- Email: [email protected]
Early electrocardiographic changes produced by ascending to high altitudes
Early Electrocardiographic Ascending
to High
Changks
Produced
by
Altitudes
Dante Pefialoza, M.D., Max Echevarria, Rat21 Gamboa, M.D., Lima, Peru
M.D.,
Emilio
Marticorena,
M.D.,
and
In a previous study 10 subjects were taken from sea level to high altitudes; where observations were carried out, first, after 1 month of residence and, then, periodically for a whole year. During the progressive acclimatization, changes in the electrocardiogram were observed which resembled, at least in part, the electrocardiographic characteristics of the native residents of high altitudes.1 Nevertheless, the early electrocardiographic response to anoxic anoxia determined by the ascent to high altitudes was not studied. On the other hand, however, recent experimental observations demonstrate that early right ventricular hypertrophy can be produced in guinea pigs exposed for several weeks to simulated high altitudes.2 Therefore, we believed that new investigations should be performed on man in order to study the early electrocardiographic changes produced by the ascent to high altitudes. MATERIAL
AND
METHODS
Thirteen normal men between the ages of 17 and 21 years were studied. In Lima, at sea level, an electrocardiogram was recorded. Afterward the subjects were taken by motorcar to Morococha, at an altitude of 4,540 meters (14,900 feet); the ascent took nearly 4 hours. In 5 subjects electrocardiographic observations were made immediately after their arrival at high altitudes; in the other 8, studies were made after 12 hours, and again on the fourth, eighth, twelfth, and sixteenth days, with prolonged observation up to 4 weeks in 3 subjects of this group. Finally, these 8 subjects were taken back to sea level where new observations were made at the time of their arrival and on the fourth, eighth and sixteenth days thereafter. All the tracings were obtained under basal conditions, employing a Sanborn Viso-Cardiette, Model 52. Standard leads, augmented unipolar limb leads, precordial leads, and additional right and high thoracic leads were taken. For vectorial determinations a model described in a previous work was used.3 In this model the sagittal plane is seen from the left and the horizontal plane from above, the latter being divided into two areas, one anterior positive, and the other posterior negative; the left posterior quadrant is between 0” and -90°, and the right posterior quadrant is between -90” and f 180”. From
the Department Biology, University This work was supported tract AF 18(600)-174. Received for publication Andean
of Pathological of San Marco% by the School May
Physiology, and the Faculty of Medicine, of Aviation Medicine,
1. 1958. 493
Heart Laboratory Lima, Peru. USAF, Randolph
of the
Institute
Field,
Tex.,
of Con-
494
PEGALOZA,
ECHEVARRiA,
MARTICORENA,
AND
Am. Heart J. October, 1958
GAMBOA
RESULTS
Heart Rate.-No significant variation of the heart rate was observed immediately after arrival at high altitude. Twelve hours later the heart rate increased, the highest values being noted between 4 and 8 days of residence at the altitude. Later, the heart rate decreased, and when the subjects returned to sea level, values similar to those of the initial control were obtained after 4 to 8 days (Table I and Fig. 1). I.
TABLE
OBSERVATIONSONTHE
HEART
PER MINUTE)
RATE(BEATS
1
2
60
70
SUBJECTS
Lima 12 hours 4 days 8 days 12 days 16 days Lima
10”: _-
8 days
107 91 71
3
___
80 90
-__-
72
----
100 95
57
60
----
72 60
100 90
_-
70
67
55
I
-
i
II.
TABLE
SUBJECTS
73
8:
-__--
65
.&P VECTOR
CHANGESOF
2
1 I
3
4
5
6
7
8
+6:’ +60”
f7.5”
+50”
I
+55”
Lima Morococha (16 days) Lima (8 days)
0”
f75”
III.
SfiQRS PROJECTION
HORIZONTAL
$20” o
OF QRS
CHANGES
+60;
+6$
$55”
TABLE
FRONTAL
5 I 6 I 7 ! 8
4
COMPLEX
SffQRS PROJECTION
TRANSITIONAL ZONE
-
SUBJECTS L
M
L
L
___-
M
L
-___
- 70” -20” - 40” - 40” -445” -60” - 60” ?
