The negative U wave: a pathogenetic enigma but a useful, often overlooked bedside diagnostic and prognostic clue in ischemic heart disease

Identification of the Vessels Causing Myocardial Ischemia by a Synthesized 18-Lead Electrocardiogram Obtained After the Master Two-Step Exercise Test in a Patient With Effort Angina

A synthesized 18-lead electrocardiograph is a specialized technology that mathematically computes the virtual electrocardiographic waveforms of the right chest leads (V3R, V4R, and V5R) and posterior leads (V7, V8, and V9) based on a standard 12-lead electrocardiograph input without additional lead placement or techniques. Synthesized 18-lead electrocardiography is a useful test for the identification of the culprit coronary arteries in patients with ST-segment elevation myocardial infarction of the right ventricular wall or the posterior/lateral left ventricular wall, which are often missed on standard 12-lead electrocardiography. However, few studies have examined the usefulness of this modality during exercise stress testing. We present a case of a 78-year-old man with a two-month history of typical angina. The synthesized 18-lead electrocardiogram obtained just after the Master two-step exercise test revealed ST-segment shifts in multiple leads, including synthesized V4R, V5R, and V7-9 leads, and U-wave changes in some leads, including the synthesized V9 lead. The diagnosis of the culprit coronary arteries causing exercise-induced myocardial ischemia is discussed with reference to coronary angiographic findings. This modality could potentially increase the sensitivity and specificity for the detection of coronary artery disease and accurately pinpoint the site of the lesion. If an electrocardiograph can display a synthesized 18-lead electrocardiogram, it should be used when evaluating the waveform due to myocardial ischemia.

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.

Early/Subtle Electrocardiography Features of Acute Coronary Syndrome and ST-Segment Elevation Myocardial Infarction

Chest pain is one of the most common presenting complaints in the emergency department. Interpreting a 12-lead electrocardiography (ECG) for evidence of ischemia is always challenging. Frank ECG changes such as ST-segment elevation and ST-segment depression can be easily identified by emergency physicians. However, identifying subtle or early features of ACS in the 12-lead ECG is essential in preventing significant mortality and morbidity from ACS. In the following case series, we describe five of the subtle/early ECG changes of ACS, namely (1) T-wave inversion in lead aVL; (2) terminal QRS distortion; (3) hyperacute T-waves; (4) negative U-waves in precordial leads; and (5) loss of precordial T-wave balance. In all these cases, the initial 12-lead ECG showed only subtle/early ECG changes which were followed up with serial ECGs which progressed to STEMI.

Cardiac Mechano-Electric Coupling: Acute Effects of Mechanical Stimulation on Heart Rate and Rhythm

The heart is vital for biological function in almost all chordates, including humans. It beats continually throughout our life, supplying the body with oxygen and nutrients while removing waste products. If it stops, so does life. The heartbeat involves precise coordination of the activity of billions of individual cells, as well as their swift and well-coordinated adaption to changes in physiological demand. Much of the vital control of cardiac function occurs at the level of individual cardiac muscle cells, including acute beat-by-beat feedback from the local mechanical environment to electrical activity (as opposed to longer term changes in gene expression and functional or structural remodeling). This process is known as mechano-electric coupling (MEC). In the current review, we present evidence for, and implications of, MEC in health and disease in human; summarize our understanding of MEC effects gained from whole animal, organ, tissue, and cell studies; identify potential molecular mediators of MEC responses; and demonstrate the power of computational modeling in developing a more comprehensive understanding of ‟what makes the heart tick.ˮ.

The electrocardiographic profile of patients with angina pectoris

Angina pectoris is a common disabling disorder and a clinical syndrome, caused by myocardial ischemia; an imbalance between myocardial oxygen supply and myocardial oxygen consumption. Thus, ischemia produces a typical series of events such as metabolic and biochemical alterations which lead to impaired ventricular relaxation and diastolic dysfunction, impaired systolic function, and electrocardiographic abnormalities and painful symptoms of angina. Transmembrane ionic currents are responsible for the cardiac potentials that are recorded as the electrocardiogram (ECG). The electrocardiographic profile of patients with angina pectoris is variate. The electrocardiogram provides critical information for both diagnosis and prognosis, particularly when a tracing is obtained during the episodes of pain. A completely normal electrocardiogram does not exclude the possibility of acute coronary syndrome. Serial ECG tracings improve the clinician's ability to diagnose acute and chronic coronary syndromes. The ECG may assist in clarifying the differential diagnosis if taken in the presence of pain. The resting ECG also has an important role in risk stratification. Exercise ECG is more sensitive and specific than the resting ECG as far as myocardial ischemia detection is concerned, and it represents the test of choice which helps identifying inducible ischemia in the majority of patients suspected of stable angina.