Diagnosis: Normal sinus rhythm, interpolated junctional premature complexes in a bigeminal pattern.

Circulation ECG Challenge Response! Regarding the 57 year old man with a cough and fever:

Diagnosis: Normal sinus rhythm, interpolated junctional premature complexes in a bigeminal pattern.

There is an irregular rhythm, although there is group beating, with long intervals that are all the same (↔) and short RR intervals that are the same. The average rate is 120 bpm. The short intervals are the result of premature complexes. There are 4 much longer RR interval (↔) and there a distinct P waves at the end of each of these longer intervals (+). The P waves are positive in leads I, II, aVF and V4-V6. Hence these are sinus P waves and they are associated with a stable PR interval (0.16 sec). Complexes 5-6 are two sequential sinus complexes; the rate is 76 bpm. Based on this PP interval it can be seen that there are P waves (*) seen before every other QRS complex and the PP interval is stable (└┘) at a rate of 76 bpm. Therefore there is an underlying sinus rhythm. The QRS morphology of the sinus complexes is normal and there is a normal duration (0.08 sec). The axis is leftward at approximately -30° (positive QRS complex in lead I, negative QRS complex in lead aVF and biphasic in lead II. There are nonspecific ST-T wave abnormalities (^) in leads I, aVL, and V6 (^). The QT/QTc intervals are normal (320/450 msec). The premature QRS complex has the same morphology as the sinus complex but there is no preceding P wave. Therefore these are premature junctional complexes. As every other QRS complex is a premature junctional complex, this is junctional bigeminy. Additionally there is no pause following the premature complex and the PP interval surround the premature complex is the same as the sinus interval. Hence these are interpolated premature junctional complexes in a bigeminal pattern. Also supporting the junctional etiology is that the junctional complexes have a different amplitude compared to the sinus complexes. This is due to the fact that the impulse generated from a junctional focus enters the bundle of His at a different location compared to impulses coming though the AV node. Conduction through the Purkinje system therefore is different.

Circ ECG Challenge Response! Regarding the 74 year old woman with SSS and a PM:

Diagnosis: normal sinus rhythm, premature atrial complexes in a bigeminal pattern, A sensed V paced, pseudofusion

The rhythm is irregular, with longer and shorter intervals which are equivalent to each other. Therefore the rhythm is regularly irregular. The average rate is 72 bpm. Each of the QRS complexes is preceded by a pacing stimulus. Therefore this is ventricular pacing. Before each QRS complex there is a P wave (+, *) with a stable PR interval. The mode of the pacemaker is A sense V paced or P wave synchronous ventricular pacing. The irregularly results from every other QRS complex which is slightly early or premature (v). The early QRS complex is preceded by a P wave (*) that has a morphology that is different from the P wave (+) of the other QRS complex. Therefore every other QRS complex is a premature atrial complex. The P wave of the QRS complex that is not premature (+) is positive in leads I, II, aVF, and V4-V6; therefore this is a normal sinus rhythm with premature atrial complexes in a bigeminal pattern. The sinus QRS complex has a normal duration (0.10 sec) with a terminal S wave in leads I and V5-V6 (←) and an R’ in V1 (→), resembling a right bundle branch block. However, it is not wide enough to be considered a full right bundle and is an intraventricular conduction delay to the right ventricle (although sometimes referred to as an incomplete right bundle branch bloc). The axis is physiologic left between 0° and -30° (positive in leads I and II and negative in lead aVF). The QT/QTc intervals are normal (400/440 msec). As this is not the morphology seen with a right ventricular pacemaker (in which there would be a left bundle branch block morphology) or a biventricular pacemaker (in which there would be a QS morphology or deep Q wave in lead I), the QRS complex is not the result of the pacing stimulus and is therefore the baseline QRS complex. There is a pacemaker stimulus which therefore does not capture. Therefore, this is termed pseudofusion and occurs because the intrinsic PR interval is the same as the AV delay of the pacemaker. The premature atrial complex is also preceded by a pacemaker stimulus. The QRS complex is slightly wider (0.12 sec) and has less of a right bundle branch block morphology with less of a terminal S wave in leads I and V5-V6. It does not have a morphology of either a right or biventricular paced complex. Therefore, there is still pseudofusion present but because the premature atrial complex is associated with a slightly longer time of AV nodal conduction (due to decrimental conduction) more of ventricular activation results from the pacemaker stimulus.