- 70” - 30” - 70” -665” -5.5” -8.5” - 60” ?
- 70” - 30” -5.5” -60” -45” -85” - 70” ?
~.--
VC
vs-ve v2-v3 v:v, v3-v4 v3-VI v3-v4 V4R 4
V-VI
V,\i”V,
Y3
VPV, Va-V, vrv4
V% v3-v4 v3-v4
v: r
VhR--+vS
were
obtained
V4R'V4
i L = Lima.
The
results
corresponding
to the
return
from
high
altitudes
8 days
after
return. M = Morococha. in this place.
The
data
correspond
to the
observations
made
on the sixteenth
day
of residence
E;r; “4”
EARLY
ECG
CHANGES
AT HIGH
ALTITUDES
495
Fig. I.--Subject 1. A, Electrocardiogram obtained in Lima, at sea level. B, ECG on the eighth day of residence in Morococha (at an altitude of 14,900 feet). C. ECG 8 days after return to sea level. Variations in the heart rate and changes of the AP vector can be observed.
Fig. Z.-Subject 6. A, The AP vector points toward 0’ on the eighth day of residence in Morococha. B. A moment later the unipolar limb leads show the iiP vector placed at +65O. C, Four days later, with the subject still in Morococha. the AP vector has returned to 0”.
496
PE%ALOZA,
ECHEVARRiA,
MARTICORENA,
AND
GAMBOA
Am. Heart J. October, 1958
P-R, QRS, and Q-1’ Intervals.-Slight variations of P-R and Q-T intervals No significant changes were related to the changes observed in the heart rate. of the QRS interval were found.
Fig. 3.-Subject 8. On the sixteenth day of residence in Morococha deviation can be noted. The T wave is negative from Lead V~R up to Lead an elevation and upward convexity in the same leads, and the transitional All these changes disappeared when the ward the left precordial leads. (E and F).
(D) left and backward SAT Va; the RS-T segment shows zone of QRS has shifted tosubject returned to sea level
P Wave.-No changes occurred immediately after the arrival at high altitude. Afterward, positional changes of the AP vector (Table II) and modifications of the P-wave direction in Leads III, aVr, and sometimes in Leads II and aVr,, were observed in some subjects. These changes were unstable, the variations occurring from one day to the next and even during the same observation (Fig. 2).
EARLY
ECG
CHANGES
AT
HIGH
ALTITI’DES
497
When the subjects returned to sea level, the AP vector and the direction of the P wave recovered their original characteristics; this occurred after 1 to 2 weeks. QRS Complex.-No variations were observed immediately after the subjects arrived at high altitude. Later, the following changes were observed in most cases: (1) The transitional zone shifted toward the left precordial leads (Table III). (2) The SAQRS vector shifted slightly to the right and backward.* (3)
Big. I.-Subject 7. On the eighth day of residence in Morococha (C) the T wave is negative from in extremity leads. The RS-T segment exhibits a slight Lea ,d V3a to Lead V4, and it shows low voltage these changes disappeared while and upward convexity in Leads V2, Va. and Vq. Afterward, El01 ration was still in Morococha (I> and E). Variations of the .&P vector and slight changes of the the subject also. QRS complex can be observed
high ward
*Only in one subject (Case altitudes. It is well known SAQRS deviation determines
4) was left AQRS deviation observed: -5O that when the AQRS vector is located between left AQRS shift on the frontal plane.
at sea level and -40’ at O0 and -90”. the back-
498
PE%ALOZA,
ECHEVARRiA,
MARTICORENA,
AND
Am. Heart J. October, 195X
GAMBOA
The S wave increased its voltage slightly in Leads I and aVL and in the left precordial leads. (4) The R wave increased its voltage slightly in Leads III 1 to 2 weeks after the and aVr (Figs. 3 and 4). These changes disappeared subjects returned to sea level. TABLE
IV.
CHANGES
1
SUBJECTS
IN THE
2
HORIZONTAL
3
OF SAT
PROJECTION
4
6
5 ~
Lima Morococha (16 days) Lima (16 days)
+20” +45” +30”
+60” +60” +60”
$55” $55” $55”
+40° +25” +40”
+SO” i-30” +55”
7*
8
i +.55” +20” +45”
*In this subject the greatest backward SAT deviation (-60°, and negative was observed on the eighth day of residence at Morococha. The ventricular became normal during the following 2 weeks of residence in this place.
