Arrhythmia Essentials E-Book

Brian Olshansky, Mina K Chung, Steven M Pogwizd, Nora Goldschlager

• Editorial: Elsevier
• Año: 2016
• ISBN:
  9780323415248
• Edición: 2
• Categoría: Medicine
• Categoría: Cardiology

Concise, compact, fully-illustrated and easy to read, Arrhythmia Essentials, 2nd Edition provides detailed, practical information on recognizing and treating heart rhythm disturbances for clinicians with any level of expertise. The author team, led by renowned authority in cardiac electrophysiology, Dr. Brian Olshansky, guides you skillfully through the different types of arrhythmias and how they present on ECGs. You'll find specific examples of each arrhythmia, numerous algorithms to facilitate an approach to arrhythmia diagnosis and management, updates on medical therapy, and indications for implantable rhythm management devices and ablation – all in a convenient, softcover volume that's perfect for on-the-go reference.

• Features a clear, consistent organization that helps you find information quickly: description, associated conditions, clinical symptoms/presentations, and management.
• Includes numerous therapy/guideline tables and treatment algorithms.

• Offers new coverage of managing arrhythmias during pregnancy and expanded information on athletes and arrhythmias.
• Incorporates recommendations based on recent published guidelines.

Chapter 1

Sinus Node

Normal and Abnormal Rhythms

Normal sinus node

Description

Normal sinus rhythm (NSR) is an atrial rhythm caused by electrical activation that originates from the sinus node, a structure located in the area of the junction of the right atrium and superior vena cava. NSR P waves, representing atrial depolarization (but not sinus node activity itself), are upright in leads I and aVL and the inferior leads (II, III, aVF), indicating the high to low atrial activation pattern (Fig. 1.1). The P wave in leads V₁-V₂ may be upright, biphasic, or slightly inverted, whereas the P waves in leads V₃-V₆ tend to be upright, indicating right to left atrial activation. The P-wave morphology may change with alterations in autonomic tone, heart rate, and atrial abnormalities such as hypertrophy. High vagal tone can be associated with a more inferior exit of the impulse from the sinus node, whereas high sympathetic tone can be associated with a more superior exit from the node.

Figure 1.1 Normal sinus rhythm.
Normal sinus rhythm is characterized by P waves that are usually upright in leads I, aVL, II, III, aVF, and V₃-V₆ at a rate between 60 and 100 bpm.

Clinical Symptoms and Presentations

NSR is generally considered to have a rate of 60 to 100 beats per minute (bpm), although 50 bpm is still normal. Rate changes with alterations in autonomic tone; at rest, most individuals have their heart rate regulated by the vagus nerve.

Individuals with high vagal tone (such as those who are in excellent physical condition) may exhibit sinus arrhythmia, a normal rhythm in which the rate varies with respiration (Fig. 1.2). In sinus arrhythmia, inspiration increases the rate and expiration decreases the rate. Sinus arrhythmia is common during sleep and in patients with obstructive sleep apnea, in which the decrease in rate can be substantial.

Figure 1.2 Normal sinus rhythm with sinus arrhythmia.
This lead V₁ and II rhythm strip shows normal sinus rhythm with sinus arrhythmia, in which the P-P intervals vary by greater than 0.16 seconds. Sinus arrhythmia is often related to respiratory cycles.

Various forms of sinus arrhythmia exist, including a non–respiration-dependent form that may indicate sinus node dysfunction (SND).

Ventriculophasic sinus arrhythmia is present when alterations in the sinus rate are due to atrioventricular (AV) block: The P-P intervals enclosing a QRS complex are shorter than P-P intervals not enclosing a QRS complex.

A change in sinus rate can be gradual or abrupt and can occur with change in body position and exercise. Patients who are in good physical condition generally have more gradual acceleration in sinus rate with exercise and a rapid slowing of the sinus rate at the end of exercise, compared with less physically fit individuals or individuals with heart disease. Higher resting sinus rates have been associated with increased risk for overall mortality.

Wandering atrial pacemaker (WAP) (Fig. 1.3) occurs in association with high vagal tone and is a benign rhythm. In WAP, there are varying exit points of the sinus impulse from the sinus node or impulses that originate from the sinus node and wander from the node to the low atrium and back. WAP is often seen in patients with sinus arrhythmia. WAP should not be confused with “multifocal atrial rhythm” (see Fig. 3.13).

Figure 1.3 Wandering atrial pacemaker.
This lead V₁ II, and V₅ rhythm strip shows wandering atrial pacemaker. There are at least three P wave morphologies.

Approach to Management

Although sinus rhythm generally does not require any treatment, an inability to increase the sinus rate appropriately in response to increases in metabolic needs (“chronotropic incompetence”) may require permanent rate responsive cardiac pacing when it is documented to cause symptoms. Definitions of chronotropic incompetence are many and varied, and there is no general agreement as to its parameters.

Sinus node dysfunction, including sinus bradycardia and tachycardia-bradycardia syndrome

Description

Sinus bradycardia (SB) (Fig. 1.4) is generally defined as sinus rates of less than 60 bpm, although 50 bpm is likely within the normal range of rate. SB is often a normal finding in young, healthy adults, especially in athletes with high vagal tone. SB frequently occurs at rest and during sleep. In trained athletes or individuals with high vagal tone, sinus rates in the 40s and even at times in the 30s, especially during sleep, are not uncommon. SB may be associated with a narrow QRS complex or, in the presence of bundle branch block (BBB) or intraventricular conduction delay, with a wide QRS complex (Fig. 1.5).

Figure 1.4 Sinus bradycardia.
This lead II rhythm strip shows SB, which is characterized by sinus P waves (usually upright in leads II, III, aVF) with rate less than 60 bpm.

Figure 1.5 Sinus bradycardia with a wide QRS complex.
Although the QRS complex is normally narrow (< 0.12 seconds), the QRS can be wide in the setting of bundle branch block or intraventricular conduction delay. This 12-lead ECG with rhythm strips of leads V₁, II, and V₅ shows sinus bradycardia with sinus arrhythmia (rates 53-56 bpm) and left bundle branch.

The sinus rate normally slows with age. SND from sinus node degeneration is more frequent in older persons. SND, sometimes termed “sick sinus syndrome,” is a very common arrhythmia and includes sinus pauses, sinus arrest, inappropriate SB, chronotropic incompetence, sinoatrial (SA) exit block, combinations of SA and AV conduction abnormalities, and tachycardia-bradycardia (tachy-brady) syndrome (e.g., paroxysmal or persistent atrial tachyarrhythmias with periods of bradycardia or postconversion sinus pauses) (Fig. 1.6).

Figure 1.6 Tachycardia-bradycardi...