Rhythms Originating in the Atria PDF

8 Rhythms Originating in the Atria CHAPTER 8 OBJECTIVES Upon completion of this chapter, the student will be able to: 䊏 State the criteria for each of the atrial 䊏 State the adverse effects for each rhythms....

8 Rhythms Originating in the Atria CHAPTER 8 OBJECTIVES Upon completion of this chapter, the student will be able to: 䊏 State the criteria for each of the atrial 䊏 State the adverse effects for each rhythms. rhythm. 䊏 Using the criteria and other rhythm analysis 䊏 State the possible treatment for each tools, interpret a variety of atrial rhythms. rhythm. What It’s All About Nurses Terry and Lacey were chatting at the intensive care unit desk when 87-year-old Ms. Avis was brought in by Monica and Lee from a medical floor. Monica and Lee reported that Ms. Avis was very pale, unresponsive to verbal commands, and drenched in a cold sweat, but she was breathing fine so far on oxygen. Her physician Dr. Granger had ordered her transferred to ICU and had arrived there with her. Terry and Lacey exchanged glances—this patient was in big trouble—and sprang into action. Terry attached the patient to the heart monitor, which showed supraventricular tachycardia (SVT) with a heart rate in the 190s. Blood pressure was 68/36 (extremely low, especially for this patient with a history of hypertension). Lacey ran to get the code cart. She removed Ms. Avis’s shirt and wiped her chest dry with it. Terry attached defibrillation pads to Ms. Avis’s chest and back. They double-checked that the IV line was working properly. Terry and Lacey looked at Dr. Granger. “Now?” they asked him. “Yes—hit her with 100 joules.” Terry depressed the synchronize button, charged up the machine, and cardioverted the patient. Ms. Avis’s chest lurched from the shock. Everyone looked at the monitor. No change in rhythm. “Does she still have a pulse?” somebody asked. By then all the ICU staff had come into the room to help. “Yes, she’s still pulsating but it’s weak and her blood pressure is really low. Let’s shock her again. And call the cardiology resident out,” called out Dr. Granger. The second cardioversion was successful—the rhythm converted to sinus rhythm with a heart rate of 88. Ms. Avis’s blood pressure improved and she woke up. It was discovered later that Ms. Avis had a history of SVT and could not refill her medication for several days because she was waiting for her social security check to come in. Introduction Atrial rhythms originate in one or more irritable foci (locations) in the atria, then depolarize the atria and head down the conduction pathway to the ventricles. Atrial rhythms, and indeed all rhythms that originate in a pacemaker other than the sinus node, are called ectopic rhythms. See Figures 8–1 and 8–2. In Figure 8–1, a single atrial impulse depolarizes the atria and writes a P wave on the EKG. The impulse then heads down the pathway normally, and a QRS is written once the impulse depolarizes the ventricle. In Figure 8–2, there are multiple atrial impulses. They write a P wave (or an alternate form of atrial wave) and then head down the pathway normally and write a QRS once the ventricles have been depolarized. The Word on Atrial Rhythms Although the atrium is not considered an inherent pacemaker like the sinus node, AV junction, and ventricle (it is highly unusual for the atrium to fire in an escape capacity), the atrium is indeed another pacemaker of the heart. It is best known for usurping the 90  CHAPTER 8 RHYTHMS ORIGINATING IN THE ATRIA 91 P wave QRS P waves QRS Atrium AV node Ventricle Atrium AV node Ventricle FIGURE 8–1 FIGURE 8–2 Conduction of a single atrial focus. Conduction of multiple atrial foci. underlying sinus rhythm and producing rhythms with rapid heart rates. Because of these rapid heart rates, patients are often symptomatic. Every now and then the atrium will fire more slowly and produce rhythms with rates less than 100. Treatment is aimed at converting the rhythm back to sinus rhythm or, if that is not possible, returning the heart rate to more normal levels. Atrial rhythms are extremely variable in their presentation. Some rhythms have obvious P waves. Others have no Ps at all—instead, they have a wavy or fluttery baseline between the QRS complexes. Some atrial rhythms are regular and others are completely irregular, even chaotic. Although most atrial rhythms are rapid; a few are slower. Unlike sinus rhythms, which have a common set of criteria, atrial rhythms have multiple and variable possible criteria. If the rhythm or beat in question meets any of these criteria, it is atrial in origin. Let’s look at these