Care of Patients with Dysrhythmias Chapter 36 Care of Patients with Dysrhythmias Automated external defibrillator with electrodes.

Review of Cardiac Electrophysiology Specialized myocardial cells Automaticity Excitability Conductivity Contractility

Cardiac Conduction System

Cardiac Conduction System (cont’d) Sinoatrial node Electrical impulses 60-100 beats/min P wave on ECG Atrioventricular junction PR segment on ECG Contraction known as “atrial kick” Bundle of His Right bundle branch system Left bundle branch system

Electrocardiographic Waveforms ECG waveforms are measured in amplitude (voltage) and duration (time).

Electrocardiographic Waveforms (cont’d) Each segment between the dark lines (above the monitor strip) represents 3 seconds when the monitor is set at a speed of 25 mm/sec. To estimate the ventricular rate, count the QRS complexes in a 6-second strip and then multiply that number by 10 to estimate the rate for 1 minute. In this example, there are 9 QRS complexes in 6 seconds. Therefore the heart rate can be estimated to be 90 beats/min.

ECG Complexes, Segments, & Intervals P wave PR segment PR interval QRS complex QRS duration ST segment T wave U wave QT interval

Normal ECG The components of a normal ECG.

Determining Heart Rate In this example, the heart rate using the big block method is 300 ÷ 4 big blocks (between QRS complexes), or 75 beats/min. The memory method is also demonstrated with a heart rate of 75 beats/min.

ECG Rhythm Analysis Determine heart rate Determine heart rhythm Analyze P waves Measure PR interval Measure QRS duration Interpret rhythm

Normal Sinus Rhythm Normal sinus rhythm. Both atrial and ventricular rhythms are essentially regular (a slight variation in rhythm is normal). Atrial and ventricular rates are both 83 beats/min. There is one P wave before each QRS complex, and all the P waves are of a consistent morphology, or shape. The PR interval measures 0.18 second and is constant; the QRS complex measures 0.06 second and is constant.

Normal Sinus Rhythm (cont’d) Rate: 60-100 beats/min Rhythm: regular P waves: Present, consistent configuration, one P wave before each QRS complex PR interval : 0.12-0.20 second and constant QRS duration: 0.04-0.10 second and constant

Sinus Rhythms Sinus rhythms. A, Sinus tachycardia (heart rate, 110 beats/min; PR interval, 0.12 second; QRS complex, 0.08 second). B, Sinus bradycardia (heart rate, 52 beats/min; PR interval 0.18 second; QRS complex, 0.08 second).

Sinus Dysrhythmias Variant of NSR Results from changes in intrathoracic pressure during breathing

Sinus Bradycardia Sinus bradycardia; heart rate, 40 beats/min.

Sinus Arrhythmias Sinus tachycardia Patient-centered collaborative care

Sinus Tachycardia Sinus tachycardia; heart rate, 110 beats/min.

Dysrhythmias Tachydysrhythmias Bradydysrhythmias Premature complexes Repetitive rhythm complexes Bigeminy Trigeminy Quadrigeminy

Atrial Dysrhythmias Atrial fibrillation. Note wavy baseline with atrial electrical activity and irregular ventricular rhythm.

Premature Atrial Complexes Ectopic focus of atrial tissue fires an impulse before next sinus impulse is due

Supraventricular Tachycardia Rapid stimulation of atrial tissue occurs at rate of 100-280 beat/min with mean of 170 beats/min (adults) Paroxysmal supraventricular tachycardia rhythm is intermittent, terminated suddenly with or without intervention

Atrial Fibrillation Associated with atrial fibrosis and loss of muscle mass Common in heart disease such as hypertension, heart failure, coronary artery disease Cardiac output can decrease by as much as 20% to 30%

Atrial Fibrillation (cont’d) Patient-centered collaborative care Risk for PE, VTE Antidysrhythmic drugs Cardioversion Percutaneous radiofrequency catheter ablation Bi-ventricular pacing Maze procedure

Ventricular Dysrhythmias More life-threatening than atrial dysrhythmias Left ventricle pumps oxygenated blood through the body to perfuse vital organs and other tissues

Ventricular Dysrhythmias (cont’d) Ventricular dysrhythmias. A, Normal sinus rhythm with unifocal premature ventricular complexes (PVCs). B, Normal sinus rhythm with multifocal PVCs (one negative and the other positive).

Premature Ventricular Complexes Result of increased irritability of ventricular cells—early ventricular complexes followed by a pause

Ventricular Tachycardia Also called V tach—repetitive firing of irritable ventricular ectopic focus, usually at 140-180 beats/min Sustained ventricular tachycardia at a rate of 166 beats/min.

Ventricular Fibrillation Also called V fib—result of electrical chaos in ventricles Coarse ventricular fibrillation.

Ventricular Asystole Also called ventricular standstill—complete absence of any ventricular rhythm Ventricular asystole with one idioventricular complex.

Atrioventricular Blocks Differentiated by their PR interval First-degree—all sinus impulses eventually reach ventricles Second-degree—some sinus impulses reach ventricles, others do not Third-degree—no sinus impulses reach ventricles

Dysrhythmias: Nonsurgical Management Antidysrhythmic agents Other drugs Drugs used during cardiac arrest Vagal maneuvers—carotid sinus massage, vagal reflex

Pacemakers Temporary pacing—invasive and noninvasive Permanent pacemakers Placement of a pacemaker in chest and heart leads.

