Compare conditions

Put any two — or three — conditions side by side, adult or pediatric, to spot the look-alike differences fast, row by row.

Unstable tachyarrhythmia

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In one line

·The heart is beating so fast that it cannot fill with blood between beats, so the amount of blood pumped out drops and the body goes into shock.

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Normal physiology

·The sinus node (a cluster of pacemaker cells in the right atrium, the top-right chamber) sets how fast the heart beats based on signals from the brain and body—faster when you run, slower when you sleep. Each heartbeat has two phases: systole (when the heart squeezes and pumps blood out) and diastole (when the heart relaxes and the ventricles, the bottom chambers, fill with blood). During diastole, the atria (top chambers) squeeze last to give the ventricles a final 20 percent push of blood—that is called the atrial kick. Then the electrical signal travels down the AV node (the connection between top and bottom chambers) into the bundle of His and then spreads through the Purkinje fibers so both ventricles squeeze together in an organized, powerful wave that pushes blood out to the lungs and body. The coronary arteries deliver oxygen-rich blood to the heart muscle itself, but only during diastole when the heart is relaxed and the vessels are not squeezed shut. Keep that picture in your head, because every weird finding in unstable tachyarrhythmia is a change from this normal flow.

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What goes wrong

·In unstable tachyarrhythmia, the normal pacemaker loses control. Instead, either a different spot in the heart starts firing electrical signals faster than the sinus node (called an ectopic focus), or electricity starts spinning around in a loop (reentry circuit) that fires over and over, or the AV node lets signals through too fast without the normal delay. Whatever the cause, the ventricles are now being told to squeeze 150, 200, or even 250 times per minute. They squeeze before they have time to fill with blood, so even though the heart is beating fast, almost no blood is pumped out with each beat. The amount of blood the body gets per minute (cardiac output) drops, and blood pressure falls. That is the core break.

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Hallmark signs

·Low blood pressure (systolic below 90)
·Confusion, trouble speaking, or acting strangely
·Chest pain or pressure
·Shortness of breath or rapid breathing
·Very fast pulse (usually over 150 beats per minute at rest)
·Feeling dizzy or about to faint (presyncope)
·Patient may look pale, sweaty, and anxious

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Red flags · escalate now

·Systolic blood pressure below 90 mmHg
·Altered mental status (confused, not responding normally, or unresponsive)
·Chest pain or signs of heart attack (acute heart attack (myocardial infarction))
·Signs of heart failure (fluid in the lungs causing extreme shortness of breath, inability to lie flat)
·Loss of consciousness or about to pass out

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Workup

·12-lead electrocardiogram (ECG)
·Serum potassium
·Serum magnesium
·Serum troponin I or T
·Thyroid-stimulating hormone (TSH)
·Serum lactate
·Chest X-ray

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Treatment

·Synchronized cardioversion (an electric shock timed to the R wave on the ECG)
·Adenosine IV push 6 mg (followed by 12 mg if no response) for stable narrow regular a fast heart rate (tachycardia)
·Diltiazem IV or metoprolol IV (beta-blocker) for stable atrial fibrillation (an irregular, quivering heartbeat) with rapid ventricular response
·Amiodarone IV 150 mg over 10 minutes or procainamide IV 20–50 mg/min for stable wide regular a fast heart rate (tachycardia)
·Immediate unsynchronized defibrillation (shock without timing) for pulseless ventricular a fast heart rate (tachycardia) or ventricular fibrillation
·Vagal maneuvers (carotid massage, bearing down as if having a bowel movement, or ice water to the face) for stable narrow regular a fast heart rate (tachycardia)
·Correct serum potassium and magnesium to normal range

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NCLEX trap

·When a patient is unstable from a fast rhythm — confused, low blood pressure, chest pain, or struggling to breathe — synchronized cardioversion (a timed shock) comes first, not a drug. Medicine takes minutes to work; electricity works in seconds. Always check for signs of instability before picking your tool.
·Instability is not about the number — it is about whether the fast rhythm is hurting the patient right now. A patient who is alert with a blood pressure of 120 and a heart rate of 160 is stable. The same heart rate with confusion and a blood pressure of 88 is unstable. Look at the whole picture, not just one vital sign.
·In unstable tachyarrhythmia, whether the rhythm is regular or irregular helps you figure out the cause later, but it does not change your first move. If the patient is unstable, use synchronized cardioversion no matter what the rhythm looks like on the monitor.
·When a patient is unstable from a fast rhythm, make them safe first. Put them on a monitor, make sure they are breathing, then shock. The 12-lead EKG can tell you what broke after the patient is stable and thinking clearly again.
·In unstable tachyarrhythmia, the low blood pressure is caused by the broken rhythm, not by dehydration. The heart is beating so fast that diastole (the filling phase) is too short, so not enough blood goes out with each beat. Fluids will not fix filling time. Stop the fast rhythm first with cardioversion, then check the blood pressure again.
·In unstable tachyarrhythmia, if the patient has shock, chest pain, confusion, or low blood pressure — whether the rhythm is wide or narrow — use synchronized cardioversion first. Figure out the exact rhythm after the patient is safe and stable.

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