Final answer:
To differentiate a Second Degree Type I (Mobitz I/Wenckebach) block from a sinus block, one can observe the ECG for a pattern of progressively lengthening PR intervals followed by a dropped beat in the case of Mobitz I, in contrast to regular pauses without progressive prolongation of PR intervals that would indicate a sinus block.
Step-by-step explanation:
To distinguish between Second Degree Type I (Mobitz I) (Wenckebach) and sinus block, you can look at the pattern on an electrocardiogram (ECG). Second Degree Type I AV block, commonly known as Wenckebach, is characterized by progressively lengthening PR intervals followed by a dropped QRS complex, which then resets the cycle. This pattern differs from a sinus block, where there would be a pause followed by the resumption of normal P waves and QRS complexes without progressive PR interval lengthening.
In a second-degree block, some P waves are not followed by a QRS complex, but this is due to impaired AV nodal conduction without direct involvement of the SA node. A sinus block, on the other hand, would indicate a pause in the atrial activity itself, with the AV node still capable of acting as a secondary pacemaker. This is not consistent with the Wenckebach phenomenon, where the problem is intermittent conduction between the atria and ventricles, not a failure of impulse initiation by the SA node.