Arrhythmia and features
Atrial fibrillation
• Atrial rhythm grossly irregular
• Ventricular rhythm grossly irregular, may be normal rate or rapid ventricular response (RVR)
• QRS complexes of uniform configuration and duration
• PR interval indiscernible
• No P waves; atrial activity appears as erratic, irregular, baseline fibrillatory waves (F waves)
Junctional rhythm
• Atrial and ventricular rhythms regular; atrial rate 40 to 60 beats per minute; ventricular rate usually 40 to 60 beats per minute (60 to 100 beats per minute is accelerated junctional rhythm)
• P waves preceding, hidden within (absent), or after QRS complex; usually inverted if visible
• PR interval (when present) ⬍0.12 second
• QRS complex configuration and duration normal, except in aberrant conduction
First-degree AV block
• Atrial and ventricular rhythms regular
• PR interval ⬎0.20 second
• P wave precedes QRS complex
• QRS complex normal
Second-degree AV block Mobitz I (Wenckebach)
• Atrial rhythm regular
• Ventricular rhythm irregular
• Atrial rate exceeds ventricular rate
• PR interval progressively longer with each cycle until QRS complex disappears (dropped beat); PR interval shorter after dropped beat
Second-degree AV block Mobitz II
• Atrial rhythm regular
• Ventricular rhythm regular or irregular, with varying degree of block
• PR interval constant for conducted beats
• P waves normal size and shape, but some aren’t followed by a QRS complex
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COMMON DISORDERS
173
Causes Treatment
• Heart failure, chronic obstructive pulmonary disease, thyrotoxicosis, constrictive pericarditis, ischemic heart disease, sepsis, PE, rheumatic heart disease, hyperten- sion, mitral stenosis, atrial irritation, or complication of coronary bypass or valve replacement surgery
• Nifedipine and digoxin use
• If patient is unstable with a ventricular rate ⬎150 beats per minute, immediate cardioversion
• If patient is stable, follow ACLS protocol and drug therapy, which may include calcium channel blockers, beta-adrenergic blockers, amiodarone, or digoxin
• Anticoagulation therapy possibly also needed
• In some patients with refractory atrial fibrillation uncon- trolled by drugs, radiofrequency catheter ablation
• Inferior wall MI or ischemia, hypoxia, vagal stimulation, and SSS
• Acute rheumatic fever
• Valve surgery
• Digoxin toxicity
• Correction of underlying cause
• Atropine for symptomatic slow rate
• Pacemaker insertion if patient doesn’t respond to drugs
• Discontinuation of digoxin, if appropriate
• Possible in healthy persons
• Inferior wall MI or ischemia, hypothyroidism, hypokalemia, and hyperkalemia
• Digoxin toxicity; use of quinidine, procainamide, beta- adrenergic blockers, calcium channel blockers, or amiodarone
• Correction of underlying cause
• Possibly atropine if severe symptomatic bradycardia develops
• Cautious use of digoxin, calcium channel blockers, and beta-adrenergic blockers
• Inferior wall MI, cardiac surgery, acute rheumatic fever, and vagal stimulation
• Digoxin toxicity; use of propranolol, quinidine, or procainamide
• Treatment of underlying cause
• Atropine or transcutaneous pacemaker for symptomatic bradycardia
• Discontinuation of digoxin, if appropriate
• Severe CAD, anterior wall MI, and acute myocarditis
• Digoxin toxicity
• Temporary or permanent pacemaker
• Atropine, dopamine, or epinephrine for symptomatic bradycardia
• Discontinuation of digoxin, if appropriate
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CARDIAC EMERGENCIES
Understanding cardiac arrhythmias (continued)
Arrhythmia and features
• Atrial rhythm regular
• Ventricular rhythm regular and rate slower than atrial rate
• No relation between P w a v e s and QRS complexes
• No constant PR interval
• QRS duration normal (junctional pacemaker) or w i d e and bizarre (ventricular pacemaker)
Third-degree AVblock (complete heart block)
Premature ventricular contraction (PVC)
Ventricular tachycardia
• Atrial rhythm regular
• Ventricular rhythm irregular
• QRS complex premature, usually followed by a complete compensatory pause
• QRS complex w i d e and distorted, usually >0.12 second
• Premature QRS complexes occurring alone, in pairs, or in threes, alternating w i t h normal beats; focus from one or more sites
• Ominous w h e n clustered, multifocal, w i t h R-wave-on- T pattern
• Ventricular rate 100 to 220 beats per minute; rhythm usually regular
• QRS complexes w i d e , bizarre, and independent of P w a v e s
• P w a v e s not discernible
• M a y start and stop suddenly
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COMMON DISORDERS
175
Causes Treatment
