Myocardial effects of halothane and isoflurane in hamsters with hypertrophic cardiomyopathy

Anesthetic Agents Isoflurane and Propofol Decrease Maximal Ca2+-Activated Force and Thus Contractility in the Failing Myocardium

In the normal heart, frequently used anesthetics such as isoflurane and propofol can reduce inotropy. However, the impact of these agents on the failing myocardium is unclear. Here, we examined whether and how isoflurane and propofol influence cardiac contractility in intact cardiac muscles from rats treated with monocrotaline to induce heart failure. We measured force and intracellular Ca²⁺ ([Ca^{2 +}]_i) in trabeculae from the right ventricles of the rats in the absence or presence of propofol or isoflurane. At low to moderate concentrations, both propofol and isoflurane dose-dependently depressed cardiac force generation in failing trabeculae without altering [Ca²⁺]_i At high doses, propofol (but not isoflurane) also decreased amplitude of [Ca²⁺]_i transients. During steady-state activation, both propofol and isoflurane impaired maximal Ca²⁺-activated force (F_max) while increasing the amount of [Ca²⁺]_i required for 50% of maximal activation (Ca₅₀). These events occurred without apparent change in the Hill coefficient, suggesting no impairment of cooperativity. Exposing these same muscles to the anesthetics after fiber skinning resulted in a similar decrement in F_max and rise in Ca₅₀ but no change in the myofibrillar ATPase-Ca²⁺ relationship. Thus, our study demonstrates that challenging the failing myocardium with commonly used anesthetic agents such as propofol and isoflurane leads to reduced force development as a result of lowered myofilament responsiveness to Ca²⁺ SIGNIFICANCE STATEMENT: Commonly used anesthetics such as isoflurane and propofol can impair myocardial contractility in subjects with heart failure by lowering myofilament responsiveness to Ca²⁺. High doses of propofol can also reduce the overall amplitude of the intracellular Ca²⁺ transient. These findings may have important implications for the safety and quality of intra- and perioperative care of patients with heart failure and other cardiac disorders.

Effect of different anesthetic agents on left ventricular systolic function assessed by echocardiography in hamsters

Determination of left ventricular ejection fraction (LVEF) using in vivo imaging is the cardiac functional parameter most frequently employed in preclinical research. However, there is considerable conflict regarding the effects of anesthetic agents on LVEF. This study aimed at assessing the effects of various anesthetic agents on LVEF in hamsters using transthoracic echocardiography. Twelve female hamsters were submitted to echocardiography imaging separated by 1-week intervals under the following conditions: 1) conscious animals, 2) animals anesthetized with isoflurane (inhaled ISO, 3 L/min), 3) animals anesthetized with thiopental (TP, 50 mg/kg, intraperitoneal), and 4) animals anesthetized with 100 mg/kg ketamine plus 10 mg/kg xylazine injected intramuscularly (K/X). LVEF obtained under the effect of anesthetics (ISO=62.2±3.1%, TP=66.2±2.7% and K/X=75.8±1.6%) was significantly lower than that obtained in conscious animals (87.5±1.7%, P<0.0001). The K/X combination elicited significantly higher LVEF values compared to ISO (P<0.001) and TP (P<0.05). K/X was associated with a lower dispersion of individual LVEF values compared to the other anesthetics. Under K/X, the left ventricular end diastolic diameter (LVdD) was increased (0.60±0.01 cm) compared to conscious animals (0.41±0.02 cm), ISO (0.51±0.02 cm), and TP (0.55±0.01 cm), P<0.0001. The heart rate observed with K/X was significantly lower than in the remaining conditions. These results indicate that the K/X combination may be the best anesthetic option for the in vivo assessment of cardiac systolic function in hamsters, being associated with a lower LVEF reduction compared to the other agents and showing values closer to those of conscious animals with a lower dispersion of results.

Effect of isoflurane on myocardial energetic and oxidative stress in cardiac muscle from Zucker diabetic fatty rat

The effect of inhalational anesthetics on myocardial contraction and energetics in type 2 diabetes mellitus is unknown. We investigated the effect of isoflurane (ISO) on force and intracellular Ca(2+) transient (iCa), myocardial oxygen consumption (MVo(2)), and energetics/redox behavior in trabecular muscles from Zucker diabetic fatty (ZDF) rats. At baseline, force and corresponding iCa were lower in ZDF trabeculae than in controls. ISO decreased force in both groups in a dose-dependent manner. ISO did not affect iCa amplitude in controls, but ISO > 1.5% significantly reduced iCa amplitude in ZDF trabeculae. ISO-induced force depression fully recovered as a result of increased iCa when external Ca(2+) was raised in controls. However, both force and iCa remained low in ZDF muscle at elevated external Ca(2+). In controls, force, iCa, and MVo(2) increased when stimulation frequency was increased from 0.5 to 1.5 Hz. ZDF muscles, however, exhibited blunted responses in force and iCa and decreased MVo(2). Oxidative stress levels were unchanged in control muscles but increased significantly in ZDF muscles after exposure to ISO. Finally, the depressive effect of ISO was prevented by 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (Tempol) in ZDF muscles. These findings suggest that ISO dose-dependently attenuates force in control and ZDF muscles with differential effect on iCa. The mechanism of force depression by ISO in controls is mainly decreased myofilament Ca(2+) sensitivity, whereas in ZDF muscles the ISO-induced decrease in contraction is due to worsening oxidative stress, which inhibits iCa and force development.

