Page 665 - Cardiac Nursing

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C HAPTER 2 7 / Sudden Cardiac Death and Cardiac Arrest 641
ventricular arrhythmias that develop during physical activity in blocking agents can be helpful in treating this condition. The first
the presence of a normal resting ECG. 20,23 episode often occurs during childhood. The arrhythmia is charac-
terized by bidirectional and polymorphic VT. The condition is
Congenital Long QT Syndrome rare, and is related to a genetic disorder. CPVT is caused by mu-
Patients with the classic long QT intervals corrected for heart rate tations involving the cardiac ryanodine receptor, and calse-
20,23,31
(QTc interval) are at increased risk for torsades. 20,23,24 Congeni- questrin, a calcium-buffering protein.
tal long QT is hereditary; mutations in eight genes have been
identified. The most common mutations are LQT1 (42%),
LQT2 (45%), and LQT3 (8%). Most mutations affect the cardiac MANAGEMENT OF SCA
potassium-channel genes KCNQ1 and KCNH2 and cause the
most frequent forms of long QT. An impaired sodium channel The outcome of cardiac arrest is determined by how promptly
gene, SCN5A, is the cause for LQT3. However, the mutation treatment is initiated with advanced cardiac life support (ACLS).
LQT4 has been identified as a mutation from a membrane adap- To improve outcome from SCA, the following must occur as rap-
tor protein, and not an ion channel. 12,23 QT interval duration was idly as possible: (1) early recognition of warning signs, (2) early
identified as the strongest predictor of SCD, even before genetic activation of the emergency medical system, (3) early basic car-
mutation identification. A QTc greater than 500 ms in a patient diopulmonary resuscitation (CPR), (4) early defibrillation, and
identified with an affected gene carries the highest risk of syncope (5) early ACLS. These events have been described as “links in a
or SCD by the age of 40. 20 Two patterns of long QT have been chain of survival,” because they are all connected and indispensa-
reported: the Romano Ward syndrome, which is an autosomal ble to the overall success of emergency cardiac care. 32,33
dominant syndrome, and the Jervell and Lange-Nielsen syn- Although this section summarizes ACLS recommendations for
drome. The latter is autosomal recessive, more severe, and often the adult patient, it is not a complete reference. For each cardiac
associated with congenital deafness. 20,25 nurse, participation in an ACLS provider course by the American
In individuals with long QT, ventricular arrhythmias often oc- Heart Association (AHA) is strongly recommended. In addition,
cur in the setting of stress and activity, but also can occur during the most current version of Emergency Cardiac Care, Basic Life
rest and sleep. Exercise, particularly swimming, is often a trigger Support for Healthcare Providers, and The Textbook of Advanced
for arrhythmias in the LQT1 patients. LQT2 patients have ar- Cardiac Life Support should be used as definitive references.
rhythmias that are triggered during both rest and emotion, often
associated with acoustic stimuli. The LQT3 patients are more
prone to having arrhythmias at rest and during sleep. 20,26 Avoid- Adult Advanced Cardiac Life Support
ance of competitive sports is recommended for LQT1 and LQT2 ACLS teaches the appropriate skills and knowledge, as deter-
patients, but not for LQT3 patients. 22
mined by leaders in emergency cardiovascular care (ECC), to im-
prove survival from SCA and acute life-threatening cardiopul-
Brugada Syndrome monary events. ACLS includes early recognition of prearrest,
Brugada syndrome is an inherited disease that is associated with a basic life support, the use of airway and circulation adjuncts, car-
high incidence of sudden death. A mutation of cardiac sodium- diac monitoring, and defibrillation and other arrhythmia control
channel gene SCN5A, has been identified in about 20% of per- techniques. ACLS also includes establishment of intravenous ac-
sons with the syndrome, and occurs more often in men. The Bru- cess, drug therapy, and postresuscitation care. This section focuses
gada syndrome is confirmed with ST-segment elevation in the on defibrillation and ACLS management of pulseless cardiac ar-
precordial leads, right bundle-branch block (RBBB) conduction rest. Postresuscitation management of SCA survivors is also in-
pattern, and history of SCD. The ECG changes may be present cluded. For discussions of basic and complex arrhythmias, con-
all the time or elicited when antiarrhythmic drugs are given that duction disturbances, electrophysiology studies, hemodynamic
block sodium channels (Chapter 15). 20,27,28 Fever has been re- monitoring, acute coronary syndrome, pacemakers, and im-
ported to unmask ECG changes of Brugada syndrome and elicit plantable defibrillators, respectively, refer to Chapters 15, 16, 18,
an electrical VT storm. 29 Globally, the syndrome is more preva- 21, 22, and 28, respectively.
lent in areas of southeast Asia. 23 In 2005, the AHA updated the guidelines for CPR and
32
ECC. The guidelines are based on the 2005 International Con-
Wolff–Parkinson–White Syndrome sensus Conference on Cardiopulmonary Resuscitation and Emer-
Wolff–Parkinson–White (WPW) is associated with an accessory gency Cardiovascular Care Science with Treatment Recommenda-
pathway that allows for conduction between the atria and ventri- tions. The classes of recommendation for ACLS management are
cles. Normally, WPW is associated with nonlethal arrhythmias. based on evidence evaluation (Display 27-3).
However, if atrial fibrillation develops and conduction is rapid
over the accessory pathway, the ventricular rate can become so fast Electrical Therapy of Malignant
that the rhythm degenerates into VF. SCD in the setting of WPW Arrhythmias
is quite low, and has been reported at 0.39% per year. 23,30 Defibrillation and cardioversion are a delivery of electrical energy
that totally depolarizes and stuns the myocardium, which allows
Catecholaminergic Polymorphic the sinus node to resume its function as the pacemaker for the
Ventricular Tachycardia heart. Defibrillation is, by definition, the therapy for VF. Car-
CVPT is a catecholamine-dependent arrhythmia that occurs in dioversion, which is a synchronized shock, is the electrical therapy
the absence of a long QT interval. The arrhythmia often occurs dur- for all other tachyarrhythmias. Transcutaneous and transvenous
ing physical activity or emotional distress; therefore, -adrenoceptor- pacing are additional types of electrical therapy used in ACLS