Definition
Arrhythmias are abnormal heart rhythms. Common types are the following:
A.Bradycardia: Heart rate less than 60 bpm; impulse originates in SA node.
B.Tachycardia: Heart rate greater than 100 to 160 bpm; impulse originates in SA node.
C.Supraventricular tachydysrhythmias (SVTs): Heart rate greater than 100 bpm; originates in the following:
1.Atrioventricular nodal reentrant tachycardia (AVNRT), which is intranodal reentry by means of fast and slow conduction pathways within the AV junction.
2.Orthodromic atrioventricular reentrant tachycardia (AVRT), which is tachycardia across accessory pathways associated with preexcitation.
D.Atrial fibrillation (AF): Chaotic electrical activity caused by rapid discharges from numerous ectopic foci in atria. Atrial rate is difficult to count. There are three types of AF:
1.Paroxysmal AF occurs in patients who usually have normal sinus rhythm (NSR). There may be an episode of faulty electrical signals and rapid heart rate. This usually starts suddenly and stops on its own. Symptoms can be mild or severe and usually stop in less than 24 hours, but may last for several days.
2.Chronic AF occurs in patients who have a permanent fibrillation rather than brief episodes of symptoms.
3.Premature ventricular contractions (PVCs) are impulses that form within the Purkinje network (see section Atrial Fibrillation
of this chapter).
Incidence
A.SVTs are the most common cardiac arrhythmias presenting to healthcare providers.
B.AVNRT accounts for 60% to 70% of all SVTs.
C.AVRTs account for 30% to 40%.
D.AF is the most common cardiac tachydysrhythmia, affecting approximately 2% of the general population. Prevalence increases with age to 5% of those older than age 69. The presence of AF is associated with a five-fold increase in risk of morbidity, a two-fold increase in mortality, and an increased incidence of embolic stroke.
E.PVCs are common, and their frequency increases with age.
Pathogenesis
A.Bradycardia: Dominance of the parasympathetic nervous system, with excessive vagal stimulation to the heart, causes a decreased heart rate of sinus node discharge.
B.Tachycardia: Dominant sympathetic nervous system stimulation of the heart or vagal inhibition results in positive chronotropic, dromotropic, and inotropic effects.
C.AVRT: The most classic form of this SVT is Wolff–Parkinson–White (WPW) syndrome. Reentry occurs in a loop using atrial myocardium, the AV node-His-Purkinje system, ventricular myocardium, and an accessory AV connection. During sinus rhythm, antegrade conduction through the accessory connection depolarizes the myocardium earlier than would occur by conduction through the AV node-His-Purkinje system, preexcitation is present, and a delta wave (slurring of initial deflection of the QRS complex) is usually seen on the surface 12-lead ECG.
D.AVNRT: The most common form is antegrade conduction, which occurs through a pathway with a short effective refractory period (ERP) and a longer conduction time. This pathway is often referred to as the slow pathway.
E.AF: Multiple, rapid impulses from many foci depolarize the atria in a totally disorganized manner. In the chaos, no P waves, no atrial contraction, loss of atrial kick, and a totally irregular ventricular response occur. The atria quiver, which leads to formation of mural thrombi and potential embolic events.
F.PVCs: These originate in the ventricles as a result of increased irritability in those cells.
Predisposing Factors
A.Bradycardia:
1.Increased vagal tone.
2.Decreased sympathetic drive.
3.Ischemia to SA node.
4.Drugs: Digitalis, propranolol, sedatives, propylthiouracil (PTU) or Tapazole, aminophylline, caffeine, alcohol, nicotine, and sympathomimetics.
5.Normal variant in athletes.
6.Normal body response to insult.
7.Atrial enlargement.
8.Acute myocardial infarction (MI).
9.Congestive heart failure (CHF).
10.Rheumatic heart disease.
11.Hypertensive heart disease.
12.Thyroid disease.
13.Hypothermia.
14.Electrolyte abnormality.
15.Acidosis.
16.Infection.
B.Tachycardia:
1.Decreased vagal tone.
2.Increased sympathetic tone.
3.MI.
C.SVT:
1.Digitalis toxicity.
2.Catecholamines.
D.AF:
1.Myocardial ischemia.
2.Thyrotoxicosis.
E.PVC:
1.Stress.
2.Myocardial ischemia.
Common Complaints
A.Symptoms may not be present; however, patient may note irregular heartbeat.
B.Palpitations.
C.Chest discomfort.
D.Shortness of breath (SOB).
E.Dizziness.
F.Diaphoresis.
G.Weakness.
H.Syncope.
I.Nausea.
Subjective Data
A.Obtain an accurate health and medical history.
B.Explore precipitating factors, such as emotional stress, alcohol or drug use, hot tub, or bath use.
