Keep The Pace

We left off last month with an inspiring quote from Neil Armstrong when he said that we’re all allotted only a limited number of heartbeats so be sure not to waste any of them. I also made the comment that, at first glance, it might be great to get some extra ones so they last a while longer.

That didn’t work out but don’t lose hope; there might be another way to game the system. Wishing that your heart would beat a little slower might actually be a better tactic since the slower your heart goes, the longer you can stretch out those allotted heartbeats. Unfortunately, the same caution applies – be really careful what you wish for because, just like with extra beats, the FAA might also not like it if your favorite AME finds your heart rate too slow at your next medical exam.

The FAA guidelines state that “resting heart rate” (up to 49 years of age) needs to be greater than 44 beats/minute at the low end but less than 110 beats/minute at the top end. If you’re more than 50 years old, your resting heart rate needs to be a little faster, more than 48 beats/minute, before you’re pulled out of line for special evaluation. The reasons for that are the same as last month on extra beats, as an abnormal heart rate might be an indication of an underlying cardiac problem. Heart rates literally vary from minute to minute so the FAA rules apply to truly resting heart rate, which is defined as your pulse after sitting or lying quietly for 5 minutes. All kinds of things affect that like age, fitness, activity levels, smoking (or former smoker), air and body temperature, diet, and obviously emotions. Body habitus (think larger = faster) and body position (sitting, standing, lying down) also have an impact on your resting pulse. There are multiple medical conditions that can raise or lower your baseline pulse rate. Common conditions like thyroid function, diabetes, and medication history (especially beta blockers and calcium channel blockers) all have direct impact on heart rate. If you’re found to have an abnormal pulse rate, both you and the FAA need to sort out if it’s just you or if it’s related to a structural heart condition, as there are lots of them.

Since all of you who have been following this series of articles on the heart are now EKG experts, a quick tour of where your heart rate comes from will be pretty easy. Normal heartbeats start at the top of your heart and the electrical impulse works its way down to the bottom. It makes sense since that’s the same path the blood flows and heart rhythm is designed to coordinate the symmetrical and effective pumping function of the heart. The cycle starts in a place called the “sinoatrial node” (nicknamed the “SA node”), which is a clump of nerve cells at the top of the right atrium. The electrical activity spreads over the two atria (small collecting chambers) and reaches another electrical node of tissue where the atria meet the main pumping chambers, the ventricles, appropriately named the “atrioventricular node” or AV node for short. This is the primary electrical “junction box” kind of thing that has a main cable leaving it (the “bundle of His”) that disperses the electrical activity through three sub-bundles over the ventricles to stimulate coordinated contraction of the muscle and pump blood to the body. All of this electrical activity through these cables is what is measured with our now well-known EKG. (Just as an aside, I’ve always wondered why it’s not abbreviated “ECG” since it stands for “electrocardiogram,” but that’s above my pay grade.)

When all these connections are working, the interaction of factors that triggers the SA node to fire off an impulse is what determines your heart rate. The node has its own intrinsic rate of about 60/minute and it also gets nerve and hormonal stimulation to speed up or slow down. The “fight or flight” sympathetic nervous system speeds your heart up and the “chill out” parasympathetic nervous system slows it down. The slow-down nerves are the vagus nerves (left and right) that come right out of the brain on their way to the SA node. The nerve is aptly named after the Latin root that means “wandering,” since it wanders all over the body and sends impulses to everything from the top of your neck to the end of the GI tract (yes, that end). The Latin root word also gave us words like vagrant, vagabond, vague, wanderlust and even the German words for hiking around (“wandern” – pronounced “vandern”) that all have the same origin.

