponade, allowed a diagnosis of subacute rupture. Direct, but indistinct visualization of myocardial rupture was obtained in 4 cases. Among the 28 patients with this complication, 4 died while awaiting surgery and 24 underwent surgical repair (mortality rate 33%). Long-term outcome of survivors was favorable. Various myocardial lesions underlie postinfarction subacute free wall rupture. Clinical presentation varied widely. The diagnosis was based, usually but not always, on the association of hemopericardium and signs of cardiac tamponade. An organized approach to management of this complication of acute myocardial infarction was suggested.

Nitric oxide production during exercise in chronic heart failure

In chronic heart failure (CHF), the ventilatory response is increased compared with normal. This response is, in part, caused by reduced perfusion to ventilated lung. Nitric oxide (NO) is a potent vasodilator and may have an important role in pulmonary vasodilatation during exercise. NO is present in exhaled air. The amount of NO in exhaled air, when breathing NO-free compressed air, is known to increase in normal subjects during exercise. In this study, we quantified NO output in exhaled air in patients with CHF during exercise. Six patients with CHF (New York Heart Association Class II and III; two with dilated cardiomyopathy, three with ischemic heart disease, and one with hypertensive heart disease) and six normal subjects were studied with a symptom-limited incremental exercise test on a cycle ergometer. Oxygen uptake (VO2), carbon dioxide output (VCO2), and minute ventilation (VE) were measured breath by breath with a mass spectrometer, flow meter, and computer. The NO concentration was continuously measured in mixed expired air by chemiluminescence. Peak exercise work rate was lower in patients with CHF than in normal subjects (71.3 +/- 41.6 W vs 257.0 +/- 49.7 W; p < 0.01). Patients with CHF showed a higher VE/VCO2 level at peak exercise than normal subjects (CHF, 47.0 +/- 10.7; normal subjects, 35.6 +/- 5.2; p < 0.01). NO concentration of exhaled air at rest was lower in CHF patients than in normal subjects (4.0 +/- 2.2 ppb vs 10.5 +/- 6.2 ppb, respectively; p < 0.05). NO output from the respiratory tract (VNO) was significantly lower in patients with CHF compared with normal subjects at rest (45.3 +/- 24.3 nl/min, 117.5 +/- 60.1 nl/min, respectively, p < 0.05), and although it increased during exercise, it did not increase in patients with CHF as much as in normal subjects (75.3 +/- 43.4 nl/min vs 512.9 +/- 253.6 nl/min, respectively; p < 0.01). The increase above rest (exercise/rest) was smaller in patients with CHF than in normal subjects (2.10 +/- 1.92 vs 4.81 +/- 2.67, p < 0.05). These data support the concept that the smaller increase in NO production (VNO) during exercise may be responsible for a blunted vasodilation in patients with CHF, resulting in a smaller reduction in dead space/tidal volume and VE/VCO2 at the lactic acidosis threshold than normal. This finding may play a role in the abnormally high ventilatory response to exercise in patients with CHF.

Effects of exercise training on left ventricular filling at rest and during exercise in patients with ischemic cardiomyopathy and severe left ventricular systolic dysfunction

The aim of our study was to determine whether exercise training can augment left ventricular diastolic filling at rest and during exercise in patients with ischemic cardiomyopathy and whether any correlation exists between changes in diastolic filling and changes in exercise tolerance. Forty-three consecutive patients (mean age, 54 +/- 8 years) with ischemic cardiomyopathy and severe left ventricular systolic dysfunction (election fraction <30%) were studied. Group T (29 patients) was exercised on a cycle ergometer 3 times a week for 8 weeks at 60% of peak oxygen uptake. Group C (14 patients) was not exercised. All patients underwent an exercise test and a radionuclide ventriculography at baseline and after 8 weeks. At the end, no changes were found in group C. In group T, exercise training increased peak oxygen uptake (1 5%; p < 0.0001), work rate (1 5%; p < 0.005), peak early filling rate (10%; p < 0.02), and peak filling rate (1 1%; p < 0.03). At submaximal exercise, peak filling rate increased at all matched heart rates. The increase in peak filling rate was correlated with the increase in cardiac index (r= 0.72; p < 0.0001) at peak exercise. The independent predictors of the increase in peak oxygen uptake were changes in work capacity and peak early filling rate. The data demonstrate that exercise training can improve the exercise capacity of patients with ischemic cardiomyopathy and severe systolic-dysfunction. The increase in early diastolic filling at rest and during exercise may contribute to the improvement in peak oxygen uptake.

