We speak of Heart Rate (how fast it beats), and Heart Rhythm (whether it’s regular or not). Heart beats begin in the fetus at about 6 weeks of pregnancy. A group of cells (Sinus Node) at the top-right of the heart has an innate ability to generate electrical impulses. A circuit runs first through both Atria (upper chambers), to the A-V Node (between Atria & Ventricles), then down to the Ventricles (lower chambers), causing the heart muscle to constrict in a coordinated way, pumping blood. See below; also Diagram: The Heart – Anatomy.
The Heart’s Electrical Conduction Circuit
The heart normally beats 60 – 100 times per minute. Rates >100 are considered “Tachycardia”, rates <60 “Bradycardia” (from Ancient Greek words for “fast” and “slow”). Normal exercise can raise the heart rate to 140; hearts of professional basketball players may be so well-conditioned that beating only 40 times per minute at rest pumps plenty of blood for the body.
The term “Arrhythmia” can mean either abnormal rate or rhythm. They’re diagnosed by an Electrocardiogram (EKG). Usually in the office we don’t find the arrhythmia since the patient may not be having symptoms at the time, so we order an “Ambulatory EKG“; a portable patch for 1-2 days, or another kind for 2-4 weeks (showering is possible). If this doesn’t show anything, we consider an indefinite monitor implanted under the skin, usually only for patients who have fainting, spells where they feel about to faint, or infrequent but disabling symptoms like shortness of breath or chest pain.
The following are the most common Arrhythmias which clinicians mention and diagnose. Asterisks denote what might be considered “diseases”; the more asterisks, the more potentially harmful.
Normal Variations in Rhythm
Sinus Arrythmia — Heart speeds up as we breathe in, slows as we breathe out. It’s 100% normal, happens in 100% of people; not a disease. Only relevant because when breathing is irregular, the heart rhythm can seem irregular, which it really isn’t.
Extra Beats — They can originate in the Atria (“Premature Atrial Contractions” – PACs) or the Ventricles (“Premature Ventricular Contractions” – PVCs). They can occur very frequently, sometimes even every 2nd or 3rd beat; might feel like a “skip” in the heart. There’s no danger at all; everyone might have some at some point. But see “Skipped Beats” under Slow Arrhythmias” below.
The main symptom of all the conditions below is palpitations, perhaps lightheadedness. If serious, there can be shortness of breath, chest pain, lightheadedness, fainting, rarely death.
Sinus Tachycardia — Heart rate speeds up, but not >140 beats/min. The rhythm is regular (normal). Can occur from Normal Exercise, Fever, Anxiety, Hyperthyroidism, Anemia, Shock, Low Oxygen, Hypoglycemia, & lots more. Sometimes palpitations occur as well, especially with Anxiety.
Inappropriate Sinus Tachycardia — Simply a Sinus Tachycardia which happens for unexplained reasons. Most common in young people (20s & 30s), more so in women than men. No treatment seems useful at this time, it’s hard to know whether there’s a danger to the condition. It’s newly-recognized, most clinicians won’t have heard of it.
* Paroxysmal Atrial Tachycardia — Now called “Supraventricular Tachycardia” (SVT) because the abnormal electrical impulse doesn’t come from the Sinus Node, but from elsewhere in either the Atria or from the A-V Node (but not the Ventricles). It’s somewhat common, can be quite bothersome, and usually isn’t hard to control.
The Heart Rate is always >160, distinguishing it from other Tachycardias above which we don’t consider “diseases.” The rhythm is completely regular. An SVT begins abruptly out of nowhere, can be brief or ongoing, can occur every few days, every 10 years, or anything in between. It’s only dangerous if it continues unstopped.
Ways to stop it abruptly include massaging the carotid pulse in our neck, or straining hard. What works better is to turn the heart upside-down by bending over, or lying shoulders down and hips high. Best of all and guaranteed to work is to thrust ones face into ice water (the “diving reflex”), though I’ve never heard of anybody doing so.
If nothing helps, paramedics & ER’s have medicine to give. And in rare cases in which that doesn’t work, a controlled shock to the heart is always successful. Ongoing daily medications may prevent future episodes. There’s a procedure called ablation, done in cardiology laboratories, that can find the abnormal focus of cells and destroy them for good.
** Atrial Fibrillation (“A. Fib”) — This is a completely irregular rhythm, no pattern to it at all. It’s easily diagnosed by an EKG. There’s an immediate risk of stress to the heart if the rate is too fast (>100), and a long-term danger of Strokes. See the link for more information.
** Atrial Flutter — Here the rhythm is regular, because the ventricles pump blood consistently. But the Atria are beating extremely fast, only noticeable by an EKG (when we hear or feel a heartbeat, it’s what the ventricles pump out to the body). It’s managed similarly to Atrial Fibrillation above.
*** Ventricular Tachycardia (“V. Tach”) — As opposed to the arrythmias discussed above, which originate in the Atria, V. Tach starts in the ventricles and is much more dangerous. If too fast, the heart won’t pump blood adequately. Treatment is by a electric shock automatically timed to protect the heart (“cardioversion”). Otherwise, the arrythmia can degenerate into “V. Fib” below, which is fatal.
**** Ventricular Fibrillation (“V. Fib”) — Here the ventricles merely wiggle & flutter, unable to pump blood. This is cardiac arrest, leading to death in 4-8 minutes. The only treatment is immediate electrical shock (“defibrillation”), terminating the deadly arrhythmia in hopes that the Sinus Node will take over again with a regular rhythm.
** Asymptomatic Arrhythmias — Two in particular may be found among patients who get EKGs for whatever reason. The danger is that they can spontaneously change into very fast rhythms, including V. Tach which is potentially lethal.
- Long Q-T Interval — A certain EKG measurement called the “QTc”, dangerous is >470 milliseconds for men and >480 msec for women. Very dangerous is >500. In some people the Long Q-T Interval is genetic, although they develop problems only rarely. But certain drugs can make it long. The most common ones (though not most dangerous) in use today are certain (not most) antibiotics, anti-psychotic medications, and cocaine.
- Wolff-Parkinson-White Syndrome — A hereditary disease, such that anyone with a family member who died suddenly for unknown reasons should be tested for it. The test is a simple EKG looking for a “delta wave.” People with this who develop palpitations should get treatment.
The main symptoms here are persistent senses of missed heart beats, maybe with lightheadedness. If serious, they can include shortness of breath, maybe chest pain, and especially fainting. The latter can lead to death if the heart rate is so slow that it stops (“flat line” on EKG).
** Bradycardia — This simply means “slow heart rate.” Reasons behind it can include any kind of heart disease (esp. heart attacks), abnormal electrolyte concentrations in the blood (potassium, magnesium, calcium), and especially medications (even certain eye drops for glaucoma). Note that very-well-conditioned athletes have extremely efficient hearts which pump so much blood that they can beat quite slowly; there’s no danger at all here.
*** Heart Block — Third degree heart block prevents the atrial beats from stimulating ventricles, so the latter are left to find their own electrical source to pump blood. That source (a group of cells somewhere) invariably discharges way too slowly (e.g. <40 times/min.). Treatment mainly involves a pacemaker.