We've all had the experience of feeling a patient's pulse and noting it to be irregular. This is a common experience. We may feel a missed beat, or perhaps an extra beat, sometimes followed by a pause.
As primary care practitioners, we should all be familiar with arrhythmias, and it's easy to learn them all. Then we can decide if the irregularity we are feeling in our patient falls within the area of concern.
Nervous control of the heart comes through the autonomic nervous system. There is a sympathetic and parasympathetic balance, constantly shifting, fine-tuned by the vagus nerve, which is capable of millisecond adjustments. Catecholamines (epinephrine, norepinephrine, and dopamine) circulating in the bloodstream cause increased speed and force of contraction, as does the thyroid hormone. Electrolyte imbalance (especially low potassium) causes increased irritability of the conduction system and the heart muscles, along with smoking, alcohol, stress or extreme exercise. Potassium tends to be low during times of stress or severe illness, due to an excess secretion of aldosterone by the adrenal glands, which tends to lower it. Overdose of digitalis causes arrhythmias as it increases the sensitivity of the heart muscle.
Arrhythmias, commonly called palpitations, are often associated with shortness of breath, lightheadedness, chest pain, sweating, an altered mental state, syncope or near-syncope (fainting). About 15 percent of the general population experience palpitations in any given year! It is one of the most common symptoms in medical clinics and in the ER. Most patients with palpitations do not have underlying heart disease and have a benign prognosis, but some are serious.
There are eight categories of irregular (or abnormal) heart rates:
- Premature ventricular or atrial contractions (PVCs or PACs);
- Paroxysmal atrial tachycardia (PAT), which is also referred to as premature supra-ventricular tachycardia (PSVT), arises in the atria or the a-v node;
- Atrial fibrillation;
- Atrial flutter;
- Ventricular tachycardia;
- Ventricular bradycardia;
- Heart block; and
- Sick sinus syndrome.
Premature Atrial or Ventricular Contractions
There is often a pause following the extra systole. The superimposed extra-contraction plus a reduced stroke volume during the extra beat may give the person a perception of a skipped beat, or a heart "flip-flop." PACs and also some PVCs occur commonly in healthy individuals, especially if highly stressed, or if they have been consuming coffee, excessive tea, or even chocolate!
One cannot reliably tell the clinical difference between PACs and PVCs. An ECG is needed to do that. PACs and most PVCs are harmless, even if they are frequent (several a minute). However, PVCs in some individuals may indicate heart disease. If there are any other symptoms or the patient is at high risk (hypertensive, diabetic, heavy smoker, or a history of heart disease), a referral to a cardiologist is needed. This is a subacute red flag. An acute red flag patient needs to go to the ER immediately (for example, chest pain with perspiration). A subacute red flag patient needs referral to a specialist promptly, within a day or two.
Paroxysmal Atrial Taccycardia or Paroxysmal Supraventricular Taccycardia
These episodes that are regular and fast at 160 to 200 beats per minute may last 20 or 30 minutes, and they start and stop suddenly. This common malady occurs in those without heart disease and is more unpleasant than dangerous, caused by a temporary increased sensitivity of the sinoatrial (SA) node in susceptible individuals. It is common in teen-agers and those in their early 20s, and a special form of it in small children is known as the Wolfe-Parkinson-White (WPW) syndrome.
PAT episodes can be treated by the Valsalva maneuver (bearing down and increasing abdominal pressure, stimulating the vagus nerve). Also effective is the carotid body massage, gently rubbing one carotid artery in the mid-neck region (never both carotid arteries together). Plunging the face in ice water works well, though it is somewhat unpleasant. All of these maneuvers increase vagal tone and slow the rapid heart rate. The patient may need a beta-blocker if attacks are frequent or disabling. Children with WPW need a radiofrequency ablation of the extra pacemaker that is causing these attacks. Temporary attacks of rapid heart rate such as this are a subacute red flag if the person has not been worked up by a cardiologist.