Comparison of impedance cardiography with thermodilution and direct Fick methods for noninvasive measurement of stroke volume and cardiac output during incremental exercise in patients with ischemic cardiomyopathy

In the last decade, an inexpensive and simple noninvasive method (i.e., transthoracic electrical bioimpedance cardiography, has been tested in healthy subjects and patients with various heart disease for measuring stroke volume and cardiac output at rest and/or during exercise. However, the results are still controversial, especially when measurements are obtained during exercise and data on reproducibility during exercise are lacking. Twenty-five consecutive patients (20 men and 5 women, mean age 48 +/- 9 years) in sinus rhythm with documented coronary artery disease and a previous myocardial infarct were studied. Patients were divided into 2 groups. Group A had ischemic cardiomyopathy, characterized by left ventricular (LV) enlargement and LV ejection fraction depression (35 +/- 8%). Group B had normal LV dimensions and ejection fraction (62 +/- 9%). After a familiarization study, all patients underwent an exercise test with gas exchange analysis and hemodynamic measurements. Stroke volume and cardiac output were simultaneously obtained at rest and at the end of each work rate stage with 3 methods: impedance, thermodilution, and direct Fick. Group A reached a lower peak oxygen uptake (56%), peak work load (60%), and peak systolic blood pressure (69%) than group B. Cardiac output and stroke volume were significantly greater at submaximal and peak exercise in group B than in group A (p < 0.0001). There were no significant differences in stroke volume and cardiac output in the 3 techniques at any matched work rate. There was no significant difference between measurements obtained by 2 experienced observers or between those obtained on 2 exercise tests performed on 2 different days. These results demonstrate that impedance cardiography is a noninvasive, simple, accurate, and reproducible method of measurement of cardiac output and stroke volume over a wide range of workloads.

Comparison of electron beam computed tomography scanning and magnetic resonance imaging quantification of right ventricular mass: validation with autopsy weights

RATIONALE AND OBJECTIVES

We compared, in the same human hearts, the ability of magnetic resonance (MR) imaging and electron beam computed tomography (CT) scanning to accurately quantify the free wall and septal components of right ventricular (RV) mass.

METHODS

Eleven hearts extracted at autopsy were subjected to MR imaging and electron beam CT scanning in short-axis projections. Regression analyses of mass determinations obtained by manual planimetry MR imaging and electron beam CT scanning and autopsy weights were performed.

RESULTS

RV free wall mass by both MR imaging (53.4 +/- 19.1 g) and electron beam CT scanning (53.9 +/- 20.4 g) correlated well with autopsy weight (57.7 +/- 20.2 g). Regression analysis showed a strong correlation for MR imaging (r = .88, slope = .88, standard error the estimate [SEE] = 7.2 g, p < .001) and electron beam CT scanning (r = .95, slope = .95, SEE = 6.6 g, p < .001). RV septal mass by MR imaging (10.8 +/- 3.5 g) and electron beam CT scanning (7.1 +/- 2.4 g) correlated less well with the autopsy weight (12.5 +/- 6.5 g). Regression analysis showed a fair correlation for MR imaging (r = .45, slope = .83, SEE = 2.05 g, p = .001) and a poor correlation for electron beam CT scanning (r = .46, slope = .17, SEE = 2.25 g, p = .57).

CONCLUSION

Both MR imaging and electron beam CT scanning accurately predict RV free wall mass but have difficulty predicting the septal component. Because the septal component constitutes only a small proportion of the total RV mass, determinations of RV mass should be based solely on the free wall component.

Low intensity exercise training in patients with chronic heart failure

OBJECTIVES

The present study was designed to evaluate whether a specific program of low intensity exercise training may be sufficient to improve the exercise tolerance of patients with chronic heart failure.

BACKGROUND

Recent studies have shown that exercise training can improve exercise tolerance in patients with stable chronic heart failure, mainly through peripheral adaptations. These changes have been observed with exercise regimens at intensities of 70% to 80% of peak oxygen uptake and > 8 weeks.

METHODS

We studied 27 patients (23 men, 4 women; mean [+/- SD] age 57 +/- 6 years) with mild chronic heart failure. We classified patients into two groups: trained group and untrained group. The trained group underwent a low intensity (40% of peak oxygen uptake) training program three times/week for 8 weeks. The untrained group performed no exercise.

RESULTS

An increase in peak oxygen uptake (17%, p < 0.0001), lactic acidosis threshold (20%, p < 0.0002) and peak work load (21%, p < 0.0002) were obtained in the trained group only. Cardiac output and stroke volume were unchanged. A high correlation was found between the increases in peak oxygen uptake and volume density of mitochondria of vastus lateralis muscle (r = 0.77, p < 0.0002).

CONCLUSIONS

Patients with stable chronic heart failure can achieve significant improvement in functional capacity from a low intensity exercise training regimen. The mechanism responsible for this favorable effect involves an increase in mitochondrial density, which reflects an improvement in oxidative capacity of trained skeletal muscles.