Management of Cardiac Arrest CPR Maintain patent airway Ventilate with mouth-to-mask device Start chest compressions Advanced cardiac life support

Cardioversion Synchronized countershock Used in emergencies for unstable ventricular/supraventricular tachydysrhythmias Used electively for stable tachydysrhythmias resistant to medical therapies

Defibrillation Asynchronous countershock that depolarizes critical mass of myocardium simultaneously to stop re-entry circuit and allow sinus node to regain control of heart

Other Therapies Automatic external defibrillation Radiofrequency catheter ablation Surgical procedures: Permanent pacemaker Coronary artery bypass grafting Aneurysmectomy Implantable cardioverter/defibrillator Open-chest cardiac massage

Community-Based Care Home care management Teaching for self-management Health care resources

A 28-year-old woman with a history of hypertension and tachycardia comes to the hospital clinic stating that she doesn’t feel well. You connect her to a cardiac monitor and observe that she is in SVT with a rate varying between 160-180. She reports shortness of breath, palpitations, and weakness. She appears very nervous and anxious, and her BP is 88/56 mm Hg. What is your first priority intervention? Oxygen should be administered at 2 L per nasal cannula.

(cont’d) Ten minutes later, the patient is still in SVT and reports substernal chest pain and dizziness. Which action will you expect the physician to take to treat the dysrhythmia? Administer amiodarone (Cordarone) IV push. Instruct the patient to take several deep breaths. Perform carotid massage. Order a 12-lead ECG. ANS: C The physician may perform vagal stimulation such as carotid massage, which may be successful in terminating the dysrhythmia; however, it may only be temporarily successful.

(cont’d) The patient’s SVT returns after 30 minutes. What medication do you anticipate will be ordered for the patient? Lidocaine (Xylocaine) 75 mg IVP Mexiletine (Mexitil) 300 mg PO q8h Magnesium sulfate 1 g IVP Adenosine (Adenocard) 6 mg IVP ANS: D The appropriate medication to administer is adenosine (Adenocard), which is the drug used for SVT. The nurse should give the medication as ordered to include 6 mg IV over 1 to 3 seconds followed by 20 mL saline flush. It may be repeated in 1 to 2 minutes if necessary. The nurse should monitor the patient’s heart rate and rhythm carefully after administration of the medication. Be sure to have the crash cart available because a short period of asystole is common after administration. Bradycardia and hypotension may also occur.

(cont’d) The SVT resolves immediately after IV adenosine (Adenocard) is administered. Because the patient has experienced repeated episodes of symptomatic SVT, a cardiologist has been consulted and treatment options discussed. What is the preferred treatment for recurrent SVT? Atrial overdrive pacing Radiofrequency catheter ablation Synchronized electrical shock Daily administration of diltiazem (Cardizem) ANS: B If SVT is continuous, the patient should be studied in the electrophysiology laboratory. The preferred treatment is radiofrequency catheter ablation. Radiofrequency ablation is a procedure that can cure many types of fast heart rates. Using special wires or catheters that are threaded into the heart, radiofrequency energy (low-voltage, high-frequency electricity) is targeted toward the area(s) causing the abnormal heart rhythm, permanently damaging small areas of tissue with heat. The damaged tissue is no longer capable of generating or conducting electrical impulses. If the procedure is successful, this prevents the dysrhythmia from being generated, thereby curing the patient.

Audience Response System Questions Chapter 36 Audience Response System Questions 42

Question 1 Patients with which type of dysrhythmia make up the largest group of those hospitalized with dysrhythmias? Sinus tachycardia Sinus bradycardia Ventricular fibrillation Atrial fibrillation Answer: D Rationale: Atrial fibrillation (AF) is the most common dysrhythmia seen in clinical practice. It is responsible for a third of hospitalizations for cardiac rhythm disturbances. Patients can live with this dysrhythmia, but most are treated with anticoagulation therapy to avoid possible blood clots.

Question 2 On a telemetry monitor, the nurse observes that a patient’s heart rhythm is sustained ventricular tachycardia (VT). The nurse checks the patient and finds him alert and oriented with no reports of chest pain, but feeling slightly short of breath. His blood pressure is 108/70. What is the nurse’s first action? Administration of oxygen and observation of the heart rhythm Administration of IV amiodarone (Cordarone) and dextrose Synchronized cardioversion CPR and immediate defibrillation Answer: A Rationale: Current advanced cardiac life support (ACLS) guidelines recommend administration of oxygen and observation of heart rhythm first, followed by administration of an IV antidysrhythmic agent such as amiodarone mixed with dextrose 5%. Synchronized cardioversion would be the next step. CPR and immediate defibrillation would be used only to treat unstable VT.

Question 3 When using a 5-electrode lead ECG monitoring system, which lead is most optimal for detecting dysrhythmias? III V1 V5 aVR Answer: B Rationale: Five-electrode ECG monitoring systems use four electrode leads to provide six limb lead tracings (leads I, II, III, aVR, aVL, or aVF) and the fifth electrode lead is a chest electrode that can be placed in any of the standard V1 to V6 locations. But in general, V1 is selected because of its value in detecting dysrhythmias (e.g., arrhythmia monitoring). (Source: Accessed August 2, 2011, http://circ.ahajournals.org/content/110/17/2721.full)