In the last two issues of the newsletter, we've discussed the anatomy of the heart and the things that can go wrong with the heart. (If you have not read them yet, it would be helpful, but not essential, before reading on.) In this issue, we're going to conclude our series by examining how your doctor unravels the secrets of your heart when you visit his / her office. My goal is not to turn you into doctors, but to take some of the mystery out of diagnosis so that you know what your doctor is looking at, listening to, and analyzing when he / she is looking at your heart – to arm you with some basic diagnostic knowledge so you are not totally at the mercy of the medical mystique when the results of your next physical are pronounced.
Before we launch into our subject, though, we have to define two terms that will be referenced throughout the newsletter: systole and diastole:
– Systole refers to the contraction of the chambers of your heart.
– Diastole refers to the relaxation of those chambers.
In fact, you can have systole and diastole in all four heart chambers, but in most cases, doctors focus on the left ventricle – the chamber that pumps blood throughout your entire body – when using the terms. Also, there are two kinds of systole and diastole: electrical and mechanical. Electrical systole is the electrical activity that precedes actual contraction. It's what stimulates the heart muscle of the different chambers to actually contract. The delay between electrical stimulation and actual contraction is about a tents of a second.
The same is true of diastole, the relaxation of the heart muscles. Electrical diastole is the recovery and repolarization of the heart in preparation for the next beat. Mechanical diastole is the actual relaxation of the muscle that follows electrical diastole. This distinction becomes important when you look at your ECG.
Incidentally, the increased pressure produced in your circulatory system by the mechanical systole (contraction) of the left ventricle is referred to as systolic pressure. The reduced pressure during relaxation is called diastolic pressure. These are the two numbers your doctor gives you when reading your blood pressure (eg, 120 over 70). We'll explore that in detail in the next series of newsletters when we explore the circulatory system.
The Sounds of Your Heart
The most basic tool your doctor has for evaluating the health of your heart is the stethoscope. It is so fundamental to medicine that it has been around in various forms for almost 200 years and is probably the most recognizable symbol of doctors in the world today. Before the stethoscope, physicians would just listen to the heart by pressing their ears against the patient's chest – not very efficient, and often very unclean.
And what do doctors hear through a stethoscope?
Surprise! It's actually not the beating of your heart. The heartbeat itself is virtually soundless. That thump … thump your doctor listens to is the sound of blood dashing against the inner walls of the heart chambers. This is a very useful distinction. Hearing the movement of blood reveals far more than would be the case if all we heard was a mechanical contraction.
More precisely, the thump … thump of your heartbeat is the sound of the turbulence of blood against the walls of the heart and the valves during systole (contraction). In fact, thump … thump is not an entirely accurate description of the sound. As it turns out, each thump is, in reality, comprised of separate sounds in both the atria and the ventricles. But because the sound in the ventricles is so loud, it drowns out the other sounds … unless there is a problem.
For example, if there's stenosis (hardening) of the mitral valve, part of the heartbeat is slowed down because it takes longer for the stiff valve to close so that the multiple sounds start to separate. Instead of the normal thump … thump, you hear something that sounds more like thump … pa pa. On the other hand, if you have incomplete closer of a valve, as in aortic regurgitation, you lose the clean thump and get sort of a chortling "woosh" sound as in whoosh … thump. (If you're interested, here's a link to more heart sounds.)
Invariably, then, listening to your heart through a stethoscope is one of the fundamental parts of any checkup. It provides the first clues as to the health of your heart.
Note: for those of you interested in coaching your doctor through anything they may have forgotten in medical school, here's a more detailed tutorial.
The ECG / EKG
When most people think of heart tests, they think of the ECG. ECG stands for electrocardiogram. It's also called an EKG, from the German elektrokardiogram. Although it may look like an ECG is recording heartbeats, it's not. In fact, it records the electrical activity (the electrical triggers, if you will) that presage the actual heartbeat. The mechanical beats follow the electrical triggers by about a tenth of a second – unless, of course, there's a problem. Or to state it in "medicalese," electrical systole and diastole precede mechanical systole and diastole (contraction and relaxation) of the heart by about a tenth of a second.
The ECG is an important tool for your doctor, but is hardly complete and comes with several limitations.
It's a static test, which means it does not necessarily identify problems that appear only when the patient's heart is under stress. An example would be a patient complaining of intermittent chest pain. This might actually be an indicator of a severe underlying problem, and yet a standard ECG could easily read as perfectly normal.
ECG readings indicate only general problems. In most cases, abnormalities in the reading are non-specific as to cause, and in fact, many times, may mean nothing all.
– A normal ECG reading does not necessarily mean that there is no problem.
– An abnormal reading does not necessarily mean that there is.
– It's merely a piece of the puzzle that can help point the doctor in a direction.
That said, an ECG provides four primary pieces of information for your doctor.
