T-waves and BBB (Bundle Branch Block)
T-waves and BBB (Bundle Branch Block)
What have T-waves and Bundle Branch Block got to do with each other?
Muscle tissue in the heart's chambers works like other muscle tissue in your body. It contracts when an electrical surge is sent through it. These electrically-caused contractions are the beating of the heart, as the contractions squeeze the blood-filled heart chambers and push the blood out and through the body. The valves in the heart are one-way valves at the outlet of each chamber that ensure that the blood can only move forward during the contractions.
Valve problems are generally one or both of the following: Stenosis, when the opening of the valve is blocked or restricted, making it hard for the blood to be pushed through it; and regurgitation (insufficiency), when the valve leaks, and some of the blood leaks backwards through the valve during the contraction, instead of all flowing forward.
The heart is a two-stage pump. The atria, which act as reservoirs to collect the blood for pumping, contract first, to fill the ventricles. The ventricles are the powerhouses. When filled from the atria, they then contract and push the blood out to and through the rest of the body. Setting these contractions off with the correct order and timing is a complex electrical ballet, which is why an EKG (ECG), which measures electrical changes in the heart, can tell so much about the heart's operating condition.
In this instance, we're dealing with the ventricles. It doesn't matter which ventricle, right or left. Although they push blood out to different places (right to lungs, left to head-heart-body), they both work the same way.
Okay, so the ventricles contract when they are depolarized. But in between beats, the ventricular chambers need to relax again, so they can be filled up by the next atrial squeeze. So, the cells "de-electrify" (repolarize) between beats. This lets them stop contracting, allowing the chambers to relax, and leaves the muscle cells receptive to the next electrical charge that will cause them to contract.
Normally, this depolarization-repolarization cycle is orchestrated by the Bundle Branch, which is a nerve bundle that extends over the ventricle and can electrically cause the ventricle’s myocardial (muscle) cells to be depolarized or repolarized nearly all at once. In Bundle Branch Block, the conductivity of the nerve bundle is compromised at some level, and the speed of the depolarization and repolarization is affected by it. The severity of the block is usually defined in three levels, the lowest of which is usually not very concerning.
Fortunately, one difference between heart muscle cells and other muscle cells is that myocardial cells can conduct electricity. The signal that is blocked in the bundle branch continues forward, although more slowly, cell by cell.
BBB (more specifically RBBB or LBBB) can be present from birth. It can also be caused by tissue damage from an MI (myocardial infarction, a.k.a. heart attack) or a lesser ischemic attack. Or it can occur as a result of some types of heart surgery. Notably, neither valve replacement surgery nor MAZE procedures are specifically mentioned as surgical causes, but that doesn’t rule them out. ToF (Tetrology of Fallot) surgeries are definitely causal to BBB.
So, where does the Inverted T-Wave tie in to this? Well, a T-wave is the electrical pulse that repolarizes the ventricle’s myocardium, relaxing it and resetting the ventricle for its next contraction (depolarization). The repolarizing current normally passes from the apex (top) of the heart downward. When it flows in the opposite direction, it may be called an Inverted, Juvenile, or Negative T-wave. An Inverted T-wave is generally a sign of a ventricular problem in an adult. An exception is that it can be normal in some American or Caribbean patients of African descent.
The main causes for an inverted T-wave are an MI or lesser ischemic attack, ventricular hypertrophy (reverts over time after surgical correction [such as valve replacement]), physical injury, mild post-AVR stenosis (usually reverts over time), disease (such as 3rd- and 4th-stage pericarditis), electrolyte imbalances, some drugs (such as Digoxin) …and… *drumroll* …BBB.
So how is it that they can become important together? BBB causes the QRS complex to take longer, because of the cell-by-cell transmission of the electrical signals. A normal QRS complex (a combination of depolarization of the ventricles and repolarization of the atria) requires between .06 and .12 seconds. With Bundle Branch Block, it takes longer. In mild BBB (particularly RBBB), there is generally a wait and watch diagnosis. With inverted T-wave, if no causation is found, there is generally a wait and watch diagnosis. However, if BBB is causing a QRS complex time of greater than .18 seconds (180 milliseconds), and there is an inverted T-wave, there is a high risk of dangerous ventricular arrhythmias. In those cases, an implanted pacing device may be in order.
By the way, studies show only a minimal risk of future problems with a Right Bundle Branch Block.
Yes, I know. A long run around the bush for a simple statement. But it also yielded an answer about the Inverted T-wave and mechanical valves. Valve replacement, mechanical or otherwise, doesn’t appear to cause inverted T-waves (I was curious). There’s no literature for it. The most likely associations the two have after surgery are lingering ventricular hypertrophy and mild, post-AVR valve-related stenosis, either of which should revert to a normal T-wave over time.
Assuming there is no underlying ischemic or other issue as noted above, another possible cause for an Inverted T-wave's continuance post-surgery is a heavy exercise load, which could keep the left ventricle somewhat enlarged. To be fair, perhaps the very minimal stenosis created by a replacement valve may also have some small bearing on it in a heavy exercise scenario. Fortunately, in the absence of other aggravators, an inverted T-wave is basically benign.
Hey, if I have to look up this stuff on a weekend, I figure you have to sit through it too...
Best wishes,
