Hypercholesterolemia

Background: Cardioprotection by preconditioning is limited in some animal models of hypercholesterolemia. We studied ischemic preconditioning induced by coronary angioplasty in hypercholesterolemic and normocholesterolemic patients by means of a beat-to-beat analysis of ST segments.

Methods: Thirty coronary disease patients were classified into normocholesterolemic and hypercholesterolemic groups. Intracoronary ECG was recorded during three consecutive balloon inflations of 2-min duration with 5-min intervals.

Results: In normocholesterolemic patients, the ST segment was continuously elevated during the occlusions and rapidly normalized after balloon deflations. Repeated occlusions significantly attenuated ST-segment elevation from 1.28 [+ or -] 0.67 to 0.88 [+ or -] 0.51 mV (p < 0.001) and decreased the time to normalization of ST segment. In hypercholesterolemic patients, the ST segment was rapidly elevated in the first 30 s of the first occlusion, and normalization of the ST segment was longer on the first reperfusion. However, in these patients, repeated occlusions abolished the initial elevation of the ST segment but did not attenuate maximal ST-segment elevation (1.24 [+ or -] 1.11 mV vs 1.21 [+ or -] 1.09 mV) and failed to decrease the time to normalization of the ST segment.

Conclusions: Hypercholesterolemia accelerates the evolution of myocardial ischemia, delays recovery on reperfusion, and deteriorates the anti-ischemic effect of preconditioning in humans.

(CHEST 2005; 128:1623-1628)

Key words: coronary angioplasty; hypercholesterolemia; ischemia; preconditioning

Abbreviations: PCI = percutaneous coronary intervention; RM-ANOVA = repeated-measures analysis of variance

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Ischemic preconditioning is a powerful adaptive response of the heart in which brief exposure to ischemia enhances the ability of the heart to withstand a subsequent ischemic injury. Although preconditioning provides a remarkable cardioprotection, its effectiveness is attenuated in some animal models of diseases, including hyperlipidemia, diabetes, nitrate tolerance, heart failure, and aging. (1,2) We have reported for the first time that cardioprotection conferred by classical preconditioning against intracavital ST-segment elevation was lost in cholesterol-fed rabbits due to hypercholesterolemia. (3) The loss of classic preconditioning was subsequently confirmed in hearts of cholesterol-fed rats in which no signs of atherosclerosis were observed. (4) Other animal studies (1,2,5,6) also confirm that hyperlipidemia, independently from the development of coronary atherosclerosis, attenuates the cardioprotective effect of preconditioning. However, little is known about the effects of hypercholesterolemia on preconditioning in humans.

Evidence in the literature (7-9) shows that preconditioning exists in humans. However, in some studies, (10-12) the absence of the cardioprotective effect of preconditioning was found in patients subjected to percutaneous coronary intervention (PCI). In these studies, (10-12) the possible effect of hypercholesterolemia on preconditioning was not investigated, and the reason for the lack of preconditioning was not shown. There is just one study (13) suggesting that hypercholesterolemia affects preconditioning in humans. In this study, (13) surface ST-segment elevation assessed at the end of three consecutive balloon inflations was the only one ischemic parameter reported; however, surface ECG signal does not provide a precise representation of transient ischemic events during PCI. The most often studied end point of human preconditioning is intracoronary ST-segment elevation as an indicator of the severity of ischemia during repeated coronary occlusions; however, different research groups use different time points to measure ST-segment elevation. Although Cribier et al (14) measured ST-segment elevations at every 30 s for 2 min during balloon inflations, the time course of ST-segment elevation during the entire periods of subsequent balloon inflations and deflations remained unknown. Therefore, it is plausible to speculate that by a beat-to-beat analysis of intracoronary ST-segment shifts, the time course of the evolution of myocardial ischemia during balloon inflations and the recovery from ischemia on reperfusion during balloon deflations can be assessed.

We hypothesized that hypercholesterolemia attenuates the cardioprotective effect of preconditioning elicited by consecutive balloon inflations during PCI in patients. Therefore, in the present study, we assessed the time course of intracoronary ST-segment shifts during repeated balloon inflations and deflations, both in hypercholesterolemic and normocholesterolemic patients undergoing PCI.

