Regular P waves and regular QRS complexes with no apparent correlation between them indicate which diagnosis?

• A. Third degree AV block
• B. First degree AV block
• C. Second degree AV block Mobitz I
• D. Sinus rhythm with dropped beats

Answer: (A)

Regular P waves and regular QRS complexes without a fixed relationship means the atrial and ventricular activities are beating independently, a sign of complete heart block. In this scenario the conduction between the atria and ventricles is entirely blocked, so the SA node governs the atrial rhythm while the ventricles escape on their own slower rhythm. The P-P and R-R intervals are each uniform, but there is AV dissociation—the P waves do not reliably lead to QRS complexes. This pattern matches complete heart block, whereas the other patterns (constant PR with 1:1 conduction, progressively lengthening PR with dropped beats, or dropped beats with preserved P–QRS relationships) describe less severe or differently patterned conduction abnormalities.