U wave inversion

Electrical Remodeling of Ventricular Repolarization Abnormality after Treatment in Pheochromocytoma: U Wave Finding in a Retrospective Analysis

Background

Pheochromocytoma is a rare neuroendocrine tumor, clinically characterized by high blood pressure, palpitations, and headache. It is often associated with abnormalities of the ventricular repolarization phase; the dispersion of ventricular repolarization is the basis for ventricular arrhythmias (torsion de point, ventricular tachycardia or ventricular fibrillation).

Objectives

Analysis of abnormal ventricular repolarization focused on the presence and amount of U wave in patients affected by pheochromocytoma and its modification after surgery.

Materials and Methods

We reviewed pathology records of 722 patients admitted for adrenal nodule or suspected chromaffin-cell tumor and identified 39 patients affected by pheochromocytoma. Metanephrine, normetanephrine, and 3-methoxytyramine have been assessed by determining concentrations in 24-hour urine collection. Standard 12-lead electrocardiogram records have been reviewed with analysis of heart rate, P wave, PR interval, QRS duration, QTc, and U wave. Then we selected and compared 22 patients of 39 affected by pheochromocytoma, with both clinical and electrocardiographic data before and after surgery.

Results

In our cohort of 39 patients affected by pheochromocytoma, we found U wave in ECG, before treatment, in 82.8 percent of patients, while only 37.0 percent after treatment (p<0.001) and we observed a statistically significant correlation between this wave and the urinary metanephrine. After surgery, in the selected 22 patients, we observed a clear significant reduction in systemic blood pressure, fasting glucose, metanephrine, normetanephrine, and 3-methoxytyramine. We found a significant reduction of U wave presence and leads involved in these patients after surgery (90.9% versus 9%). We observed a linear correlation between the amount of U waves in 12-lead electrocardiogram and metanephrine (r²=0.333, p=0.015), 3-methoxytyramine levels (r²=0.458, p=0.006), and tumor size (r²=0.429, p=0.003).

Conclusions

In our retrospective analysis, patients affected by pheochromocytoma presented U wave in electrocardiogram. The presence and amount of U wave were associated with the metanephrine levels and the tumor size with significant reduction after surgical removal.

The measurement of the Q-T interval of the electrocardiogram

The sources of error in determination of the beginning of QRS and the end of T during measurement of the Q-T duration are analyzed. An important error is confusion of an elevated U wave with the T wave, resulting in the diagnosis of a prolonged Q-T. In such cases, some of the precordial leads usually show a notch or kink between T and U which indicates approximately the end of T. If these criteria are used, the true corrected Q-T duration in hypopotassemia without hypocalcemia is not prolonged, but normal or shortened, corresponding to an earlier appearance of the second heart sound.

Transient terminal U wave inversion as a more specific marker for myocardial ischemia

Transient U wave inversion can be caused either by regional myocardial ischemia or by an elevation of systemic blood pressure. The characteristics of U wave inversion during chest pain attacks in 21 patients with variant angina were compared with those observed in 38 patients with hypertension without apparent ischemic heart disease. Differentiation was possible according to the ECG phase in which U wave inversion appeared. U wave inversion was considered to be significant if there was a discrete negative deflection of more than 0.05 mV within the TP segment. U wave inversion proceeded to positive deflection of U wave in patients with hypertension without ischemic heart disease (initial U wave inversion). In contrast, inverted U wave occurred after positive U wave deflection during attacks in patients with variant angina (terminal U wave inversion). When cold pressor test was performed in patients with variant angina during treatment with calcium entry blockers, no patient had either anginal attacks or ischemic ST-segment deviation, but 9 of 21 patients (43%) had transient initial U wave inversion, which was followed by positive U wave deflection. U wave inversion can be classified as initial U wave inversion and terminal U wave inversion according to the phasic relationship to positive U wave deflection; the latter is observed in association with regional myocardial ischemia. The former seems to be related to elevated blood pressure rather than to myocardial ischemia.

Exercise-induced U-wave inversion as a marker of stenosis of the left anterior descending coronary artery

The prevalence and cineangiographic correlates of exercise-induced inversion of U waves were studied in 248 patients. Exercise-induced U-wave inversion was observed in 36 patients (15%), of whom 35 had greater than or equal to 75% stenosis in one or more of the major coronary arteries. The proximal left anterior descending or left main coronary artery was involved in 33 of these patients, including 24 patients with no electrocardiographic evidence of anterior myocardial infarction. Exercise-induced U-wave inversion was observed in the absence of an abnormal resting 12-lead ECG. Only one of the 82 patients (1.2%) without significant coronary artery disease demonstrated exercise-induced U-wave inversion, and this patient had a primary cardiomyopathy. We conclude that exercise-induced inversion of the U-wave is highly predictiveof significant coronary artery disease and, more specifically, of disease of the proximal left anterior descending coronary artery.

Morphologic aspects of the negativity of the U wave and their corresponding electrocardiographic and clinical data

The negative U wave has been studied in 200 electrocardiograms. Six different types of negativity of the U wave are recognized; a seventh type includes the alterations of the T-U segment. Electrocardiographic and clinical data are correlated with these changes. Two hypotheses to explain the varying morphology of the negative U wave are discussed.

Isolated U wave negativity

Inversion of U as the only abnormal electrocardiographic finding is here shown to be the first change to occur in certain cases of hypertension, coronary artery sclerosis, and other organic heart disease. It is also found in association with certain metabolic and electrolyte changes. Its recognition will enhance the value of the electrocardiogram in clinical diagnosis.

The lesser electrocardiographic signs of cardiac pain

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