+35” +lO” +25”
T wave up repoladzation
$45” - 60” +45” to Lead V4) process
RS-T Segment and T Wave.-Immediate changes after arrival at high altitudes were not noted. Afterward, in most cases the T wave showed an abnormal contour in the right precordial leads. Some few days later the T wave became negative and the RS-T segment showed a slight elevation and upward convexity in the same leads (Figs. 3 and 4). The forward SAT orientation decreased, not varying its frontal projection* (Table IV). When the SAT deviation was slight, the T wave was negative in Leads V 4R and VBs and sometimes in Lead Vi. On the other hand, when the SAT vector shifted to a backward position, negative T waves were observed in the right and medial precordial leads up to Lead Va (Figs. 3 and 4). In only one case was regression of the changes observed in the last 2 weeks of residence at high altitudes (Fig. 4). When the subjects returned to sea level the ventricular repolarization process became normal again in all cases in the course of 1 to 2 weeks. DISCUSSION
Heart Rate.-A rise in the heart rate was the first circulatory response produced by the ascent to high altitude. After the first week the heart rate decreased, but figures similar to those at sea level were not obtained. In a previous work an important decline in the heart rate was only observed after 30 to 60 days of residence at high altitudes, with bradycardia and sinus arrhythmia in some of cases. i The decline in the heart rate is probably related to the preponderance the vagal tone4 and to the development of more definitive mechanisms of adaptation, cardiopulmonary5 and hematite-8 in nature. Auricular Activation Process.-The variations observed in the mean direction of the auricular activation process are apparently related to a wandering pacemaker in the sinoatrial node, or to synchronous activity, in some periods, of the sinus node and the sinocoronary node. g The wandering pacemaker is probably determined by the modifications of the vagal tone. ation
*Only in Case on the frontal
8, the subject who showed the greatest plane observed: + 15’ at sea level and
backward SAT deviation, -30” at high altitudes.
was moderate
devl-
ieli%z“4”
EARLY
ECG
CHANGES
AT
HIGH
ALTITUDES
499
Ventricular Activation Process.-In a previous investigation important changes of the QRS complex were observed after 1 year of residence at high altitudes, and these changes were ascribed to two factors: (1) variations in the cardiac position, and (2) a moderate development of right ventricular hypertrophy, the latter being a consequence of pulmonary hypertension.’ In the native residents of high altitudes the QRS complex shows signs of right ventricular hypertrophy,lO and in the same subjects pulmonary hypertension has been proved6 and right ventricular hypertrophy verified anatomically.” When these subjects are brought to sea level the QRS changes regress slowly,i2 as occurs in some heart diseases after surgical treatment. In the present investigation the QRS changes are early and slight, and they promptly disappear when the subjects return to sea level. Therefore, it is probable that these changes are fundamentally related to variations in the cardiac position : clockwise rotation around the long axis of the heart with backward rotation of the apex. This change of the cardiac position would be determined in part by the hyperventilation observed at high altitudes,13 and in part by the subacute overloading of the right ventricle as a consequence of the modifications of the pulmonary circulation in an environment of anoxic anoxia.5J4-r’ The short time of residence at high altitudes is insufficient for determination in these subjects of the development of an incipient right ventricular hypertrophy. Nevertheless, on the basis of recent experimental data,2 this possibility cannot be discounted. Ventricular Recovery Process.LThe SAT deviation to the left, backward, and downward (upward in only one case), and the negative T waves in the right precordial leads, suggest the possibility of right ventricular ischemia,12 which would be related to subacute overloading of the right ventricle produced by the new conditions of the pulmonary circulation as a result of the anoxic anoxia.6J4-17 The changes in the T wave can be observed from the first days of residence at high altitude, and these changes are similar to those occurring in the residents when they lose their adaptation.‘O Therefore, it is probable that the changes observed in the present investigation indicate delayed or impaired adaptation to the high altitudes, The duration of these changes is quite variable: the Twave changes regress in less than a month in some subjects, while in others the changes persist after 1 year of residence. * This variable behavior would depend on a differing capacity for adaptation to the life at high altitudes. SUMMARY
1. Electrocardiographic observations were made in subjects taken from sea level to high altitudes, where they remained from 16 to 30 days. The first changes were observed a few hours after the arrival at high altitude, and the modifications were evident some days later. The changes disappeared 1 to 2 weeks after the subjects returned to sea level. 2. The following changes were observed: (a) variations of the AP vector, which are probably related to wandering pacemaker in the sinus node; (b) changes of the QRS complex, which are explained by variations in the cardiac position; and (c) modifications of the ventricular recovery process, which are prob-
500
PEfiALOZA,
ECHEVARRiA,
MARTICORENA,
AND
GAMBOA
Am. Heart J. October, 1958
ably related to subacute overloading of the right ventricle and to right ventricular ischemia, as a consequence of the modifications of the pulmonary circulation in an environment of anoxic anoxia. REFERENCES
1. 2. 3. 4. 5. 6. 7. 8.
