Learning about the heart is like growing in the knowledge of God. At first you know the heart as a simple pump, but as you dig deeper, the more complex and awesome it becomes. The physiology of the heart is full of the knowledge of the glory of God (Hab 2:14).The heart is glorious because God is glorious, and He created it. For the sake of this post, we will focus on one area of the heart: the atrioventricular (AV) node. Below provides context for why this node is so important.
Why is the heart amazing?
A normal heart pumps at a rate of 60-100 beats per minute. It circulates all the blood in your body in roughly 1.5 minutes. The heart has four compartments: the top right and left portions are known as the atria; the lower right and left portions are known as the ventricles.
With every mechanical heartbeat, there’s associated electrical activity. There’s an electrical pathway within the heart that, in a healthy individual, synchronizes perfectly with mechanical contraction. The electrical activity precedes and stimulates the mechanical activity. Without an electrical impulse there would be no beat.
The sinoatrial (SA) node, the first part of the electrical pathway, sets the pace of the heart; it receives stimulation from special nerves in your brain that set the rate according to physiologic input from various feedback loops in your body. The SA node fires at a potential of 60-100 beats per minute (the normal parameters for heart rate). The firing of the SA node stimulates the atria to contract and blood is pumped into the ventricles. The electric impulse travels to the AV junction site. This site is small and ten times slower at transmitting the impulse, thus there is a delay in stimulation. The AV node fires and the impulse transmits to the Bundle of His and then to the Purkinje fibers, which cause your ventricles to contract. The right ventricle pumps blood to your lungs to be oxygenated. The left side pumps oxygenated blood to your body.
Why the delay?
The AV node is ten times slower than the SA node and forty times slower than the Bundle of His and Purkinje fibers. If you just look at the electrical activity of the heart, the small AV junction site and delay seems to be a barrier to more effective contractility. It seems as though there is a deficiency in the system.
We must take a look at the big picture of the cardiac cycle. When the signal reaches the AV junction site, the atrial muscles are still contracting. The small junction site provides a delay that perfectly allows the atria to complete their ejection of blood into the ventricle before the ventricles receive stimulation and contract. The amount of blood in your ventricles before they contract ultimately determines how well all of your organs will be perfused, it’s why you can breathe, it’s why you can think.
This small delay in the system keeps you alive. The most common occurring electrical pathology that occurs with cardiac arrest is when the signal of electricity is initiated past the AV junction site, also known as ventricular fibrillation. The ventricles contract without any consideration of atrial activity, and the heart does not effectively pump blood out to your body.
Again, why the delay?
In the same way, we ask about our life, “Why the delay? Why this circumstance?” We are blind in our foresight. We lack perspective, as if we were just looking at the electrical activity of the heart and not anything else. We see delays as barriers to success. We think unhappy circumstances keep us from experiencing joy. We are incredibly impatient.
Let’s not forget these words from Paul: Therefore, since we have been justified by faith, we have peace with God through our Lord Jesus Christ. Through him we have also obtained access by faith into this grace in which we stand, and we rejoice in hope of the glory of God. Not only that, but we rejoice in our sufferings, knowing that suffering produces endurance, and endurance produces character, and character produces hope, and hope does not put us to shame, because God’s love has been poured into our hearts through the Holy Spirit who has been given to us. For while we were still weak, at the right time Christ died for the ungodly. For one will scarcely die for a righteous person—though perhaps for a good person one would dare even to die—but God shows his love for us in that while we were still sinners, Christ died for us (Rom 5:1-8).
We can react to delays and unhappy circumstances in two ways. First, we can focus inwardly amidst the circumstance. True, there are probably practical, maybe even good, desires not being met. We have an idea of how to make things right and so we manipulate the situation to get what we want. Another option is to trust that there is a bigger lens by which God works. This bigger picture not only has our greatest happiness in mind, but simultaneously, and more importantly, brings God the greatest glory.
Delays and unhappy circumstances are means by which God uses to make us holy and more affected by His Spirit. It’s too easy to look inward and in a self-absorbed tone ask God, “Why me?” What is difficult and rewarding is to be thankful for these circumstances. We must be thankful that the greatest, most loving Father is trying to make us holy and pursuing us for right relationship with Him. Let’s try to not only do that in hindsight, but when difficulty is before us; as it says, “Give thanks in all circumstances; for this is the will of God in Christ Jesus for you” (1 Thess 5:18).
We rejoice because we have hope from God who admidst these circumstances “pours love into our hearts” (Rom 5:5). Be thankful for the AV node delay, because every second it keeps you alive. Be even more grateful that it exists to represent the great patience of God who at the right time saves you and makes you holy.