MATERIALS AND METHODS

Patients

The study protocol was approved by the Ethics Committee of the University of Szeged. A written informed consent was obtained from all patients enrolled in the study. The investigations were carried out in single-vessel coronary disease patients elected for PCI (Table 1). Exclusion criteria were as follows: (1) angina pectoris or other signs of myocardial ischemia 1 week before intervention; (2) Lown 3-4 ventricular arrhythmia before the intervention; (3) left ventricular dysfunction (< 35% ejection fraction or greater than New York Heart Association functional circulatory stage II); (4) treatment with adenosine 5'-triphosphate-sensitive potassium channel inhibitors; (5) history of myocardial infarction or baseline ST-segment abnormalities; (6) serum electrolytes out of the physiologic range; (7) serum creatinine level < 1.50 [micro]mol/L; (8) hypothyreosis; and (9) angiographically visible collateral vessels interfering with the treated coronary artery. Based on the exclusion criteria, 41 patients were included in our study. A further 11 patients were excluded from the study due to unsuccessful registration of intracoronary ECG, such as lack of ST-segment elevation during the first occlusion in 5 patients, occurrence of arrhythmias that made the beat-to-beat evaluation of ST segments impossible in 4 patients, and poor quality of recordings in 2 patients. The remaining 30 patients were classified into normocholesterolemic (3.5 to 5.3 mmol/L, n = 15) aim hypercholesterolemic (5.5 to 7.8 mmol/L, n = 15) groups. Our boundary cholesterol value (5.3 mmol/L) is associated with borderline high risk of ischemic heart disease according to various recommendations including the National Cholesterol Education Program. Time to normalization of the ST segment during reperfusion could be assessed only in 13 patients in each group due to various technical problems unrelated to the end points of the study.

Angioplasty Protocol

PCI was performed using a standard femoral approach in all patients after premeditation with 100 mg of aspirin and 75 mg of clopidogrel daily for 2 days. The coronary artery lesion was crossed with a 0.014-inch guide wire (BMW; Guidant; Santa Clara, CA). PCI was performed with semicompliant balloon dilatation catheters (Medtronic Vascular; Santa Rosa, CA). Balloon size was determined individually (digital caliper method, Siemens Hicor System; Siemens; Erlangen, Germany). After the balloon was positioned in the lesion, patients underwent three balloon inflations for 2-min each, interspersed with 5-min periods of reperfusion during which the balloon was deflated and withdrawn proximal to the lesion with the guide wire remaining across the lesion. One minute after each occlusion, coronary angiography was performed to assess the result of the dilation. Five minutes after the end of the third inflation, the study protocol was terminated and decisions regarding further inflations or other interventional procedures were made on an individual basis. (15)

Assessment of Myocardial Ischemia and Reperfusion

Myocardial ischemia was assessed by measurement of intracoronary ST-segment elevation. Lead C1 of the ECG monitoring system was connected to the coronary guide wire and recorded online with Wsmon Application Version 3.3 software (Z. Gingl; Szeged, Hungary) throughout the procedure. Every cardiac cycle on the ECG was evaluated by an independent physician in a blind arrangement. ST-segment elevation was defined as the difference between voltage values 80 ms after the J point and that in the PQ segment, as described. (13) Time to normalization of ST segment was calculated from the time of the balloon deflation until the ST-segment elevation became < 0.1 mV.

Data Analysis

ECG recordings were analyzed using software (WinDaq Version 1.78; Dataq Instruments; Akron, OH). The number of heart beats in each ischemic period were separated into 15-s intervals, and the ST-segment elevation values of each cardiac cycle in the 15-s periods were averaged to get an eight-point curve (Fig 1). The effects of repeated occlusions were analyzed by repeated-measures analysis of variance (RM-ANOVA) with Greenhouse-Geisser adjustment if needed (SPSS version 11.0; SPSS; Chicago, IL); p values were corrected according to Bonferroni for repeated measurements. Differences between the normocholesterolemic and hypercholesterolemic groups were analyzed using independent-samples t test with corrected p values for repeated measurements (Fig 2). Effect of repeated occlusions on time to normalization of the ST segment in the normocholesterolemic group was also analyzed by RM-ANOVA. Confidence intervals in pairwise comparisons were adjusted to multiplications according to the Sidak formula. All data were expressed as means [+ or -] SEM; p < 0.05 was considered significant in every statistical test.