criteria now: 䊏 Matching upright Ps, atrial rate (the heart rate of the P waves) 7160 at rest or 䊏 No Ps at all; wavy or sawtooth baseline between QRSs present instead or 䊏 P waves of Ú 3 different shapes or 䊏 Premature abnormal P wave (with or without QRS) interrupting another rhythm, or 䊏 Heart rate Ú 130, rhythm regular, P waves not discernible (may be present, but can’t be sure) It’s important to note that atrial rhythms can have a positive QRS or a negative QRS depending on the lead in which the patient is being monitored. For example, in Lead II the QRS should be positive, but in V1 it should be negative. Reread Chapter 3 to review this if needed. Now let’s look at these rhythms in detail. Wandering Atrial Pacemaker/Multifocal Atrial Tachycardia Wandering atrial pacemaker (WAP) and multifocal atrial tachycardia (MAT) are rhythms that occur when the pacemaking impulses originate from at least 3 different foci in the atria. Each focus produces its own unique P wave, resulting in a rhythm with at least 3 different shapes of P waves. WAP is an example of a slow atrial arrhythmia. MAT is rapid. WAP and MAT are exactly the same rhythm, just with differing heart rates. 92 PART 1 THE BASICS Rate WAP: mean rate 6100, usually a mean rate in the 50s to 60s MAT: mean rate 7100 Regularity Irregular P waves At least 3 different shapes. Some beats may have no visible P waves at all. Intervals PR varies QRS 60.12 seconds Cause WAP: Medication side effects, hypoxia, vagal stimulation, or MI MAT: COPD, heart disease Adverse WAP: Usually no ill effects effects MAT: Signs of decreased cardiac output if heart rate is too fast Treatment WAP: Usually none needed MAT: Beta blockers or calcium channel blockers if signs of decreased cardiac output exist Figure 8–3A shows QRS complexes, all shaped the same. Regularity is irregular. Heart rate is 50 to 60, with a mean rate of 50. At least 3 different shapes of P waves precede the QRS complexes. P-P interval varies. PR interval varies from 0.24 to 0.32. QRS interval is 0.08. Interpretation: wandering atrial pacemaker. Figure 8–3B shows QRS complexes of uniform shape. Regularity is irregular. Heart rate is 107 to 187, with a mean rate of 120. P waves vary in shape. P-P interval varies. PR interval varies. QRS interval is 0.06. Interpretation: multifocal atrial tachycardia. Remember: To differentiate between WAP and MAT, check the heart rate! I ⴛ2 25mm/s FILTER FIGURE 8–3A Wandering atrial pacemaker. II FIGURE 8–3B Multifocal atrial tachycardia.  CHAPTER 8 RHYTHMS ORIGINATING IN THE ATRIA 93 Premature Atrial Complexes (PACs) Premature atrial complexes (PACs) are premature beats that are fired out by irritable atrial tissue before the next sinus beat is due. The premature P wave may or may not be followed by a QRS, depending on how premature the PAC is. If the PAC is very premature, it will not be conducted to the ventricle because it will arrive during the ventricle’s refractory period. Rate Can occur at any rate Regularity Regular but interrupted (by the PACs) P waves Shaped differently from sinus P waves. The premature P waves of PACs may be hidden in the T wave of the preceding beat. If so, they will deform the shape of that T wave. Always be suspicious when a T wave suddenly changes shape. If the QRS complexes look the same, then the T waves that belong to them should also look the same. If one T wave is different, there’s probably a P wave hiding in it. If the PAC’s P wave is inverted, the PR interval should be the normal 0.12 to 0.20 secs. Intervals PR 0.12 to 0.20 secs QRS 60.12 secs QRS will be absent after a nonconducted PAC. The most common cause of an unexplained pause is a nonconducted PAC. If you see a pause and you’re tempted to call it a sinus arrest or sinus block, make sure there’s no P hiding in the T wave inside the pause. It might just be a nonconducted PAC. Cause The atria become “hyper” and fire early, before the next sinus beat is due. This can be caused by medications (stimulants, caffeine, bronchodilators), tobacco, hypoxia, or heart disease. Occasional PACs are normal. Adverse Frequent PACs can be an early sign of impending heart failure or effects impending atrial tachycardia or atrial fibrillation. Patients usually have no ill effects from occasional PACs. Treatment Usually none needed. Omit caffeine, tobacco, and other stimulants. Can give digitalis, calcium channel blockers, or beta blockers to treat PACs if needed. These medications all slow the heart rate and can decrease atrial irritability, decreasing PACs and other atrial arrhythmias. Treat heart failure if present. Consider starting oxygen. In Figure 8–4, the