The ECG of a 40-year old male was recorded using standard bipolar limb leads. The sum of voltages of the three standard leads was found to be 5 millivolts. This indicates:
Ans. is 'd' i.e. Increased cardiac muscle mass Guyton writes - "'Normally, the voltages in the three standard bipolar limb leads, as measured from the peak of the R wave to the bottom of the S wave, vary between 0.5 to 2.0 millivolts, with lead III usually recording the lowest voltage and lead II the highest.In general when the sum of the voltages of all the QRS complexes of the three standard leads is greater than 4 millivolts the patient is considered to have a high voltage electrocardiogram.The cause of high-voltage QRS complexes most often is increased muscle mass of the heart, which ordinary results from hypertrophy of the muscle in response to excessive load on one part of the heart or the other. The increased quantity of muscle causes generation of increased quantities of electricity around the heart. As a result, the electrical potentials recorded in the electrocardiographic leads are considerably greater than normal" * It is not able to differentiate whether its right or left heart hypertrophy.
A normal heart
Right ventricular hypertrophy
Left ventricular hypertrophy
Increased cardiac muscle mass
Heart: Electrocardiographic Interpretation Blood Flow Abnormalities