Natural history of the proximal aorta in patients with descending thoracic aortic disease

Abstract

Objective:

This study investigated the growth and behavior of the ascending aorta in patients with descending thoracic aortic disease.

Methods:

We examined 200 patients with descending thoracic aortic disease including acute type B dissection (n = 95), chronic type B dissection (n = 38), intramural hematoma (n = 23), and thoracoabdominal aortic aneurysms (n = 44). Images from computed tomography and magnetic resonance imaging were evaluated after three-dimensional reconstruction to examine the growth rate in those with >1 year of imaging follow-up (n = 108). Survival data were derived from all 200 patients in this study.

Results:

Average proximal aortic dimensions at the index image were relatively small, measuring 3.65 ± 0.51 cm in the root, 3.67 ± 0.48 cm in the ascending aorta, and 3.50 ± 0.44 cm in the proximal arch. Average growth rate was low for the aortic root, ascending aorta, and proximal arch at 0.36 ± 0.64 mm/y, 0.26 ± 0.44 mm/y, and 0.25 ± 0.44 mm/y, respectively. There was no difference in baseline proximal aortic dimensions and growth rate between the four subgroups. An index aortic diameter ≥4.1 cm grew faster than those <4.1 cm at the ascending aorta (P = .028) and proximal arch (P = .019). There was no difference in aortic growth rates at the aortic root (P = .887). After the index scan, five patients underwent six ascending aortic replacement procedures, leading to a 3% ascending aortic intervention rate. Overall median life expectancy was 86.15 years.

Conclusions:

Native ascending aortic growth in patients with descending thoracic aortic disease is slow. We suggest regular follow-up for index ascending aorta ≥4.1 cm because of its larger initial size and more rapid growth. (J Vasc Surg 2018;67:1659–63.)

The incidence of descending thoracoabdominal aortic aneurysms (TAAAs) and Stanford type B dissections is 5.9 to 10.4 cases and 4 cases per 100,000 person-years, respectively.^1–3 Historically, the natural history and treatment outcomes for larger TAAAs and type B dissection were associated with significant morbidity and mortality. However, with the advent of modern therapeutic strategies such as endovascular stent grafts, survival for patients with descending thoracic aortic diseases has improved.^4–7 This has implications for the remaining native aorta and the likelihood of needing therapy for it in the future. In this single-institution study, we focused on the proximal aorta. We evaluated its growth rate and the risk of future intervention.

METHODS

Patients.

This study was approved by the University of Wisconsin-Madison Institutional Review Board. A waiver of the need to obtain consent from patients was approved. We conducted a retrospective review of 200 consecutive patients with available imaging who were diagnosed with descending thoracic aortic diseases and who presented to the University of Wisconsin Hospitals and Clinics between April 1999 and February 2014. These included acute type B dissection (n = 95), chronic type B dissection (n = 38), descending thoracic aortic intramural hematoma (IMH; n = 23), and TAAA (n = 44). Of these, a total of 108 patients had serial chest imaging taken at >1-year intervals for calculation of aortic growth rates.

Imaging analysis.

Three-dimensional reconstruction of computed tomography and magnetic resonance scan images was performed using iNtuition image analysis software (TeraRecon, Foster City, Calif). Measurements of the aortic annulus, aortic root, ascending aorta, and proximal arch were made using a centerline method that yields aortic cross-sectional images orthogonal to the direction of blood flow. Computed tomography scan measurements were performed by a faculty cardiothoracic surgeon with expertise in image analysis, clinical evaluations, and operative intervention for aortic disease.

Follow-up.

Survival data were available for all 200 patients with descending thoracic aortic diseases. Midterm survival data were obtained through detailed clinical follow-up. The maximum imaging follow-up was13.5 years, with a total follow-up of 504.3 patient-years and a mean follow-up of 4.6 ± 2.8 years.

Statistical methods.