9. 10. 11. 12. 13. 14. 15. 16. 17.
Pefialoza, D., and Echevarria, M.: AM. HEART J. 54:811, 1957. Valdivia, E.: Circulation Res. 5:612, 1957. Peiialoza, D., and Tranchesi, J.: AM. HEART J. 49:51, 1955. Aste-Salazar, H.: An. Fat. Med. Lima 19:226, 1936. Rotta, A., Gnepa, A., Hurtado, A., Velasquez, T., and Chbvez, R.: 9:328, 1956. Hurtado, A., Merino, C., and Delgado, E.: Arch. Int. Med. 75:284, 1945. Hurtado, A., and Aste-Salazar, H.: J. Appl. Physiol. 1:304, 1948. Hurtado, A., Velasquez, T., Reynafarje, C., Lozano, R., Chlvez, R., Reynafarje, B., Sanchez, C., and Mufioz, J.: Mechanisms of Natural Studies on the Native Resident of Morococha, Peru, at an Altitude Report to the School of Aviation Medicine! USAF, Ran$o!ph Fiel$, Latouz,I., and Puech, P.: filectrocardlographle Endo-Cavltau-e, Parls,
J. Appl.
Physiol.
Aste-Salazar, H., Acclimatization. of 14,900 Feet. 1956. 1957, Masson et
Pefialozk,’ D.: The Electrocardiogram at High Altitudes: Scalar and Vectorial Observations. Paper presented at the XII Congress0 da Sociedade Brasileira de Cardiologia, SHo Paulo, July, 1955. Campos, J.: Report to the USAF School of Aviation Medicine, 1956. (Not published.) Peiialoza, D., et. al.: Unpublished observations. Hurtado, A. : Unpublished observations. Motley, L. H., Cournand, A., WerkG, L., Himmelstein, ,4., and Dresdale, D.: Am. J. Physiol. 150:315, 1947. Aviado, D. M., Jr., Cerletti, A., Alanis, J., Bulle, P. H., and Schmidt, C. F.: Am. J. Physiol. 169:460, 1952. Hurlimann, A., and Wiggers, C. J.: Circulation Res. 1:230, 1953. Cournand, A.: Cardiologia 10:429, 1955.
