[Metabolism of the afferent system]

The delayed activation wave in non-ST-elevation myocardial infarction

BACKGROUND

Little is known about the relationship between the electrocardiographic characteristics and the infarct related artery (IRA) in non-ST-elevation myocardial infarction (NSTEMI). We found a curious phenomenon in electrocardiograms of patients with acute occlusion of left circumflex artery in NSTEM: A notch or deflection was often present in the terminal QRS complex in leads II,III and aVF or I,aVL . The objective of this study was to determine whether the previously unreported ECG phenomenon that we have found in NSTEMI could identify the culprit artery in non-ST-elevation myocardial infarction.

METHODS AND RESULTS

Our study included 218 NSTEMI patients who presented to our institution and underwent coronary angiography within 24 hours of admission. For convenience, 'N' wave was defined as a notch or deflection in the terminal QRS complex of the surface ECG. The duration of QRS with N wave before PCI was more prolonged than the duration of QRS without N wave (121 ± 12 ms vs 106 ± 11 ms, P<0.01). In the LCX group, 66(77%) patients had N wave in leads II, III and aVF, whereas only 5(6%) patients in the LAD group and 9(18%) patients in the RCA group had such ECG feature (P<0.001). A greater proportion of patients in the LCX group also had N waves in leads I and aVL (P<0.001). N wave in leads II, III and aVF was associated with 77% sensitivity and 89% specificity, respectively. N wave in leads I and aVL was associated with 64% sensitivity and 96% specificity, respectively.

CONCLUSION

The abnormal waveform in terminal QRS complex in NSTEMI ,which is described above, is the delayed activation wave of left ventricular basal region which the left circumflex artery supplies. It is associated with a higher specificity and higher sensitivity for culprit LCX in non-ST-elevation myocardial infarction. The delayed activation wave is a new pattern of ischemia in ECG.

Myocardial salvage for ST-elevation myocardial infarction with terminal QRS distortion and restoration of brisk epicardial coronary flow

Recently, it has been reported that large infarcts associated with terminal QRS distortion (QRSDIS) on the admission electrocardiograms of patients with ST-elevation myocardial infarctions (STEMIs) may be caused by a failure to achieve thrombolysis in myocardial infarction (TIMI) grade 3 flow after primary percutaneous coronary intervention (PCI). However, the relationship between QRSDIS and final infarct size when TIMI grade 3 flow could be achieved by primary PCI is still unclear. Sixty-two consecutive patients with first anterior STEMI and who achieved TIMI grade 3 flow by primary PCI were classified into two groups according to the presence (Group A, n = 18) or absence (Group B, n = 44) of QRSDIS. Two weeks after the onset of acute myocardial infarction, Group A had a larger left ventricular (LV) end-systolic volume index (LVESVI) and a lower LV ejection fraction (LVEF) than Group B (LVESVI: 38 +/- 13 vs 31 +/- 12 ml/m(2), P = 0.025: LVEF: 42% +/- 10% vs 51% +/- 10%, P = 0.004). Through multivariate analysis, independent predictors of poor LV systolic function (LVEF < 40%) were determined to be the presence of QRSDIS (odds ratio 21.04, P = 0.021) and proximal left anterior descending artery occlusion (odds ratio 16.15, P = 0.033). Myocardial damage could not be reduced in patients experiencing STEMI with QRSDIS, even when TIMI grade 3 flow could be achieved by primary PCI, as much as in patients experiencing STEMI without QRSDIS.

Grade 3 ischemia on the admission electrocardiogram predicts rapid progression of necrosis over time and less myocardial salvage by primary angioplasty

BACKGROUND

Among patients with ST-elevation acute myocardial infarction, those with terminal QRS distortion (grade 3 ischemia) have higher mortality and larger infarct size (IS) than patients without QRS distortion (grade 2 ischemia).

METHODS

We assessed the relation of baseline electrocardiographic ischemia grades to area at risk (AR) and myocardial salvage [100 (AR-IS)/AR] in 79 patients who underwent primary angioplasty for first ST-elevation acute myocardial infarction and had technetium Tc 99m sestamibi single-photon emission computed tomography before angioplasty (AR) and at predischarge (IS). Patients were classified as having grade 2 ischemia (ST elevation without terminal QRS distortion in any of the leads, n = 48), grade 2.5 ischemia (ST elevation with terminal QRS distortion in 1 lead, n = 16), or grade 3 ischemia (ST elevation with terminal QRS distortion in >2 adjacent leads, n = 15).