fourth beat is premature, as evidenced by the shorter R-R interval there. Recall that premature beats are followed by a short pause immediately afterward. The QRS complexes are all the same shape. Regularity is regular but interrupted (by a premature beat). Heart rate is 54. P waves precede each QRS complex, and all but the fourth P wave are the same shape. Thus the matching upright P waves are sinus Ps, and the premature P wave is not a sinus P since it has a different shape. P-P interval is irregular because of the premature P wave. PR interval is 0.16, and QRS interval is 0.08. Interpretation: sinus bradycardia with a PAC. 94 PART 1 THE BASICS 25mm/s FIGURE 8–4 PAC. FIGURE 8–5 Nonconducted PAC. Figure 8–5 shows QRS complexes, all the same shape. Regularity is regular but interrupted (by a pause). Heart rate is 43 to 75, with a mean rate of 70. P waves are biphasic (half up, half down) and matching, except for the P wave that’s at the end of the third beat’s T wave. See the little hump there under the dot? That’s a P wave. That P wave is shaped differently from the sinus P waves, and it is premature. How do we know it’s premature? Look at the P-P intervals, the distance between consecutive P waves. All the sinus P waves are about 4 big blocks apart. This abnormal P wave is only 21/2 blocks from the P wave that precedes it. Thus it is premature. A premature P wave that is not followed by a QRS complex is a nonconducted PAC. Note the long pause that this nonconducted PAC causes. Nonconducted PACs are the most common cause of otherwise unexplained pauses. It is important to note that many nonconducted PACs do not have such easily noticeable P waves. Much of the time the premature P wave is hidden inside the T wave of the preceding beat, deforming that T wave’s shape. PR interval here is 0.16, and QRS interval is 0.10. Interpretation: sinus rhythm with a nonconducted PAC. chapter CHECKUP We’re about halfway through this chapter. To evaluate your the 50s but the multiple P wave shapes continue. His blood understanding of the material thus far, answer the following pressure with this new rhythm is good and he feels fine now. questions. If you have trouble with them, review the material again before continuing. 1. What was his rhythm before the medication? Mr. Sulu’s rhythm is very irregular, with a heart rate in the 2. What’s his rhythm after? 130s and multiple P wave shapes. His QRS is narrow 3. What treatment, if any, is indicated for this new rhythm? (60.12 secs). Medication is given and the heart rate slows to  CHAPTER 8 RHYTHMS ORIGINATING IN THE ATRIA 95 Paroxysmal Atrial Tachycardia (PAT) Paroxysmal atrial tachycardia (PAT) is a sudden burst of 3 or more PACs in a row that usurps the underlying rhythm and then becomes its own rhythm for a period of time. The term paroxysmal refers to a rhythm that starts and stops suddenly. PAT resembles sinus tach, but with a faster heart rate. In order to diagnose PAT, the PAC that initiates it must be seen. Rate 160 to 250 on the atrial tachycardia itself. The rhythm it interrupts will have a different rate. Regularity The atrial tachycardia itself is regular; but since it interrupts another rhythm, the rhythm strip as a whole will be regular but interrupted. P waves The atrial tachycardia Ps will be shaped the same as each other, but differently from sinus P waves. Intervals PR 0.12 to 0.20 secs, constant QRS 60.12 secs Cause Same as PACs or sinus tach Adverse Prolonged runs of PAT can cause decreased cardiac output. effects Healthy people can tolerate this rhythm for a while without symptoms, but those with heart disease may develop symptoms rapidly. Treatment Digitalis, calcium channel blockers, beta-blockers, sedation, amiodarone (a medication that helps abolish atrial and ventricular arrhythmias), adenosine (another medication to slow the heart rate), and oxygen. Elective cardioversion (a small electrical shock to the heart to restore sinus rhythm) can be done if the patient is unstable because of the rhythm. Figure 8–6 shows 4 sinus beats and then a run of 5 PACs. This run of PACs is called PAT. There are QRS complexes, all the same shape. Regularity is regular but interrupted (by a run of premature beats). Heart rate is 75 for the sinus rhythm, and 187 for the atrial tachycardia. P waves precede each QRS complex but are not all the same shape. The sinus beats have one shape of P wave, and the atrial tachycardia has a different shape P that is deforming the T waves. Note the dots over the premature P waves. Wait a minute, you say! What P waves? We can’t see them! Here’s a rule to help you: If the QRS complexes on the strip look alike, the T waves that follow them FIGURE 8–6 Paroxysmal atrial tachycardia. 