Fusion Session - Workshop Analysis of Rhythm and Conductivity Disorders Part 2 PDF

Fusion Session | Workshop: Analysis of Rhythm and Conductivity Disorders Part 2: Supraventricular Arrhythmias  Learning Objectives This page covers the following learning objectives:...

Fusion Session | Workshop: Analysis of Rhythm and Conductivity Disorders Part 2: Supraventricular Arrhythmias  Learning Objectives This page covers the following learning objectives: 4. Define supraventricular arrhythmias and list the common types. 5. Explain premature atrial contraction, and describe the etiology, clinical presentation, diagnosis on ECG, and management. 6. Explain the diagnosis on ECG of atrial fibrillation and atrial flutter. 7. Explain the diagnosis on ECG of multifocal atrial tachycardia. 8. Explain the electrophysiological basis of re-entry mechanism. Content and images for this lecture are used with permission from ScholarRx. Click the following link for a direct link to the page: Supraventricular Arrhythmias- Analysis of Rhythm and Conductivity Disorders (https://exchange.scholarrx.com/brick/2jk54vwq5wmo). CC BY- SA 4.0. (https://creativecommons.org/licenses/by-sa/4.0/)  CASE CONNECTION PV, a 64-year-old male, comes to the emergency department with increasing shortness of breath. PV has a history of chronic obstructive pulmonary disease (COPD). “It’s been getting worse over the past few days, and I am coughing up more sputum,” PV says. “My inhalers aren’t helping.” On exam, PV is afebrile. His heart rate is 110/min and irregular, blood pressure is 142/78 mm Hg, and respiratory rate is 26 breaths/min. He has decreased breath sounds but no rales. Treatment for his COPD flare begins, and you turn your attention to his cardiac status. His ECG shows a narrow QRS complex irregular rhythm with a rate of 112/min. You see a few different P waves. What is PV’s rhythm disturbance? How should PV’s arrhythmia be treated? Consider your answers as you read, and we’ll revisit at the end of the brick. Go to Conclusion  What Are Supraventricular Arrhythmias? Supraventricular arrhythmias are abnormal heart rhythms that originate above the ventricles, most commonly in the atria. QRS complexes are usually narrow (normal) because the ventricles are still contracting in a normal, coordinated fashion once the depolarization impulse reaches them. Types of Supraventricular Arrhythmias The five types of arrhythmias we cover here are premature atrial contractions (PACs), atrial fibrillation (AF), atrial flutter (AFL), multifocal atrial tachycardia (MAT), and wandering atrial pacemaker. A word on terminology: although all the above arrhythmias are supraventricular, and most present with tachycardia, the actual term “supraventricular tachycardia” is reserved in most clinical practice for one specific type, AVNRT, discussed below. Supraventricular arrhythmias are typically less serious because the left ventricle contracts normally, so the heart can still pump enough blood.  Turn Card 1 of 1  Retry  What Are Premature Atrial Contractions? PACs are the most common type of supraventricular arrhythmia and are usually experienced by patients as an extra heartbeat or “skipping a beat.” They are the least dangerous of these arrhythmias. Pathophysiology The causes are mostly unknown. They arise from an ectopic focus within the atria, producing an abnormal P wave on ECG. They are more common in patients after myocardial infarction (MI) or in those with other structural heart disease. Secondary Causes. PACs are often worsened by alcohol, stimulant drugs like cocaine and amphetamines, caffeine, and tobacco. Some patients note increased frequency during exercise or when they are anxious. Diagnosis OnECG, PACs produce wide, aberrant P waves that differ from typical P waves because of a PR interval longer than 120 msec (3 small boxes) (Figure 1, dark green). Figure 1. Premature atrial contractions. Image credit: ScholarRx, used with permission These P waves can be either conducting (followed by ventricular contractions) or nonconducting (not followed by ventricular contractions). Management PACs tend to resolve on their own, without the need for medication. Patients should avoid nicotine, alcohol, and caffeine. Frequent PACs warrant additional testing because they may be associated with underlying structural heart disease.  Such patients may have an underlying structural heart disease, or may have had a recent myocardial infarction, which precipitated the contractions.  Turn Card 1 of 1  Retry B re ak !  