RESULTS

Time Course of ST-Segment Elevation During Ischemia

In the normocholesterolemic group, ST-segment elevation showed a continuous rise during the 2-min occlusions (Fig 1). Repeated occlusions resulted in lower ST-segment elevations, which reached a statistically significant level in the last 30-s periods of the occlusions, showing the anti-ischemic effect of preconditioning. In the hypercholesterolemic group, a rapid elevation of the ST segment was developed in the initial 30 s of the first occlusion, which was not observed in the subsequent two occlusions. However, from 45 to 120 s of the occlusions, there was no difference between ST-segment elevations. This shows that in hypercholesterolemic patients, preconditioning only slowed down the rapid onset of ischemia seen at the initial 30 s of the first occlusion but did not protect against the evolution of ST-segment elevation observed by the end of the occlusions.

Time to Normalization of the ST Segment During Reperfusion

We determined the time to normalization of intracoronary ST segment during the reperfusion periods on balloon deflations as an indicator of the recovery of the heart from ischemia. In normocholesterolemic patients, we observed a significant decrease in time to normalization of the ST segment during repeated reperfusions, showing the preconditioning effect (Fig 2). In the hypercholesterolemic group, time to normalization of the ST-segment after all the three ischemic periods was significantly prolonged as compared to the normocholesterolemic group, and repeated occlusion/reperfusion periods did not decrease time to normalization of ST segment. This shows the lack of the protective effect of preconditioning in hypercholesterolemia.

DISCUSSION

We investigated if hypercholesterolemia attenuates ischemic preconditioning in 30 patients. We have shown here for the first time in the literature that in hypercholesterolemic patients, there is a rapid elevation of ST segment during the initial 30 s of the first balloon inflation, a phenomenon not seen in normocholesterolemic patients. Our results further show that in hypercholesterolemic patients, the repeated occlusions although abolished the initial rapid elevation of ST segment but did not attenuate ST-segment elevation when measured at 45 to 120 s, and failed to decrease the time to normalization of ST segment after balloon deflations when compared to normocholesterolemic patients. Our results provide clear-cut evidence that hypercholesterolemia enhances the evolution of myocardial ischemia on coronary occlusion and significantly inhibits the anti-ischemic effect of preconditioning in humans.

A high-cholesterol diet is regarded as an important factor in the development of ischemic heart disease. There is a linear relationship between elevation of serum total cholesterol concentration and the incidence of myocardial infarction; furthermore, the heart of hyperlipidemic/atherosclerotic patients is hardly capable of adapting to physical exercise or other kinds of stress. (16,17) This has been attributed solely to the development of atherosclerosis, and the possibility of the deterioration of endogenous adaptive mechanisms against myocardial ischemia, ie, preconditioning, has not been considered in hypercholesterolemic patients. Although the majority of animal studies (1,2,13) show that experimental hypercholesterolemia interferes with the cardioprotective effect of preconditioning, little is known about the effect of hypercholesterolemia on human preconditioning.

Our present study provided solid evidences showing that hypercholesterolemia inhibits the cardioprotective effect of acute preconditioning in man. We have assessed the time course of the evolution of myocardial ischemia and that of the recovery from ischemia by a beat-to-beat analysis of the intracoronary ST-segment shifts induced by balloon inflations and deflation during PCI and observed that in hypercholesterolemic patients, there is a rapid increase in ST-segment elevation at the beginning (0 to 30 s) of the first balloon inflation; however, this is not seen in the second and third occlusions. This phenomenon could be considered as a preconditioning effect; however, if one looks at ST-segment elevation at 45 to 120 s of the occlusions, no preconditioning effect can be observed in hypercholesterolemic patients. This shows that a week preconditioning effect can be observed in hypercholesterolemic patients, but it only slightly delays the evolution of ischemia and does not alleviate the severity of ischemia. Our results support that of Kyriakides et al, (13) who reported that ST-segment elevation on the surface ECG measured at 120 s of balloon inflations was not attenuated during repeated occlusions in hypercholesterolemic patients. Furthermore, we have found that the time to normalization of the ST segment was decreased after repeated coronary occlusions/reperfusion periods in normocholesterolemic patients, showing the beneficial effect of preconditioning. However, in hypercholesterolemic patients, time to normalization of the ST segment was significantly longer even after the first occlusion, and repeated occlusion/reperfusion periods did not decrease this parameter. These results clearly show that hypercholesterolemia aggravates ischemia/reperfusion injury and impairs the anti-ischemic effect of preconditioning in humans.

