ously, diagnoses rhythm changes, and treats life- threatening ventricular dysrhythmias. Similar to a pacemaker, the ICD consists of a lead system and a pulse generator. Ideally, the ICD generator is
Morton_Chap08.indd 88
Dysrhythmia Interpretation and Management C H A P T E R 8 89
AP = atrial pacing spike VP = ventricular pacing spike
AP AP Pacing rate V-A interval A-V interval VP VP
F I G U R E 8 - 2 7 The intervals measured on an electrocardiogram
(ECG) strip for a patient with a pacemaker.
implanted in the left pectoral area so that the heart is central to the vector of the defi brillation current (Fig. 8-28).
ICDs have been categorized into “generations,” based on their functionality.
• The fi rst-generation ICDs were nonprogram- mable devices that used a factory-specifi ed rate criterion.
• The second-generation ICDs have programmable features, including bradycardia and antitachycar- dia pacing and synchronized cardioversion. These features allow the use of tiered therapy (ie, differ- ent levels of therapy to treat a dysrhythmia). The fi rst tier of therapy is usually antitachycardia pac- ing, which involves the carefully timed delivery of pacing stimuli. If antitachycardia pacing is not successful, the second tier of therapy (low-energy synchronized cardioversion) is initiated. Some devices allow multiple attempts at cardioversion. If cardioversion is not successful, the third tier of therapy, defi brillation, is used. The number of defi - brillation attempts varies with different devices, but six attempts is usually the maximum. If the patient is successfully converted to a life-com- patible rhythm, but the rate is slow, ventricular demand pacing is initiated. Bradycardia pacing is usually intended for brief periods of pacing until normal rhythm resumes.
TA B L E 8 - 1 1
Troubleshooting a Temporary PacemakerProblem Cause Intervention
Failure to pace: No evidence of pacing stimulus, patient’s heart rate below programmed rate
Battery depletion or pulse generator failure, output or timing circuit failure Loose cable connection
Replace battery or generator. Check all connections for tightness. Failure to capture: Pacing
stimulus not followed by electrocardiogram (ECG) evidence of depolarization
Lead dislodgment
Broken connector pins or fractured extension connecting cable Incompatibility of wire pins with cable
or to generator
Output setting (mA) too low Perforation
Lead fracture without insulation break Increase in pacing threshold from
medication or metabolic changes
Review chest fi lm, turn patient to left lateral decubitus position until lead can be replaced.
Connect wire directly to generator to diagnose cable problem, replace connecting cable.
Ascertain a secure fi t of the exposed pin to the cable or the generator, adjust connection or replace pulse generator. Check capture thresholds and adjust
output to a two- to threefold safety margin.
Review 12-lead ECG, report signs of perforation, stabilize hemodynamics. Check intracavitary ECG; if evidence of
fracture in one pole, unipolarize lead; if total fracture, replace lead.
Check laboratory test results, correct metabolic alterations, review medications and vital signs, increase output.
Oversensing: Device detects noncardiac electrical events and interprets them as depolarization
Oversensitive setting
Device detecting tall T waves and interpreting them as R waves
Reduce sensitivity (value [in millivolts] should be larger to make pacer less sensitive); if patient is pacer dependent (no intrinsic R wave), program to asynchronous mode until problem is corrected.
Increase ventricular refractory period beyond T wave.
Morton_Chap08.indd 89
TA B L E 8 - 1 1
Troubleshooting a Temporary Pacemaker (continued)Problem Cause Intervention
In dual-chamber pacing, cross talk is a form of oversensing: The device detects signals from the other chamber and inhibits; in atrial channel, R waves are detected as P waves.
Atrial lead dislodgment Recheck atrial capture thresholds; if high, dislodgment is probable.
In ventricular channel, atrial pacing stimulus afterpotential is detected as an R wave, with V pacing inappropriately inhibited
High output from atrial channel Reduce output from atrial channel, decrease ventricular channel sensitivity (higher millivolt value).
Electrical interference, improperly grounded electrical devices
Remove nongrounded equipment. Undersensing: Device fails to
detect intrinsic cardiac activity and fi res inappropriately
Asynchronous mode setting (VOO, DOO, AOO)
Reprogram to synchronous mode (VVI, DDD, AAI).
Small intrinsic amplitude Increase sensitivity (turn sensitivity dial toward lower millivolt value).
