Index Of Ischemic Injury Research Articles

A comparison of serial 49-lead precordial ECG maps and standard 6-lead precordial ECGs in patients with acute anterior Q wave myocardial infarction

A comparison of 265 pairs of standard ECGs and 49-lead precordial maps in 20 patients with ST-segment elevations in anterior ECG leads on admission who eventually were diagnosed as having suffered an anterior Q wave myocardial infarction was carried out to investigate the diagnostic performance provided by the standard ECG in serial studies. Ten patients received intravenous methylprednisolone and 10 were given placebo on admission, and paired mapstandard ECG studies were done. ST-segment elevations were taken as an index of ischemic injury and reduction of R wave amplitude or development of Q waves as a marker of developing necrosis. Methods of measurements and derivation of ECG parameters used in the analysis were the same for the standard ECGs and maps. Comparisons of percent change of five ECG-derived variables between 13 time points and admission, as assessed by the six precordial leads of the standard ECGs and the paired 49-lead maps, were made for the entire data base. A separate analysis to assess the performance of the standard ECG was carried out in a comparison of the methylprednisolone and placebo subgroups. In this latter assessment results of comparisons of the standard ECGs from the treatment and placebo cohorts were similar to the conclusions from the comparisons of the corresponding 49-lead maps. Comparisons for the entire 265 pairs of tracings by the two ECG systems demonstrated that the standard ECG is adequate to monitor quantitatively the ischemic injury and necrosis as reflected by the ECG in serial studies throughout the hospitalization and can be effectively employed in lieu of multilead precordial maps in the evaluation of therapeutic modalities for patients with anterior Q wave myocardial infarction.

Relationship between extracellular potassium accumulation and local TQ-segment potential during acute myocardial ischemia in the porcine

Depolarization of resting membrane potential during acute myocardial ischemia is strongly correlated with the accumulation of extracellular potassium ([K+]e). Also, diastolic currents of injury flowing across the ischemic border that occur as a result of local differences in resting membrane potentials cause changes in the TQ-segments of unipolar, DC-coupled, extracellular electrograms. Further, the changes in [K+]e and TQ-segment potentials during acute ischemia and reperfusion follow a similar time course. For these reasons, a predictable relationship between [K+]e and TQ potentials might be expected to exist. If found, easily obtainable local TQ potential measurements could serve as an index of the resting membrane depolarization induced by [K+]e accumulation and, by extension, as an index of ischemic injury. We measured local [K+]e and TQ potentials from 30 mid-myocardial sites in central and marginal ischemic zones in 2 isolated, Langendorff-perfused porcine hearts during a single, 10-min ligation of the left anterior descending coronary artery. In general, we found a linear relationship between [K+]e and TQ potential for both ischemic zones when data was taken as a whole, but the slopes (S) and correlation coefficients (R) were markedly different between the two locations (-2.24 vs -1.28 and -0.73 vs -0.51 for central and marginal zones, respectively). Further, we found a time dependent change in both S and R that was biphasic. Both were low during the first minutes, attained their maximum values at 4 mins, and then fell during the remainder of the occlusion. We conclude, therefore, that local TQ potentials cannot be used as an index of the severity of ischemic changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Bile flow—An index of ischemic injury

Bile formation is an active secretory process involving bile salt-dependent and -“independent” mechanisms. This study was performed to determine the effect of selected periods of warm ischemia on biliary secretion. Rats were studied using an in situ liver perfusion system after stabilization of bile flow with intravenous sodium taurocholate. Bile flow remained stable in control livers and ceased during ischemic periods of 15 or 25 min. After reperfusion of 15-min ischemic livers, bile flow was depressed but returned to normal by 45 min of reperfusion. After 25 min of ischemia, bile flow remained depressed. A similar depression in bile salt secretion was observed. These studies indicate that both bile flow and bile salt secretion reflect the degree of ischemia in this isolated perfused system, and further use of this model for the investigation of biliary flow as an index of ischemic injury is warranted.

Precordial ST-segment mapping: 6. Evaluation of serial changes in ST-segment elevations and QRS complexes of precordial maps and standard ECGs in patients with acute myocardial infarction.

A total of 21 patients, 10 with anterior and 11 with inferior myocardial infarction (MI) had serial precordial 49-lead ECG maps or standard ECGs on admission, and 2, 6, 12, 24 hours, and 7 days thereafter, to evaluate the natural course of ST-segment elevation (index of ischemic injury) and QRS changes (index of necrosis), and their relationship. ECG parameters used included the sum of ST-segment elevations, number of sites showing such changes, the sum of R waves from all leads with ST-segment elevations, and a QRS score of all leads showing ischemic injury on admission. Sums of ST-segment elevations either did not show statistically significant change throughout the study or showed unexplained re-elevation (anterior MI), or completed their downward course in 6 hours (inferior MI). The number of sites showing ST-segment elevations either remained unchanged (inferior MI), or declined at 2 hours without further change. However changes in the sum of R waves or QRS scores were gradual and completed most of their overall course within 24 hours. Decline of sums of R waves correlated well with sums of ST-segment elevations on admission (inferior MI), and the number of sites showing changes (anterior MI). The course of changes in QRS complexes is more reliable than the alterations of ST-segment elevations for the monitoring of evolution of MI. The former, assessed frequently in the first 24 hours, should be useful in the evaluation of therapies for patients with MI.

Precordial ST-segment mapping 3. Stability of maps in the early phase of acute myocardial infarction

To evaluate the stability of precordial ST-segment mapping techniques in assessing ischemic myocardial injury, we studied 28 patients with acute anterior myocardial infarction using a 49-lead electrocardiographic system (1 mV. = 10 mm.). The sum of ST elevations in millimeters was taken as an index of ischemic injury, and remained stable in two consecutive maps made approximately one hour apart (65.8 +/- 8.4 vs. 63.8 +/- 8.7 mm.). The number of sites showing ST elevation larger than or equal to one mm. was taken as an index of extent of injury, and showed a small but statistically significant decline (23.9 +/- 4.5 vs. 22.3 +/- 4.2 mm.) during the same time interval. Blood pressure and heart rate remained stable. Changes in the map were observed in five patients, but could be explained in four by abrupt alterations in clinical status. In one patient no explanation for alterations in the map was apparent. We conclude that precordial ST segment maps are usually stable in the early stages of anterior myocardial infarction, but should be used to evaluate interventions only with careful clinical monitoring, and with the knowledge that occasional unexplained variations do occur.

LDH release into perfusates of preserved kidneys.

The measurement of lactate dehydrogenase (LDH) release into perfusates after hypothermic storage was found to be a reliable index of ischemic injury of rabbit kidneys. Kidneys were exposed to warm and cold ischemia for varying periods. Each kidney was perfused before and after storage at simple hypothermia with 25 ml of a modified Collins solution. The venous effuent was collected in 5 ml fractions. Total LDH activity was measured in the first fraction after storage and used as a measure of ischemic tissue damage. It was confirmed that increasing the period of cold ischemia result in significant increases in LDH activity. The release of LDH into perfusates was then used to compare kidney damage after preservation with various fluids. With this method, it was not possible to demonstrate any difference in the extent of tissue damage after preservation with sodium-rich vs. potassium-rich perfusion fluid. Addition of steroids, vitamins and essential amino acids did not prevent or reduce tissue damage, estimated in this way. The effects of adding cryoprotectants to the perfusion fluid varied; LDH release following addition of 5% DMSO was significantly greater, and after addition of 5% glycerol smaller than the release after perfusion with a modified Collins solution alone. Stepwise addition of DMSO up to 20% resulted in serious tissue damage with a large LDH release into the perfusate.