The mechanism by which hypercholesterolemia may influence the severity of myocardial ischemia and the effects of preconditioning in humans is not known; however, several mechanisms have been suggested in animal studies, (1,2) such as deterioration of myocardial nitric oxide metabolism, (4) increased formation of reactive oxygen species such as superoxide and peroxynitrite, (18) disruption of the mevalonate pathway, (20) attenuation of heat shock response, (20) and the accumulation of cholesterol in the sarcolemmal and mitochondrial membranes. (21,22) However, it seems that hypercholesterolemia induces very complex changes in cellular mechanisms of the myocardium, as our study (23) using DNA microarray assay of 3,200 genes showed that hypercholesterolemia leads to significant alterations in the expression of 51 genes (4% of the examined genes) in the rat heart.

There appears a controversy in some studies (10-12) on the effectiveness of preconditioning induced by PCI in humans. We assume that the reasons for the controversy among others might be the following: (1) that hypercholesterolemic and normocholesterolemic patients have not been separated in these studies, and (2) that ST-segment elevation in myocardial ischemia was evaluated by different ways. Study protocols usually include an arbitrarily selected time point to assess ischemia during balloon inflations. Dupouy et al (11) failed to show preconditioning induced by 2-min balloon inflations when measured intracoronary ST-segment elevation at 90 s of balloon inflations in 13 patients. Billinger et al (10) failed to observe the anti-ischemic effect of pharmacologic preconditioning induced by intracoronary adenosine before angioplasty when measuring intracoronary ST-segment elevation at 60 s of balloon inflations in 30 patients. Laskey and Beach (12) studied preconditioning in 382 patients by the assessment of the maximal ST-segment elevations on either surface or intracoronary ECG during two 90-s balloon occlusions, and they could elicit preconditioning only in 80% of their patients. In these studies, the reason for the lack of preconditioning was not shown. Our present findings, ie, the differences in the time course of ST-segment elevation between normocholesterolemic and hypercholesterolemic patients and the limitation of preconditioning in hypercholesterolemic patients, show the necessity to distinguish between normocholesterolemic and hypercholesterolemic patients and emphasize the importance of a beat-to-beat analysis of ST-segment elevation during the entire periods of balloon inflations and deflations in human preconditioning studies. It should be noted here that similarly to hypercholesterolemic patients, in patients with other diseases such as diabetes, heart failure, and aging, the time course of ischemia during PCI may also be altered that can be assessed only by a beat-to-beat analysis of ST-segment elevation.

In summary, we conclude that hypercholesterolemia attenuates the anti-ischemic effect of preconditioning, accelerates the evolution of myocardial ischemia, and delays the recovery from ischemia on reperfusion in humans. These findings further emphasize the importance of serum cholesterol as a predictive risk factor for the incidence and severity of myocardial ischemic events, and call for the development of new cardioprotective drugs that reverse the increased susceptibility of hearts to ischemic stress and recapture the cardioprotective effect of preconditioning in hypercholesterolemic patients.

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Imre Ungi, MD; Tamas Ungi, MD; Zoltan Ruzsa, MD; Edit Nagy, MD; Zsolt Zimmermann, MD; Tamas Csont, MD, PhD; and Peter Ferdinandy, MD, PhD, DSc

* From the Second Department of Internal Medicine and Cardiology Center (Drs. I. Ungi, Nagy, Ruzsa, and Zimmerman) and Cardiovascular Research Group (Drs. T. Ungi and Csont), and Pharmahungary 2000 Ltd. (Dr. Ferdinandy), Department of Biochemistry, University of Szeged, Szeged, Hungary.

This work was performed at the University of Szeged.

This work was supported by grants from the Hungarian Ministry of Health (ETT 616/2003, ETT 515/2003) and the Hungarian Scientific Research Found (OTKA F 046810, OTKA T 046417). Dr. Csont is a Bekesy Fellow of the Ministry of Education of the Republic of Hungary. Dr. Ferdinandy holds an Istvan Szechenyi

Professorship of the Hungarian Academy of Sciences.

Manuscript received November 22, 2004; revision accepted March 8, 2005.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal. org/misc/reprints.shtml).

Correspondence to: Peter Ferdinandy, MD, PhD, DSc, Cardiovascular Research Group, Department of Biochemistry, University of Szeged, Faculty of Medicine, Dom ter 9, Szeged, H-6720 Hungary; e-mail: peter@bioch.szote.u-szeged.hu

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