A Pearson χ² test or Fisher exact test was used to analyze categorical variables. Kaplan-Meier survival analysis with Mantel-Cox statistics was used to analyze survival data. Student t-test and analysis of variance with Tukey post hoc testing were used to compare continuous variables across groups. Life expectancy was calculated using life-table analysis. Statistics were performed using Statistical Package for the Social Sciences software (SPSS Inc, Chicago, Ill).

RESULTS

Demographics of the patients.

Patients with chronic type B dissection at the time of their first available scan at our institution were younger (59.7 ± 16.9 years; P < .05; Table I) than patients with descending thoracic IMH (70.3 ± 9.8 years) and TAAA (68.7 ± 13.4 years). This may represent a referral bias whereby patients with chronic type B dissection referred from outside institutions for surgery tend to be younger because of the perception that they are more likely to tolerate operative intervention. TAAA has a lower proportion of men (43.2%; P < .05; Table I) compared with acute (69.5%) and chronic (73.7%) type B dissections. Creatinine concentration was highest in the chronic dissection group (1.7 ± 1.3 mg/dL) compared with acute type B dissection (1.1 ± 0.3 mg/dL), descending thoracic IMH (1.0 ± 0.3 mg/dL), and TAAA (1.2 ± 0.5 mg/dL). Acute type B dissections had a lower incidence of coronary artery disease (7.4%; P < .05; Table I) compared with chronic type B dissection (21.1%) and TAAA (29.5%). Acute type B dissections had a lower incidence of peripheral vascular disease (3.2%; P < .05; Table I) than TAAA (13.6%). There were five (2.5%) patients with Marfan syndrome and four (2%) patients with known bicuspid aortic valves.

Table I.

Demographics of the patients

Variable	Acute B (n = 95)	Chronic B (n = 38)	Descending IMH (n = 23)	TAAA (n = 44)	All (N = 200)	P value
Age, years	64.1 ± 14.0	59.7 ± 16.9	70.3 ± 9.8	68.7 ± 13.4	65.0 ± 14.4	.008
Male sex	66 (69.5)	28 (73.7)	12 (52.2)	19 (43.2)	125 (62.5)	.007
Weight, kg	92.1 ± 6.3	94.1 ± 28.6	81.0 ± 16.8	83.0 ± 19.4	89.1 ± 24.8	.069
Height, cm	174.1 ± 13.4	176.1 ±14.6	169.5 ± 12.7	168.1 ± 7.99	172.8 ± 13.2	.054
Initial creatinine concentration, mg/dL	1.1 ± 0.3	1.7 ± 1.3	1.0 ± 0.3	1.2 ± 0.5	1.2 ± 0.7	<.001
Ejection fraction, %	62.5 ± 9.0	61.2 ± 7.0	64.2 ± 6.1	59.3 ± 10.0	61.6 ± 8.7	.283
Hypertension	79 (83.2)	33 (86.8)	18 (78.3)	39 (88.6)	169 (84.5)	.671
Dialysis	1 (1.1)	2 (5.3)	0 (0)	0 (0)	3 (1.5)	.188
Coronary artery disease	7 (7.4)	8 (21.1)	3 (13.0)	13 (29.5)	31 (15.5)	.006
Cerebrovascular disease	5 (5.3)	2 (5.3)	3 (13.0)	7 (15.9)	17 (8.5)	.138
Peripheral vascular disease	3 (3.2)	4 (10.5)	0 (0)	6 (13.6)	13 (6.5)	.045
Lung disease	7 (7.4)	5 (13.2)	3 (13.0)	12 (27.3)	27 (13.5)	.170
Liver disease	2 (2.1)	0 (0)	0 (0)	1 (2.3)	3 (1.5)	.719
Diabetes	7 (7.4)	6 (15.8)	2 (8.7)	5 (11.4)	20 (10.0)	.516
Hyperlipidemia	29 (30.5)	15 (39.5)	6 (26.1)	18 (40.9)	68 (34.0)	.458
Cancer within 5 years of surgery	7 (7.4)	4 (10.5)	1 (4.3)	7 (15.9)	19 (9.5)	.339
Smoking	47 (49.5)	21 (55.3)	13 (56.5)	31 (70.5)	112 (56.0)	.146
Marfan syndrome	2 (2.1)	3 (7.9)	0 (0)	0 (0)	5 (2.5)	.097
Bicuspid aortic valve	3 (3.2)	0 (0)	0 (0)	1 (2.3)	4 (2)	.591