What Is Atrial Fibrillation? AF is the most common arrhythmia requiring treatment and can be secondary to many medical conditions. It is a supraventricular tachyarrhythmia in which the rate of atrial depolarization greatly exceeds the rate of ventricular depolarization. The resultant ventricular rate is quite variable (90-170 beats/min). In AF, the atrium fibrillates, or quivers, because the rapid atrial depolarizations lead to a lack of true coordinated atrial contractions. The quivering atrium is at risk for developing blood clots, with the resultant risk of stroke when these clots dislodge and migrate to the brain. Clinical Presentation Patients with AF often show symptoms that are connected to heart rate: faster heart rates (>110 beats/min) often lead to dizziness, palpitations, fatigue, mild dyspnea, and even chest pain. Patients with lower heart rates are often asymptomatic. The most concerning consequence of AF is the development of atrial mural thrombus (clot) in which blood stasis in the left atrium leads to the formation of clots there. These can break off and migrate to the brain, causing stroke. This may cause sudden weakness, numbness, or speech impediments. Pathophysiology AF is more common in older patients, affecting 4% of patients ages 60 years and older. AF often stems from atrial pathology—such as increased atrial pressure or atrial dilation as might occur in mitral valve stenosis. The atrial wall pathology disrupts the underlying conduction pathway. Because of these disruptions, multiple electrical foci form, each of which is capable of emitting impulses independently and at different rates. The resultant atrial rate is the sum of all the independent impulses. Secondary Causes. AF is associated with a spectrum of diseases: Cardiac causes include left ventricular hypertrophy due to longstanding hypertension, ischemic heart disease, valvular heart disease, and cardiomyopathies. AF can also occur as a complication of cardiac surgery. Pulmonary causes include chronic obstructive pulmonary disease (COPD), pulmonary embolism (PE), and obstructive sleep apnea (OSA). Other systemic causes include chronic kidney disease (CKD), hyperthyroidism, diabetes, obesity, and metabolic syndrome. Diagnosis The classic phrase for describing AF on ECG is “irregularly irregular.” This means that the R-R interval varies from beat to beat, unpredictably without a pattern (Figure 2). Figure 2. ECG showing “irregularly irregular” R-R intervals indicating Afib. Image credit: ScholarRx, used with permission Note that the P waves cannot truly be distinguished because the atrium is not contracting in a coordinated fashion. Instead, the baseline looks wavy and haphazard. Ventricular (and pulse) rates can vary between 90 and 170 beats/min. If the ventricular rate is more than 100 beats/min, it is called atrial fibrillation with rapid ventricular response (RVR). This is the normal response in an otherwise healthy heart. A lower rate (100 beats/min) and WAP has a rate less than 100 beats/minute. Both MAT and WAP are seen most often in patients with lung disease. Clinical Presentation MAT and WAP are often asymptomatic, and the pulmonary symptoms of the lung disease are dominant. It can sometime show the same rate-related symptoms described above under AF or AFL. Pathophysiology MAT and WAP occur when three or more distinct impulses arise in the atria; all travel to the AV node and cause depolarization. Unlike AF, in which hundreds of impulses are generated around the atria, and AFL, which involves a reentrant circuit, MAT stems from multiple but limited distinct areas where the impulse arises from a distended right atrium due to high right ventricular pressures.  What causes MAT?  Turn Card 1 of 1 Secondary Causes. Causes of MAT and WAP include mostly pulmonary disease (eg, COPD, pneumonia). Other causes include cardiac diseases, hypokalemia, hypomagnesemia, CKD, and digitalis toxicity. Diagnosis On ECG, MAT and WAP show an irregular rhythm, MAT tachycardic while WAP normal rate, because the timing of depolarization differs from site to site, and at least three different morphologies of P waves (Figure 5). Figure 5. ECG showing MAT and WAP irregular rhythm. Image credit: ScholarRx, used with permission. Atrial and ventricular rates are often more than 100 beats/min.   