Question

You are studying the heart of a strange newly-discovered primate species. Its basic structure is like that of the human heart, but the timing of the wave of excitation which emanates from the SA-node and spreads throughout the atria and ventricles are quite different. The figure below shows the time of arrival of the wave at various points in the heart relative to its generation at the SA-node.

· SA node 6.0 · AV node 0.55

Cardiac action potentials were recorded at different points in the atrial and ventricular tissue, and were found to be quite consistent in terms of their form within each tissue type. In other words, all atrial cells exhibit the same AP duration of 200 ms, and all ventricular cells exhibit an AP duration of 250 ms. Examples of an atrial and ventricular action potential are shown below.

You now record this primate’s ECG (VB-A) using the bipolar chest leads as discussed in class. Sketch one full cardiac cycle of the ECG you would expect from this heart, showing all important time intervals and indicate the relative amplitudes of various portions the signal (i.e., not necessary to indicate mV, but show relative amplitudes at reasonable scale with respect to each other). Label each major portion of the ECG with an 'A', 'B', 'C',... and explain with a sentence or two why each portion looks the way it does. Justify the relative amplitude, duration, and polarity, but don't worry about fine details of the recorded signal.

Answer 1

Segmen - 9.2 sec 0 -0.25 sec? PR OT Interval Interval Piave - Atrial depolarization ORS – ventorulan depolarizato I ventricular repolarizate