So far we have touched on the anatomy of the heart and the blood supply to it via the coronary arteries. A muscle that contracts and pushes blood around the body is pretty cool. But how does it do this? How does it make the coordinated effort to first contract the atria to push the blood into the ventricles, and then contract the ventricles to push blood to the lungs and body in a perfect two-step sync? Simple. Electricity.
The Royal Wave
Travel with me to Kansas City. Home to many things, but for our purposes we are most interested in two of their sports teams: the Kansas City Chiefs of the NFL and the Royals of Major League Baseball. Well, to be exact, we are actually interested in their stadiums. The Chiefs play in Arrowhead Stadium, with a capacity of 79,451 fans and the Royals play in Kauffman Stadium, with a full house maximum of 37,903. Now, why would be interested in this city and these sports teams and those particular stadiums? Geography. These stadiums have a unique configuration of being built about 200m (650ft) apart, and are a perfect setting for how the heart contracts electrically. Watch....
The Royal Wave
Travel with me to Kansas City. Home to many things, but for our purposes we are most interested in two of their sports teams: the Kansas City Chiefs of the NFL and the Royals of Major League Baseball. Well, to be exact, we are actually interested in their stadiums. The Chiefs play in Arrowhead Stadium, with a capacity of 79,451 fans and the Royals play in Kauffman Stadium, with a full house maximum of 37,903. Now, why would be interested in this city and these sports teams and those particular stadiums? Geography. These stadiums have a unique configuration of being built about 200m (650ft) apart, and are a perfect setting for how the heart contracts electrically. Watch....
Picture in your mind both of these stadiums being filled with rabid KC sports fans, with games occurring simultaneously. Now to be proper fans in any sport, you need to do the "wave" to support your team. But for this scenario, the fans are going to try to coordinate a wave between BOTH stadiums to support the Royals and Chiefs. The most enthusiastic of all the fans is the Royals mascot, Sluggerrr (I'm not making this up), so all waves will start with him in Kauffman Stadium. Now, there is only one problem - the fans in the separate stadiums cannot see or hear the other fans (and there are no cells phones or two way radios) so someone is going to have to run from the Royals stadium to the Chiefs stadium for each wave to try and coordinate the effort. Who should do the run? Well it needs to be done as quick as possible to try and do the waves at the same time, so why not have world-record holder Usain Bolt do the honors, who can run 200m in 19.19 seconds. Perfect.
Wave. Bolt. Repeat.
Sluggerrr is very enthusiastic about doing the wave for the Royals, so he is going to start a wave about once per minute. The fans for the Chiefs are expecting this and will be ready. So Sluggerrr starts a wave by standing up and all 37,000+ fans follow in perfect unison. Royals wave complete, and time to signal the Chiefs. At this exact moment, Usain begins his sprint across the parking lot into Arrowhead Stadium to let all the fans there know it's time to cheer. They respond appropriately with insane enthusiasm and the KC wave cycle is complete. Usain returns back to Kauffman Stadium and awaits the next signal to come from Sluggerrr and the rest of the crew there. This is the exact same process the heart goes through for each and every beat, done perfectly every time.
Hinge Bolt
Kauffman Stadium is the representation of the upper atria of the heart. These contract simultaneously after an electrical signal is initiated from a single source (located in the right atrium) called the Sinoatrial (SA) Node, who in our example is the mascot for the Royals. This SA node has an "internal pacemaker" and regulates the beginning of all normal contractions in the right and left atria. This signal must now reach the ventricles, or Arrowhead Stadium, and start an electrical signal and contraction there. This is done quickly (Usain Bolt), but also allows for two things. First, it creates a delay between the upper and lower chambers of the heart to allow contraction of the atria and blood to get to the ventricles before they contract. Second, it takes some time for Usain to get back to Kauffman Stadium. This is good. The ventricles need a bit of time to recuperate (or repolarize) after they have completed a contraction. It doesn't matter if Sluggerrr has started another wave while Usain is gone, the signal that this wave has begun will not reach the Arrowhead ventricles because Usain is not ready to bring it there.
1,2,3....ECG
So how does the electrical signal, contraction, atria, ventricles, repolarization, and all that other stuff relate to us? Well, the electrical signals generated by the heart with each beat can be measured and recorded, and yes, analyzed. This is a very common practice, and is called an ELECTROCARDIOGRAM (or ECG for short). Now, some of you may say EKG versus ECG, but these abbreviations are interchangeable. The 'K' stems from the German and/or Greek spelling of the prefix kardio, not the usual cardio, which is also of Greek origin.....so.....never mind......I digress.....
Here is a sample tracing of a portion of a normal ECG:
Wave. Bolt. Repeat.
