[Ischemic preconditioning. Is it always a beneficial phenomenon?]

Mechanisms of Cardiovascular Protection Associated with Intermittent Hypobaric Hypoxia Exposure in a Rat Model: Role of Oxidative Stress

More than 140 million people live and works (in a chronic or intermittent form) above 2500 m worldwide and 35 million live in the Andean Mountains. Furthermore, in Chile, it is estimated that 55,000 persons work in high altitude shifts, where stays at lowlands and interspersed with working stays at highlands. Acute exposure to high altitude has been shown to induce oxidative stress in healthy human lowlanders, due to an increase in free radical formation and a decrease in antioxidant capacity. However, in animal models, intermittent hypoxia (IH) induce preconditioning, like responses and cardioprotection. Here, we aimed to describe in a rat model the responses on cardiac and vascular function to 4 cycles of intermittent hypobaric hypoxia (IHH). Twelve adult Wistar rats were randomly divided into two equal groups, a four-cycle of IHH, and a normobaric hypoxic control. Intermittent hypoxia was induced in a hypobaric chamber in four continuous cycles (1 cycle = 4 days hypoxia + 4 days normoxia), reaching a barometric pressure equivalent to 4600 m of altitude (428 Torr). At the end of the first and fourth cycle, cardiac structural, and functional variables were determined by echocardiography. Thereafter, ex vivo vascular function and biomechanical properties were determined in femoral arteries by wire myography. We further measured cardiac oxidative stress biomarkers (4-Hydroxy-nonenal, HNE; nytrotirosine, NT), reactive oxygen species (ROS) sources (NADPH and mitochondrial), and antioxidant enzymes activity (catalase, CAT; glutathione peroxidase, GPx, and superoxide dismutase, SOD). Our results show a higher ejection and shortening fraction of the left ventricle function by the end of the 4th cycle. Further, femoral vessels showed an improvement of vasodilator capacity and diminished stiffening. Cardiac tissue presented a higher expression of antioxidant enzymes and mitochondrial ROS formation in IHH, as compared with normobaric hypoxic controls. IHH exposure determines a preconditioning effect on the heart and femoral artery, both at structural and functional levels, associated with the induction of antioxidant defence mechanisms. However, mitochondrial ROS generation was increased in cardiac tissue. These findings suggest that initial states of IHH are beneficial for cardiovascular function and protection.

Sum of effects of myocardial ischemia followed by electrically induced tachycardia on myocardial function

BACKGROUND

The alteration of contractile function after tachyarrhythmia ceases is influenced by the type of prior ischemia (acute coronary syndrome or ischemia inherent in a coronary revascularization procedure). We aimed to analyze cardiac dysfunction in an acute experimental model of supraphysiological heart rate preceded by different durations and types of ischemia.

MATERIAL AND METHODS

Twenty-four pigs were included in: (S1) series of ventricular pacing; (S2, A and B) series with 10 or 20 min, respectively, of coronary occlusion previous to ventricular pacing; S3 with 20 brief, repeated ischemia/reperfusion processes prior to ventricular pacing and; (S4) control series. Overall cardiac function parameters and regional myocardial contractility at the apex and base of the left ventricle were recorded, as were oxidative stress markers (glutathione and lipid peroxide serum levels). Left ventricular pacing at 60% over baseline heart rate was performed for 2 h followed by 1 h of recovery.

RESULTS

High ventricular pacing rates preceded by short, repeated periods of coronary ischemia/reperfusion resulted in worse impairment of overall cardiac and regional function that continued to be altered 1 h after tachycardia ceased. There was significant reduction of stroke volume (26.9 ± 5.3 basal vs. 16 ± 6.2 ml; p<0.05), LVP; dP/dt and LAD flow (13.1 ± 1.5 basal vs. 8.4 ± 1.6 ml/min; p<0.05); the base contractility remained altered when recovering compared to baseline (base SF: 5.6 ± 2.8 vs. 2.2 ± 0.7%; p<0.05); and LPO levels were higher than less aggressive series at the end of recovery.

CONCLUSIONS

Ischemia and tachycardia accumulate their effects, with increased cardiac involvement depending on the type of ischemia.

[The influence of angina the week before a first myocardial infarction on short and medium-term prognosis]

INTRODUCTION AND OBJECTIVES

The implications of early angina on the prognosis of myocardial infarction are controversial. The aim of this study was to assess the effect of angina one week before the first myocardial infarction on short and medium-term prognosis.

