T-wave Polarity Research Articles

Ionic Current Basis of Electrocardiographic Waveforms

Body surface electrocardiograms and electrograms recorded from the surfaces of the heart are the basis for diagnosis and treatment of cardiac electrophysiological disorders and arrhythmias. Given recent advances in understanding the molecular mechanisms of arrhythmia, it is important to relate these electrocardiographic waveforms to cellular electrophysiological processes. This modeling study establishes the following principles: (1) voltage gradients created by heterogeneities of the slow-delayed rectifier (I(Ks)) and transient outward (I(to)) potassium current inscribe the T wave and J wave, respectively; T-wave polarity and width are strongly influenced by the degree of intercellular coupling through gap-junctions. (2) Changes in [K+]o modulate the T wave through their effect on the rapid-delayed rectifier, I(Kr). (3) Alterations of I(Ks), I(Kr), and I(Na) (fast sodium current) in long-QT syndrome (LQT1, LQT2, and LQT3, respectively) are reflected in characteristic QT-interval and T-wave changes; LQT1 prolongs QT without widening the T wave. (4) Accelerated inactivation of I(Na) on the background of large epicardial I(to) results in ST elevation (Brugada phenotype) that reflects the degree of severity. (5) Activation of the ATP-sensitive potassium current, I(K(ATP)), is sufficient to cause ST elevation during acute ischemia. These principles provide a mechanistic cellular basis for interpretation of electrocardiographic waveforms.

Electrical behavior of T-Wave polarity alternans in patients with congenital long QT syndrome

OBJECTIVESThis study was designed to evaluate the incidence and characteristics of onset of T-wave polarity alternans (TWPA) in patients with long QT syndrome.BACKGROUNDThe T-wave alternans is a phenomenon that consists of beat-to-beat variability in the amplitude, morphology, and sometimes polarity of the T-wave, and it may trigger life-threatening arrhythmias.METHODSThe 24-h Holter recordings of 11 patients with congenital long QT syndrome were studied. Episodes of TWPA with 10 or more consecutive cycles were selected and analyzed as follows: 1) mean cycle length (MCL) and QTc interval duration (QTcI) of the episodes of TWPA and the 10 cycles preceding and succeeding the TWPA; 2) MCL and QTcI of the third, second, and first minute before onset (Mn−3, Mn−2, Mn−1); 3) MCL and QTcI from the tenth to the first cycle immediately preceding the onset of TWPA (R−10 to R−1); 4) MCL and QTcI from the first to the fourteenth cycle during alternans (R0 to R14); 5) MCL and QTcI from the first to the tenth cycle immediately succeeding TWPA (R+1 to R+10); 6) linear correlation (Lnc) between QT interval and cycle length (CL) (LncQT/CL) during alternans and for the 10 preceding cycles; 7) Lnc between the first three alternans cycles and episode duration (Lnc 3CL/EpD); and 8) difference between the longest and shortest QTc interval. We also selected episodes consisting of four or more consecutive cycles in order to analyze daily rhythms of the phenomenon.RESULTSThe TWPA was observed in 5 (45%) out of the 11 patients studied. The alternans process is initiated by a sudden shortening of the first alternans cycle without previous heart rate changes and ends at the moment when prolongation of the cycle tends to occur. LncQT/CL–alternans: r = 0.38 ± 0.2 (p = 0.20); without alternans: r = 0.81 ± 0.06 (p = 0.01). Lnc 3CL/EpD: r = 0.002 (p = 0.992). The QTc difference during alternans: 312.0 ± 52.1 ms; without alternans: 86.0 ± 36.4 ms (p = 0.001). Daily rhythm: 71% of the episodes occurred between 8 am and 8 pm, with higher incidence during the morning.CONCLUSIONSThe TWPA was dependent on the cardiac CL; there was loss of the LncQT/CL and an increase in the QT interval variability. Like other biological variables, T-wave polarity alternans has a higher density during the morning.