What Is The Electrophysiological Basis Of Re-Entry Mechanism ? The heart's electrical system is responsible for initiating and coordinating the contraction of the heart muscle, ensuring efficient blood circulation. Under normal conditions, this electrical impulse originates from the sinoatrial (SA) node, located in the right atrium. This impulse then travels through the atria, to the atrioventricular (AV) node, and finally through the ventricles, causing them to contract in a synchronized manner. However, certain conditions can disrupt this orderly process, leading to arrhythmias. One of the primary mechanisms behind many types of arrhythmias is known as the "re-entry mechanism." What is Atrioventricular Nodal Re-entry? Re-entry refers to a phenomenon where an electrical impulse, rather than fading after stimulating the heart muscle, continues to circulate within the heart. This happens when the impulse finds a pathway to re-enter and activate tissues that have already recovered from their previous activation. This can lead to the development of sustained arrhythmias, such as atrial fibrillation, atrial flutter, ventricular tachycardia, and ventricular fibrillation. Electrophysiological Basis of Re-entry The re-entry mechanism can occur due to several factors that alter the normal propagation of the electrical impulse through the myocardium. These factors include:  (1) Heterogeneity in Refractory Periods  (2) UnidirectionalTop Block  (3) Slow Conduction Re-entry has significant clinical implications. It is the underlying mechanism for many arrhythmias that can lead to symptoms like palpitations, dizziness, syncope, or even sudden cardiac death. Treatments may include medications that alter electrical properties of the heart tissue, or interventional procedures like catheter ablation, which aims to interrupt the re-entrant circuit.  CASE CONNECTION Thinking back to PV, what is his rhythm disturbance? How should his arrhythmia be treated? The ECG highlights four important points that lead to the diagnosis of PV’s rhythm disturbance: increased rate (tachycardia), narrow QRS complex, irregular rhythm, and three or more distinctly different P waves. PV is in multifocal atrial tachycardia, which is secondary to his underlying COPD. After treating his COPD flare, his MAT resolves, restoring normal sinus rhythm. When you look at an ECG done 24 hours after admission, PV is in normal sinus rhythm. Back to Introduction  Summary Supraventricular arrhythmias are deviations from normal sinus rhythm arising above the ventricles. Because the left ventricle contracts normally, they are less likely to cause cardiac arrest compared to ventricular arrhythmias. Premature atrial contractions (PACs) are common, minimally symptomatic arrhythmias that cause an extra heartbeat. Treatment involves avoiding precipitants like nicotine, alcohol, or caffeine. Atrial fibrillation (AF) is a supraventricular tachycardia in which the atria fibrillate, or quiver. AF can present with palpitations, tachycardia, fatigue, weakness, dizziness, lightheadedness, and development of mural thrombi. On ECG, AF is described as an irregularly irregular pattern with nonidentifiable P waves. Atrial flutter (AFL) is a supraventricular tachycardia in which the atria beat faster than the ventricles. The ECG baseline with AFL is described as a sawtooth pattern, most distinct in leads II, III, and avF.  Multifocal atrial tachycardia (MAT) and wandering atrial pacemaker (WAP) are seen in patients with chronic lung disease, especially chronic obstructive pulmonary disease (COPD). MAT and WAP show multiple foci of P waves on ECG, with at least three different morphologies. Re-entry mechanisms occur when there is an abnormal circuit in the myocardium causing tachyarrhythmias.  Check Your Knowledge A female is brought to the emergency department after she felt her heart beat very fast and nearly passed out. An ECG shows atrial flutter with 1:1 conduction, with a ventricular and atrial rate of 150 beats/min. Which of the following ECG findings is most specific for this type of arrhythmia? Retrograde P waves Delta wave  Sawtooth C o r pattern r e c t a n s w e r. The correct answer is sawtooth pattern (D), which are inverted but rapid P waves. A delta wave (A) is a characteristic finding in Wolff-Parkinson-White syndrome, which occurs due to conduction along the aberrant fast pathway. Indistinguishable P waves (B) are a finding of atrial fibrillation. Retrograde P waves (C) are found in atrioventricular nodal reentrant tachycardia due to the impulse being conducted backward from the AV node to depolarize the atrium. Wide QRS complexes (E) are seen most often with ventricular, not supraventricular arrhythmias like atrial flutter. Indistinguishable P waves Wide QRS complexes 1/1 You got 1 out of 1 points