Lead dislodgment Recheck capture thresholds; if high,
lead probably dislodged and needs repositioning.
Lead insulation break Check lead with pacing system analyzer, if impedance too low (<200 Ω), insulation break is likely, and lead needs to be replaced or can be temporarily placed in unipolar confi guration.
F I G U R E 8 - 2 8 Positioning of the implantable cardioverter–defi brilla-
tor (ICD).
• Third-generation devices have many programma- ble features that allow the physician to tailor the device to the patient’s needs and that provide mem- ory and event retrieval capabilities. Bradycardia pacing therapies with biventricular pacing are
common features of current ICDs. To improve discrimination of tachydysrhythmias, the device allows programming of discrimination algorithms, which withhold therapy for ventricular tachycar- dia when PSVT is confi rmed. The availability of an atrial sensing lead allows for a more specifi c PSVT discrimination algorithm. Some devices also have separate tiers of therapy for atrial tachycardia and atrial fi brillation or fl utter. All third-generation ICDs are “noncommitted” (ie, therapy is aborted if the tachycardia terminates even while the ICD is charging).
As with cardiac pacemakers, a coding system, known as the NBD defi brillator code, has been developed to describe modes of ICD function. The fi rst position of the code indicates the shock chamber—none, atrium, ventricle, or dual (O, A, V, or D). The second position indicates the chamber in which antitachycardia pac- ing is delivered—also coded O, A, V, or D. Position three indicates the means by which tachydysrhythmia is detected, either with the intracardiac electrogram (E) or by hemodynamic means (H). Most current ICDs detect dysrhythmias through intracardiac elec- trograms. The fourth position of the code is the three- or fi ve-letter code for the pacemaker capability of the device. For example, a ventricular defi brillator that detects tachydysrhythmias using intracardiac electrograms and with adaptive rate ventricular antibradycardia pacing would be labeled VOE-VVIR.
Morton_Chap08.indd 90
Dysrhythmia Interpretation and Management C H A P T E R 8 91
R e f e r e n c e s
1. Collins M: Using continuous ST segment monitoring. Nursing 40:11–13, 2010.
2. Pickham D, et al: How many patients need QT interval monitor- ing in critical care units? J Electrocardiol 43(6):572–576, 2010. 3. Advanced Cardiovascular Life Support (ACLS) for Healthcare
Providers. (2010); American Heart Association.
4. Wilber DJ, et al.: Comparison of antiarrhythmic drug ther- apy and radiofrequency catheter ablation in patients with paroxysmal atrial fi brillation: a randomized controlled trial. JAMA 303(4):333–340, 2010.
5. Wigand, D. (ed): AACN Procedure Manual for Critical Care, 5th ed. Philadelphia: Elsevier, 2011.
C A S E S T U D Y
M
r. M. is a 64-year-old man admitted to the critical care unit for unstable angina and to rule out non-ST-segment elevation myocardial infarction (NSTEMI). He is placed on a continuous cardiac monitor using a fi ve-lead placement. The monitor is set to read leads II and MCL1 and display the ECG waveform continuously. A 12-lead ECG is obtained to assess for signs of ischemia, injury, or infarction. Mr. M is noted initially to be in a sinus tachycardia (rate of 110 beats/min). Two hours later, the high rate alarms sound on the cardiac monitor and he is found to have an irregular rhythm with indiscernible P waves. On further assessment, he is noted to have the following vital signs: BP, 97/64 mm Hg; HR, 140 beats/min; RR, 32 breaths/min, as well as increasing chest pain and shortness of breath. The physician decides to perform synchronized cardioversion. The nurse prepares Mr. M. for the procedure and seda- tion is administered. The rhythm is converted with 50 J into a sinus tachycardia with a rate of 106 beats/ min. On assessment, Mr. M.’s blood pressure is increased to 138/74 mm Hg. An antidysrhythmic is ordered and cardiac monitoring is continued.1. What are the advantages of monitoring in leads I and MCL1?
2. What rhythm did Mr. M. develop?
3. What are the immediate nursing priorities for a patient who develops a rhythm change?
4. Why was synchronized cardioversion used for
Mr. M.?
Want to know more? A wide variety of resources to enhance your learn-
ing and understanding of this chapter are available on . Visit
http://thepoint.lww.com/MortonEss1e to access chapter review questions and more!
Morton_Chap08.indd 91
92