RESULTS

Time to treatment was comparable among groups. AR was comparable among groups (38% +/- 20%, 33% +/- 23%, and 34% +/- 23%, respectively; P = .70). There were no differences among groups in residual myocardial perfusion (severity index 0.28 +/- 0.12, 0.29 +/- 0.16, and 0.30 +/- 0.15 in grades 2, 2.5, and 3 ischemia, respectively; P = .97). In contrast, there was a trend toward lower myocardial salvage (45% +/- 32%) in the grade 3 group than in the grade 2 (65% +/- 33%) and grade 2.5 (65% +/- 40%) groups ( P = .16). Salvage was dependent on time only in the grade 3 group. Spearman rank correlation coefficients between time to treatment and percentage salvage were 0.003 ( P = .99), -0.24 ( P = .38), and -0.63 ( P = .022) for grades 2, 2.5, and 3, respectively.

CONCLUSIONS

Patients with grade 3 ischemia have rapid progression of necrosis over time and less myocardial salvage. This admission pattern is a predictor of myocardial salvage by primary angioplasty.

The electrocardiogram in ST elevation acute myocardial infarction: correlation with coronary anatomy and prognosis

The electrocardiogram is considered an essential part of the diagnosis and initial evaluation of patients with chest pain. This review summarises the information that can be obtained from the admission electrocardiogram in patients with ST elevation acute myocardial infarction, with emphasis on: (1) prediction of infarct size, (2) estimation of prognosis, and (3) the correlations between various electrocardiographic patterns and the localisation of the infarct and the underlying coronary anatomy.

Differentiation of the atrioventricular conducting system of the heart

The structure and function of the atrioventricular conducting system of the heart, and its relationship to the myocardium, are examined from a developmental point of view. On the basis of information derived from electron micrographic, electrophysiologic, and developmental studies of heart tissue, it is concluded that: (1) The idea of the syncytial nature of the heart lacks a sound anatomic basis. (2) Cytodifferentiation during embryonic cardiogenesis results in the development of at least 2 distinct populations of cells: those comprising the bulk of the myocardium and a second type, the specialized cells of the conductive tissue, which differs in histology, biochemistry, and physiology. (3) The common view of the myocardium as a spontaneously active tissue may require revision, since several lines of evidence appear to indicate that myocardial cells are quiescent until stimulated by an extrinsic source. Under normal circumstances, this stimulus source is the conductive tissue.

Prognostic significance of the admission electrocardiogram in acute myocardial infarction

OBJECTIONS

We sought to access the ST segment and the terminal portion of the QRS complex in the initial electrocardiogram (ECG) as tools to predict outcome in patients with acute myocardial infarction given thrombolytic therapy.

BACKGROUND

Previous studies assessing early risk stratification of patients with acute myocardial infarction by ECG criteria have focused on the number of leads with ST segment elevation or the absolute magnitude of ST deviation. A new classification independent of the absolute values of ST deviation was pursued.

METHODS

Patients with ST elevation and positive T waves in at least two adjacent leads who received thrombolytic therapy were classified into two groups based on the absence (1,232 patients) or presence (1,371 patients) of distortion of the terminal portion of the QRS complex on the admission ECG.

RESULTS

There were no differences between groups in the prevalence of previous angina, hypertension, current smoking, anterior infarction, time from onset of symptoms to therapy of type of thrombolytic regimen. Patients with QRS distortion were less likely to have had a previous infarction (12.0% vs. 18.4%, p = 0.02) or diabetes mellitus (16.9% vs. 21.4%, p = 0.003). They had higher peak creatine kinase levels (1,617 +/- 1,670 vs. 1,080 +/- 1,343 IU, p = 0.00001). Hospital mortality for those with and without QRS distortion was 6.8% and 3.8%, respectively (p = 0.0008). Multivariable logistic regression analysis confirmed that hospital mortality was independently associated with distortion of terminal portion of the QRS complex (odds ratio 1.78, 95% confidence interval 1.19 to 2.68, p = 0.004).

CONCLUSIONS

Distortion of the terminal portion of the QRS complex on the admission ECG is independently associated with a higher hospital mortality rate in patients with acute myocardial infarction given thrombolytic therapy.

