Q: My daughter sometimes feels like her heart skips a beat. Her doctor did some tests and said it was due to premature ventricular contractions. Should I be worried?
A: The heartbeat is controlled by electrical signals that tell the heart cells when they should squeeze (all heart cells not only participate in the heart squeezing to pump blood, but also pass on electrical signals to their neighbors, so are part of the electrical system as well). Normally the electrical signal begins in the area called the sinoatrial (SA) node by the top of the heart. The electrical signal then propagates through the atria (the top smaller chambers of the heart), then through the atrioventricular node (an area between the atria and ventricles) and on to the ventricles (the big chambers of the heart, the right ventricle pumping the blood to the lungs and the left ventricle pumping the blood to the entire body). This orchestrated flow of electricity (called normal sinus rhythm) is responsible for the carefully synchronized muscle contractions of the heart that makes it such a reliable and amazing pump. Just in case there is some problem with the signal from the SA node, every cell in the heart is able to initiate an electrical signal. As clever a backup system as this is, it can lead to problems if some heart cells, for whatever reason, initiate electrical activity out of turn.
A premature ventricular contraction (PVC) occurs when one (or more) of the cells in the ventricle doesn’t “wait its turn” (called an ectopic focus of pace making activity) and instead tries to initiate a heartbeat. Since this electrical impulse begins in the ventricle it does not initiate a signal that can cause a coordinated ‘squeeze’ of the heart (the electrical activity is not orchestrated in an effective manner), and so blood is not successfully pumped from this event.
PVCs are extremely common. Overall, up to 60 percent of the population have at least occasional PVCs, with the prevalence being greater in older people, in men and in people of African American descent.
Most patients who have PVCs have no symptoms and may not be aware that this is happening. When a patient does ‘sense’ something, it may feel like a fluttering, pounding or ‘skipped heartbeat’ sensation.
PVCs are thought to occur from several different mechanisms.
A reentry PVC (the most common type) is when an electrical signal takes a ‘short cut’ and travels back to the ectopic focus area in the ventricle, which then initiates the PVC.
An enhanced activity PVC occurs when the area of ectopic focus initiates an electrical signal at a lower than normal threshold.
A triggered PVC occurs when the area of ectopic focus is stimulated to initiate electrical activity (for example by a hormone such as from an adrenalin surge, from a chemical such as a high level of caffeine, or by an electrolyte abnormality).
From this it is not surprising that risk factors for having PVCs may include:
Structural heart disease such as having some damaged heart cells after a heart attack, or from many other heart conditions such as cardiomyopathy, valve disease, or other causes, which may increase the risk of a reentry PVC.
Toxic effects from caffeine (although some research questions whether this is true), tobacco, alcohol, drug abuse, certain medications, adrenalin surges (for example from anxiety or other causes) and other causes may increase the risk of triggered PVCs.
Electrolyte abnormalities and many other causes may increase the risk of enhanced activity PVCs.
The number of PVCs is sometimes quantified on the Lown grading system, with Grade 0 being none, Grade 1 being less than 30 per hour, Grade 2 being over 30 per hour, Grade 3 being PVCs occurring from more than one area of ectopic focus, Grade 4 having multiple PVCs in a row (as opposed to isolated PVCs with normal beats between them), and Grade 5 having PVCs with an “R on T” pattern (a specific timing of when the PVC occurs).
Most patients with PVCs have no symptoms, although some research indicates that even asymptomatic patients with PVCs may, over time, have an increase in overall mortality (the risk is thought to be greater with a higher Grade on the Lown scale, although whether this is true for all patients is not certain). In some conditions patient’s PVCs may signify a risk of the patient developing an arrhythmia (possibly, but rarely leading to sudden death).
The evaluation of suspected PVCs includes an electrocardiogram (ECG), and depending on the patient’s risk factors and presence (or absence) of symptoms may also include a Holter monitor (where the heart’s electrical activity is monitored for a prolonged period of time), an echocardiogram (an ultrasound evaluation of the heart to look for possible structural heart disease), blood tests (to look for electrolyte abnormalities, or even to look for certain hormone levels), a drug screen, and possibly other tests.
Patients with no (or minimal) symptoms from their PVCs, and who have no underlying structural heart disease, especially if the patient is young, may not need any treatment other than avoiding possible triggers (such as avoiding caffeine, quitting smoking, etc.). Some patients may benefit from medications to minimize their frequency of PVCs (such as certain classes of blood pressure medications like beta blockers or calcium channel blockers), more aggressive medical treatment (such as medications specifically designed to treat arrhythmias), and in some patients ablation therapy (where a minimally interventional procedure is performed by placing a specially designed device through a catheter into a blood vessel and then threaded up to the heart where energy, such as radiofrequency or other energy type, is used to ablate the cells in the area of the ectopic focus) may be indicated.
If you have symptoms suggestive of PVCs, or if they are discovered when an ECG or other monitoring of your heart is done for other reasons, you should speak with your healthcare provider to discuss what evaluation may be indicated.
Jeff Hersh, Ph.D., M.D., can be reached at DrHersh@juno.com