The sensation of a “skipped heartbeat,” medically known as a palpitation, is a common experience that prompts many people to seek medical evaluation. The diagnostic tool used to capture the heart’s electrical activity is the Electrocardiogram (ECG or EKG). This non-invasive test translates the heart’s rhythm into a visual tracing, allowing healthcare providers to determine the precise cause of the perceived irregularity.
The Baseline Normal Heart Rhythm on an ECG
A normal heart rhythm, called sinus rhythm, generates a predictable and repetitive pattern on the ECG tracing. This pattern is composed of three main electrical deflections representing the coordinated contraction and relaxation of the heart chambers.
The first wave is the P wave, a small, rounded bump that signifies the electrical activation of the upper chambers (atria). Following the P wave is the QRS complex, a sharp, larger spike marking the rapid electrical activation and contraction of the lower chambers (ventricles). The entire QRS complex typically has a very short duration, usually between 0.06 and 0.10 seconds, reflecting the efficiency of the heart’s internal electrical wiring.
The final deflection is the T wave, representing the electrical recovery of the ventricles before the next beat begins. In a normal rhythm, the time interval between each complete cycle (the R-R interval) is consistent, resulting in a regular heartbeat.
What a Skipped Beat Really Is
The feeling of a “skipped beat” is physiologically misleading because the heart does not actually stop beating. Instead, the sensation is caused by an extra, premature beat that interrupts the normal rhythm. This premature contraction occurs when an electrical impulse originates from a site other than the heart’s natural pacemaker.
The two most frequent types are Premature Ventricular Contractions (PVCs) and Premature Atrial Contractions (PACs). A PVC arises from the lower chambers (ventricles), while a PAC originates in the upper chambers (atria).
The perceived “skip” is the brief pause immediately following the premature beat. This pause allows the ventricles to fill with a larger volume of blood, making the subsequent normal beat much more forceful. This stronger-than-normal beat is what the person perceives as a disruption. These isolated premature beats are common, often occurring without underlying heart disease.
How Premature Beats Appear on the ECG Trace
Premature Ventricular Contractions (PVCs)
A Premature Ventricular Contraction (PVC) is immediately recognizable because it looks distinctly different from the surrounding normal beats. Since the electrical impulse originates outside the normal conduction system, it spreads slowly and inefficiently through the muscle. This creates a wide, unusually shaped QRS complex lasting 0.12 seconds or longer.
This wide complex is typically not preceded by a P wave, confirming the impulse did not start in the atria. The QRS complex and the following T wave often point in opposite directions (discordance), which is a sign of ventricular origin. A PVC is usually followed by a “compensatory pause,” a long gap before the next normal beat arrives.
Premature Atrial Contractions (PACs)
In contrast, a Premature Atrial Contraction (PAC) also appears early but is marked by a premature P wave that looks different from the normal P waves. This difference in shape occurs because the impulse starts in an abnormal location within the atria.
Since the impulse still travels through the normal pathway to the ventricles, the QRS complex following the PAC is typically narrow and normal in appearance. A PAC is also followed by a pause, but this pause is often shorter and considered non-compensatory because the premature beat usually resets the heart’s natural pacemaker.
Seeking Interpretation and Next Steps
The presence of a premature beat on an ECG should be interpreted within the context of an individual’s overall health history. Occasional PACs or PVCs are often considered benign, especially in healthy individuals without other symptoms or structural heart disease.
They can frequently be triggered by common factors like high caffeine consumption, emotional stress, anxiety, or dehydration. A healthcare professional is needed to accurately analyze the ECG tracing, especially to differentiate between isolated events and patterns that might suggest a more significant underlying condition.
If these palpitations are frequent, cause symptoms like dizziness, or are accompanied by chest pain, a detailed medical evaluation is important. This ensures that any necessary lifestyle modifications or medical treatments can be properly considered.