Atrial Fibrillation and Atrial Flutter
I will discuss these two heart conditions together. The pulse of atrial fibrillation is totally irregular and fast; the pulse of flutter is regular and fast (both range from 160 to 200/min). Both can be idiopathic (unknown cause), but in most cases are due to hypertension, coronary artery disease, rheumatic heart disease, hyperthyroidism or alcohol abuse. The fast but regular heart rate of atrial flutter can be clinically distinguished from PAT because it doesn't go away, whereas PAT resolves after an episode of up to 30 minutes.
Both of these sustained atrial arrhythmias can be treated with conversion to a normal sinus rhythm by electroconversion or long-term coverage with anticoagulants if conversion is not successful, or if the arrhythmia returns after conversion. Thousands of people with unresolved atrial fibrillation do fine as long as they are anticoagulated with Coumadin (clots can otherwise form in the heart and embolize to the brain). These patients have subacute red flags and need prompt referral to a cardiologist, but they do not need immediate admission to an emergency room.
Ventricular Tachycardia
The term tachycardia refers to a rapid heart rate, from 120 beats per minute to as high as 200. A rapid heart rate is a normal response to exercise, stress reactions or sexual activity (due to sympathetic nerve stimulation at the finish of orgasm). In a normal heart, this is a sinus tachycardia, initiated by the sinoatrial node in the right atrium. If there is sustained tachycardia without external provocation, this suggests that it might be VT, in which the rapid heartbeat is initiated in the ventricles themselves. VT almost always occurs in patients who have underlying structural heart disease. Coronary artery disease is the most common cause, but it can also be due to hypertension, drugs and Chagas disease (disease related to a heart parasite) in Central and South America.
An ECG is required to determine the nature of the rapid heart rate. If sustained over a period of time, VT causes an inefficient cardiac output. It can lead to shock, loss of consciousness and finally, death. VT places the patient at risk for going into ventricular fibrillation, which is fatal. The treatment is electric cardioversion, and then maintenance with beta-blocker drugs. These patients have either acute or subacute red flags, depending on how ill they are when you see them, but all need prompt evaluation and treatment by a cardiologist.
Bradycardia
A pulse of less than 60/min is defined as bradycardia. This can be a sign of a very healthy heart in athletic individuals, due to increased heart efficiency and increased vagal tone. Some marathon runners have normal heart rates of 46 beats per minute. In the non-athlete, there are multiple causes of an abnormally slow heart rate. Some are extrinsic to the heart (drugs, hypothyroidism, central nervous system disorders, high potassium levels, etc.). Others are due to heart disease, caused by a dysfunction of the sinus node or the AV conduction system, which may lead to heart block (see below).
Symptoms of abnormal bradycardia are usually non-specific, including fatigue, lightheadedness or exercise intolerance. These are subacute red-flag cases, and should be referred to an experienced Western clinician, who will need an ECG to establish the diagnosis and to check for heart block.
Heart Block
Three degrees of heart block are possible. These are easy to remember.
With first-degree heart block, every impulse reaches the ventricles, but it is slowed in the AV node. It is seen in teen-agers, athletes and also in many heart diseases. First-degree heart block has no symptoms, and requires no treatment (it is an electrical event only).
Second-degree heart block is more severe. The impulses from the atrium are slowed so that not every beat gets through to the ventricles. This causes bradycardia. These patients may need a pacemaker, although usually they do not. The cardiologist makes these decisions, in close consultation with the patient.
Complete heart block is also known as third-degree block. In this situation, all the impulses from the atria to the ventricles are completely blocked at the AV node. The ventricles then beat on their own, usually at an inefficient, slow rate, often below 40/min. Syncope, heart failure, shock and death can occur. All cases require a permanent external pacemaker.
Sick Sinus Syndrome
Also referred to as sinus node dysfunction, this category includes a wide variety of abnormalities of the heart's pacemaker function. Those with this syndrome may experience alternating bradycardia and tachycardia. Many cases require a permanent external pacemaker. These patients are subacute red flags.
An internist or a cardiologist will be glad to receive your call referring a patient with a cardiac arrhythmia. He or she will thank you for the referral and will remember you later on. The call will also give you the opportunity to tell this clinician what you do to help those who are ill, if you have not already done so. Other referrals will then come back to you, as all Western clinicians need the resources you can provide.
Click here for previous articles by Bruce H. Robinson, MD, FACS, MSOM (Hon).