ECG of the Beagle Dog: Distribution and Stability of the Three T-Wave Polarities and In-house Reference Values for Selected Parameters

ECG of the Beagle Dog: Distribution and Stability of the Three T-Wave Polarities and In-house Reference Values for Selected Parameters

ECG of the beagle dog: Distribution and stability of the three T-wave polarities and in-house reference values for selected parameters

ECG of the beagle dog: Distribution and stability of the three T-wave polarities and in-house reference values for selected parameters

Improved Detection of Silent Cardiac Ischemia With a 12-Lead Portable Microprocessor-Driven Real-Time Time Electrocardiographic Monitor

To compare a microprocessor-driven real-time 12-lead electrocardiographic monitoring device with Holter monitoring for detection of ischemia. Electrocardiographic monitoring was conducted in 110 patients at bed rest or undergoing surgical procedures. In three groups of patients, simultaneous monitoring with a 12-lead real-time device and a 2-channel Holter system was performed to detect ischemic episodes. The differences in the number of ischemic events and the total time of ischemia revealed by the two devices were analyzed statistically. In patients with coronary artery disease, more ischemic ST-segment shifts were detected by the 12-lead device than by Holter monitoring (44 versus 16 events; P < 0.05). Total time of ischemia was also greater with the 12-lead device (879 versus 273 minutes; P < 0.05). Ischemia was detected by both techniques in 6 patients, only by the 12-lead device in 12, and only by Holter monitoring in 1. Neither device detected ischemia in control subjects. The 12-lead device had an advantage in detecting inferior ischemia, and it identified an additional 13 patients with unstable angina who had changes in T-wave polarity but did not exhibit ST-segment shifts. The 12-lead real-time electrocardiographic monitoring device is superior to Holter monitoring in detecting and facilitating real-time identification of myocardial ischemia in patients at bed rest.

Cardiac depolarization and repolarization in Wolff-Parkinson-White syndrome

Delta wave and QRS complex polarities have been extensively studied in preexcitation syndromes. However, only limited data exist about ventricular depolarization and repolarization in the setting of maximal preexcitation in relation to the site of insertion of the accessory pathway. Therefore this study was designed to systematically analyze cardiac depolarization and repolarization in patients with maximal preexcitation. We analyzed the polarity of the QRS complex and T wave on the frontal plane on the conventional 12-lead electrocardiogram in 118 patients with maximal preexcitation. Fast atrial pacing was used to provoke maximal ventricular preexcitation. The 32 patients with a left lateral accessory pathway showed right-axis deviation of the QRS complex (110 ± 20 degrees) with a left-axis deviation of the T-wave axis (−40 ± 25 degrees). The 54 patients with a posteroseptal accessory pathway had a left axis of the QRS complex (−50 ± 20 degrees) with a right-axis deviation of the T-wave axis (95 ± 15 degrees). The 11 patients with a right lateral accessory pathway had a left axis of the QRS complex (−40 ± 20 degrees) and a right axis of the T wave (110 ± 10 degrees).In 7 patients with a left anterolateral accessory pathway and 14 patients with a right anteroseptal accessory pathway, the axis of the QRS complex was 50 ± 25 degrees and 45 ± 20 degrees, respectively. T-wave polarity, however, showed two distinct patterns with a vertically directed T-wave axis (60 ± 25) in left anterolateral pathways and a T-wave axis directed in the upper right quadrant (−145 ± 20) in right anteroseptal pathways. In conclusion, electrocardiographic analysis of ventricular depolarization and repolarization in Wolff-Parkinson-White syndrome revealed characteristic polarities for the QRS complex and T wave depending on accessory pathway localization. These data are helpful in noninvasively localizing the site of insertion of the accessory pathway.

Relation of T-Wave Polarity in Precordial V1Lead to Right or Left Circumflex Coronary Pathoanatomy in Acute Inferior Myocardial Infarction

