The skeptical cardiologist has a question for all patients who have elevated blood pressure: has your doctor ever taken your BP in both the right and left arms?
Have you ever noted a difference in the systolic BP between arms (interarm difference or IAD) when you do home recordings?
Although UK and USA national hypertension guidelines recommend measuring BP in both arms on a first visit and most PCPs are aware of the recommendation, only 30% agree with it and few actually adhere to it. (2007) Hypertension guideline recommendations in general practice: awareness, agreement, adoption, and adherence. Br J Gen Pract 57(545):948–952.
It’s important to measure the difference between right and left arm BP at least once because:
- An IAD >10 mm Hg often indicates peripheral artery disease (such as a blocked subclavian artery to the arm with the lower BP) and is associated with higher cardiovascular disease risk.(Clark, et al (2006) Prevalence and clinical implications of the inter-arm blood pressure difference: a systematic review. J Hum Hypertens 20(12):923–931)
- A blocked subclavian artery can cause neurological symptoms, dizziness or loss of
consciousness (termed subclavian steal syndrome and typically occurring after using the arm with the blocked artery.)
- A consistently lower BP in the left arm compared to the right arm can be a sign of a serious and correctable congenital heart disease called coarctation of the aorta.
- The true BP (i.e. the one we should be treating) is the higher of the two. Thus, if you do have a consistent IAD, you should only measure the higher one for monitoring BP.
In 2009, Parker and Glasziou noted that whereas 13 of 15 national hypertension guidelines recommend measuring BP in both arms:
“only seven guidelines gave some justification, with only one quantifying the prevalence of substantial arm differences and only one providing a reference to the evidence. No guideline provided a description of appropriate techniques for reliably measuring blood pressure in both arms. “
they speculated that if PCPs were given better justification and precise details on how to reliably measured the IAD they would be more likely to do it.
I’ve mentioned the “why” for measuring IAD above.
The “why” is so compelling that if you have hypertension or pre-hypertension (SBP 120-140) and you’ve never had the BP compared in both arms you should do it yourself.
The “how” of IAD is more complicated.
In a subsequent post I will give my recommendations on how to reliably measure IAD and I will tell the story of a 75 year old competitive ice hockey player with a totally blocked subclavian artery to his right arm.