The term sinus arrhythmia refers to a normal phenomenon of mild acceleration and slowing of the heart rate that occurs with breathing in and out. It is usually quite pronounced in children, and steadily lessens with age. Some arrhythmias are very minor and can be regarded as variants of normal. Often most people will sometimes feel their heart skip a beat, or give an occasional extra strong beat - neither of which are usually a cause for alarm.
But some arrhythmias are life-threatening medical emergencies that can result in cardiac arrest and sudden death. Others may not be associated with any symptoms at all, but pre-dispose toward potentially life threatening stroke or embolus. Determination and distinction should be made by a cardiologist.
Non-specific intraventrcular conduction delay may indicate some interference with the passage of impulses along a ventricular pathway, impulses that contracts and relaxes heart ventricles. Can cause a skipped beat, etc.