The atria are depolarized in a retrograde fashion, and the corresponding P is masked by the QRS complex. Usually a benign arrhythmia which can often be found in patients with long sinus pauses. This is either sinus arrest, or a sinus exit block. This arrhythmia will only cause a problem if the sinus arrest is of long duration and there are no nodal escape beats. If sustained, this arrhythmia results in cardiac decompensation.
Ventricular filling is affected, resulting in a decrease of cardiac output.
This arrhythmia does not occur in the absence of significant cardiac abnormalities. Depending upon the ventricular capture rate, this can result in cardiac decompensation. In situations where atrial contraction is needed for adequate cardiac performance, this arrhythmia is also a significant problem. Note the non-conduction of every other P wave. This arrhythmia can be a benign occurrence without other heart problems.