Chapter 100. Tachyarrthymias

1. How do you initially manage a patient with a hemodynamically unstable wide complex tachyarrhythmia?

2. What are the electrocardiographic features that suggest that a wide complex tachyarrhythmia is of ventricular origin?

3. What are the electrocardiographic features that suggest that a wide complex tachyarrhythmia is of supraventricular origin?

4. What is the differential diagnosis for short RP tachycardia? What is the differential diagnosis for long RP tachycardia?

5. Radiofrequency ablation often cures which tachycardias?

This chapter will review the initial bedside approach to a hospitalized patient with a new, potentially life-threatening tachycardia, defined as a heart rate ≥ 100 beats per minute (bpm). The reader is then referred to the cardiology chapters for definitive management of specific arrhythmias.

Normally, the sinoatrial node spontaneously activates the right atrium, then the interatrial septum, and then the left atrium. The initial portion of the P wave represents depolarization of the right atrium and the last portion depolarization of the left atrium. Normally, the atrioventricular (AV) node, His bundle, and bundle branches transmit impulses anterogradely from the atria to the ventricles. The QRS complex represents ventricular depolarization and the ST-T-U complex represents repolarization (Figure 100-1).

Unlike the normal AV conducting pathway, anomalous bands of tissue—accessory pathways—may be able to conduct in both directions between the atria and ventricles in a retrograde and antegrade fashion. Some anomalous bands of tissue, concealed bypass tracts, can conduct in a retrograde direction only from the ventricles to the atria.

Supraventricular tachycardias (SVTs) include all tachycardias that arise above the bifurcation of the bundle of His or that have mechanisms depending on the bundle of His.

Paroxysmal supraventricular tachycardias usually have narrow complexes with a normal QRS duration of < 90 ms; some, however, may have aberrant conduction notable for a different QRS configuration from the baseline ECG. Intraventricular conduction disturbances may be incomplete (100–120 ms) or complete bundle branch blocks (QRS ≥ 120 ms in duration) and may be rate related. A right bundle branch block (RBBB) configuration is more common than a left bundle branch block (LBBB) aberrant pattern. The altered depolarization causes secondary repolarization ST-T abnormalities, discordance of QRS-T wave vectors. Ischemia, electrolyte disturbances, and digitalis cause primary depolarization ST-T abnormalities independent of the QRS vector. Sudden death from SVT is rare.

Ventricular tachycardia (VT) arises from the ventricles and is more likely to cause cardiac compromise and sudden death.