Prognostic significance of the initial electrocardiographic pattern in a first acute anterior wall myocardial infarction

The availability of potent, but potentially dangerous, types of reperfusion therapy for acute myocardial infarction (AMI) has forced us to refine our tools for early and accurate diagnosis and for early risk stratification of patients with evolving AMI. The estimation of risk has to be made shortly after admission, when only the history, physical examination, and the ECG are available. This study was undertaken to compare in-hospital mortality with different patterns of the ECG obtained at admission in 147 consecutive patients with an evolving first AMI of the anterior wall. By using a new classification of the admission ECG, it was possible to divide the patients into 3 groups: (1) group A contained 12 patients with tall peaked T waves in the involved leads, without ST segment elevation; (2) group B comprised 77 patients with abnormal T waves and ST elevation, but without major changes in the terminal portion of the QRS complex; and (3) group C comprised 58 patients with abnormal T waves, ST elevation, and distortion of the terminal portion of the QRS. The mortality was 0, 3 percent, and 29 percent in groups A, B, and C, respectively (chi 2 = 22.91; p = 0). By using a logistic regression model, it was found that the initial ECG pattern alone is a strong predictor of in-hospital mortality in patients with an evolving anterior wall AMI. The predicted probabilities of death in groups A, B, and C are 0.0016, 0.025, and 0.29, respectively. This simple classification of the initial ECG pattern in patients with a first AMI of the anterior wall may enable the differentiation of patients with low in-hospital mortality (groups A and B) and of those with an in-hospital mortality of almost 30 percent (group C).

Ultrastructural effects induced by global ischaemia on the AV node compared with the working myocardium. A qualitative and morphometric investigation on the canine heart

The cardiac conduction system is considered to be particularly resistant to ischaemia. Nevertheless, following open heart surgery with short periods of ischaemia disturbances in AV conduction or ventricular arrhythmia have been reported. We compared the ultrastructure of AV node and working myocardium following 30 min global ischaemia at 25 degrees C, during pure ischaemia and with HTK cardioplegia qualitatively and morphometrically. After 30 min of pure ischaemia, interstitial and intracellular oedema together with considerable changes in organelles in AV nodes predominate over mainly cellular oedema in working myocardium. Sometimes irregular overcontractions of sarcomeres occur in the AV node, though very seldom in working myocardium. In pure ischaemia, mitochondrial swelling is comparable in both types of tissue. Following HTK cardioplegia and 30 min ischaemia, cellular oedema and mitochondrial swelling are significantly reduced in AV nodal cells and working myocardium, but remain more extensive in the AV nodes. Irregularities in the contractile state of sarcomeres are not observed. The extent of the ultrastructural alterations corresponds to the degree of metabolic change in the working myocardium. Thus, despite considerable differences during pure ischaemia and HTK cardioplegia, ultrastructurally the AV nodal cells do not display a greater resistance to ischaemia than working myocardium.

Differentiation of Purkinje fibres and ordinary ventricular and atrial myocytes in the bovine heart: an immuno- and enzyme histochemical study

The differentiation of Purkinje fibres and ordinary ventricular and atrial myocytes in bovine hearts was studied with specific antibodies against M-line proteins (MM-creatine kinase and myomesin) and with enzyme histochemistry (succinate dehydrogenase and mitochondrial glycerol-3-phosphate dehydrogenase). MM-creatine kinase was detected at an earlier stage in Purkinje fibres and atrial myocytes than in ordinary ventricular myocytes. The findings are in agreement with previous ultrastructural observations that an earlier appearance of a dense M-band occurs in Purkinje fibres than in ordinary ventricular myocytes. Myomesin was detected in all three cell types even at early foetal stages, in accordance with suggestions that it is an integral component of the myofibrillar structure. The activity of succinate dehydrogenase gradually increased in both ordinary ventricular and atrial myocytes, while the activity of mitochondrial glycerol-3-phosphate dehydrogenase was high at different stages of early foetal development in the two tissues, finally becoming low in the adult stage. The activity of succinate dehydrogenase and mitochondrial glycerol-3-phosphate dehydrogenase seemed to remain unchanged in the Purkinje fibres from early to late foetal stages. The present study shows that the Purkinje fibres are already different from ordinary ventricular myocytes at early foetal stages and that the two cell types differentiate in different ways. It is concluded that there are also developmental differences between ordinary ventricular and atrial myocytes.