96 PART 1 THE BASICS should also look alike. A T wave that changes shape when the QRSs don’t is hiding a P wave inside it. Look at the T waves of the first 4 beats. They have rather broad sloping T waves. The PAT’s T waves are pointy—totally different in shape. They’re hiding a P wave. Now to continue with our interpretation: P-P interval is regular during the sinus rhythm, and regular, though different, during the atrial tachycardia. PR interval of the sinus beats is 0.16. We cannot measure the PR interval of the PAT beats, since the P wave is hidden. QRS 0.08. Interpretation: sinus rhythm with a 5- beat run of PAT. Atrial Flutter Atrial flutter is a rhythm that results when one irritable atrial focus fires out regular impulses at a rate so rapid that a fluttery pattern is produced instead of P waves. The atrium is firing out its impulses so fast that the AV node, bombarded with all these impulses, lets some through but blocks others. Imagine a tennis ball machine firing out tennis balls so fast that there’s no way you can hit them all. You end up ducking to protect yourself. The AV node is the gatekeeper—the protector—of the ventricles. Impulses must pass through it to reach the ventricles. Impulses that are too fast would provide a dangerously fast heart rate, so the AV node selectively blocks out some of the impulses, letting only some through. Rate Atrial rate 250 to 350. Ventricular rate depends on the conduction ratio. Regularity Regular if the conduction ratio (ratio of flutter waves to QRS complexes) is constant; irregular if the conduction ratio varies; can look regular but interrupted at times P waves No P waves present. Flutter waves are present instead. These are sawtooth-shaped waves between the QRS complexes. Flutter waves are also described as picket-fence-shaped, V-shaped, or upside-down-V shaped. There will be 2 or more flutter waves to each QRS. All flutter waves march out—they’re all the same distance apart. Flutter waves are regular. They do not interrupt themselves to allow a QRS complex to pop in. Some flutter waves will therefore be hidden inside QRS complexes or T waves. The easiest way to find all the flutter waves is to find 2 flutter waves back-to-back and note the distance between them (go from top to top of the flutter waves or bottom to bottom). Then march out where the rest of the flutter waves should be using this interval. Although most flutter waves will be easily visible using this method, some will not be as obvious, as they are hidden inside the QRS or the T wave. Even though you can’t see these flutter waves, they are there and they still count. Intervals PR not measured, since there are no real P waves QRS 60.12 secs Cause Almost always implies heart disease; other causes include pulmonary embolus, valvular heart disease, thyrotoxicosis, or lung disease  CHAPTER 8 RHYTHMS ORIGINATING IN THE ATRIA 97 Adverse Can be well tolerated at normal heart rates; at higher or lower effects rates, signs of decreased cardiac output can occur. Cardiac output is influenced not by the atrial rate, but by the heart rate. Treatment Digitalis, calcium channel blockers, beta-blockers, adenosine, carotid sinus massage (rubbing the carotid artery in the neck to stimulate the vagus nerve) to slow the ventricular rate. Electrical cardioversion can be done if medications are ineffective or the patient is unstable. Figure 8–7 shows QRS complexes, all shaped the same. Regularity is regular. Atrial rate is 250; heart rate is 65. P waves are not present; flutter waves are present instead, as evidenced by the V-shaped waves between the QRS complexes. Flutter waves are all regular. PR interval is not measured in atrial flutter. QRS interval is approximately 0.08, although it’s difficult to measure as the flutter waves distort the QRS complex. Interpretation: atrial flutter with 4:1 conduction (4 flutter waves to each QRS). See the dots under the flutter waves? There are 4 dots for each QRS. What if we measured from the top of the flutter waves instead of the bottom? Same thing. See the asterisks above the flutter waves? There are 4 of them (the fourth flutter wave is inside the QRS, but it still counts) to each QRS complex. FIGURE 8–7 Atrial flutter. Atrial Fibrillation During atrial fibrillation, hundreds of atrial impulses from different locations all fire at the same time. As a result, the atria depolarize not as a unit as they usually do, but rather in small sections. This causes the atria to wiggle instead of contract. The AV node is bombarded with all these