Lab 6

What does QTcB stand for in the "corrected" Q-T interval formula?

"Corrected" Q-T interval

What does the Q-T interval represent?

Complete depolarization and repolarization of ventricles.

How can hypercalcemia cause an increase in the Q-T interval?

High blood calcium would delay the repolarization by prolonging the plateau phase

How can hypocalcemia cause an increase in the Q-T interval?

Low blood calcium would cause premature depolarization. Calcium blocks sodium channels, so a decrease in calcium means more sodium channels are open, leading to increased excitability.

What factors might lead to differences in the relative magnitude of waveforms?

Mass of tissue involved (more tissue mass=greater amplitude); fluid in pericardial cavity (more fluid=less amplitude)

What does QT stand for in the "corrected" Q-T interval formula?

QT interval; for males=450 ms (.450 sec); for females=470 ms (.470 sec) (convert to sec)

What is the formula for a "corrected" Q-T interval?

QTcB=(QT)/√RR

The length of the corrected QT interval is associated with variations in the NOSIAP gene. Long QT syndrome is a rare, inherited condition associated with delayed repolarization of the ventricles. The gene regulated various K+ channels in the heart. Explain why abnormal activity of these channels would cause delayed repolarization.

Repolarization is due to the efflux of K+ ions. If these channels fail to open in a timely fashion, repolarization will be delayed.

What does √RR stand for in the "corrected" Q-T interval formula?

Square root of R-R interval (in sec)

How can heart rate be calculated?

The R-R interval represents the time required for one complete cardiac cycle. Using this information, the number of cardiac cycles (beats) per minute can be calculated as follows: (1 beat/R-R interval in seconds) x (60 seconds/minute)=beats/minute

What does the time between the R wave and the peak volume pulse represent?

The elapsed time between the electrical depolarization of the ventricles and the physical contraction of the ventricles.

What does the peak of the volume pulse represent?

The maximum pressure in the vessel when the left ventricle ejects blood into the systemic circulation

What does the P-Q interval represent?

The time between depolarization of S-A node and depolarization of A-V node. Represents time it takes for signal to travel throughout atria.

What does the QRS complex represent?

The time necessary for complete depolarization of ventricular fibers. Signal travels down A-V bundle and out through Purkinje fibers.

What can a lengthened Q-T interval increase the risks of?

Ventricular tachyarrhythmia and sudden death

Could you calculate heart rate from an ECG tracing using other waveforms?

Yes, any two wave forms may be used as long as you measure from the same point in two successive wave forms.

What does the P wave on an ECG tracing represent?

atrial depolarization

What does the QRS complex on an ECG tracing represent?

atrial repolarization & ventricular depolarization

What does the T wave on an ECG tracing represent?

ventricular repolarization