25 September 2009

Arrhythmias and EKGs



Arrhythmias and EKGs

Outline
* Sinus Arrhythmia and Sick Sinus Syndrome
* Multifocal Atrial Tachycardia
* Bigeminal Rhythms
* Preexcitation and AVRT

Mechanisms of Arrhythmogenesis
Sinus Arrhythmia
EKG Characteristics: Presence of sinus P waves
Variation of the PP interval which cannot be q attributed to either SA nodal block or PACs

When the variations in PP interval occur in phase with respiration, this is considered to be a normal variant. When they are unrelated to respiration, they may be caused by the same etiologies leading to sinus bradycardia.

Sick Sinus Syndrome
* Characterized by a collection of symptoms and ECG findings due to chronic dysfunction of the sinoatrial (SA) node:
o Chronic and severe sinus bradycardia
o Sinus pauses
o Sinus arrhythmia
o Complete sinus arrest
o Progressive development of atrial arrhythmias (a-flutter, a-fib, atrial tachycardia)
* Patients are usually elderly and present with lightheadedness and/or syncope, but it can also manifest as angina, dyspnea, and palpitations.

* About 50% of people with SSS also display some degree of dysfunction of the AV node
Sinus bradycardia (rate of ~43 bpm) with a sinus pause

Etiologies of Sick Sinus Syndrome
Familial SSS (due to mutations in SCN5A)
Infiltrative diseases
Pericarditis
Lyme disease
Hypothyroidism
Rheumatic fever
Sinus node firbosis
Atherosclerosis of the SA artery
Congenital heart disease
Excessive vagal tone
Drugs
Tachycardia-Bradycardia Syndrome
* Common variant of sick sinus syndrome severe bradycardia alternates with paroxysmal tachycardias, most often atrial fibrillation.
* There is usually a prolonged pause in the cardiac rhythm following cessation of the tachyarrhythmia.
Tachycardia-Bradycardia Syndrome
Abrupt termination of atrial flutter with variable AV block, followed by sinus arrest with a junctional escape beat.

Multifocal Atrial Tachycardia
Bigeminal Rhythms
* Arrhythmias in which each normal sinus beat is followed by a premature contraction (PAC, PJC, or PVC).
* Results in a couplet rhythm which can be detected by pulse or auscultation.
* Generally benign
Atrial Bigeminy
Ventricular Bigeminy
Preexcitation
ECG Characteristics of WPW:
1. Short PR interval
2. QRS prolongation
3. Delta wave
Preexcitation is a condition characterized by an accessory pathway of conduction, which allows the heart to depolarize in an atypical sequence.
The most common form of preexcitation is called Wolfe-Parkinson-White (WPW) syndrome, in which a direct atrioventricular connection allows the ventricles to begin depolarization while the standard action potential is still traveling through the AV node.

AV Reentrant Tachycardia (AVRT)
In patients with WPW, a reentrant rhythm can be generated where the AV node serves as one arm of the reentrant circuit, and the accessory pathway as the other.

Types of AVRT
* Orthodromic AVRT (More common) – Narrow complex tachycardia in which the wave of depolarization travels down the AV node and retrograde up the accessory pathway.
* Antidromic AVRT (Less common) – Wide complex tachycardia in which the wave of depolarization travels down the accessory pathway and retrograde up the AV node.

Mechanism of orthodromic AVRT
Mechanism of antidromic AVRT
What is this arrhythmia?
Antidromic AVRT
Classification Scheme for Arrhythmias

Arrhythmias and EKGs.ppt

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