A comparison of retrospectively self-gated magnetic resonance imaging and high-frequency echocardiography for characterization of left ventricular function in mice

Non-invasive imaging methods like echocardiography and magnetic resonance imaging (MRI) are very valuable in longitudinal follow-up studies of cardiac function in small animals. To be able to compare results from studies using different methods, and explain possible differences, it is important to know the agreement between these methods. As both self-gated high-field MRI and high-frequency echocardiography (hf-echo) M-mode are potential methods for evaluation of left ventricular (LV) function in healthy mice, our aim was to assess the agreement between these two methods. Fifteen healthy female C57BL/6J mice underwent both self-gated MRI and hf-echo during the same session of light isoflurane anaesthesia. LV dimensions were estimated offline, and agreement between the methods and reproducibility for the two methods assessed using Bland-Altman methods. In summary, hf-echo M-mode had better inter-observer repeatability than self-gated MRI for all measured parameters. Compared with hf-echo, systolic posterior wall thicknesses were significantly higher when measured by MRI, while diastolic anterior wall thicknesses were found to be significantly smaller. MRI measurements of diastolic LV diameter were also higher using MRI, resulting in larger fractional shortening values compared with the values obtained by hf-echo. In conclusion, hf-echo M-mode is easy to apply, has high temporal and spatial resolution, and good reproducibility. Self-gated MRI might be advantageous in cases of abnormal LV geometry and heterogeneous regional myocardial function, especially with improvements in spatial resolution. The moderate agreement between the methods must be taken into account when comparing studies using the two modalities.

Refinement of cardiac NMR imaging in awake hamsters: proof of feasibility and characterization of cardiomyopathy

The goal of this study was to demonstrate the feasibility of cardiac NMR imaging in conscious hamsters and its usefulness in evaluating cardiac abnormalities in a small-animal model of cardiomyopathy. Awake hamsters, controls and cardiomyopathic ones (CHF 147), were immobilized in a dedicated holder. Half-Fourier single-shot FSE imaging, with outer-volume suppression and 'black-blood' contrast provided images free from motion artifact with good visualization of cardiac anatomy at any point in the cardiac cycle. Series of double-oblique views were acquired with or without electrocardiograph gating. Image acquisition time was 55 ms, with an in-plane resolution of 470 x 625 microm2. Left ventricular volumes, ejection fraction, and myocardium NMR signal heterogeneity were compared in CHF 147 and control hearts. Left ventricles of CHF 147 hamsters were dilated, as indicated by the increase in end-diastolic cavity volume (299 +/- 79 mm3 compared with the controls (141 +/- 39 mm3; P = 0.0002). Left ventricular ejection fraction was largely reduced (45 +/- 9% vs 86 +/- 4%; P < 0.0001). The NMR signal distribution at an effective echo time of 41 ms was more heterogeneous in the myocardial wall of CHF 147 hamsters than in controls (1.87 +/- 0.37 a.u. vs 0.98 +/- 0.12 a.u., respectively; P = 0.0002). This study is a refinement of animal experimentation, as it demonstrates for the first time that characteristic features of cardiac pathology can be evaluated with ultra-fast NMR imaging in conscious small rodents.

Diastolic heart failure in anaesthesia and critical care

Diastolic heart failure is an underestimated pathology with a high risk of acute decompensation during the perioperative period. This article reviews the epidemiology, risk factors, pathophysiology, and treatment of diastolic heart failure. Although frequently underestimated, diastolic heart failure is a common pathology. Diastolic heart failure involves heart failure with preserved left ventricular (LV) function, and LV diastolic dysfunction may account for acute heart failure occurring in critical care situations. Hypertensive crisis, sepsis, and myocardial ischaemia are frequently associated with acute diastolic heart failure. Symptomatic treatment focuses on the reduction in pulmonary congestion and the improvement in LV filling. Specific treatment is actually lacking, but encouraging data are emerging concerning the use of renin-angiotensin-aldosterone axis blockers, nitric oxide donors, or, very recently, new agents specifically targeting actin-myosin cross-bridges.

Asthma as a risk factor for respiratory complications after adenotonsillectomy in children with obstructive breathing during sleep

BACKGROUND

Children with asthma are at increased risk for obstructive breathing during sleep. Adenotonsillectomy, the treatment of choice for obstructive breathing during sleep, is associated with significant postoperative respiratory morbidity.

OBJECTIVE

To determine whether asthma is a risk factor for respiratory complications after adenotonsillectomy in children with obstructive breathing during sleep.

METHODS

This case-control study compared 115 children aged 3 to 18 years with respiratory complications after adenotonsillectomy (study group) with 115 children without respiratory complications after adenotonsillectomy (control group).