• Inferior or anterior wall MI, congenital abnormality, rheumatic fever, hypoxia, postoperative complication of mitral valve replacement, postprocedure complication of radiofrequency ablation in or near AV nodal tissue, Lev disease (fibrosis and calcification that spreads from cardiac structures to the conductive tissue), and Lenègre disease (conductive tissue fibrosis)
• Digoxin toxicity
• Atropine, dopamine, or epinephrine for symptomatic bradycardia
• Transcutaneous or permanent pacemaker
• Heart failure; old or acute MI, ischemia, or contusion;
myocardial irritation by ventricular catheter or a pace- maker; hypercapnia; hypokalemia; hypocalcemia; and hypomagnesemia
• Drug toxicity (digoxin, aminophylline, tricyclic antide- pressants, beta-adrenergic blockers, isoproterenol, or dopamine)
• Caffeine, tobacco, or alcohol use
• Psychological stress, anxiety, pain, or exercise
• If warranted, procainamide, amiodarone, or lidocaine IV
• Treatment of underlying cause
• Discontinuation of drug causing toxicity
• Potassium chloride IV if PVC induced by hypokalemia
• Magnesium sulfate IV if PVC induced by hypomagnesemia
• Myocardial ischemia, MI, or aneurysm; CAD; rheumatic heart disease; mitral valve prolapse; heart failure;
cardiomyopathy; ventricular catheters; hypokalemia;
hypercalcemia; hypomagnesemia; and PE
• Digoxin, procainamide, epinephrine, or quinidine toxicity
• Anxiety
• If regular QRS rhythm (monomorphic), administer amiodarone (follow ACLS protocol); if drug is unsuccess- ful, cardioversion
• If irregular QRS rhythm (polymorphic) and QT interval is prolonged, stop medications that may prolong QT interval;
correct electrolyte imbalance; administer magnesium;
if ineffective, cardioversion
• If irregular QRS rhythm (polymorphic) and QT interval is normal, stop medications that may prolong QT interval;
correct electrolyte balance; administer amiodarone;
if ineffective, cardioversion
• If the patient with monomorphic or polymorphic QRS complexes becomes unstable, immediate defibrillation
• If pulseless, initiate CPR; follow ACLS protocol for defibrillation, ET intubation, and administration of epinephrine or vasopressin, followed by amiodarone or lidocaine and, if ineffective, magnesium sulfate or procainamide
• Implantable cardioverter–defibrillator (ICD) if recurrent ventricular tachycardia
(continued)
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176
CARDIAC EMERGENCIESVentricular irritability is a sure
sign of cardiac contusion.
Understanding cardiac arrhythmias (continued)
Arrhythmia and features
Ventricular fibrillation
• Ventricular rhythm and rate chaotic and rapid
• QRS complexes wide and irregular; no visible P waves
Asystole
• No atrial or ventricular rate or rhythm
• No discernible P waves, QRS complexes, or T waves
And also . . .
Keep these signals in mind as well:
• arrhythmias due to ventricular irritability • cardiac tamponade
• hemodynamic instability • pericardial friction rub.
What tests tell you
• ECG will reveal rhythm disturbances, such as premature ventricular contractions, premature atrial contractions, ventricular tachycardia, atrial tachycardia, and ventricular fibrillation, along with nonspecific ST segment or T wave changes occurring within 24 to 48 hours after the injury.
• Echocardiogram will show evidence of abnormal ventricu- lar wall movement and decreased ejection fraction.
• Multiple-gated acquisition scan will show decreased ability of effective heart pumping.
• Cardiac enzyme levels will show elevations of CK-MB to greater than 8% of total CK within 3 to 4 hours after the injury.
• Cardiac troponin I levels may be elevated 24 hours after the injury.
How it’s treated
Maintaining hemodynamic stability and adequate cardiac output are key. IV fluid therapy may be necessary. Continuous ECG
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COMMON DISORDERS
177
Causes Treatment
• Myocardial ischemia, MI, untreated ventricular tachy- cardia, R-on-T phenomenon, hypokalemia, hyperkalemia, hypercalcemia, hypoxemia, alkalosis, electric shock, and hypothermia
• Digoxin, epinephrine, or quinidine toxicity
• CPR; follow ACLS protocol for defibrillation, ET intuba- tion, and administration of epinephrine or vasopressin, amiodarone, or lidocaine and, if ineffective, magnesium sulfate or procainamide
• ICD if risk of recurrent ventricular fibrillation
• Myocardial ischemia, MI, aortic valve disease, heart failure, hypoxia, hypokalemia, severe acidosis, electric shock, ventricular arrhythmia, AV block, PE, heart rupture, cardiac tamponade, hyperkalemia, and electromechanical dissociation
• Cocaine overdose
• Continue CPR; follow ACLS protocol for ET intubation, temporary pacing, and administration of epinephrine or vasopressin and atropine
monitoring is used to detect arrhythmias. Amiodarone or lidocaine may be administered to treat ventricular arrhythmias, and digoxin may be given to treat pump failure. Inotropic agents may be used to assist with improving cardiac output and ejection fraction.