Slide 1: Pacemakers recapped. We revisit 4 of our past bytes to illustrate the basics of pacemakers.

Slide 2: Who gets them? 2 big buckets. Conduction Disease. Heart Failure.

Slide 3: Conduction Disease. See this byte. Ah, the age-old question. What’s the rhythm? Some useful context. 80-year-old male, history of prior CABG. Now with: progressive decrease in exercise tolerance.

Slide 4: Class I indications for pacemakers. Above or at AV node. Any symptomatic bradycardia – sinus bradycardia, 2nd degree type 1 AV block. Atrial fibrillation with pauses of 5+ seconds. Tachy/brady syndrome.

Below AV node. High degree AV block (2nd degree type 2, 3rd degree). Ventricular arrhythmias due to AV block. Escape rhythm with rate <40 bpm. Iatrogenic AV ablation/injury. Slide 5: Heart Failure. See this byte. 60-year-old male with symptomatic heart failure (EF 35%) who has been on guideline-directed medical therapy comes to your office with this EKG... Slide 6: Indications for cardiac resynchronization therapy (CRT). EF less than or equal to 35%, LBBB with QRS >150 ms, symptomatic while on optimal GDMT. CRT = biventricular (BiV) pacing

Slide 7: In summary. PPM indications. Dual chamber. Conduction disease. In or above AV node with symptomatic bradycardia (i.e., sick sinus, 1 AV block, Mobitz I) or Below the AV node regardless of symptoms (i.e., Mobbitz II, 3 AV block).

BiV. BiV pacing or CRT is reserved for advanced heart failure: LVEF less than or equal to 35%. NYHA Class II or greater, wide QRS with LBBB (QRS greater than or equal to 150 ms). Cardiac resynchronization therapy improves quality of life, NYHA class, CHF admission, and mortality

For CRT, NNT for 1 life saved over 2.5 years is 10. Check out the 12-lead Thursday post from 1/24/19 for a CRT case.

Slide 8: Where are pacemaker leads? Single chamber. RV apex only. Dual chamber. RV apex and RA. BiV. RV apex, RA, and coronary sinus (epicardial lead around LV). New research looking at direct pacing of the bundler of His (also direct L bundle pacing). In newest generation of leadless pacemakers, devices are able to A-sense even without having a lead there.

Slide 9: How do you use EKGs to determine where leads are/settings? See this byte. You are admitting a new patient for heart failure. What information can you procure from the baseline EKG?

Slide 10: RV apex lead. Rv will depolarize first. LV will depolarize later. EKG will usually result in LBBB-like morphology: wide QRS, deep S in V1, and tall R in lateral leads.

Coronary sinus lead = epicardial to LV. LV and RV may depolarize nearly at same time (resynchronizing the ventricles). Usually LV depolarizes first, followed by RV. EKG will usually result in RBBB-like morphology: wide QRS, tall R in V1, deep S in lateral leads.

RA lead. EKG will show pacing spikes with relation to p-waves (either before or after)

Slide 11: Use EKG to determine sensing/pacing mode. V-paced. Pacer spike right before wide QRS without relation to p waves.

A-paced. Spike before p waves followed by a narrow QRS.

A-sensed, V-paced. Spike right before wide QRS following native p waves.

A-paced, V-paced. Spike before a p wave and then spike before a wide QRS.

Slide 12: Monitoring. See this byte. Your patient presents for routine follow-up in cardiology clinic. What’s the underlying rhythm? Let’s start with the ventricular rhythm?

Slide 13: Atrial activity should be assessed in any patient regardless of the presence of a pacemaker. Despite pacing, patients should be evaluated for anticoagulation if found to have underlying atrial arrhythmia.

What’s the atrial rhythm? Regular “saw-tooth” flutter waves best seen in II, III, aVF. The rhythm is atrial flutter!

Slide 14: Takeaways. Pacemakers are indicated for patients with symptomatic or high risk conduction disease and severe heart failure and wide QRS. You can use 12-lead EKGs to determine lead location and sensing. Patients with pacemakers should be monitored for arrhythmia events and appropriate function of their devices.


  • Core IM 12 Lead Thursday: 80M with prior CABG. Link.
  • Core IM 12 Lead Thursday: 60M with symptomatic heart failure. Link.
  • Core IM 12 Lead Thursday: New patient being admitted for heart failure. Link.
  • Core IM 12 Lead Thursday: Your patient presents for routine follow-up. Link.

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