Significance of negative U waves in the precordial leads during anterior wall acute myocardial infarction

Inverted U Waves-Red Flags in Electrocardiograms

This case report presents the electrocardiogram findings of a patient in their 50s with intermittent compression-like pain in the chest and a history of hypertension and diabetes.

The U-wave: A remaining enigma of the electrocardiogram

The U-wave's electrophysiological origin remains unknown and is subject to debate. It is rarely used for diagnosis in clinical practice. The aim of this study was to review new information regarding the U-wave. Further to present the proposed theories behind the U-wave's origin along with potential pathophysiologic and prognostic implications related to its presence, polarity and morphology.

METHOD

Literature searches were conducted to retrieve publications related to the electrocardiogram U-wave in the literature database Embase.

RESULTS

The review of the literature revealed the following major theories that will be discussed; late depolarisation, delayed or prolonged repolarisation, electro-mechanical stretch and IK1 dependent intrinsic potential differences in the terminal part of the action potential. Various pathologic conditions were found to correlate with the presence and properties of the U-wave, such as its amplitude and polarity. Abnormal U-waves can, for example, be observed in coronary artery disease with ongoing myocardial ischemia or infarction, ventricular hypertrophy, congenital heart disease, primary cardiomyopathy and valvular defects. Negative U-waves are highly specific for the presence of heart diseases. Concordantly negative T- and U-waves are especially associated with cardiac disease. Patients with negative U-waves tend to have higher blood pressure and history of hypertension, higher heart rate, cardiac disease and left ventricular hypertrophy compared to subjects with normal U-waves. Negative U-waves have been found to be associated with increased risk of all-cause mortality, cardiac death and cardiac hospitalisation in men.

CONCLUSIONS

The origin of the U-wave is still not established. U-wave diagnostics may reveal cardiac disorders and the cardiovascular prognosis. Including the U-wave characteristics in the clinical ECG assessment may be useful.

Validation of an algorithm to reveal the U wave in atrial fibrillation

Major cardiac organisations recommend U wave abnormalities should be reported during ECG interpretation. However, U waves cannot be measured in patients with atrial fibrillation (AF) due to the obscuring fibrillatory wave. The aim was to validate a U wave measurement algorithm for AF patients. Multi-beat averaging was applied to ECGs of 25 patients during paroxysms of AF and the presence of U waves compared to those from the same patients during sinus rhythm (SR). In a further database of 10 long-term AF recordings, the number of beats for effective U wave extraction by the algorithm was calculated. U waves were revealed in all AF recordings and there was no significant difference between the presence of U waves in AF and SR (p = 0.88). U wave amplitude was significantly increased in AF (mean (s.d.) amplitude 55 (39) AF vs 37 (28) μV SR, p = 0.005). The presence of U waves could easily be discerned when as few as 10 beats were used in the algorithm. The study demonstrates the validity of the algorithm to reveal U waves in AF recordings. The algorithm offers the potential to detect U wave abnormalities in patients with AF.

Wellens' syndrome or inverted U-waves?

This report describes an example of a patient with chest pain and classic electrocardiographic changes consistent with ischemia in the proximal left anterior descending coronary artery (LAD) territory. This electrocardiogram (ECG) abnormality is known as Wellens' syndrome. However, the same abnormality is also described as inverted U-waves. The significance of this abnormality and the controversy of describing this syndrome is reviewed and discussed.

Exercise-induced negative U waves in precordial leads as a marker of viable myocardium in patients with recent anterior myocardial infarction

Patients with recent anterior myocardial infarction and a significant stenosis in the left anterior descending coronary artery were divided into two groups according to the presence (Group A, n=24) or absence (Group B, n=77) of negative U waves in the precordial leads during exercise stress test to compare the coronary arteriographic findings. Both total occlusion of the left anterior descending coronary artery (79% vs. 31%, P<0.01)) and good (index=2, 3) collateral circulation to the territory of this artery (92% vs. 36%, P<0.01) were observed more often in group A than in group B. In order to determine whether detection of exercise-induced negative U waves in precordial leads can predict the presence of viable myocardium, the 56 patients (20 of group A and 36 of group B) with total or subtotal occlusion of the left anterior descending coronary artery were studied further. The coronary arteriographic and exercise 201Tl scintigraphic findings were compared between the groups. Good collateral circulation to the territory of this artery was observed significantly (P<0.05) more often in group A (100%) than in group B (61%). Patients with multivessel disease were significantly (P<0.05) more prevalent in group A (70%) than in group B (33%). The incidence of a significant partial redistribution in the anteroseptal area in the 20Tl images 4 h after exercise was significantly (P<0.01) higher in group A (85%) than in group B (39%). In 29 patients with anterior Q-wave myocardial infarction and exercise-induced ST elevation in precordial leads, a significant 201Tl redistribution in the anteroseptal area was observed in 8 (80%) of 10 patients of group A in contrast to only 4 (21%, P<0.05) of 19 in group B. In the diagnosis of the viability associated with 201Tl redistribution in the anteroseptal area by the finding of exercise-induced negative U waves, the sensitivity was 67% and the specificity was 88% in these patients. We conclude that exercise-induced negative U waves in precordial leads are a convenient and specific marker for the presence of viable myocardium in patients with recent anterior myocardial infarction.