RESULTS

The postoperative respiratory complications ranged from oxygen desaturation to respiratory failure that required mechanical ventilation. The study group had a higher proportion of children with asthma (P < .01). Logistic regression analysis showed that asthma increases the odds of postoperative respiratory complications to 4.4 (95% confidence interval, 2.13-9.0), after controlling for age, weight greater than the 97th percentile for age, sex, race, and medical conditions other than asthma.

CONCLUSIONS

In children with obstructive breathing during sleep, the presence of asthma is associated with an increased risk of respiratory complications after adenotonsillectomy.

Structural cardiac changes as a predictor of respiratory complications after adenotonsillectomy for obstructive breathing during sleep in children

BACKGROUND AND PURPOSE

To determine the association between structural cardiac changes and postoperative respiratory complications after adenotonsillectomy for obstructive breathing during sleep.

PATIENTS AND METHODS

Forty-eight children, ages 2-18 years, undergoing adenotonsillectomy for obstructive breathing during sleep were recruited for this case control study. The case group consisted of 24 children with postoperative respiratory complications after adenotonsillectomy who also had an echocardiogram. An equal number of children without postoperative respiratory complications after adenotonsillectomy were recruited as controls. Left ventricular mass (LVM) was calculated from 2D guided M mode echocardiographic measurements of the left ventricle. Left ventricular mass index (LVMI) was calculated as left ventricular mass/height(2.7). Left ventricular hypertrophy (LVH) was defined as LVMI index greater than the 95th percentile for age. The two groups were compared for demographic variables and cardiac structure.

RESULTS

The two groups did not significantly differ by age, height, gender or racial distribution. LVH and right ventricular (RV) dimension greater than the 95th percentile for age remained significantly associated with the occurrence of postoperative respiratory complications after controlling for body mass index (BMI) Z score, age, gender, race, systolic and diastolic blood pressure.

CONCLUSIONS

The increased prevalence of structural cardiac changes in the group with complications (P<0.01) suggests an underlying cardiac origin for postoperative respiratory complications in this group of children.

The paradoxical positive inotropic effect of sevoflurane in healthy and cardiomyopathic hamsters

We investigated the effects of sevoflurane (0.7 to 3.6 vol%) on inotropy and lusitropy in left ventricular papillary muscles of healthy hamsters and genetically induced cardiomyopathic (strain BIO 14.6) hamsters in vitro (29 degrees C, pH 7.40, Ca(2+) 2.5 mM, stimulation frequency three per minute) under low (isotony) and high (isometry) loads. Sevoflurane induced a moderate positive inotropic effect in healthy hamsters (maximum unloaded shortening velocity and isometric active force at 3.6 vol%: 115% +/- 12% and 128% +/- 21% of baseline values, respectively; P < 0.01) and in cardiomyopathic hamsters (maximum unloaded shortening velocity and isometric active force at 3.6 vol%: 115% +/- 20% and 124% +/- 31% of baseline values, respectively; P < 0.05). This positive inotropic effect did not differ between healthy and cardiomyopathic hamsters, even when sevoflurane concentrations were corrected for minimum alveolar anesthetic concentration values in each strain, and was unchanged after alpha- and beta-adrenoceptor blockade. After calcium-channel blockade, this positive inotropic effect was abolished in healthy hamsters but enhanced in cardiomyopathic hamsters. In both strains, sevoflurane induced a moderate negative lusitropic effect under low and high loads.

IMPLICATIONS

A paradoxical moderate positive inotropic effect of sevoflurane was observed in hamster ventricular muscle. This effect was likely related to calcium channel interaction, because after calcium-channel blockade, it was abolished in healthy hamsters and enhanced in cardiomyopathic hamsters.

Minimum alveolar anesthetic concentration of volatile anesthetics in normal and cardiomyopathic hamsters

Minimum alveolar anesthetic concentrations (MAC) values of volatile anesthetics in cardiovascular diseases remain unknown. We determined MAC values of volatile anesthetics in spontaneously breathing normal and cardiomyopathic hamsters exposed to increasing (0.1%-0.3% steps) concentrations of halothane, isoflurane, sevoflurane, or desflurane (n = 30 in each group) using the tail-clamp technique. MAC values and their 95% confidence interval were calculated using logistic regression. In normal hamsters, inspired MAC values were: halothane 1.15% (1.10%-1.20%), isoflurane 1.62% (1.54%-1.69%), sevoflurane 2.31% (2.22%-2.40%), and desflurane 7.48% (7.30%-7.67%). In cardiomyopathic hamsters, they were: halothane 0.89% (0.83%-0.95%), isoflurane 1.39% (1.30%-1.47%), sevoflurane 2.00% (1.85%-2.15%), and desflurane 6.97% (6.77%-7.17%). Thus, MAC values of halothane, isoflurane, sevoflurane, and desflurane were reduced by 23% (P < 0.05), 14% (P < 0.05), 13% (P < 0.05), and 7% (P < 0.05), respectively in cardiomyopathic hamsters.

IMPLICATIONS

Minimum alveolar anesthetic concentrations of volatile anesthetics were significantly lower in cardiomyopathic hamsters than in normal hamsters.