Page 423 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 37: Myocardial Ischemia 293

■ ICD ISSUES IN THE ICU SETTING CHAPTER Myocardial Ischemia

Similar device malfunctions as described in the section on cardiac pac-
ing may occur in the ICD patient. If the patient experiences AF/flutter 37 Steven M. Hollenberg
or other SVT, this may be classified by the ICD as V T resulting in
inappropriate ICD therapies. Transthoracic cardioversion or defibril-
lation in the region of, or over, an ICD or pacemaker may damage the
electronic circuits. If performed, the device should be interrogated
following the procedure to ensure that the device is functioning appro- KEY POINTS
priately. If a patient is experiencing frequent incessant V T, cardioversion
and defibrillation therapies may need to be programmed OFF until • Myocardial ischemia results from an imbalance between myo-
pharmacologic therapy has been initiated to suppress the frequency of cardial oxygen demand and supply. The major determinants of
episodes. If surgery is urgently required, precautions must be imple- myocardial oxygen requirements are heart rate, contractility, and
mented to minimize the likelihood that electrocautery signals will be wall stress (afterload).
detected by the ICD resulting in inappropriate shocks or withholding • Patients with myocardial ischemia are divided by presentation into
pacing due to oversensing. 66,67 those with or without ST elevation, in accordance with treatment
strategies. Patients with ST elevation benefit from immediate reperfu-
sion with percutaneous coronary intervention or fibrinolytic agents.
KEY REFERENCES • Myocardial infarction is diagnosed by a compatible clinical his-
tory, evolution of characteristic ECG changes, and an increase and
• Bernstein AK, Parsonnet V. Pacemaker, defibrillator, and lead decrease in cardiac enzymes.
codes. In: Ellenbogen KA, Kay GN, Lau CP, Wilkoff B, eds. Clinical • All patients with suspected myocardial ischemia should be given
Cardiac Pacing, Defibrillation, and Resynchronization Therapy. 3rd aspirin upon presentation.
ed. Philadelphia, PA: Saunders Elsevier; 2007:279-287.
• Connolly SJ, Hallstrom AP, Cappato R, et al. Meta-analysis of the • Prognosis after myocardial infarction is most closely related to the
degree of left ventricular impairment.
implantable cardioverter defibrillator secondary prevention trials.
AVID, CASH and CIDS studies. Antiarrhythmics vs Implantable • Risk stratification is the key to initial management of patients with
Defibrillator study. Cardiac Arrest Study Hamburg. Canadian non-ST elevation acute coronary syndromes.
Implantable Defibrillator Study. Eur Heart J. 2000;21(24):2071-2078. • In patients with high-risk non-ST elevation acute coronary syn-
• Dorian P. Mechanisms of action of class III agents and their dromes, an early invasive approach is preferred.
clinical relevance. Europace. 2000;1(suppl C):C6-C9. • Aspirin, clopidogrel, β-blockers, angiotensin converting enzyme
• Fuster V, Ryden LE, Cannom DS, et al. ACC/AHA/ESC inhibitors, and statins have been shown to decrease mortality after
2006 guidelines for the management of patients with atrial myocardial infarction.
fibrillation— executive summary: a report of the American • Echocardiography is extremely useful for the diagnosis of compli-
College of Cardiology/American Heart Association Task Force cations after myocardial infarction. Invasive hemodynamic moni-
on Practice Guidelines and the European Society of Cardiology toring may be necessary in some cases as well.
Committee for Practice Guidelines (Writing Committee to Revise • Patients with cardiogenic shock should be stabilized with an intra-
the 2001 Guidelines for the Management of Patients With Atrial aortic balloon pump and revascularized promptly with percutane-
Fibrillation). J Am Coll Cardiol. 2006;48(4):854-906. ous coronary intervention or bypass surgery.
• Gillis AM. Class I antiarrhythmic drugs. In: Zipes DP, Jalife
J, eds. Cardiac Electrophysiology: From Cell to Bedside. 4th ed.
Philadelphia, PA: WB Saunders and Co; 2004:911-917.
• Link MS, Atkins DL, Passman RS, et al. Part 6: electrical therapies:
automated external defibrillators, defibrillation, cardioversion, INTRODUCTION
and pacing: 2010 American Heart Association Guidelines for Myocardial ischemia can go unrecognized in an ICU setting. Signs
Cardiopulmonary Resuscitation and Emergency Cardiovascular of myocardial ischemia may be obscured by other illnesses present in
Care. Circulation. 2010;122(18 suppl 3):S706-S719. the critically ill patient. Physical examination in these patients often is
• Moss AJ, Zareba W, Hall WJ, et al. Prophylactic implantation of limited, or its results altered, by the presence of other disease processes.
a defibrillator in patients with myocardial infarction and reduced Myocardial ischemia and attendant left ventricular dysfunction may
ejection fraction. N Engl J Med. 2002;346(12):877-883. complicate the course and treatment of a particular illness. Conversely,
• Neumar RW, Otto CW, Link MS, et al. Part 8: adult advanced cardio- multisystem illness may set the conditions for increased oxygen demand,
vascular life support: 2010 American Heart Association Guidelines often accompanied by diminished delivery of oxygen to the heart. For
for Cardiopulmonary Resuscitation and Emergency Cardiovascular these reasons, the critical care physician must maintain a high index
Care. Circulation. 2010;122(18 suppl 3):S729-S767. of suspicion for myocardial ischemia in the ICU setting, especially in
• Roden DM. Antiarrhythmic drugs. In: Hardman JG, Limbird the patient with a prior history of or multiple risk factors for coronary
artery disease.
LE, eds. Goodman and Gilman’s The Pharmacological Basis of
Therapeutics. 10th ed. New York, NY: McGraw-Hill; 2001:933-970. ■ TERMINOLOGY
• Zipes DP. Mechanisms of clinical arrhythmias. J Cardiovasc Myocardial ischemia results from an imbalance of oxygen supply and
Electrophysiol. 2003;14(8):902-912. oxygen demand. The heart is an aerobic organ whose capacity for
anaerobic glycolysis is limited; it makes use of oxygen avidly and effi-
ciently, extracting 70% to 80% of the oxygen from coronary arterial
1
REFERENCES blood. Because the heart extracts oxygen nearly maximally independent
of demand, any increases in demand must be met by commensurate
Complete references available online at www.mhprofessional.com/hall increases in coronary blood flow.

section03.indd 293 1/23/2015 2:07:17 PM