[00:00:00] DR. AHMED: Good morning, everyone. Today we're going to be discussing cardiac arrhythmias, which are essentially abnormal heart rhythms. This is a fundamental topic in cardiology, and understanding these conditions is crucial for any medical professional.
[00:00:15] Before we dive in, let me clarify some terminology. When we talk about arrhythmias, we're referring to any deviation from the normal sinus rhythm. The normal heart rate ranges from 60 to 100 beats per minute in a resting adult.
[00:00:32] STUDENT: Dr. Ahmed, can you explain the difference between bradycardia and tachycardia?
[00:00:37] DR. AHMED: Excellent question. Bradycardia is defined as a heart rate less than 60 beats per minute, while tachycardia is a heart rate greater than 100 beats per minute. However, it's important to note that these definitions can vary based on the clinical context. For example, in a well-trained athlete, a resting heart rate of 50 beats per minute might be completely normal.
[00:01:05] Now, let's talk about atrial fibrillation, or AFib, which is one of the most common arrhythmias we encounter in clinical practice. Atrial fibrillation is characterized by chaotic electrical activity in the atria. The sinoatrial node, or SA node, is no longer functioning as the primary pacemaker.
[00:01:28] Instead, you have multiple ectopic foci firing at rates of 350 to 600 beats per minute. Now, thankfully, the atrioventricular node, or AV node, acts as a gatekeeper, so your ventricular rate is much lower—typically 100 to 160 beats per minute in untreated atrial fibrillation.
[00:01:52] STUDENT: Is that why the pulse feels irregular?
[00:01:55] DR. AHMED: Exactly. The irregularly irregular pulse—that's your clinical hallmark. No pattern to predict. And that's different from, say, atrial flutter, where you might see a regular irregularity with characteristic sawtooth waves on the ECG.
[00:02:15] When we're diagnosing atrial fibrillation, the ECG shows several key features. First, there are no distinct P waves. Instead, you see fibrillatory waves, which appear as fine or coarse undulations in the baseline. Second, the QRS complexes are irregularly irregular. Third, the ventricular rate is typically rapid unless the patient is on rate-controlling medications.
[00:02:45] Now, let's discuss management. The goals of treatment for atrial fibrillation are threefold: rate control, rhythm control, and stroke prevention. For rate control, we typically use beta-blockers like metoprolol, calcium channel blockers like diltiazem, or sometimes digoxin.
[00:03:08] For rhythm control, we have several options. We can attempt chemical cardioversion using medications like amiodarone or flecainide. Or we can perform electrical cardioversion, which involves delivering a synchronized electrical shock to restore normal sinus rhythm.
[00:03:30] However, the most critical aspect of AFib management is stroke prevention. Patients with atrial fibrillation are at significantly increased risk of stroke due to blood stasis in the atria, which can lead to thrombus formation. This is why we use anticoagulation therapy.
[00:03:52] We typically use the CHA2DS2-VASc score to assess stroke risk. This scoring system takes into account factors like congestive heart failure, hypertension, age, diabetes, previous stroke, vascular disease, and sex. Based on this score, we determine whether a patient needs anticoagulation.
[00:04:18] For anticoagulation, we have several options. The traditional choice was warfarin, but now we also have direct oral anticoagulants, or DOACs, such as apixaban, rivaroxaban, dabigatran, and edoxaban. These newer agents have several advantages, including no need for regular monitoring and fewer drug interactions.
[00:04:45] STUDENT: What about patients who can't take anticoagulants?
[00:04:49] DR. AHMED: That's a great clinical question. For patients who have contraindications to anticoagulation, we might consider a left atrial appendage closure device, such as the Watchman device. This is a procedure where we essentially close off the left atrial appendage, which is where most thrombi form in atrial fibrillation.
[00:05:15] Let's move on to another important arrhythmia: ventricular tachycardia, or VT. This is a potentially life-threatening condition. Ventricular tachycardia is defined as three or more consecutive ventricular beats at a rate greater than 100 beats per minute.
[00:05:35] The ECG characteristics include wide QRS complexes, typically greater than 120 milliseconds, because the electrical impulse is not traveling through the normal conduction system. The rhythm is usually regular, and you won't see P waves associated with the QRS complexes.
[00:05:58] Ventricular tachycardia can be monomorphic, meaning all the QRS complexes look the same, or polymorphic, where the QRS complexes vary in morphology. Polymorphic VT, especially torsades de pointes, is particularly dangerous and can quickly degenerate into ventricular fibrillation.
[00:06:20] Treatment for ventricular tachycardia depends on whether the patient is stable or unstable. If the patient is unstable—meaning they have signs of poor perfusion like hypotension, altered mental status, or chest pain—we immediately perform synchronized cardioversion.
[00:06:42] If the patient is stable, we have more time to think. We might try medications like amiodarone or procainamide. However, it's important to remember that any wide-complex tachycardia should be treated as ventricular tachycardia until proven otherwise, especially in patients with structural heart disease.
[00:07:05] Now, let's discuss some preventive measures and lifestyle modifications that can help reduce the risk of arrhythmias. First, managing underlying conditions like hypertension, diabetes, and sleep apnea is crucial. Second, limiting alcohol and caffeine intake can help, as both can trigger arrhythmias in susceptible individuals.
[00:07:30] Regular exercise is generally beneficial, but patients with known arrhythmias should discuss their exercise regimen with their cardiologist. Finally, stress management techniques can be helpful, as emotional stress can sometimes trigger arrhythmias.
[00:07:50] Are there any questions before we move on to the next topic?
[00:07:54] STUDENT: Yes, can you explain the difference between supraventricular tachycardia and ventricular tachycardia on an ECG?
[00:08:00] DR. AHMED: Absolutely. The key distinguishing feature is the QRS width. In supraventricular tachycardia, or SVT, the QRS complexes are narrow, typically less than 120 milliseconds, because the electrical impulse is traveling through the normal conduction system. In ventricular tachycardia, as we discussed, the QRS complexes are wide.
[00:08:25] However, there's an important caveat: if a patient has a bundle branch block, an SVT can present with wide QRS complexes. This is why clinical context is so important. We need to look at the patient's history, their symptoms, and other ECG features to make the correct diagnosis.
[00:08:50] That's an excellent question, and it highlights why understanding the underlying pathophysiology is so important. Any other questions?