IMH, Intramural hematoma; TAAA, thoracoabdominal aortic aneurysm.

All nominal data are presented as number and percentage of total population and compared with Pearson χ² or Fisher exact test. Continuous data are expressed as mean ± standard deviation with comparisons calculated with two-tailed paired Student t-test or one-way analysis of variance.

Proximal aortic diameters and growth rates.

For the index imaging study, there was no difference in proximal aortic dimensions between the four groups (P > .05; Table II). The ascending aortic diameter of 3.67 ± 0.48 cm in our study population is similar to the normal ascending aortic diameter in the age-matched general population of 3.50 to 3.72 cm described by other authors.^8,9 The aortic root and proximal arch measured 3.65 ± 0.51 cm and 3.50 ± 0.44 cm, respectively. The proportion of patients presenting with aortic diameters ≥4.1 cm at the aortic root, ascending aorta, and proximal arch was 15.0%, 15.5%, and 9.5%, respectively.

Table II.

Initial proximal aortic diameters

Diameter	Acute B (n = 92)	Chronic B (n = 36)	Descending IMH (n = 23)	TAAA (n = 42)	Total (N = 193)	P value
Annulus, cm	2.46 ± 0.36	2.46 ± 0.40	2.37 ± 0.25	2.40 ± 0.27	2.44 ± 0.34	.549
Aortic root, cm	3.71 ± 0.48	3.71 ± 0.65	3.53 ± 0.42	3.56 ± 0.44	3.65 ± 0.51	.216
Ascending aorta, cm	3.69 ± 0.46	3.63 ± 0.45	3.53 ± 0.38	3.77 ± 0.59	3.67 ± 0.48	.255
Proximal arch, cm	3.50 ± 0.44	3.51 ± 4.33	3.36 ± 0.35	3.54 ± 0.49	3.50 ± 0.44	.428

IMH, Intramural hematoma; TAAA, thoracoabdominal aortic aneurysm.

Continuous data are expressed as mean ± standard deviation with comparisons calculated with two-tailed paired Student t-test or one-way analysis of variance.

There was no difference in aortic root and ascending aortic growth rate between the four groups (Table III; P > .05). The average growth rate was low for the aortic root, ascending aorta, and proximal arch at 0.36 ± 0.64 mm/y, 0.26 ± 0.44 mm/y, and 0.25 ± 0.44 mm/y, respectively. However, the proximal arch grew faster in TAAA (0.49 ± 0.65 mm/y) compared with the patients with acute type B dissection (0.15 ± 0.30 mm/y; P = .03).

Table III.

Proximal aortic growth rates

Growth rate	Acute B (n = 49)	Chronic B (n = 24)	Descending IMH (n = 13)	TAAA (n = 22)	Total (N = 108)	P value
Aortic root, mm/y	0.30 ± 0.64	0.50 ± 0.87	0.24 ± 0.33	0.41 ± 0.46	0.36 ± 0.64	.538
Ascending aorta, mm/y	0.24 ± 0.29	0.19 ± 0.27	0.23 ± 0.40	0.41 ± 0.76	0.26 ± 0.44	.365
Proximal arch, mm/y	0.15 ± 0.30	0.28 ± 0.46	0.18 ± 0.33	0.49 ± 0.65	0.25 ± 0.44	.026

IMH, Intramural hematoma; TAAA, thoracoabdominal aortic aneurysm.