C.Inquire about onset and duration of symptoms, also noting the age of the patient when symptoms began.
D.Explore whether the patient has had concomitant weight loss, mood changes, and tremor, which
are often associated with hyperthyroidism.
E.Carefully determine the number of previous episodes of palpitations or symptoms and what treatment, if any, was initiated.
F.Review all medications including prescription, over-the-counter (OTC), and herbal products.
Physical Examination
A.Check pulse, respirations, blood pressure (BP), and weight:
1.Sinus bradycardia: Pulse rate decreased.
2.ECG: Normal.
3.Sinus tachycardia:
a.Pulse regular.
b.Systolic blood pressure (SBP) constant.
4.AF:
a.Pulse irregular.
b.SBP changing.
5.AVNRT:
a.Pulse regular; AV block usual.
b.SBP constant; electrical alternans rare.
6.AVRT:
a.Pulse regular; AV block not present.
b.SBP constant; electrical alternans common, especially at high heart rates.
7.PVC: Pulse diminished or absent.
B.Inspect:
1.General appearance:
a.Is the patient in respiratory distress? Note SOB, chest pain, dyspnea.
b.Does the patient look apathetic? This is a sign of a thyroid problem.
2.Inspect the skin for flushing or pallor.
3.Examine the eyes, noting lid lag.
4.Assess the neck for jugular vein distension or thyromegaly:
a.With sinus tachycardia, neck vein pulsation is normal.
b.With AF, neck vein pulsation is irregular; assess for thyromegaly.
c.AVNRT: Assess the neck veins for frog sign,
in which the atria contract against closed AV valves, producing rapid, regular, expansive venous pulsation in the neck, resembling the rhythmic puffing motion of a frog.
d.AVRT: Assess for frog sign.
C.Auscultate the neck for carotid artery bruits and the heart for abnormal heart sounds. Heart rhythm may be regular or irregular, depending on type of dysrhythmia. Have the patient perform a vagal maneuver (Valsalva’s maneuver). If the vagal maneuver responds to rapid heart rate and the cycle is broken, it is likely the patient has AVRT. If it does not respond, it is possible the patient has AVNRT:
1.Sinus bradycardia:
a.Rate less than 60 bpm.
b.Rhythm regular.
2.Sinus tachycardia:
a.Rate equals 160 to 200 bpm.
b.Rhythm regular; gradual onset and cessation.
c.Constant loudness of first heart sound.
3.AF:
a.Rate: Atrial rate is nonmeasurable, ventricular rate is variable, usually rapid at onset.
b.Rhythm: Atrial and ventricular rhythms are irregular.
c.Loudness of first heart sound changes.
4.AVNRT:
a.AV block is usually present.
b.Loudness of first heart sound is constant.
5.AVRT:
a.AV block is not present.
b.Constant loudness of first heart sound.
6.PVC:
a.Rate depends on underlying rhythm.
b.Rhythm: Prematurity interrupts regularity of rhythm.
Diagnostic Tests
A.ECG.
B.Drug screen:
1.Digitalis.
2.Aminophylline.
3.Illicit drugs.
C.Electrolytes.
D.Arterial blood gases (ABGs) if indicated.
Differential Diagnoses
A.Multifocal atrial tachycardia.
B.Sinus tachycardia with multiple premature atrial contractions.
C.Atrial flutter.
D.Ventricular tachycardia.
E.AV blocks.
Plan
A.General interventions:
1.Remove as many predisposing factors as possible.
2.Stop smoking.
B.Patient teaching:
1.Teach relaxation techniques.
2.Teach the patient and his or her family signs of hemodynamic compromise, including rapid heart rate, unexplained weight gain, worsening dyspnea on exertion, and decreased exercise tolerance.
3.Teach and reassure the patient about long-term medication therapy and its side effects.
4.Educate the patient and family regarding safety, dietary restrictions, and complications that may occur (bleeding) with the use of anticoagulant therapy.
5.Discuss the need for a pacemaker/defibrillator or surgical ablation.
C.Pharmaceutical therapy:
1.Initial treatment usually is prescribed by a physician.
2.Selection of treatment modality should be based on underlying pathophysiology.
3.For reentrant cases (AVNRT, AVRT), agents that block the reentrant circuit are more effective:
a.Digitalis.
b.Beta-blockers.
c.Calcium channel blockers (CCBs).
4.Episodes caused by increased automaticity are treated with the following:
a.Quinidine gluconate (Quinaglute).
b.Procainamide HCl (Procan SR).
c.Disopyramide phosphate (Norpace CR).
5.Chronic AF is treated with anticoagulants such as warfarin sodium (Coumadin):
a.Start therapy as soon as possible if a history of underlying heart disease is present.