Sluggerrr is very enthusiastic about doing the wave for the Royals, so he is going to start a wave about once per minute. The fans for the Chiefs are expecting this and will be ready. So Sluggerrr starts a wave by standing up and all 37,000+ fans follow in perfect unison. Royals wave complete, and time to signal the Chiefs. At this exact moment, Usain begins his sprint across the parking lot into Arrowhead Stadium to let all the fans there know it's time to cheer. They respond appropriately with insane enthusiasm and the KC wave cycle is complete. Usain returns back to Kauffman Stadium and awaits the next signal to come from Sluggerrr and the rest of the crew there. This is the exact same process the heart goes through for each and every beat, done perfectly every time.
Hinge Bolt
Kauffman Stadium is the representation of the upper atria of the heart. These contract simultaneously after an electrical signal is initiated from a single source (located in the right atrium) called the Sinoatrial (SA) Node, who in our example is the mascot for the Royals. This SA node has an "internal pacemaker" and regulates the beginning of all normal contractions in the right and left atria. This signal must now reach the ventricles, or Arrowhead Stadium, and start an electrical signal and contraction there. This is done quickly (Usain Bolt), but also allows for two things. First, it creates a delay between the upper and lower chambers of the heart to allow contraction of the atria and blood to get to the ventricles before they contract. Second, it takes some time for Usain to get back to Kauffman Stadium. This is good. The ventricles need a bit of time to recuperate (or repolarize) after they have completed a contraction. It doesn't matter if Sluggerrr has started another wave while Usain is gone, the signal that this wave has begun will not reach the Arrowhead ventricles because Usain is not ready to bring it there.
1,2,3....ECG
So how does the electrical signal, contraction, atria, ventricles, repolarization, and all that other stuff relate to us? Well, the electrical signals generated by the heart with each beat can be measured and recorded, and yes, analyzed. This is a very common practice, and is called an ELECTROCARDIOGRAM (or ECG for short). Now, some of you may say EKG versus ECG, but these abbreviations are interchangeable. The 'K' stems from the German and/or Greek spelling of the prefix kardio, not the usual cardio, which is also of Greek origin.....so.....never mind......I digress.....
Here is a sample tracing of a portion of a normal ECG:
Now, from this diagram, you can appreciate that there are three distinct segments of this tracing, and the combination of these three forms creates one beat of the heart. The first segment is called the "P" wave, the second is the "QRS" complex, and the third is the "T"wave. But what the heck are those things?
The P wave - this is the electrical signal generated during atrial contraction, or for our purposes, the electrical "sound" created by the wave that originated in Kauffman Stadium.
The QRS complex - this is the loud spike of "noise" generated from ventricular contraction, or better know as the wave from the larger Arrowhead stadium.
The T wave - this is actually the electrical signal that comes from the repolarization of the ventricle (or the electrical "resetting" of the system). Think of this as the noise that is made by the 79,000+ fans sitting back down in their seats after they have done the wave. But wait! Where is the noise made by the Kauffman fans sitting down?? That wave is actually buried within the signal of the QRS complex. As the ventricles are contracting, the atria are also repolarizing (or resetting), thus generating a single electrical wave (and one much larger than either of the P or the T waves).
One more important part that relates to our example - the PR segment. This short flatline between the P wave and the start of the QRS complex is the representation of Usain Bolt running between the stadiums. He has gotten the signal from the first stadium (P wave) and is relaying this to the larger Arrowhead Stadium to start the wave (contraction) there (i.e. the QRS complex).
Sorry to be so long winded on this topic. Hope you found it interesting. Please note I neglected to mention arrhythmias and heart attacks and other (awesome) topics as it relates to the ECG on purpose. Way too much ground to cover in one post. I will definitely talk about these on a later date.
Stay tuned for next time, when I will be talking about Cardiodiagnostics (...uh what?)
The P wave - this is the electrical signal generated during atrial contraction, or for our purposes, the electrical "sound" created by the wave that originated in Kauffman Stadium.
The QRS complex - this is the loud spike of "noise" generated from ventricular contraction, or better know as the wave from the larger Arrowhead stadium.
The T wave - this is actually the electrical signal that comes from the repolarization of the ventricle (or the electrical "resetting" of the system). Think of this as the noise that is made by the 79,000+ fans sitting back down in their seats after they have done the wave. But wait! Where is the noise made by the Kauffman fans sitting down?? That wave is actually buried within the signal of the QRS complex. As the ventricles are contracting, the atria are also repolarizing (or resetting), thus generating a single electrical wave (and one much larger than either of the P or the T waves).
One more important part that relates to our example - the PR segment. This short flatline between the P wave and the start of the QRS complex is the representation of Usain Bolt running between the stadiums. He has gotten the signal from the first stadium (P wave) and is relaying this to the larger Arrowhead Stadium to start the wave (contraction) there (i.e. the QRS complex).
Sorry to be so long winded on this topic. Hope you found it interesting. Please note I neglected to mention arrhythmias and heart attacks and other (awesome) topics as it relates to the ECG on purpose. Way too much ground to cover in one post. I will definitely talk about these on a later date.
Stay tuned for next time, when I will be talking about Cardiodiagnostics (...uh what?)