First, an ECG can show how fast your heart is beating – or more accurately, how fast the electrical activity is moving through your heart. By measuring the intervals between beats, your doctor can determine if the electrical signal is moving through your heart too slow or too fast.
It also shows the strength and timing of the beat. By measuring the amount of electrical activity passing through your heart muscle, your doctor can get an indication as to which parts of your heart are too large or are overworked or if it's not pumping forcefully enough.
It can provide evidence of damage to various parts of the heart muscle caused by:
– Previous heart attacks.
– Congenital heart abnormalities.
– Diseases such as thyroid problems, rheumatic fever, diabetes, and high blood pressure.
– Inflammation to either the heart muscle or its lining (inside and out).
– Very low or very high levels of electrolytes including calcium, magnesium, and potassium.
– And it can indicate problems with impaired blood flow in the coronary arteries supplying oxygen to your heart muscle.
Reading the ECG
Your doctor performs an ECG by hooking you up to a series of electrodes scattered over your chest, arms, and legs. (Accurate placement is important.) Each electrode reads the same signal, but because of its unique vantage point, provides a different view of that signal. Think of it like watching a speeding train from the front coming at you, from behind racing away, and from the side whizzing by. It's the same train, at the same point in time, but each vantage point provides very different information about the train.
Here's a snippet of an EKG showing several electrodes tracking a heart. Notice how the electrodes start providing noticeably different information concerning the same beat about 2/3 of the way through.
All well and good you might say, but what does it mean? How do I read it? Does it mean I'm healthy or unhealthy? Can I run a marathon, or do I need bypass surgery? All good questions.
In order to understand better what your doctor sees when he looks at an ECG printout, let's focus on a single beat from a single electrode.
Alright, I agree. That's certainly pretty meaningless at first glance. However, with a little decoding, it starts to make much more sense. In fact, the heartbeat as represented in an ECG breaks down into four primary pieces: the PR interval, the Q wave, the QRS complex, and the T wave. Let's explore them for a bit. (Refer back to the graphic as needed.)
The PR interval on the left side of the graph shows the electrical impulse for the contraction of the atria, immediately followed by its depolarization (or clearing of the electrical charge to that part of the heart muscle) so it can relax and gear up for the next contraction. As mentioned earlier, the actual contraction of the muscle follows the signal by about 1/10 of a second – in this case during the PR segment.
The Q wave (labeled Q above) is the initial downward (negative) deflection related to the initial phase of depolarization of the ventricular heart muscle. Again, depolarization is preparation for receiving an electrical stimulus.
The QRS complex in the center of the graphic shows the electrical stimulation of the ventricles, immediately followed by their depolarization. Not surprisingly (considering how much more powerful ventricular contraction is), the amplitude of the electrical signal for the ventricles is much larger than that of the atria.
The T wave on the right side shows the repolarization of the ventricles in preparation for the next beat. Note: The ST segment represents the period from the end of ventricular depolarization to the beginning of ventricular repolarization. In English, the T wave represents the recovery period of the ventricle in preparation for the next beat.
Now, if you've really been paying attention, you might be asking yourself an obvious question, "Where's the corresponding T wave for the atria following their PR interval. Do not the atria have to repolarize just like the ventricles?" And the answer is, "Yes, they do." Good call there! The problem is that the repolarization of the atria happens during the QRS complex, and because the ventricular signal is so much stronger than the atrial signal, you can not see the atrial repolarization – kind of like a flashlight turned on during the midday sun . Give yourself a pat on the back for catching its existence though.
And lastly, we have the QT interval. The QT interval is not a separate section, but is a combination of the QRS complex and its following T wave. It represents the time between the start of ventricular depolarization and the end of ventricular repolarization. It is useful as a measure of the duration of repolarization.
So what's your doctor looking for when she examines your ECG? To put it simply, she's looking for normal intervals and normal amplitudes in all key segments of the wave. For example:
The PR interval is indicative of the movement of the cardiac impulse from the atria to the ventricles via the atrioventricular node (see The Anatomy of the Heart), which is normally between 0.12 – 0.20 sec (3 – 5 small boxes wide). If the PR interval is greater than 0.20 sec, that's an indicator that an AV block is present (see Heart Problems).
The QT interval will vary depending on the heart rate, age, and gender of the patient. It increases with bradycardia (slow heartbeat) and decreases with tachycardia (rapid heartbeat). Men have shorter QT intervals (0.39 sec) than women (0.41 sec). The QT interval is also influenced by the electrolyte balance, drugs, and ischemia. Your doctor will be looking for any interval outside the norm.
A QRS interval of 0.04 to 0.10 seconds – no larger than half a large box – and of normal amplitude.
Differences in the sizes of the Q waves read from different electrodes at the same point in time are indicative of previous heart attacks – the differences are usually caused by areas of dead muscle tissue. A trained cardiologist can accurately pinpoint the area of damage according to which leads are producing which signals.
Inverted T waves may indicate ischemia, or low blood flow to the heart.
