Premature Ventricular Contractions
Premature ventricular contractions (PVCs) are beats which are initiated in the ventricles or lower chambers of the heart, prematurely. As opposed to PACs, when the SA node (the natural pacemaker of the heart) gets interrupted, PVCs do not interrupt the SA node. However, with a PVC the ventricles contract, which normally causes the impulse from the atria to be blocked from reaching the ventricles.
PVCs are one of the two most common heart rhythm abnormalities, the other being PACs (premature atrial contractions). They are frequently benign and require no treatment. However, in some cases they may be so frequent (over 15-20/minute) that they may cause the heart to beat inefficiently enough to cause symptoms which may need to be addressed.
PVCs may occur singly or in pairs (generally referred to as couplets), every other beat (bigeminy) or interpolated and may also be described as multiform. Examples of all of these are shown below. (Three or more consecutive PVCs is technically referred to as ventricular tachycardia.) Patients who have these types of rhythm abnormalities may often refer to them as palpitations, skipped beats, hard beats, irregular beats, missing beats or extra beats. They may also complain of feeling dizzy or lightheaded or experience chest pain. Some patients may have no symptoms at all.
Just to reiterate, PVCs are premature beats or beats occurring earlier than they should. Many patients describe them as skipped beats, because when they check their pulse, they don’t feel anything for a moment. However, your heart is not actually skipping or missing a beat. What is happening is that when a beat occurs prematurely, the normal volume of blood has not yet returned from your body from the previous beat. So, even though your heart contracts, not enough blood has returned from the previous beat for it to pump the normal amount of blood. Because of reduced blood being pumped, it may feel like you have skipped a beat, but you have not, although the beat was certainly not as effective as a normal beat.
Patients frequently experience more of these palpitations at night or when they are relaxing. This is because when the natural pacemaker of the heart (the SA node) slows down as it frequently will when you are relaxed, these ectopic (out of the wrong place) foci (point of origins) do not get reset soon enough to stop them.