Continuous data are expressed as mean ± standard deviation with comparisons calculated with two-tailed paired Student t-test or one-way analysis of variance.

Using a diameter of 4.1 cm as a differentiator (Table IV), index aortic diameter ≥4.1 cm grew faster than those <4.1 cm at the ascending aorta (P = .028) and proximal arch (P = .019). There was no difference in aortic growth rates at the aortic root level (P = .887). As expected, those with aortic diameters ≥4.1 cm at each level reach dimensions that warrant surgical intervention (5.0–5.5 cm) sooner (Table IV). For an ascending aorta measuring ≥4.1 cm, a sustained growth rate of 0.56 mm/y would lead to the aorta’s reaching 5 cm and 5.5 cm at a calculated 10.2 years and 19.1 years after the index image.

Table IV.

Proximal aortic growth rates based on initial diameter

Aortic diameter	Average initial diameter, cm	Growth rate, mm/y	Years to reach 5 cm	Years to reach 5.5 cm	Average follow-up, years
Aortic root ≥4.1 cm (n = 17)	4.47 ± 0.30	0.43 ± 0.71	12.33	23.95	4.37 ± 2.16
Aortic root <4.1 cm (n = 91)	3.49 ± 0.35	0.34 ± 0.63	44.41	59.12	4.62 ± 2.92
Ascending aorta ≥4.1 cm (n = 16)	4.43 ± 0.25	0.56 ± 0.85	10.18	19.11	4.08 ± 2.25
Ascending aorta <4.1 cm (n = 92)	3.52 ± 0.33	0.21 ± 0.29	70.48	94.29	4.67 ± 2.89
Proximal arch ≥4.1 cm (n = 10)	4.24 ± 0.12	0.71 ± 0.88	10.70	17.75	3.91 ± 2.19
Proximal arch <4.1 cm (n = 98)	3.40 ± 0.32	0.21 ± 0.35	76.19	100	4.65 ± 2.86

Continuous data are expressed as mean ± standard deviation with comparisons calculated with two-tailed paired Student t-test or one-way analysis of variance.

Operative interventions and survival of patients with descending thoracic aortic disease.

Before the index imaging for descending thoracic aortic disease, seven (3.5%) patients underwent seven surgical ascending aortic replacements. These were excluded from imaging analysis because their ascending aorta had been replaced with a prosthesis. After the index scan, five patients underwent six ascending aortic replacement procedures, leading to an ascending aortic intervention rate of 3% (6/200). All ascending aortic replacements in this series of patients were performed for progressive aneurysmal degeneration. For the descending thoracic aorta, a total of 98 patients underwent 58 open repairs of the descending thoracic aorta, 46 thoracic endovascular aortic repairs, and 2 aortic fenestrations for thoracic aortic dissection. The operative indications for thoracic aortic surgery were degenerative descending thoracic aortic aneurysms (n = 40), aortic dissection (n = 57), aortic stent complication (n = 1), and IMH (n = 11). For the infrarenal abdominal aorta, abdominal aortic aneurysms were addressed with 7 abdominal endovascular aortic repairs and 15 open abdominal aortic repairs.

The life expectancy curve is shown in the Fig. Overall median life expectancy for patients with descending aortic disease with appropriate intervention was 86.15 years. Median life expectancy was 88.48 years for acute type B dissection, 83.77 years for chronic type B dissection, 85.00 years for descending thoracic aortic IMH, and 86.46 years for TAAA. The intervention-free survival from the time of the first imaging study was 65.3% at 1 year, 52.8% at 5 years, and 49.0% at 10 years.

Fig.

Life expectancy of patients with descending thoracic aortic disease. IMH, Intramural hematoma; TAAA, thoracoabdominal aortic aneurysm.

