Monitor atlas: perioperative cardiac events
Why examiners ask this
The cardiac clips in the monitors station are the ones with the highest stakes and the shortest window. A rhythm strip, an arterial trace, a pulmonary artery or central venous waveform, or a wedge, cardiac output or mixed venous saturation value comes up,1 and I have one minute to say what it is, why it happened and what I do. It tests application of knowledge and organization; the examiners want to see that a consultant can read the pattern without a cardiologist.
The 60-second answer
I read every cardiac clip in the same order: rhythm, rate, pressure, waveform shape, then the trend. For the ECG I say the rhythm and the rate, then look at the ST segment in the lead shown and at the QRS width. For the arterial line I read the number, the slope of the upstroke, the position of the dicrotic notch and whether the trace swings with ventilation. For a central or pulmonary artery trace I identify the waveform by its pressures and its components, then look for the abnormal wave. I then state the diagnosis as one physiological sentence and give the first three actions. Every answer ends with the one thing I am watching to know the treatment worked.
Decision points and the "why"
The patterns in the outline, with the two or three features that identify each and the action attached.
| Pattern | Identifying features | What it changes |
|---|---|---|
| ST depression, lead V5 | Horizontal or downsloping ST ≥1 mm, rate often high | Subendocardial ischemia; slow the rate, raise the pressure, 100% oxygen, 12-lead, consider nitroglycerin |
| ST elevation, lead II | Convex elevation ≥1 mm, reciprocal depression | Transmural ischemia or coronary air or spasm; call cardiology, aspirin, heparin discussion with surgeon |
| Ventricular fibrillation | Chaotic, no QRS, pulse oximeter pleth lost | Defibrillate at the manufacturer's energy (typically 120–200 J biphasic), CPR, epinephrine 1 mg every 3–5 min2 |
| Monomorphic ventricular tachycardia | Wide regular QRS >120 ms, rate >100 | Pulse present: amiodarone 150 mg over 10 min or synchronized cardioversion; pulseless: shock |
| Torsades de pointes | Twisting polymorphic QRS, long QT on prior strip | Magnesium 2 g IV, stop QT-prolonging drugs, overdrive pacing |
| Atrial fibrillation with rapid response | Irregularly irregular, no P waves, rate >100 | Unstable: cardiovert; stable: beta-blocker or diltiazem, rate control to <110 |
| Complete heart block | P waves and QRS independent, slow ventricular escape | Atropine rarely works; pacing, epinephrine or dopamine infusion |
| Hyperkalemia | Peaked T, wide QRS, loss of P, sine wave | Calcium chloride 1 g, insulin 10 units with dextrose, bicarbonate, hyperventilation |
| Tamponade on CVP | CVP rises, arterial pulse pressure narrows, pulsus paradoxus >10 mmHg | Fluid, keep the rate up, no positive pressure surge, drain |
| Right ventricular failure | CVP climbs, PA pressure climbs then falls as output fails, arterial pressure falls | Inotrope, pulmonary vasodilator, avoid further fluid |
| PA catheter wedge | PA trace changes to an a-c-v venous pattern on balloon inflation | Large v wave means mitral regurgitation or ischemic papillary muscle |
| Overwedging | Trace climbs steadily without a venous pattern | Deflate the balloon immediately; risk of PA rupture |
| Arterial line dampening | Slurred upstroke, lost notch, narrow pulse pressure | Flush, check for bubbles or kinks; do not treat the number as hypotension |
| Pulse pressure variation | Arterial trace swings >13% with the ventilator | Patient is fluid responsive if in sinus rhythm with tidal volume 8 mL/kg |
- The lead matters — the ECG is displayed continuously from the start of every anesthetic,3 and V5 catches most intraoperative ischemia; lead II catches inferior ischemia and is the rhythm lead. I say which lead I am reading.
- The PA waveform tells me where the catheter sits — right atrium 0–8 mmHg, right ventricle 25/0–5, pulmonary artery 25/10 with a dicrotic notch, wedge 6–12 with a venous pattern. A right ventricular trace that persists means the catheter has coiled back.
- A pressure I do not believe gets a pulse check — ventricular fibrillation on the ECG with a normal arterial trace is artifact; I check the patient before I shock. In an arrest, an arterial waveform or an abrupt rise in ETCO2 after a shock is the evidence of return of circulation.2
The complication they will inject
The second clip adds a second monitor to the first. The ST depression from clip one is followed by an arterial trace that falls from 120 to 70 systolic with a central venous pressure rising from 8 to 18, and the pulse oximeter pleth fades. I state the combined picture: ischemia has progressed to acute pump failure, and the rising filling pressure with falling output is cardiogenic shock. I say the actions: 100% oxygen, epinephrine or norepinephrine to restore coronary perfusion pressure, call cardiology, consider intra-aortic balloon pump, and tell the surgeon to stop. I do not give fluid to a full heart. The alternative inject is the balloon that stays inflated on the PA trace while the facilitator asks what I see; the answer is overwedging and the action is deflation now.
Pitfalls that cost points
- Calling a rhythm without a rate.
- Shocking a strip without confirming there is no pulse.
- Giving fluid for hypotension when the central venous pressure is already high.
- Reading the number on an obviously dampened arterial trace.
- Forgetting to say which lead or which transducer I am reading.
Rapid-why
Q: Why does ST depression appear in V5 first? A: V5 overlies the largest mass of left ventricular subendocardium, the region with the lowest perfusion reserve when demand rises.
Q: What is the first drug for torsades? A: Magnesium 2 g IV, regardless of the serum level, because the arrhythmia is driven by early afterdepolarizations that magnesium suppresses.
Q: How do I tell a wedge trace from an overwedged one? A: A true wedge has a venous a-c-v pattern below the PA diastolic pressure; overwedging climbs without a pattern and I deflate the balloon.
Q: Why does pulsus paradoxus appear in tamponade? A: Inspiration fills the right ventricle, which shifts the septum into a left ventricle that cannot expand against the fluid, so stroke volume and systolic pressure fall by more than 10 mmHg.
Numbers to know
| Item | Value |
|---|---|
| Ischemic ST change | ≥1 mm, 60–80 ms after the J point |
| Defibrillation | Manufacturer's dose, typically 120–200 J biphasic2 |
| Amiodarone, stable VT | 150 mg over 10 min |
| Magnesium, torsades | 2 g IV over 2–15 min |
| Normal PA pressure | ~25/10 mmHg, mean 15 |
| Normal wedge | 6–12 mmHg |
| Pulsus paradoxus threshold | >10 mmHg fall in systolic on inspiration |
Links
- The monitors and echo station: format and timing, Perioperative myocardial ischemia and infarction, Cardiac tamponade, including post-cardiac surgery, Pulmonary artery catheter: indications, waveforms, complications, Intraoperative cardiac arrest
- Atlas: Monitor atlas: perioperative respiratory events; Monitor atlas: other perioperative and peripartum events (coming)
- AHA ACLS Guidelines 2020 with 2023 focused update
Sources
- 1.OSCE Content Outline · ABA · theaba.org
- 2.Part 3: Adult Basic and Advanced Life Support (2020 AHA Guidelines for CPR and ECC) · AHA, 2020 · cpr.heart.org
- 3.Standards for Basic Anesthetic Monitoring · ASA, 2025 · asahq.orgLast amended October 15, 2025; Standard II, circulation.
Facts on this page were checked against these sources on Oct 14, 2026. Guidelines change; confirm doses against current institutional protocols.