12 lead ECG – Normal ECG 12 lead ECG 12 lead ECG consists of three standard limb leads (Leads I, II and III), three augmented limb leads (aVR, aVL, and aVF) and six chest leads (V1 to V6). All the twelve leads have recorded ECG of three cardiac cycles in this tracing. There is a long lead II recording at the bottom of the tracing which is a rhythm strip enabling better assessment of the cardiac rhythm. 12 Leads can be acquired simultaneously and printed sequentially as in a 12 channel machine or can be acquired sequentially as in a single channel ECG machine. This particular tracing was recor ..read more

Temporary pacing ECG Temporary pacing ECG What are the findings in this ECG and possible explanations? ECG shows a paced rhythm at around 60 per minute, with pacing spikes preceding each QRS complex. At first look it may seem that there is P wave before each QRS with a reasonable PR interval suggesting atrial sensed ventricular pacing (A sense – V pace sequence or tracking). But close scrutiny shows that PR interval is gradually varying. The atrial rate is also close to 60/minute, making false appearance of an AV synchronous pacing in some beats. In analog ECGs the pacing spikes in temporary ..read more

Pacemaker sensing failure Pacemaker sensing failure Click here for a larger image What are the findings in this ECG and possible explanations? ECG shows PR interval prolongation, Q and ST elevation with T inversion in lead III, small q and T inversion in aVF along with lateral ST depression and T wave inversion indicating an inferolateral myocardial infarction with first degree AV block. The interesting part is evident in the rhythm strip. Multiple pacemaker spikes or pacing artefacts are visible. The spike marked with blue arrow has come a short while after the preceding QRS complex and has ..read more

Paced rhythm with very wide QRS Paced rhythm with very wide QRS Findings and possible etiology? Most of the beats show a large pacing spike just before the QRS complex, indicating a ventricular paced beat, possibly with unipolar pacing mode. In unipolar pacing the lead tip in the right ventricle acts as the negative electrode (cathodal pacing) and the pacemaker can acts as the positive electrode. This causes a long electrical circuit between the two so that surface ECG detects a large pacing spike. Unipolar pacing In bipolar pacing, the lead tip is negative, and a proximal ring electrode is p ..read more

Incognito Paced Rhythm! Click here for a larger image At one look it looks like left bundle branch block (blue arrows – lead I and aVL). But V5 shows negative complexes which is not typical of LBBB (violet arrow). There is left axis deviation as indicated by negative complexes in the inferior leads (green arrows). PR interval can be seen as varying on scrutiny of multiple beats. But PP interval is constant (red arrows). Atrial rate is higher than the ventricular rate (PP interval shorter than RR interval). Hence the four criteria for complete heart block are satisfied: Regular PP interval R ..read more

Intermittent LBBB and P Mitrale or Tricuspidale? Intermittent LBBB and P Mitrale or Tricuspidale Intermittent left bundle branch block pattern is seen as wide notched QRS complexes with cycle length of 570 ms. Narrower QRS complexes at cycle length of 600 ms are seen towards the end of the tracing. This can be considered as phasic aberrancy which is rate dependent. Classically rate dependent left bundle branch block is deceleration dependent rather than acceleration dependent. Acceleration dependent block is usually right bundle branch block. P waves are wide and notched, suggesting left atri ..read more

Giant T inversion and NSVT Giant T inversion with NSVT Holter tracing showing giant T wave inversion and non sustained ventricular tachycardia, both at the beginning of the tracing and at the end. Ventricular ectopic beats are also seen in between. Variation in QRS amplitude of the NSVT beats are evident. It is likely that this will soon progress to torsades des pointes in the setting of gross QT interval prolongation. QT interval is seen as 640 ms in a cycle with cycle length of 600 ms. So, the QTc will be 640 ms. The first ventricular ectopic is followed by a good compensatory pause while t ..read more

ECG Quiz 62 At one look it appears like an evolved inferior wall myocardial infarction. But on close scrutiny, the inverted P waves in lead I and inferior leads catch your attention. PR interval is 200 milliseconds. Some would think that this could be a rhythm other than sinus rhythm, originating from the lower left portion of the atrium. In left atrial rhythm one would expect P inversion in lead I, V6 and inferior leads. But that will not change the QRS pattern or T waves. Here we have QS complexes in inferior leads with T wave inversion. Down sloping ST with T wave inversion is seen in lea ..read more

ECG Quiz 61 – Discussion Lead I and aVL shows wide notched QRS complexes suggestive of left bundle branch block. PR interval for the sinus beat is 200 ms, at the upper limit. Rhythm strip shows sinus bradycardia with junctional escape beats (blue arrow) without preceding P waves, but same QRS morphology as the succeeding sinus beat (violet arrow). The sequence of junctional escape followed by a sinus capture beat continues throughout the rhythm strip. This constitutes an escape – capture bigeminy. Other common varieties of bigeminy are: Ectopic bigeminy Block bigeminy Echo bigeminy Ec ..read more