PATIENTS AND METHOD

A total of 290 consecutive patients (107 with previous angina and 183 without it) with the first myocardial infarction were studied to determine the effect of preceding angina on short and medium-term prognosis. Further criteria for inclusion were no previous history of angina > 1 week before the first myocardial infarction, and no evidence of prior structural cardiopathy. The end points studied were death and congestive heart failure in the acute phase of myocardial infarction and during the follow-up.

RESULTS

Patients with a history of prodromal angina were less likely to experience in-hospital death, heart failure or combined end-point (3.7 vs 11.5%; 4.6 vs 15.8%; 7.5 vs 21.3%) (p = 0.002). There was also a difference between groups in the follow-up (4.1 vs 13.2%; p = 0.03). Multivariate analysis confirmed that the presence of preinfarction angina was an independent predictor of death and heart failure in the acute phase of myocardial infarction as well as in the follow-up.

CONCLUSIONS

The occurrence of angina one week before the first myocardial infarction protects against death and heart failure in the acute phase of myocardial infarction as well as in the medium follow-up.

[Troponine T as possible myocardial injury marker. Its application in myocardial stunning and silent ischemia]

INTRODUCTION AND OBJECTIVES

The need for more specific, more sensitive and earlier biochemical markers of acute myocardial infarction, has led to the development of alternative methods to CK-MB). The aim of this work is to assess the usefulness of TnT measurement, in comparison with other markers for detecting transitory ischemic processes without necrosis in some experimental models.

METHODS

The plasma levels of Troponine T, CK, CK-MB and adenosine were assessed as markers of ischemic myocardial injury. Two protocols were used: in Series I and II very brief (2 min ischemia with 3-min reperfusion) repeated (20 episodes) ischemias were induced, while Series III involved a single 15-min ischemia with a 60-min reperfusion. In Series I the coronary occlusor was placed close to the anterior descending coronary artery (AD); in Series II and III it was placed distally in the AD. Blood samples were taken from the peripheral vein (PVB) and corresponding coronary segment vein; in a basal situation, during ischemia, upon reperfusion, after 24 hours, and after 5 and 10 days. The plasma levels of adenosine, troponine T, CK and CK-MB as well as general and regional function parameters were measured.

RESULTS

In Series I we observed hypokinesis that lasted 10 days, reaching its maximum on days 4-5. In Series II and III regional function was restored by 24 hours. CK and CK-MB showed similar behaviour; they rose significantly when the chest was opened (p < 0.05) reaching the highest value at 24 hours in all the series. Adenosine rose significantly only during reperfusion (p < 0.05). Troponine T increased after ischemia but not before, remained high for 5 days in all series (PVB).

CONCLUSIONS

Troponine T rises in absence of necrosis, preferably when the ischemia is longer.

[Influence of pre-infarction angina on mid-term mortality after acute myocardial infarction]

INTRODUCTION AND OBJECTIVES

Pre-infarction angina may reduce the extent of myocardial cell necrosis and improves the prognosis after myocardial infarction. The aim of this study was to analyze the total mortality six-month after acute myocardial infarction according to the presence or absence of pre-infarction angina.

METHODS

One hundred seventy-five consecutive patients with acute myocardial infarction were prospectively included, 72 (41.4%) with pre-infarction angina. They were followed for 6 months. There were 16 deaths (15.5%) in the group of patients without pre-infarction angina and 7 (9.7%) in the group with pre-infarction angina (log-rank = 1.03; p = 0.311). The hazard-risk function curves showed a higher risk of death during the entire follow-up in the group without pre-infarction angina. In the multivariate logistic regression model, the presence of pre-infarction angina does not significantly reduce the risk of death (OR = 0.43; CI 95% = 0.09-2. 22; p = 0.303). We detected a significant interaction between treatment with sulfonylureas before the infarction and the presence of pre-infarction angina (p = 0.017).

CONCLUSIONS

In this study no significant differences were observed in total mortality six months after acute myocardial infarction according to the presence of pre-infarction angina. However, the risk of death seemed to be higher in the group of patients without pre-infarction angina during the entire follow-up. A significant interaction was found between the treatment with sulfonylurea drugs before infarction and the presence of pre-infarction angina.