18-year-old male; palpitations lasting hours, beginning at the age of 10. What arrhythmia is present? Let's first consider the heart rate: with a heart rate of 194 beats/min, the heart rate is too low for atrial flutter (1:1) (except in patients who have been pre-treated with medication), and the rate would be unusually high for atrial flutter with 2:1 conduction. Due to the regularity of the heart rhythm, atrial fibrillation can also be ruled out. This leaves atrial tachycardia, junctional tachycardia, AVNRT, and AVRT as possibilities.

A common cause of pauses and bradycardia are non-conducted PACs, which generally do not require treatment. Therefore, it is important to differentiate between pauses or bradycardia that require treatment.

This EKG shows a sinus rhythm with ventricular bigeminy and retrograde conduction leading to retrograde depolarization of the sinus node, resulting in a longer pause (sinus node reset).
Then, a polymorphic ventricular tachycardia occurs over 7 beats. The QT interval of the sinus beats does not appear prolonged, thus ruling out Torsades de Pointes tachycardia. The most likely cause of this type of polymorphic ventricular tachycardia during a stress EKG is cardiac ischemia/coronary artery disease.

This EKG shows the classic features of sick sinus syndrome. Initially, there is an accelerated atrial rhythm/atrial tachycardia. After a pre-automatic pause of 2609 ms, a ventricular premature beat occurs, followed by a junctional escape rhythm. Pre-automatic pause is a pause after a tachycardia and before an automatic rhythm, like sinus rhythm or, in this case, junctional escape rhythm. Therefore, there is an alternation between tachycardic phases and very bradycardic rhythms, the classic bradycardia/tachycardia syndrome. Paper speed is 12.5 mm/sec.

Here we see the EKG of a 63-year-old man with CAD without relevant coronary stenosis. He complains of slightly reduced performance, but no other symptoms. The ECG shows the following changes:

The tachycardia starts with a premature broad QRS complex. We see nonconducted sinus P waves. There are more QRS complexes than P waves, so it is AV-dissociation. There is no doubt that there is a VT present here.

Here we see the EKG of a 15-year-old girl. The rhythm is irregular, with the heart rate fluctuating between approximately 60 and 90 beats per minute. All P waves are identical, and the PR interval is always constant. Therefore, a sinus arrhythmia is present. In this case, it is a respiratory sinus arrhythmia, which is commonly found in younger individuals. The heart rate increases reflexively during inspiration and decreases during exspiration. This physiological sinus arrhythmia is usually no longer present in older individuals.

We see the EKG of an 81-year-old patient with a pacemaker; the PM was briefly deactivated to assess the patient's intrinsic heart rhythm. At the beginning of the EKG, there is already a prolonged AV conduction time, which progressively lengthens from beat to beat. The last conducted P-wave has a PR interval of nearly 800 ms (!). The next P-wave is blocked, but the subsequent displayed P-waves are conducted again, with the PR interval increasing from beat to beat. This indicates a classic second degree AVB Type Mobitz I (Wenckebach).

Why does this EKG indicate a sick sinus node? First, we observe a sinus rhythm with a rate just below 60 bpm. Then, there is a pause of approximately 3000 ms, followed not by a sinus beat, but by a junctional escape beat (retrograde/inverted P-wave immediately after the QRS complex). This ECG was recorded at the general practitioner's office, and it can be assumed that no vagal stimulus contributed to the arrhythmia.