Mr. M, 52, comes to the ED complaining of intermittent palpitations, shortness of breath, and lightheadedness. Triage takes Mr. M back into the treatment area after a quick evaluation. His vital signs are BP, 140/80; pulse, 148 and regular; respirations, 18; and SpO2, 97% on room air. While a colleague obtains peripheral I. V. access, you attach a cardiac monitor, which shows sinus tachycardia with frequent premature ventricular contractions (PVCs). Next, you use the SAMPLE mnemonic to conduct a secondary survey:
Signs and symptoms: palpitations, shortness of breath with exertion; lightheadedness when changing from a supine to a sitting position; no chest pain, nausea, or other signs and symptoms Allergies: none known Medications: none Past medical history: none Last meal: light breakfast 2 hours ago Event history: signs and symptoms started about a half-hour ago while working in his basement. Mr. M says that now his chest “feels funny,” and he feels as if he’s “going to pass out. ” Mr. M becomes unresponsive, apneic, and pulseless and the monitor shows a wide-complex tachycardia.
In a previous Heart Beats, we reviewed the five basic steps of rhythm analysis: * Determine the rhythm by measuring the distance between R waves and noting any variations in R-wave regularity. Determine if a 0. 12-second or greater variance exists between the shortest and longest R-wave variations. Figure. Rhythm strip * Calculate the heart rate, using the rapid rate calculation (counting the number of R waves in a 6-second strip and multiplying by 10 to calculate the heart rate per minute), for regular or irregular rhythms.
For a regular rhythm, you can also use the precise rate calculation: Count the number of small squares between two consecutive R waves, and divide this number into 1,500 (the number of small squares in a 1-minute rhythm strip) to obtain the heart rate in beats per minute. Report the atrial and ventricular rates separately if they’re different. * Identify and examine P waves to see if one precedes each QRS complex, and if they’re all identical in size, shape, and position. * Measure the PR interval, which should be 0. 12 to 0. 20 second. * Measure the QRS complex, which should be 0.
10 second or less. Looking at the mystery rhythm Let’s quickly analyze this new rhythm (see illustration) using the five steps: * The ventricular rhythm is regular. * The ventricular rate is 140 to 160 beats/minute. * P waves aren’t seen. * The PR interval can’t be determined. * The QRS interval is wide at 0. 16 to 0. 20 second. The rhythm is monomorphic (consistent QRS morphology) ventricular tachycardia (VT), meaning it comes from a single focus in the ventricles. (Polymorphic VT is an irregular rhythm with varying QRS morphology because of multiple foci.)
Sustained VT lasts more than 30 seconds and can result in inadequate cardiac output, leading to hypotension and heart failure. Causes of VT include acute coronary syndromes, cardiomyopathy, heart failure, myocarditis, valvular heart disease, use of sympathomimetic agents, electrolyte imbalance (especially hyperkalemia, hypokalemia, and hypomagnesemia), and hypoxemia. Signs and symptoms may start or stop suddenly, and include chest discomfort and palpitations, syncope, dizziness, shortness of breath, hypotension, decreased mentation, and rapid or absent pulse.
Helping Mr. M Management of monomorphic VT varies depending on whether the patient is hemodynamically stable, unstable, or (as in Mr. M’s case), pulseless. Call a code and begin CPR immediately and continue with minimal interruptions (no more than 10 seconds). Defibrillation is indicated as soon as possible using the manufacturer recommended device-specific energy level. If the device-specific energy level is unknown, use the default setting of 200 joules for a biphasic defibrillator and 360 joules for a monophasic defibrillator.
1 Administer vasopressors (I. V. epinephrine, vasopressin) and amiodarone as per the American Heart Association Advanced Cardiac Life Support guidelines for pulseless VT/ventricular fibrillation (VF). Perform a rhythm check every 2 minutes during the compressor role change; if you detect a shockable rhythm (pulseless VT or VF), give 1 shock (defibrillate) and resume CPR immediately for 2 minutes after the shock. 1 Consider treatable causes (see Know your H’s and T’s) early in management. Because Mr.
M’s cardiac arrest was identified early and CPR started immediately, he converted to normal sinus rhythm after one defibrillation (200 joules). His 12-lead ECG now shows evidence of an anterior wall ST-segment elevation myocardial infarction (STEMI). Postarrest management includes maintaining optimal oxygenation, ventilation, and perfusion; maintaining BP above 90 mm Hg with I. V. fluids and vasopressors if indicated; and considering therapeutic hypothermia if he remains unresponsive after return of spontaneous circulation.
Notify the cardiac catheterization lab and transfer Mr. M to the CCU. Sudden cardiac death accounts for about half of all deaths from cardiovascular disease and is generally caused by VT or VF. 2 Because VT can present many ways-stable, unstable, or pulseless-prompt identification and management may prevent patient mortality. Know your H’s and T’s The H’s and T’s are common, reversible causes of cardiac arrest. They include: * Hypovolemia * Hypoxia * Hydrogen ion (acidosis) * Hypo- or hyperkalemia * Hypothermia * Tension pneumothorax.
* Tamponade, cardiac * Toxins * Thrombosis, pulmonary * Thrombosis, coronary REFERENCES 1. American Heart Association. Advanced Cardiovascular Life Support (ACLS) Provider Manual. Dallas, TX: American Heart Association; 2011. [Context Link] 2. Compton S. Ventricular tachycardia. eMedicine. http://emedicine. medscape. com/article/159075-overview. [Context Link]
RESOURCE 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation. 2010;122(18 suppl 3):S640-S933.