Enzyme histochemical studies on the conducting system of the human heart

In this communication, the results of applying various histochemical techniques for the localization of oxidoreductases, transferases, hydrolases and isomerases in the human heart are presented. The Purkinje fibres of the atrioventricular conducting system of the human heart differ from the myocardium proper in containing a slightly higher activity of most of the glycolytic and gluconeogenetic enzymes investigated. The relatively higher activity of 6-phosphofructokinase, the key enzyme in anaerobic carbohydrate metabolism, is especially noteworthy. On the other hand, the activities of some of the enzymes that play a part in the aerobic energy metabolism is slightly less than those in the myocardium fibres. As for the activity of the NADPH regenerating enzymes, the activity of 6-phosphogluconate dehydrogenase and malate dehydrogenase (oxaloacetate-decarboxylating) is somewhat higher, and the activity of glucose-6-phosphate dehydrogenase similar, in the Purkinje fibres compared to that in the myocardial fibres. The activity of myosin ATPase is similar for both types of fibre. Likewise, the fibres of the conducting system and of the myocardium show a similar activity of acid phosphatase, beta-glucuronidase, non-specific naphthylesterase and peroxidase. The neurogenic function of the conducting system of the human heart was demonstrated by the high activity of acetylcholinesterase in the Purkinje fibres and in the atrioventricular node. All these histochemical findings in Purkinje fibres are similar at widely differing levels of the conducting system.

Enzyme histochemical studies on the Purkinje fibers of the atrioventricular system of the bovine and porcine hearts

In this communication the results of applying various histochemical semipermeable membrane techniques to the localization of several enzymes in bovine and porcine heart are presented. The Purkinje fibers of the atrioventricular conducting system of the bovine heart differ from the myocardium proper in containing a greater activity of the glycolytic and gluconeogenetic enzymes--lactate dehydrogenase, glyceraldehyde-phosphate dehydrogenase, hexokinase, glucosephosphate isomerase and phosphoglucomutase, and less activity of the aerobic enzymes--NADH: nitroBT oxidoreductase and isocitrate dehydrogenase (NADP+). The metabolic reactions obtained with Purkinje fibers of the porcine heart are less pronounced. These histochemical findings are in accordance with the impression that Purkinje fibers, compared with the common myocardial fibers, have a higher rate of anaerobic metabolism and a lower rate of aerobic metabolism. The activity of the NADPH regenerating enzymes glucose-6-phosphate dehydrogenase and phosphogluconate dehydrogenase (decarboxylating), and the activity of acid hydrolases such as non-specific esterase and acid phosphatase is higher in the Purkinje fibers of both the bovine and porcine heart.

Intra-His bundle block complicating acute inferior myocardial infarction

The unexpected findings of atrioventricular block or delay in the His bundle and proximal branches are described in a 51-year-old man with acute inferior myocardial infarction with narrow QRS complexes. With the information from the His bundle electrogram, the site of atrioventricular block is precisely localized.

Early and late effects of coronary artery occlusion on canine Purkinje fibers

The electrophysiological characteristics of subendocardial Purkinje and myocardial cells were studied during acute (within 30 minutes) and chronic (after 10 days) phases of myocardial infarction. Endocardial Purkinje and myocardial electrograms were recorded in vivo with bipolar electrodes before and after occlusion of the anterior descending coronary artery. Also, intracellular and extracellular potentials were recorded in vitro from the endocardial surface of infarcted regions of hearts excised during the acute and chronic phases. In the acute phase, Purkinje and myocardial potentials within the ischemic zone deteriorated in vivo, but they were not markedly delayed. Intracellular recordings in vitro showed partial depolarization of both Purkinje and myocardial cells. In the chronic phase, extracellular and intracellular Purkinje potentials recorded in vivo and in vitro from the infarcted zone usually did not differ from normal. No myocardial potentials were recorded from the endocardial surface of the chronic infarcts. Thus, subendocardial Purkinje and myocardial cells are affected early in infarction, but many Purkinje cells survive and return to normal.

Histopathology of heart block complicating acute myocardial infarction. Correlation with the His bundle electrogram

Histopathological studies of the conduction system were related to His bundle electrogram recordings in seven patients with acute myocardial infarction and atrioventricular (A-V) conduction disturbances. The three patients with inferior infarctions had normal width QRS complexes and delay or block of the impulses above the His bundle. Recent ischemic changes were present in the A-V node in two cases and in the distal conduction system in all three cases. In the four patients with antero-septal infarction and right bundle branch block (RBBB), either the H-V interval was prolonged or block was present below the H spike. The A-H interval was normal in each of these cases, and the A-V node was not affected by the recent infarction. The right bundle branch was involved in all four of these cases and two patients also had involvement of the left bundle branch. In general there was a good correlation between the sites of heart block as defined by the His bundle electrogram and the histopathological analysis of the cardiac conduction system.