DISCUSSION

Whereas a small proportion (3.5%) of patients presenting with descending thoracic aortic disease have previously undergone ascending aortic replacement for aneurysm disease, most still retain their native ascending aortas. As therapeutic strategies to address existing descending thoracic aortic diseases are formulated, it is important for both the physician and patient to understand ascending aortic growth behavior and to anticipate need for future interventions. Indeed, the surgical intervention rate for the ascending aorta after the index imaging study is low at only 3%. Our studies revealed that the remaining native ascending aorta grows at a very slow rate of 0.25 to 0.36 mm/y. This is slower than the 0.7 mm/y that was noted by Davies et al,¹⁰ who examined established ascending thoracic aortic aneurysms. However, this is comparable to a study of small ascending aortic aneurysms between 4 and 5 cm that found a growth rate of 0.42 mm/y.¹¹ Interestingly, there was no difference in growth rates among the different descending thoracic aortic diseases.

Ascending aortas and proximal arches ≥4.1 cm tend to grow at a higher rate. This is consistent with previous studies by Dapunt et al¹² and Davies et al¹⁰ showing that aneurysms expand at a higher rate in patients with larger aortic diameters. Given that the group with aortic diameter ≥4.1 cm also has larger aortic dimensions to begin with, it likely warrants regular follow-up. On average, for index ascending aortas and root ≥4.1 cm, it would take approximately 10 years and almost 20 years to reach dimensions of 5 cm and 5.5 cm, respectively. Given the median life expectancy of 86 years and a mean presenting age of 65 years, patients with larger initial diameters (eg, ≥4.1 cm) should be closely observed as guided by the age and surgical candidacy of the patient. On the other hand, patients with aortas <4.1 cm would take 44 to 76 years to reach a final diameter of 5 cm. This is very likely beyond their life expectancy, and follow-up imaging should be determined on an individual basis.

Our recommendation for proximal aortic surveillance in the context of descending aortic disease is as follows. If the ascending aorta is ≥4.1 cm, we recommend continued annual imaging studies for timely surgical intervention to avoid acute aortic syndromes. An ascending aorta <4.0 cm in diameter does not require regular surveillance.

Our findings are limited by their retrospective nature with inherent limitations and biases. Other limitations include the comparison of images taken by computed tomography and magnetic resonance imaging, which can confound our measurements. However, we have taken measurements at the same aortic levels with these modalities and avoided using echocardiographic images, which can introduce greater measurement inconsistencies. Whereas we have calculated the time taken to reach aortic dimensions of 5 cm and 5.5 cm, this assumes that the growth rate is constant. This provides an approximation of the time needed to reach criteria for intervention. However, we recognize that there are likely to be incremental changes in growth rates during aneurysm progression. It is possible that the relatively low numbers of patients were not sufficient to reveal differences in growth rates between subgroups. In terms of subsequent ascending aortic operation from the time of the index scan, there is a possibility that the patient was operated on elsewhere and was not captured in our data set.

CONCLUSIONS

Patients undergoing surveillance and eventual treatment of descending thoracic aortic disease demonstrate very slow growth rates (0.25–0.36 mm/y) in the ascending thoracic aorta. However, patients with larger index ascending aortic diameters have higher growth rates. Therefore, we recommend closer imaging surveillance for patients with an ascending aortic diameter of ≥4.1 cm.

ARTICLE HIGHLIGHTS.

• Type of Research: Single-center retrospective cohort study

• Take Home Message: In 200 patients with descending thoracic aortic disease, average growth rates for the aortic root, ascending aorta, and proximal arch were 0.36 ± 0.64 mm/y, 0.26 ± 0.44 mm/y, and 0.25 ± 0.44 mm/y, respectively. Patients with an index ascending and proximal aortic diameter ≥4.1 cm grew at a faster rate.

• Recommendation: This study suggests that in patients with descending thoracic aortic diseases, those with ascending or proximal aortic diameters ≥4.1 cm likely warrant closer longitudinal imaging follow-up as guided by the clinical scenario.