As your resting heart rate increases, it is common to feel palpitations, a sensation that your heart is beating more strongly than usual, or a sensation that your heart is beating with some kind of irregularity. The heart rate in pregnant women normally increases by about 20-25 beats per minute (bpm), or 25 percent. Since many women have a resting heart rate of around 80 bpm, the normal pregnancy increase in heart rate can take you into the range of 100 bpm at rest (not exercising). You have what is called a tachyarrhythmia (a higher than normal heart rate), or a tachycardia, if the heart rate exceeds 100 bpm during rest. The risk of developing tachycardia increases as pregnancy progresses toward, and through, labor and delivery
Usually, you feel perfectly normal with a heart rate of 100 bpn, but as the resting heart rate increases into the realm of tachycardia, it is common to feel palpitations. Typically, tachycardia during pregnancy is merely what is called sinus tachycardia, the same kind of tachycardia that occurs during exercise, or when you get excited or frightened suddenly, although it goes on for a long time during pregnancy. If you have sinus tachycardia, it means that your heart is absolutely normal, but it’s beating fast because outside forces are causing the heart’s natural pacemaker, the sinoatrial (SA) node to work faster than it usually does. Located in the upper right region of the heart, the SA node consists of specialized muscle cells that send out electrical impulses that cause the muscle cells surrounding the heart’s two upper chambers, the right and left atria, to contract simultaneously. For each atrial contraction to occur, a wave of electrical impulses must travel throughout the heart’s two atria. The walls of the atria are made of muscle cells that contract when they are stimulated.
In one area of the right atrium, downward from the SA node, is another node of specialized muscle fibers, called the atrioventricular (AV) node. When stimulated by the impulse from the SA node, the cells of the AV node react, not by contracting, but by sending out their own impulse, this one bound for the heart’s two lower chambers, the right and left ventricles. The AV node is thus a kind of relay station for signals arriving from the SA node. As long as the AV node is receiving impulses only from the SA node, and as long as the ventricles are contracting only as a result of the impulses relayed by the AV node, the pathways of electrical signals in the heart are normal. In such cases, if you have a rate above 100 bpm, the condition is sinus tachycardia, and it is not in itself dangerous. On the other hand, sinus tachycardia can be a warning sign of some underlying problem. Thus, if you feel palpitations during pregnancy, you must make an appointment to see your doctor to have your condition evaluated
In some cases, the AV node can be stimulated to send impulse toward the ventricles before the signal impulse wave from the SA has time to arrive. This can happen because of the presence of what is known as an ectopic pacemaker, a node of impulse-transmitting muscle cells, other than the SA node, yet located somewhere in the atria, usually near the AV node. Competing with the SA node, an ectopic pacemaker causes the AV node to fire too frequently, resulting in tachycardia. This is called a supraventricular tachyarrhythmia (SVT), since the problem is coming from “above” the ventricles. It is different from tachycardia that is generated from problems within the ventricles themselves, namely ventricular tachycardia (VT or “v-tach”), the worst kind of tachycardia, which fortunately is rare in pregnancy.
Present in about 24 per 100,000 patients who are admitted to the hospital, SVT is the most common heart arrhythmia in women of reproductive age. About 20 percent of pregnant women have an SVT that was diagnosed previously that is exacerbated by the pregnancy. The risk of developing SVT increases as pregnancy progresses toward, and through, labor and delivery. The commonality of particular types of SVT varies greatly in pregnancy.
Tachyarrhythmia is diagnosed by way of electrocardiography (ECG, sometimes abbreviated EKG), and also through Holter monitoring. Both are non-invasive procedures that work through electrodes that are attached to your skin. In ECG, electrodes are attached on your arms, leg, and chest, and in some cases additional sites, to provide your family doctor, obstetrician, and cardiologist with detailed information of the heart’s electrical activity from numerous angles in order to detect problems in different regions of the heart. This is done in the doctor’s office, or in the hospital. Holter monitoring, the principle is the same as ECG, but you are fitted with a device that you wear for a day or more while you go about your normal activities. Various types of Holter monitors are available with varying numbers of electrodes, depending on how detail is needed concerning different parts of your heart. In all cases, however, unlike ECG, the Holter monitor records data constantly, and transmits those data to your doctor (or the data are downloaded when you return to the doctor). Consequently, if some electrical event happens just once in a while, your doctors can see it.
Various types of SVT are treated effectively, with permanent cure, with a technique called ablation, in which a specially-trained cardiologist guides instruments through tubes through your blood vessels to the site of the ectopic pacemaker and destroys it. This procedure can be done safely during pregnancy. A short-term treatment that often can end an SVT episode in an emergency is vagus nerve stimulation. This can be achieved by massaging the carotid area of the neck, or by dipping the woman’s head partly in cold water. In the event that you have an SVT episode that cannot be stabilized, a cesarean section
Even if ECG or Holter shows that you merely have sinus tachycardia, doctors may run tests for some common conditions, other than pregnancy, that cause the SA node to work too quickly and that are common in young to middle age women. Such conditions include anemia and an overactive thyroid, and they entail a range of treatments.