Near infrared spectroscopy and changes in skeletal muscle oxygenation during incremental exercise in chronic heart failure: a comparison with healthy subjects

Near infrared spectroscopy (NIRS) is a noninvasive technique of monitoring tissue oxygen saturation by detecting changes in tissue absorbance of two wavelengths (850 and 760 nm) reflecting the relative oxygenation of hemoglobin and myoglobin. Aim of the present study was to determine whether changes in skeletal muscle oxygen saturation during incremental exercise detected by NIRS can reflect an impared oxygen delivery and an early onset of anaerobic metabolism in patients with chronic heart failure (CHF). We studied 19 subjects (mean age 43 +/- 16 years). Seven patients had a history of CHF with a diagnosis of ischemic cardiomyopathy (Group A) and 12 were healthy sedentary (Group B). All patients had a history of dyspnea on exertion (NY-HA II), peripheral edema, pulmonary rales and cardiac gallop sounds over the last 6 months. They were in sinus rhythm and stable clinical condition in the last 3 months. They were well matched regarding age, sex and body surface area. All subjects performed an incremental work rate test in a ramp pattern on a upright cycle ergometer until volitional fatigue. Gas exchange was measured breath by breath with a metabolic chart. Muscle oxygenation was determined, transcutaneously, during the exercise test over the vastus lateralis muscle with NIRS. At peak exercise, work rate, VO2, anaerobic threshold (LAT), heart rate and systolic blood pressure were significantly lower in Group A compared to Group B (92 +/- 28 vs 232 +/- 17 watts; 14 +/- 2 vs 21 +/- 2 ml/kg/min; 868 +/- 225 vs 1317 +/- 354 ml/min; 149 +/- 7 vs 172 +/- 18 b/min; 145 +/- 18 vs 195 +/- 21 mm Hg, respectively; p < 0.0001 for all). In both groups, as work rate increased, tissue oxygenation initially either remained constant near resting levels or decreased. In both groups, muscle oxygenation decreased more steeply near the work rate where lactic acidosis (LAT) was detected. However, patients with CHF had an earlier acceleration in muscle deoxygenation compared to the other group, indicating a premature onset of anaerobic metabolism. Moreover, Group A had a flatter increase in both heart rate and systolic blood pressure and a steeper slope of oxygenation profile at all matched workloads compared to normals (Group A: -0.13 +/- 0.03 ml/min; Group B: -0.06 +/- 0.015 ml/min; p < 0.0001). The LAT correlated with the work rate at which the rate of tissue O2 desaturation accelerated (r = 0.94; p < 0.0001).(ABSTRACT TRUNCATED AT 400 WORDS)

Exercise training improves left ventricular diastolic filling in patients with dilated cardiomyopathy. Clinical and prognostic implications

BACKGROUND

Patients with dilated cardiomyopathy (DCM) often have left ventricular (LV) diastolic dysfunction that can precede the development of systolic dysfunction. Recent reports showed that exercise training (ET) improves the exercise capacity of these patients. Although this improvement is primarily due to peripheral adaptations, the contribution of LV diastolic filling has not been well defined. The purpose of this study was to determine whether ET can induce changes in LV diastolic filling that can account for an increase in exercise capacity and whether these changes can influence prognosis.

METHODS AND RESULTS

We prospectively studied 55 consecutive patients (mean age, 55 +/- 7 years) with DCM. Patients were randomized into a training group (36 patients) or a control untrained group (19 patients) and matched for clinical and functional characteristics. All patients underwent a pulsed Doppler echocardiographic study, a radionuclide angiographic study, and a cardiopulmonary exercise test before and after a 2-month ET program. On the basis of the Doppler LV diastolic filling pattern at the beginning of the study, patients were prospectively divided into three subgroups: A (restrictive pattern), B ("normal" pattern), and C (abnormal relaxation pattern). In the trained group, peak VO2 (+12%; P < .0001), peak workload (+8.5%; P < .005), and lactic acidosis threshold (+12%; P < .0001) were significantly increased after training without changes in LV ejection fraction. However, only subgroup C demonstrated significant improvement in peak VO2 (+15%; P < .005). No changes were observed in the untrained group. In the trained subgroups a significant increase in rapid filling fraction (RFF), peak filling rate (PFR), peak early filling velocity (E), and E/A ratio was noted. A significant decrease in atrial filling fraction (AFF), peak atrial filling velocity (A), deceleration time of early filling velocity (EDT), and isovolumic relaxation time (IVRT) was observed only in subgroup C. No changes were found in untrained subgroups. A good correlation was found between Doppler and radionuclide LV diastolic filling parameters before and after training (P < .0001). Multiple stepwise regression analysis demonstrated that pretraining E/A ratio (P < .0001) and peak heart rate (P < .0002) were positive predictors of pretraining peak VO2. Posttraining increase in exercise tolerance (P < .0001) and increase in E/A ratio (P < .0001) were the strongest predictors of an increase in peak VO2. The independent predictors of cardiac events were a greater RFF and a shorter IVRT and EDT. Stepwise logistic regression showed that Doppler LV diastolic filling patterns are independent predictors of overall cardiac events (P = .02), and restrictive pattern has a worse prognosis compared with B (P = .04) and C (P = .007). However, ET did not reach statistical significance (P = .54) as a predictor of cardiac events.

CONCLUSIONS

These data demonstrate that ET induces significant improvement in exercise capacity only in patients with DCM and a pattern of abnormal LV relaxation. The improvement in peak VO2 is significantly correlated with an increase in peak early filling rate and peak filling rate as well as a decrease in atrial filling rate. Doppler echocardiography may be a valuable tool in the prognostic assessment of patients with DCM who will benefit from exercise training.