Deviations in the ST segment can show ischemia and infarction (ie, lack of blood flow to the heart muscle and dead muscle tissue). In general, a depression in the ST segment indicates ischemia while an elevation indicates infarction.
If you got lost in the last few bullet points, do not worry about it. The important point is to understand the "kinds" of anomalies your doctor is looking for – not necessarily to identify them yourself.
However, for those of you interested in keeping up with your doctor, here's a more detailed tutorial.
And for those of you who just want to walk away with something to hold onto, you can use your ECG to easily calculate your heart rate by counting the number of large squares between R waves (the high point in each beat).
1 square = 300 bpm
2 squares = 150 bpm
3 squares = 100 bpm
4 squares = 75 bpm
5 squares = 60 bpm
6 squares = 50 bpm
The easiest way to do this is find an R wave that coincides with the beginning of a large box and then simply count over to the next R wave. In our ECG snippet (two graphics above), we can find such a point in the middle of the graph. A quick count to the right shows 5 large boxes, or approximately 60 beats per minute. Is that cool or what? You can now read a good chunk of an ECG – and without going to medical school.
Seeing the Heart
Listening to your heart and monitoring its electrical activity, may not be enough. Your doctor may also want to see the heart, and there are several ways to do that.
The most basic heart picture is the chest X-ray. Skilled doctors can actually interpret a great deal from an X-ray, but that's also the problem with the technology – it requires a great deal of interpretation. That means its accuracy, at times, can be less than desirable.
Arteriogram / angiogram
You can think of the arteriogram (AKA angiogram, angiograph, etc.) as an X-ray on steroids. It's a procedure that uses a special dye (contrast material) and X-rays to see how blood flows through your heart.
An area of your body, usually the arm or groin, is cleaned and numbed with a local anesthetic. An IV (intravenous) line is inserted into the area. A thin hollow tube called a catheter is placed through the IV and carefully moved up into one of the heart's arteries. (X-ray images help the doctor see where the catheter should be placed.)
Once the catheter is in place, the dye (contrast material) is injected into the IV. X-ray images are taken to see how the dye moves through the artery. The dye helps highlight any blockages (dark areas) in blood flow.
Thallium Stress Test
Sometimes heart problems do not show up during normal activity; they only manifest under stress (ie, an increased load on the heart). In those cases, an arteriogram will not reveal the problem. The thallium stress test, then, is used by your doctor to determine whether exercise causes a decreased blood flow to the heart muscle. This test incorporates elements from the ECG, the angiogram, and an MRI. An IV is inserted into your hand and ECG wires are hooked up to your chest. You then walk on a treadmill until you experience symptoms such as chest pain or shortness of breath, or until you are too tired to continue walking. During the whole procedure, your blood pressure and ECG are monitored continuously. Approximately one minute before you stop walking on the treadmill, the thallium is injected. Thallium is an isotope which is "taken up" by the heart and the coronary arteries. (It flows more easily through non-diseased arteries.) You then lie down on a table, and a scanner takes a picture of your heart. Areas where blood can not flow easily under stress appear dark. (See below, lower left corner.)
The thallium stress test certainly provides more information than a simple ECG. Unfortunately, stress tests do not detect atheromata present throughout the heart or other body arteries, nor do they reveal the vulnerable plaques, which are typically flat against the walls of the arteries and which are the cause of most heart attacks.
An echocardiogram uses high frequency ultrasound waves to produce a moving image of your heart. Such an image can help your doctor assess:
– The size of your heart – both the thickness of the heart muscle and the size of the pumping chambers.
– How well your heart is pumping blood.
– Any valve problems: An echocardiogram can easily detect valve leaks and incomplete closure.
– Blood clots or tumors inside the chambers of the heart.
– Any holes in the walls of the heart.
– It's the same technology used to look at babies in the womb. Check it out.
Full Motion MRI
The big new gun in heart diagnostics is the moving MRI. Recent advances in the technology now allow for full motion images of the heart that can be done quickly enough to even accommodate emergency room patients. This tool is proving to be one of the most accurate heart assessment tools yet.
Sometimes technology really does work.
The purpose of this newsletter (in fact, this entire series on the heart, covering anatomy, physiology, and concluding in this issue with diagnostics) was not to turn you into a doctor. My goal was merely to take away some of the mystery and fear that comes from not knowing what's being done to you when it comes to your heart. There's no question that ignorance and the sense of fear and victimization that come with it contribute greatly to both the anxiety and depression so often associated with heart disease and its treatment. Now, though, you should be able to partner to some degree with your doctor when it comes to your treatment – to be proactive, and less anxious.
Keep in mind, there are some doctors who will not like the fact that you can now ask questions and participate in your own healing – to question a diagnosis or treatment option. Unfortunately, insecurity does not brook a challenge. My advice is to stop working with those doctors. Find a doctor that will work with you. Good doctors welcome informed patients.
And that concludes our discussion of the heart. When we return to our series on the human body, we will take on the circulatory system.