If your heartbeat is found to be too slow, the first question to answer is why. The best reason is that you’re a great athlete in top shape and your heart just doesn’t need to beat faster than 45 or 50 times a minute since it’s pumping so much blood with each beat (called “stoke volume”). If that’s the case your AME will just have you jump up and down a few times, recheck your pulse and sign you off. But there’re also a bunch of reasons your pulse might be too slow and not speed up with activity that are related to structural heart disease (SHD). The most common structural defect that causes a slow heart rate is disease of that conducting bundle of nerves I talked about a few paragraphs ago. That can be age related from calcification (the same stuff that gets into your coronary arteries), a heart attack that damages the conducting system, or infection that has caused inflammatory damage in the bundles. The work-up for all of these conditions is pretty much the same that I detailed last month. If your cardiologist finds you have a block in your conducting system or malfunction of the SA node where your heartbeat originates you will likely need to have something fixed. If the nodes or conducting bundles are shot, the treatment of choice is to get a pacemaker implanted.

Late-model pacemakers are pretty slick little devices that are about the size of a couple of silver dollars stacked on each other and implanted with a small operation into a little pocket under your pectoralis muscle at the top of the chest (don’t worry, it might bulge a little but you can say you have really buffed up “pecs”). Two wires come off the box and are threaded through veins to your heart. One wire goes into your atrium to stimulate the SA node and the other is advanced into the tip of the ventricle on the right side of your heart. The computer in the device senses if an electrical signal fires off in the atrium and checks the time interval from the last one. If it’s not detected in about one second (a heart rate of 60/minute) it will fire off an impulse. The rate the pacer fires can be changed by your cardiologist to anything that works for you. It can even sense when you’re active and speed itself up when you exercise. The wire in the ventricle is also checking things. If it senses an electrical burst from the atrium it will wait around a few hundredths of a second (think back a few months to the article on PR interval), but if there’s a block and it hits the time limit (usually about 300 msec like we talked about) and the ventricles don’t beat on their own, it will send another little burst of electricity to pace them too. Every second the whole cycle repeats.

Another really awesome feature of modern pacemakers is that a third wire can be added that senses if your heart rate is too fast or in a dangerous rhythm (arrhythmia). Fast heart rates are called tachycardias (tachy comes from Greek word for swift, takhus,” + cardia = heart) and can be very dangerous and even occasionally fatal. One of the most malignant fast heart rates, called “ventricular tachycardia” (V-tach for short), is an unfortunately really quick way to use up all of your allotted heartbeats. With the third wire in place the device is known as an “ICD” (internal cardioverter defibrillator), since it now has an anti-tachycardia capacity. It will sense a dangerously fast heart rate and deliver an internal little jolt to convert a chaotic irregular heart rate back to a regular rhythm and slow it down. It’s kind of like carrying one of the AED (automatic external defibrillator) devices that you see all over public places these days right around inside of you and it is truly life-saving.

The FAA will let you back in the cockpit with a pacemaker or ICD on a special issuance ticket, but you will have to wait two months after the procedure and pass a pacemaker evaluation check. You will also need periodic pacemaker status checks to make sure the device is working properly so you can keep flying. Of all the structural problems you might develop with your heart, conduction blocks are straightforward to fix with one of these devices. But the same admonition goes out this month as last month; don’t go around wishing for this as a way to live longer and slow your heart rate to stretch out your “assigned” heartbeats. If you want to slow your resting pulse get in shape and exercise, don’t smoke, lose weight, get lots of sleep, cut out stress in your life and get your blood pressure down, and of course eat right and don’t drink (too much). Ha – tough assignment – but it’s certainly worth the effort.

Kenneth Stahl, MD, FACS

Kenneth Stahl, MD, FACS is an expert in principles of aviation safety and has adapted those lessons to healthcare and industry for maximizing patient safety and minimizing human error. He also writes and teaches pilot and patient safety principles and error avoidance. He is triple board-certified in cardiac surgery, trauma surgery/surgical critical care and general surgery. Dr. Stahl holds an active ATP certification and a 25-year member of the AOPA with thousands of hours as pilot in command in multiple airframes. He serves on the AOPA Board of Aviation Medical Advisors and is a published author with numerous peer reviewed journal and medical textbook contributions. Dr. Stahl practices surgery and is active in writing and industry consulting. He can be reached at [email protected].

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