Premature Ventricular Contraction, PVC (article2)

Premature Ventricular Contraction, PVC

Lab Studies
- Obtain serum electrolyte levels, in particular potassium levels. Consider checking the magnesium level, especially in patients with low potassium levels.
- In selected patients, a drug screen may be helpful.
- For patients taking medication with known proarrhythmic effects (eg, digoxin, theophylline), drug levels may be useful.

Other Tests
- ECG allows the physician to characterize the ventricular ectopy and determine its cause. In addition to the standard 12-lead ECG, a 2-minute rhythm strip may help in determining frequency of the ectopy and capture infrequent PVCs. Findings may include the following:

- Left ventricular hypertrophy
- Active cardiac ischemia (ST-segment depression or elevation and or T-wave inversion)
- In patients with previous MI - Q waves or loss of R waves, bundle branch block
- Electrolyte abnormalities (hyperacute T waves, QT prolongation)
- Drug effects (QRS widening, QT prolongation)
- On ECG, PVCs may be premature in relation to the next expected beat of the basic rhythm. The pause after the premature beat is usually a fully compensatory pause. The R-R interval surrounding the premature beat is equal to double the basic R-R interval, showing that the ectopic beat did not reset the sinus node.
- PVCs may appear in a pattern of bigeminy, trigeminy, or quadrigeminy, which describe a pattern of PVCs occurring every other, every third, or every fourth beat, respectively.
- PVCs with identical morphologies on a tracing are called monomorphic or unifocal. If the PVCs demonstrate 2 or more different morphologies, they are referred to as multiform, pleomorphic, or polymorphic.
- PVCs usually are described in terms of the Lown grading system for premature beats. The higher the grade, the more serious the ectopy.
- Grade 0 = No premature beats
- Grade 1 = Occasional ( <30/h)>
- Grade 2 = Frequent (>30/h)
- Grade 3 = Multiform
- Grade 4 = Repetitive (A = Couplets, B = Salvos of = or > 3) Grade 5 = R-on-T pattern
- Holter 24-hour monitors are useful in quantifying and characterizing ventricular ectopy.
- Holters also have been used to determine treatment efficacy in patents with frequent or complex PVCs.
- Suppression of ectopy on Holter monitoring is not always predictive of survival.
- The most important role for Holter monitoring is risk stratification of patients with a recent MI or known left ventricular dysfunction.
- More than 60% of healthy, middle-aged men have ventricular ectopy on Holter monitoring.

-Signal-averaged ECG
- Signal-averaged ECGs (SAECGs) may have a future role in identifying patients at risk for complex ventricular ectopy and nonsustained ventricular tachycardia (NSVT).
- SAECGs may have a role in identifying patients with complex ectopy who may benefit from electrophysiologic studies (EPS).
- Echocardiography is useful not only in evaluating the ejection fraction, which is important in determining the prognosis and also in identifying valvular disease or ventricular hypertrophy.

Procedures
- Exercise stress testing (EST) is best used complementary to Holter monitoring. In patients with complex ectopy, EST can unmask NSVT triggered by increased catecholamines or myocardial ischemia.
- The role of EPS in complex ventricular ectopy is an area of both intense research and debate. A joint American Heart Association (AHA)/American College of Cardiology (ACC) statement suggested the following:
- Routine EPS are not indicated in low-risk patients after MI. Low risk refers to simple ectopy, good left ventricular function, and low congestive heart failure (CHF) class.
- EPS are indicated in high-risk patients with complex ectopy.
- EPS are though to be beneficial in patients with sustained ventricular tachycardia more than 24 hours after MI.

Article sorce: eMedicine