T Wave Ventricular Repolarization Representation

T Wave Ventricular Repolarization Representation is the deflection recorded on the surface electrocardiogram that corresponds to the return of the ventricular myocardium from its depolarized state back to the resting membrane potential. It reflects the phase 3 repolarization of ventricular myocytes, during which outward potassium currents predominate and progressively restore the transmembrane voltage of each cell toward baseline, generating a net electrical vector detectable at the body surface because, unlike depolarization, repolarization does not proceed uniformly across the ventricular wall.

Physiological Origin

Repolarization Currents

Following the plateau phase of the action potential, ventricular myocytes undergo phase 3 repolarization, driven primarily by the activation of delayed rectifier potassium currents and the progressive inactivation of inward calcium current. This shift in ionic balance drives the membrane potential from the plateau level back toward the resting potential established by inward rectifier potassium channels.

Transmural Repolarization Gradient

Repolarization does not occur simultaneously throughout the ventricular wall. Epicardial cells generally repolarize before endocardial cells, despite endocardial cells being depolarized first, because epicardial action potentials are typically shorter in duration. This creates a voltage gradient across the ventricular wall during repolarization, in contrast to the roughly uniform depolarization wavefront of the QRS complex.

Direction of the Net Vector

Because the epicardium repolarizes before the endocardium, the repolarization wavefront effectively proceeds from epicardium toward endocardium, which is opposite in spatial direction to the endocardium-to-epicardium spread of depolarization. Since repolarization represents a return toward the resting state, this reversal of both current direction and wavefront direction results in a T wave that is normally concordant in polarity with the preceding QRS complex in most leads.

Vectorial Representation

Instantaneous Repolarization Vector

At each moment during ventricular repolarization, the differing membrane potentials of not-yet-repolarized and already-repolarized regions generate a net instantaneous vector, analogous in principle to the depolarization vector but arising from voltage gradients associated with recovery rather than activation.

Concordance with the QRS Complex

Under normal conditions, the T wave points in the same general direction as the dominant deflection of the QRS complex in a given lead, a relationship that follows directly from the opposite directions of the depolarization and repolarization wavefronts combined with the opposite sense of current flow each represents.

Morphological Features

Shape

The T wave is normally a smooth, rounded, asymmetric deflection, typically rising more gradually than it descends, reflecting the relatively gradual and dispersed nature of repolarization compared to the rapid, synchronized nature of depolarization mediated by the specialized conduction system.

Amplitude

The amplitude of the T wave reflects the magnitude of the net repolarization vector at its peak, influenced by the degree of dispersion in repolarization timing across the ventricular myocardium and by the mass of myocardium repolarizing at that moment.

Temporal Characteristics

Onset and Termination

The onset of the T wave marks the beginning of measurable net repolarization current following the plateau phase, and its termination marks the point at which essentially all ventricular myocardium has returned to the resting membrane potential.

Relationship to the QT Interval

The end of the T wave defines the termination of the QT interval, which together represents the total duration of ventricular electrical activity, encompassing both depolarization and repolarization.

Lead-Dependent Appearance

Precordial and Limb Lead Variation

The polarity and amplitude of the T wave vary across leads according to the projection of the net repolarization vector onto each lead's viewing axis, following the same vectorial projection principles that govern QRS morphology, since both waveforms derive from the same underlying ventricular anatomy and conduction pathways.

Relationship to Ventricular Mass

Because repolarization of the larger left ventricular mass contributes more substantially to the net surface vector, leads oriented toward the left ventricle typically display more prominent T wave deflections than leads oriented primarily toward the right ventricle.

Functional Significance of the Representation

Marker of Ventricular Recovery

The T wave serves as the electrocardiographic representation of the period during which the ventricular myocardium regains its electrical excitability, transitioning from the absolute refractory period through the relative refractory period as repolarization proceeds.

Vulnerability of the Ascending Limb

The ascending portion of the T wave corresponds to the relative refractory period, during which the ventricular myocardium, though not fully recovered, can be reactivated by a sufficiently strong stimulus, linking this segment of the representation directly to the tissue's variable excitability during recovery.