Page 408 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

278 PART 3: Cardiovascular Disorders

• Burger W, Jockwig B, Rucker G, Kober G. Influence of right ventricular • Knowledge of antiarrhythmics for prophylaxis, acute management,
pre- and afterload on right ventricular ejection fraction and preload
recruitable stroke work relation. Clin Physiol. 2001;21(1):85-92. and long-term management are necessary for successful arrhyth-
mia management.
• Chadda K, Annane D, Hart N, Gajdos P, Raphael JC, Lofaso F.
Cardiac and respiratory effects of continuous positive airway • The proarrhythmic potential of antiarrhythmic drugs must be recog-
pressure and noninvasive ventilation in acute cardiac pulmonary nized and preventative measures should be taken whenever possible.
edema. Crit Care Med. 2002;30(11):2457-2461. • Knowledge of antiarrhythmic drug pharmacokinetics and phar-
• Cooper DJ, Walley KR, Wiggs BR, Russell JA. Bicarbonate does macodynamics and the impact of multisystem organ disease on
not improve hemodynamics in critically ill patients who have these parameters are important in preventing drug toxicity.
lactic acidosis. A prospective, controlled clinical study. Ann Intern • The intensivist should be skilled in the implantation of temporary
Med. 1990;112(7):492-498. pacing systems, external cardioversion, and defibrillation.

• Guarracino F, Ferro B, Morelli A, Bertini P, Baldassarri R, Pinsky • Role of cardiac pacing, electrical cardioversion, and defibrillation
MR. Ventriculo-arterial decoupling in human septic shock. Crit should be clear to physicians managing patients with arrhythmias.
Care. 2014;18:R80. • Recognition of malfunctioning temporary and permanent
• Henderson WR, Griesdale DE, Walley KR, Sheel AW. Clinical implantable pacemakers or cardioverter defibrillators is crucial in
review: Guyton—the role of mean circulatory filling pressure the management of patients with such devices.
and right atrial pressure in controlling cardiac output. Crit Care.
2010;14(6):243.
• Labovitz AJ, Noble VE, Bierig M, et al. Focused cardiac ultrasound
in the emergent setting: a consensus statement of the American Cardiac arrhythmias are common in the critical care setting. Many
Society of Echocardiography and American College of Emergency arrhythmias detected are benign, may occur in healthy individuals and
Physicians. J Am Soc Echocardiogr. 2010;23(12):1225-1230. require no investigation or treatment, for example, sinus tachycardia,
• Lorigados CB, Soriano FG, Szabo C. Pathomechanisms of myo- sinus bradycardia, Mobitz type I second-degree AV block or premature
cardial dysfunction in sepsis. Endocr Metab Immune Disord Drug atrial and ventricular beats. At times, the arrhythmia may be the clue to
Targets. 2010;10(3):274-284. a sick patient, such as sinus tachycardia in a patient developing sepsis
• Paulus WJ. Novel strategies in diastolic heart failure. Heart. or atrial fibrillation due to a pulmonary embolus. Correct diagnosis
and understanding arrhythmia mechanisms as well as knowledge of
2010;96(14):1147-1153. antiarrhythmic drug pharmacology and nonpharmacologic therapies
• Sevilla Berrios RA, O'Horo JC, Velagapudi V, Pulido JN. of arrhythmias are crucial for successful arrhythmia management. This
Correlation of left ventricular systolic dysfunction determined by chapter focuses on the mechanisms, investigation, and management of
low ejection fraction and 30-day mortality in patients with severe the most common, clinically significant arrhythmias encountered.
sepsis and septic shock: a systematic review and meta-analysis.
J Crit Care. 2014;29(4):495-499. TACHYARRHYTHMIAS
• Vincent J-L, Rhodes A, Perel A, et al. Update on Hemodynamic
Monitoring: a Consensus of 16. Critical Care. 2011;15:229. ■ MECHANISMS
Tachycardia mechanisms have been classified as due to abnormalities of
impulse formation or impulse conduction. Abnormalities of impulse
1-3
formation may be due to normal automaticity, abnormal automaticity or
REFERENCES triggered activity occurring within atrial or ventricular muscle tissue
1,3
Complete references available online at www.mhprofessional.com/hall or the specialized conduction system (Fig. 36-1A). Natural pacemaker
cells are found in the sinus node, parts of the atria, the atrioventricular
node, and the His-Purkinje system. These cells exhibit phasic sponta-
neous depolarization during diastole, resulting in an action potential
1
the sinus node is the dominant pacemaker, subsidiary pacemakers may
CHAPTER Cardiac Arrhythmias, when the threshold potential is reached. Although in the normal heart,
become dominant under certain conditions, for example, sympathetic
36 Pacing, Cardioversion, and stimulation or digitalis toxicity (Fig. 36-1). Normal atrial and ven-
Defibrillation in the Critical tricular muscle maintains a high negative resting potential (−90 mV)
and only depolarizes when stimulated. Under certain pathophysiologic
Care Setting conditions, for example, electrolyte abnormalities or ischemia, the rest-
ing membrane potential may decrease (−60 mV) and cells may now
Vikas P. Kuriachan spontaneously depolarize.
Anne M. Gillis Triggered activity is caused by afterdepolarizations that occur early
in repolarization (early afterdepolarizations [EADs]) or after repolariza-
tion is complete (delayed afterdepolarizations [DADs]) (Fig. 36-1B).
1,3
KEY POINTS EADs may reach threshold to activate the slow inward current generat-
• Correct diagnoses and understanding of arrhythmia mechanisms ing a new action potential and this cycle may repeat generating a sus-
are crucial to successful arrhythmia management. tained tachycardia. EADs are believed to be the mechanism of torsade de
pointes ventricular tachycardia (V ). DADs initiate a triggered response
3
t
• The hemodynamic effects of an arrhythmia are important in devel- only when their amplitude reaches a critical threshold (Fig. 36-1C).
oping an appropriate treatment strategy. Increasing the heart rate or the prematurity of an extrastimulus increases
• Predisposing conditions and reversible causes should be recog- the amplitude of a DAD thus increasing the probability of inducing a
nized and corrected. tachycardia. DADs are thought to cause arrhythmias secondary to digi-
talis toxicity and in the setting of heart failure.

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