Exercise-induced U-wave alterations as a marker of well-developed and well-functioning collateral vessels in patients with effort angina

OBJECTIVES

We sought to determine whether exercise-induced U-wave alterations are observed in association with well-developed and well-functioning collateral vessels.

BACKGROUND

Although exercise-induced electrocardiographic (ECG) U-wave alterations including negative and prominent U waves have been established as a marker of significant or critical narrowing of a major coronary artery, the relation between this finding and the degree of collateral development has not yet been determined.

METHODS

Patients with stable effort angina were divided into two groups according to the presence (group A, n = 46) or absence (group B, n = 79) of exercise-induced either negative or prominent U waves in the precordial leads; the clinical profiles, coronary angiographic findings and also ischemic status during 60 s of coronary balloon occlusion were compared between the two groups.

RESULTS

The incidence of severe angina (CCS [Canadian Cardiovascular Society] class III or IV) was higher (p < 0.05) in group A (52%) than in group B (32%) patients. Good collateral vessels (Rentrop grade 2 or 3) into the perfusion territory of the culprit vessel were observed more frequently (p < 0.05) in group A (70%) than in group B (43%) patients. Coronary balloon angioplasty was carried out in 23 patients of group A and 40 patients of group B. Both ischemic ST changes (52% vs. 85%) and angina (57% vs. 80%) during balloon inflation were less (p < 0.05) frequently observed in group A than in group B. The incidence of no apparent myocardial ischemia with ST deviation or angina during the balloon inflation was higher (p < 0.05) in group A (39%) than in group B (10%) patients. In the prediction of the absence of myocardial ischemia during balloon inflation by the presence of exercise-induced U-wave alterations, the sensitivity was 69% (9/13) and the specificity was 72% (36/50) in the study patients.

CONCLUSIONS

Exercise-induced U-wave alterations are a marker for well-developed collateral circulation in patients with stable but severe effort angina. This finding is also highly predictive of the absence of myocardial ischemia during transient coronary balloon occlusion and possibly of low-risk for development of acute myocardial infarction or hemodynamic instability upon abrupt closure of the culprit coronary artery.

Associations between different status of myocardial ischemia and ischemia-related negative or positive epicardial U-waves: observations during coronary angioplasty

This study examined the relationships between the polarity of the U wave on intracoronary electrocardiogram (ECG) and the status of myocardial ischemia during angioplasty. The ECG features of ischemia-related U waves were also evaluated. Among 63 patients with intracoronary ECGs adequate for analysis of U waves, there were 26 patients showing a change of the U wave to a negative direction and 18 patients showing a change to a positive direction from baseline to coronary occlusion. Among these patients, 10 of the former showed a distinct change in polarity of the U wave from positive to negative (group A), and 7 of the latter patients showed the opposite change (group B). Patients in group B had a higher incidence of prior myocardial infarction (86% vs 30%; P < .05), presence of an abnormal Q wave on intracoronary ECG (71% vs 20%; P < .05), poor wall motion in the angioplasty-related area (100% vs 30%; P < .01), and lower left ventricular ejection fraction (55.7% +/-8.1% vs 66.6% +/- 4.5%; P < .01) than patients in group A. The remaining patients (other than groups A and B) showing U wave change in a negative (n = 16) or positive (n = 11) direction presented with similar features to those in groups A or B, respectively. The ECG features of several types of ischemia-related U wave were determined by analysis of intracoronary ECG obtained from the patients in groups A and B. In group A, the Bazett-corrected Q (positive U) interval measured at baseline (myocardial state; near normal) was significantly shorter than the Q-(negative U) interval measured during coronary occlusion (acute ischemia) (0.518 +/- 0.031 s vs 0.579 +/- 0.046 s; P < .01). In group B, the Q-(negative U) interval measured at baseline (chronic ischemia) was longer than the Q-(positive U) interval measured during angioplasty (acute-on-chronic ischemia) (0.582 +/- 0.034 s vs 0.501 +/- 0.027 s; P < .001). Thus, intracoronary ECG recorded during angioplasty in the present study revealed physiologic U wave, two types ("acute" and "chronic") of ischemia-related negative and one type ("pseudonormal") of ischemia-related positive U waves, each of which appeared in a different status of myocardial ischemia and possessed characteristic ECG features in its appearance.

Relation between negative U waves in precordial leads on the admission electrocardiogram and time course of left ventricular wall motion in anterior wall acute myocardial infarction

This study indicates that patients with anterior wall acute myocardial infarction showing negative U waves in the precordial leads on the admission electrocardiogram have greater improvement in left ventricular wall motion in the infarct region between 1 and 6 months after acute myocardial infarction. This suggests that these patients have a larger amount of stunned myocardium in the infarct region.