Video

Transcript

 Let’s check out this EKG and learn to read it like a cardiologist! Whenever you’re reading an ECG, you wanna approach it in a systematic way. So look at the rate,  the rhythm,  the axis,  the intervals,  the waveform, so anything with the chamber size or the voltage, and of course,  ischemic changes.  Why don’t you   pause the video right now, see if there’s anything wrong? Approach it in a systematic way, and then we’ll come back together and review.  Well, if you’ve gone through your ECG thoroughly, you’ll notice that the  rate is normal,  the rhythm is normal,  the axis is normal,  the intervals are normal, and  there are no ischemic changes. So what is abnormal then?  For one thing, the voltage is quite low!

You might be thinking, “Is this an EKG for ants?”  Let’s get into what makes this EKG low voltage. Low voltage is defined by a QRS height less than five millimeters in the limb leads.  And a QRS height less than ten millimeters in the precordial leads, so leads V1 through V6. One way you can remember this is by placing your left hand over the left side of the EKG. So five fingers for five millimeters.  And then place a second hand over the right side of the ECG or the precordial leads, and that’ll make 10 fingers. 10 fingers for 10 millimeters.

But why do we even care?  Well, low voltage can be caused by  increased impedance or something between the EKG leads and the heart.  Or something that is impairing the heart’s ability to generate force.  For example, some things between the ECG leads and the heart can be tissue like adipose from obesity.  Air like big old lungs with COPD or emphysema or  fluid like a pericardial effusion.  And some things that can impact the heart’s ability to generate force is like after a heart attack when you have a lot of scarring or even in myocarditis. You could also have an  infiltrate like in amyloidosis or sarcoidosis. And don’t forget  metabolic abnormalities like hypothyroidism.  Knowing this differential is gonna help you interpret the clinical significance next time you see low voltage on an EKG. 

For example, let’s say you have this seventy-four-year-old gentleman who presents for heart failure with preserved ejection fraction.  He’s got a normal BMI of 20 kg/m2, no pulmonary disease, no hypertension, but an  echo that shows a severe left ventricular hypertrophy with biatrial enlargement, an apical sparing strain pattern, and no pericardial effusion. So combine  this clinical presentation with an ECG that shows low voltage  despite the severe left ventricular hypertrophy. Hmm. Maybe that’s a clue for amyloidosis.  So let’s review. A low voltage ECG is defined by a QRS height less than five millimeters in the limb leads, so leads I, II, and III. And a QRS height less than ten millimeters in the precordial leads V1 through V6. This can be caused by either increased impedance or something between the ECG leads and the heart, or by something impairing the heart’s ability to generate electrical force. And knowing the causes of low voltage is going to be an important clinical clue in the care of these patients.