The only cardiac question: is this patient perfusing?

Every cardiac finding in this book is an answer to one question: is this patient perfusing? Cardiac output is heart rate multiplied by stroke volume, and stroke volume is only ever preload, afterload, or contractility. When you can say which lever a finding moved, you can usually say what to do about it.

Panel 1 · Preload

• The volume that arrives in the ventricle at the end of diastole.
• Raised by fluid, by venous return, by lying flat, and by raising the legs.
• Dropped by hemorrhage, vomiting, diuresis, vasodilation, and nitrates.
• Clinical read: jugular venous distention, crackles, a weight change on the same scale, flat neck veins when the volume is gone.
• The Starling curve matters here. Filling improves output until the muscle is overstretched, and past that point more volume lowers output rather than raising it.

Panel 2 · Afterload

• The resistance the ventricle has to push against to open the aortic valve.
• Raised by vasoconstriction, hypertension, and aortic stenosis.
• Lowered by vasodilation and by warmth.
• Clinical read: cold mottled extremities, delayed capillary refill, and a narrow pulse pressure.
• High afterload makes the ventricle work harder for less forward flow, so oxygen demand climbs while delivery does not.

Panel 3 · Contractility and time

• Contractility is the strength of the squeeze itself, weakened by ischemia, acidosis, and infarcted muscle.
• Rate buys or spends the diastolic window, and diastole is when the coronary arteries actually fill.
• A ventricle beating at 180 per minute has almost no filling time, so it delivers less volume per beat and feeds itself less well at the same time.
• That is why rate control is perfusion care, not comfort care.

Margin noteoutput is a product, so one lever at zero ends the sentence.

Watch outtachycardia is a cue, never a diagnosis. Treating the number without finding the cause hides bleeding, hypoxia, fever, and pain.

For any cardiac output or infusion math, → BOOK 06 · P6. For every value named on this page, → BOOK 07 · P4.

Takeawaycardiac output is rate times stroke volume, and stroke volume is only ever preload, afterload, or contractility.