To test the hypothesis that right ventricular (RV) involvement in inferoposterior wall acute myocardial infarction (AMI) may affect precordial T-wave polarity, relation of T-wave polarity in lead V1 to right (RCA) or left circumflex (LCX) coronary pathoanatomy was examined. The study population included the patients with initial inferoposterior wall AMI due to RCA (n = 61) or LCX (n = 19) occlusion within 5 h of symptom onset and 100 normal controls. The patients with RCA disease were further divided into four subgroups based on the site of coronary occlusion and the direction of the ST shift in lead V1: group A1 (n = 27), proximal RCA occlusion with isoelectric or elevated ST segment; group A2 (n = 7), proximal occlusion with ST depression; group B1 (n = 8), distal RCA occlusion with isoelectric or elevated ST segment; group B2 (n = 19), distal occlusion with ST depression. Presence or absence of an upright T wave in lead V1 (> or = 0.15 mV) was evaluated. The patients with proximal RCA disease showed a higher incidence of upright T wave (71 percent) than the controls (27 percent) (p < 0.001), patients with LCX disease (26 percent) (p < 0.01), and those with distal RCA disease (19 percent) (p < 0.001). Among the four subgroups of RCA disease, the incidence of upright T wave was highest in group A1 (90 percent), lowest in group B2 (6 percent), and intermediate in controls (27 percent) (p < 0.001) for group A1 vs controls, and p < 0.05 for controls vs group B2). These findings suggest that concomitant RV involvement in inferoposterior wall AMI modifies T-wave polarity of lead V1, which is ordinarily expected to be reciprocally drawn to negativity when infarct is limited to the inferoposterior wall of the left ventricle, to the positivity.

Precordial T-wave Polarity Changes in Acute Inferior Infarction: A Poor Indicator of Associated Disease of the Left Anterior Descending Coronary Artery

T-wave polarity in V1 to V3 was examined in 70 patients with acute inferior wall myocardial infarctions (IWMI) as an indicator of significant disease in the left anterior descending coronary artery (LAD). Fifty-three percent (37/70) had precordial T-wave inversions, and of these 38 percent (14/37) had angiographically significant LAD disease. Conversely, 47 percent (33/70) had upright T waves in V1 to V3, and of these, 52 percent (17/33) had significant LAD disease. Likewise, 41 percent of the patients with ST segment depression in V1 to V3 had significant LAD disease, while 50 percent of those with isoelectric ST segments were similarly affected. Finally only 39 percent of those patients with both precordial ST segment depression and T-wave inversion had significant LAD disease. We conclude that neither anterior ST depression, T-wave inversion, nor a combination of both is a sensitive or specific indicator of LAD disease in patients with acute IWMI.

Coexistence of pupillary and heart sympathergic asymmetries in cluster headache.

Ten cluster headache patients and 10 healthy controls were subjected to electrocardiographic and pupillometric procedures in a search for cardiac and pupillary sympathergic asymmetry. Sympathergic stimulation was provoked by hyperventilation and by instilling tyramine into both eyes. In the control group, hyperventilation changed neither the T-wave form and polarity nor the QTc. Tyramine provoked an equal mydriasis on the two sides. In cluster headache sufferers, hyperventilation produced changes in the T-wave form and polarity as well as an increase of the QTc due to a disproportionate shortening of the R-R and Q-T intervals. An unequal mydriasis was noted after tyramine instillation due to less marked response on the symptomatic side. The observed electrocardiographic abnormalities are considered an expression of an asynchronous repolarization attributed to a sympathergic asymmetry. It is postulated that both the cardiac and pupillary sympathetic imbalance associated with cluster headache are central in origin.

Theoretical analysis of T-wave polarity based on a model of cardiac electrical activity

The effect of the gradient of transmembrane action potential duration through the ventricular wall on T-wave polarity and QRS-T angle was investigated using a mathematical model of the electrical activity of the heart which incorporates the characteristic electrophysiological properties of the left ventricular wall. Two models, a rectangular solid model and a concave model, were constructed to simulate a part of the left ventricular wall. The ventricular gradient was defined as a linear decrease (beta msec/cm) of the action potential duration from the endocardium to epicardium. The theoretically-obtained relationship between the QRS-T angle and the ventricular gradient revealed that the transmural gradient (beta) was 10--40 msec/cm when the QRS-T angle was within the normal range. The positive T wave was obtained at the observation point which would correspond to the precordial lead when the transmural gradient was more than 30 msec/cm. The amplitude of the simulated T-wave increased with the ventricular gradient. Thus, our mathematical models can provide the quantitative relationship between the transmural ventricular gradient and T-wave polarity and are compatible with further simulation study for various pathological conditions.

T-Wave Changes With Inspiration

Two instances of T-wave changes without evidence of underlying organic disease occurred. In the first case, T-wave inversion uniquely responded to inspiration. This phenomenon was consistently repeated for six years. In the second case, atrial depolarization and ventricular repolarization appeared to be influenced by inspiration. Whenever nonspecific T-wave changes in the precordial leads are found, inspiration may influence T-wave polarity to suggest causes other than organic heart disease.