Extreme dipping: More complex than it looks

Abstract

Information on clinical and prognostic implications of the extreme dipping (ED) pattern is scanty and findings provided by studies are controversial. Increasing evidence suggests than mean night‐time blood pressure (BP), a powerful predictor of cardiovascular outcomes, in ED can be markedly different between patients and distributed over a wide range of values ranging from hypotension to hypertension. On the whole, these findings emphasize the need to know that the ED pattern is a heterogeneous phenotype that deserve to be evaluated more in detail in future studies.

Current evidence on clinical and prognostic implications of the extreme dipping (ED) pattern (ie, a marked decrease in nighttime systolic and/or diastolic blood pressure equal to or higher than 20% compared with daytime values) is scanty, and the findings provided by studies are not univocal.

The prevalence of this circadian blood pressure (BP) rhythm alteration has been reported varying from 5% to 30%, depending on diagnostic criteria used, demographic and clinical characteristics of individuals included in the various studies.1

The mechanism underlying an exaggerated nocturnal BP fall is probably multifactorial; nevertheless, an agreement exists about a direct association between the magnitude of nighttime drop and the decrease in sympathetic nervous activity driving a marked reduction in both cardiac output and peripheral resistances.

As for the prognostic importance, some authors have shown that cardiovascular risk entailed by the ED pattern is similar as to dipping one, whereas other researchers have suggested either a better or a worse prognosis.2, 3

Numerous issues can be taken into account to explain these conflicting results, including differences in ethnic, demographic, and clinical features of the population samples examined as well as differences in comorbidities and prevalence and magnitude of nocturnal hypotension associated with ED pattern. In this regard, the role of systemic hypotension can be of special relevance because in ED an excessive fall in nocturnal BP may potentially induce cardiac and/or cerebral hypoperfusion and consequently organ ischemia leading to an increased likelihood of cardiovascular events. Despite the potential importance of this mechanism in determining cardiovascular complications, a comprehensive piece of information on the prevalence and correlates of nocturnal hypotension in ED is lacking. We have recently investigated this issue in a cohort of patients referred to a single outpatient hypertension clinic.4 A total of 7074 individual 24‐hour ambulatory BP recordings (ABPM) from untreated individuals with a history of hypertension and treated hypertensive patients were analyzed.

Approximately 4.5% of them presented with an ED phenotype (207 had a nighttime reduction in both systolic and diastolic BP ≥ 20% compared with daytime values, and 132 had a nighttime reduction in diastolic BP ≥ 20%). Among the ED group, the prevalence of nocturnal hypotension varied from 9% to 45% depending on the criteria adopted (ie, mean nighttime BP < 90/50 mm Hg or <100/60 mm Hg). On the other hand, it is worth noting that nocturnal hypertension (ie, mean nighttime BP ≥ 120/70 mm Hg) was found in about 20% of the sample. This means that mean nighttime BP, a powerful predictor of cardiovascular outcomes, in ED can be markedly different between patients and distributed over a wide range of values ranging from hypotension to hypertension.

A further contribution regarding the heterogeneity of the ED pattern comes from the Pressioni Arteriose Monitorate E Loro Associazioni (PAMELA) study, an ongoing epidemiologic observation survey initially designed to determine normal values and prognostic significance of ambulatory and home blood pressure (BP) carried out in 2051 individuals aged between 25 and 74 years, randomly selected from the residents in Monza (a town near Milan, Italy).5

In the PAMELA population, ED prevalence varied from 7.7% to 39.5% depending on whether this BP phenotype was defined by systolic or diastolic BP nocturnal drop equal to or higher than 20%, or both.1

As for the ED subtypes, we have found that in only one out of 155 participants (0.6%) the circadian profile was characterized by an exaggerated systolic BP fall dissociated from a parallel drop in diastolic BP (<20%). This finding suggests that in members of the general population an extreme nocturnal systolic BP fall almost invariably involved diastolic BP. This was not the case for diastolic ED, in which a decrease ≥10% and <20% in mean systolic BP at night compared with mean daytime values was observed in 76% of the cases and a <10% BP reduction in nighttime vs daytime BP was approximately 4% of the cases, respectively. This highlights that a reduced nocturnal systolic BP drop (ie, systolic nondipping) can coexist with an extreme nighttime diastolic BP fall in non‐negligible fraction of the general population.

In conclusion, our observations emphasize the need to know that the ED pattern is a heterogeneous phenotype that deserves to be evaluated more in detail in future studies.

CONFLICT OF INTEREST

The authors report no conflicts of interest.

Cuspidi C, Tadic M, Grassi G. Extreme dipping: More complex than it looks. J Clin Hypertens. 2019;21:1284–1285. 10.1111/jch.13656