impulses and simply cannot depolarize fast enough to let them all through. Every now and then one of these impulses does get through to the ventricle and provides a QRS. Rate Atrial rate is 350 to 700; ventricular rate varies. Atrial fibrillation with a mean ventricular rate 7100 is said to have RVR (rapid ventricular response). Remember ventricular rate is the same as heart rate. Regularity Irregularly irregular, completely unpredictable 98 PART 1 THE BASICS P waves No P waves are present. Fibrillatory waves are present instead. These are undulations or waviness of the baseline between QRSs. If there are P waves, the rhythm is not atrial fibrillation. Intervals Since there are no P waves, there is no PR interval. QRS 60.12 secs Cause MI, lung disease, valvular heart disease, hyperthyroidism Adverse Atrial fibrillation can cause a drop in cardiac output because of the effects loss of the atrial kick, which accounts for 15% to 30% of the cardiac output. One possible complication of atrial fibrillation is blood clots, which can collect in the sluggish atria. This can result in MI, strokes, or blood clots in the lung. Treatment Depends on the duration of atrial fibrillation. Since the atria are wiggling, not contracting, blood flow is stagnant and clots can develop. If there are atrial clots and the rhythm is converted back to sinus, the restored atrial contraction (atrial kick) can dislodge these clots, propelling them out of the atrium into the circulation. If atrial fibrillation duration is less than 48 hours, the goal is to convert the rhythm back to sinus. Digitalis, calcium channel blockers, beta-blockers, amiodarone, or electrical cardioversion can be utilized. In atrial fibrillation less than 48 hours old, the likelihood that there are blood clots in the atria is low, so there is minimal chance of showering clots to the brain, heart, lungs, and other organs once the atrial kick is reestablished in sinus rhythm. In stable patients who have been in atrial fibrillation for greater than 48 hours, the risk of blood clots is greater, so initial treatment is aimed at controlling the heart rate rather than converting the rhythm back to sinus. Anticoagulants (blood thinners) are given to prevent any more blood clots from forming, and cardioversion is delayed 2 to 3 weeks to allow any clots that are there to dissolve on their own. Meanwhile, medications can be given to regulate the heart rate to a more normal level. In emergencies, patients in atrial fibrillation greater than 48 hours will be started on heparin (an anticoagulant) intravenously, given a transesophageal echocardiogram (TEE—a sonarlike test using a probe inserted into the esophagus) to rule out blood clots in the atria, then electrically cardioverted. Consider starting oxygen. Figure 8–8 shows QRS complexes, all the same shape. Regularity is irregular. Heart rate is 65 to 100, with a mean rate of 90. P waves are absent; fibrillatory waves are present instead. PR interval is not applicable, and QRS interval is 0.10. Interpretation: atrial fibrillation.  CHAPTER 8 RHYTHMS ORIGINATING IN THE ATRIA 99 FIGURE 8–8 Atrial fibrillation. Supraventricular Tachycardia (SVT) Supraventricular tachycardia (SVT) is a catchall term given to tachycardias that are supraventricular; that is, they originate above the ventricles (the prefix supra- means “above”) in either the sinus node, the atrium, or the AV junction, but whose exact origin cannot be identified because P waves are not discernible. Rate About 130 or higher (usually 7 150) Regularity Regular P waves Not discernible Intervals PR cannot be measured since P waves cannot be positively identified. QRS 60.12 secs Cause Same as PAT Adverse Decreased cardiac output secondary to the rapid heart rate effects Treatment Adenosine, digitalis, ibutilide (a medication to control atrial arrhythmias), calcium channel blockers, beta-blockers. Consider starting oxygen. Elective cardioversion can also be done if the patient is unstable. Figure 8–9 shows QRS complexes, all shaped the same. Rhythm is regular. Heart rate is 150. P waves are not identifiable. PR interval is not measurable. QRS interval is 0.08. Interpretation: SVT. The origin of this rhythm is not clear, but we know that it originated in a pacemaker above the ventricle, since the QRS complex is narrow, less than 0.12 secs. (Rhythms that originate in the ventricle have a wide QRS complex, greater than 0.12 secs.) Bottom line: If the QRS is 60.12 secs, the heart rate is around 130 or higher, the rhythm is regular, and you can’t pick out the P waves, call the rhythm SVT. FIGURE 8–9 SVT (supraventricular tachycardia).