Am J Med. 2015 Oct;128(10):1140-3. doi: 10.1016/j.amjmed.2015.05.016.

Summer syncope syndrome redux.

Huang JJ1, Desai C2, Singh N2, Sharda N2, Fernandes A2, Riaz IB2, Alpert JS3.
  • 1University of Arizona at South Campus, Tucson. Electronic address:
  • 2University of Arizona at South Campus, Tucson.
  • 3University of Arizona, Sarver Heart Center, Tucson.



BACKGROUND: While antihypertensive therapy is known to reduce the risk for heart failure, myocardial infarction, and stroke, it can often cause orthostatic hypotension and syncope, especially in the setting of polypharmacy and possibly, a hot and dry climate. The objective of the present study was to investigate whether the results of our prior study involving continued use of antihypertensive drugs at the same dosage in the summer as in the winter months for patients living in the Sonoran desert resulted in an increase in syncopal episodes during the hot summer months.

METHODS: All hypertensive patients who were treated with medications and admitted with International Classification of Diseases, 9th Revision code diagnosis of syncope were included. This is a 3-year retrospective chart review study. They were defined as “cases” if they presented during the summer months (May to September) and “controls” if they presented during the winter months (November to March). The primary outcome measure was the presence of clinical dehydration. The statistical significance was determined using the 2-sided Fisher’s exact test.

RESULTS: A total of 834 patients with an International Classification of Diseases, 9th Revision code diagnosis of syncope were screened: 477 in the summer months and 357 in the winter months. In patients taking antihypertensive medications, there was a significantly higher number of cases of syncope secondary to dehydration during the summer months (40.5%) compared with the winter months (29%) (P = .04). No difference was observed in the type of antihypertensive medication used and syncope rate. The number of antihypertensives used did not increase the cases of syncope in either summer or winter.

CONCLUSIONS: An increased number of syncope events was observed in the summer months among people who reside in a dry desert climate and who are taking antihypertensive medications. The data confirm our earlier observations that demonstrated a greater number of cases of syncope among people who reside in a dry desert climate who were taking antihypertensive medications during summer months. We recommend judicious reduction of antihypertensive therapy in patients residing in a hot and dry climate, particularly during the summer months.

KEYWORDS: Heat syncope; Hypertension; Summer; Summer syncope

PMID: 26052028



Maintenance of consciousness, or a fully awake cognitive state, depends on, among other factors, a relatively constant supply of blood to the brain. Syncope is defined as a transient loss of consciousness due to interruption in this supply of blood. This results in both unconsciousness and loss of postural tone—muscles that usually work to maintain a standing or upright sitting posture shut off, resulting in a person falling, or what is more commonly referred to as ‘fainting’ or ‘passing out.’ A recumbent state, or lying flat, increases blood return to the heart, which in turn temporarily increases blood output to the rest of the body—consciousness thus rapidly returns as blood flow is restored to the brain. There are numerous possible causes of syncope, and the U.S. is estimated to spend roughly $2 billion annually on hospital visits alone evaluating cases of syncope. This fact combined with the significant risk for injury following syncopal events, particularly in the elderly, makes efforts to prevent syncopal episodes an important public health priority.



Figure 1: Determinants of mean arterial blood pressure


The possible causes of syncope are numerous, and understanding which are preventable requires an understanding of how the body maintains a relatively constant blood pressure (fig 1). Among the various influencing factors, intravascular volume—or ‘hydration’ status– emerges as one of the most readily variable, particularly in climates that vary widely in temperature, as in Tucson, Arizona (fig 2). Among the various blood pressure medicines in use today, some of the most commonly used are diuretics—they lower blood pressure by causing patients to lose more water. In theory, patients who live in hotter climates are likely to be somewhat volume depleted—ie. ‘dehydrated’—during the summer months. We would observe this as an increase in hospital visits for syncope due to dehydration during the summer compared to winter months in patients who are taking blood pressure medicines. The objective of this study was to look specifically at people taking pressure medicines who ended up in the hospital for syncope from dehydration and answer the following question: were hospital visits for dehydration syncope more common during the summer?

When we looked at three years’ worth of hospital visits for syncope determined to be from ‘dehydration,’ we compared how often patients already taking blood pressure medicines ended up in the hospital during the hot summer months compared to the winter. As we suspected, for those patients taking blood pressure medicines who ended up in the hospital after passing out from dehydration, it appeared to occur more often in the summer than the winter. This is despite the dramatic increase in the Tucson population (and hence the total number of people in the city taking blood pressure medicines) during the winter. The effect was most noticeable among people 60 years of age or older—a group of people who are particularly vulnerable to injury when they fall outside the hospital not to mention complications any time they do end up in the hospital. Of note, no link between the number of blood pressure medicines patients were taking or whether one of them was a diuretic and what season they ended up in the hospital for syncope was found—put another way, although it would seem logical that anyone who either (1) was taking more medicines for blood pressure, or (2) was taking a medicine that already tends to dehydrate, would be more likely to end up in the hospital for dehydration during the summer, but this did not pan out in our results. It is possible that our study did not have enough patients to show this difference, so this remains an interesting possibility worth studying further.

While it is very important to control blood pressure to help reduce the chance for heart attack and stroke among other possible ill health effects, our results suggest overcorrection of blood pressure can be just as dangerous. Patients who take blood pressure medicines and live in an arid desert climate seem to be most at risk. These results are far from conclusive, and any decisions about adjusting medications should always be made on an individual basis under the guidance of a licensed healthcare provider. However it is our hope that our results will at least open the discussion on how best to use blood pressure medicines in dry desert climates.



Figure 2: Ambient High and Low Temperature, Tucson, AZ, 2016



Kumar, Vinay, Abul K. Abbas, and Jon C. Aster. “Chapter 11,” Robbins and Cotran Pathologic Basis of Disease. Philadelphia, PA: Elsevier Saunders, 2015. N. pag. Print.

“Tucson, AZ Monthly Weather Forecast.” Tucson, AZ Monthly Weather Forecast., 1 Apr. 2016. Web. 6 Apr. 2016. <>



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