to High
Changks
Produced
by
Altitudes
Dante Pefialoza, M.D., Max Echevarria, Rat21 Gamboa, M.D., Lima, Peru
M.D.,
Emilio
Marticorena,
M.D.,
and
In a previous study 10 subjects were taken from sea level to high altitudes; where observations were carried out, first, after 1 month of residence and, then, periodically for a whole year. During the progressive acclimatization, changes in the electrocardiogram were observed which resembled, at least in part, the electrocardiographic characteristics of the native residents of high altitudes.1 Nevertheless, the early electrocardiographic response to anoxic anoxia determined by the ascent to high altitudes was not studied. On the other hand, however, recent experimental observations demonstrate that early right ventricular hypertrophy can be produced in guinea pigs exposed for several weeks to simulated high altitudes.2 Therefore, we believed that new investigations should be performed on man in order to study the early electrocardiographic changes produced by the ascent to high altitudes. MATERIAL
AND
METHODS
Thirteen normal men between the ages of 17 and 21 years were studied. In Lima, at sea level, an electrocardiogram was recorded. Afterward the subjects were taken by motorcar to Morococha, at an altitude of 4,540 meters (14,900 feet); the ascent took nearly 4 hours. In 5 subjects electrocardiographic observations were made immediately after their arrival at high altitudes; in the other 8, studies were made after 12 hours, and again on the fourth, eighth, twelfth, and sixteenth days, with prolonged observation up to 4 weeks in 3 subjects of this group. Finally, these 8 subjects were taken back to sea level where new observations were made at the time of their arrival and on the fourth, eighth and sixteenth days thereafter. All the tracings were obtained under basal conditions, employing a Sanborn Viso-Cardiette, Model 52. Standard leads, augmented unipolar limb leads, precordial leads, and additional right and high thoracic leads were taken. For vectorial determinations a model described in a previous work was used.3 In this model the sagittal plane is seen from the left and the horizontal plane from above, the latter being divided into two areas, one anterior positive, and the other posterior negative; the left posterior quadrant is between 0” and -90°, and the right posterior quadrant is between -90” and f 180”. From
the Department Biology, University This work was supported tract AF 18(600)-174. Received for publication Andean
of Pathological of San Marco% by the School May
Physiology, and the Faculty of Medicine, of Aviation Medicine,
1. 1958. 493
Heart Laboratory Lima, Peru. USAF, Randolph
of the
Institute
Field,
Tex.,
of Con-
494
PEGALOZA,
ECHEVARRiA,
MARTICORENA,
AND
Am. Heart J. October, 1958
GAMBOA
RESULTS
Heart Rate.-No significant variation of the heart rate was observed immediately after arrival at high altitude. Twelve hours later the heart rate increased, the highest values being noted between 4 and 8 days of residence at the altitude. Later, the heart rate decreased, and when the subjects returned to sea level, values similar to those of the initial control were obtained after 4 to 8 days (Table I and Fig. 1). I.
TABLE
OBSERVATIONSONTHE
HEART
PER MINUTE)
RATE(BEATS
1
2
60
70
SUBJECTS
Lima 12 hours 4 days 8 days 12 days 16 days Lima
10”: _-
8 days
107 91 71
3
___
80 90
-__-
72
----
100 95
57
60
----
72 60
100 90
_-
70
67
55
I
-
i
II.
TABLE
SUBJECTS
73
8:
-__--
65
.&P VECTOR
CHANGESOF
2
1 I
3
4
5
6
7
8
+6:’ +60”
f7.5”
+50”
I
+55”
Lima Morococha (16 days) Lima (8 days)
0”
f75”
III.
SfiQRS PROJECTION
HORIZONTAL
$20” o
OF QRS
CHANGES
+60;
+6$
$55”
TABLE
FRONTAL
5 I 6 I 7 ! 8
4
COMPLEX
SffQRS PROJECTION
TRANSITIONAL ZONE
-
SUBJECTS L
M
L
L
___-
M
L
-___
- 70” -20” - 40” - 40” -445” -60” - 60” ?
- 70” - 30” - 70” -665” -5.5” -8.5” - 60” ?
- 70” - 30” -5.5” -60” -45” -85” - 70” ?
~.--
VC
vs-ve v2-v3 v:v, v3-v4 v3-VI v3-v4 V4R 4
V-VI
V,\i”V,
Y3
VPV, Va-V, vrv4
V% v3-v4 v3-v4
v: r
VhR--+vS
were
obtained
V4R'V4
i L = Lima.
The
results
corresponding
to the
return
from
high
altitudes
8 days
after
return. M = Morococha. in this place.
The
data
correspond
to the
observations
made
on the sixteenth
day
of residence
E;r; “4”
EARLY
ECG
CHANGES
AT HIGH
ALTITUDES
495
Fig. I.--Subject 1. A, Electrocardiogram obtained in Lima, at sea level. B, ECG on the eighth day of residence in Morococha (at an altitude of 14,900 feet). C. ECG 8 days after return to sea level. Variations in the heart rate and changes of the AP vector can be observed.
Fig. Z.-Subject 6. A, The AP vector points toward 0’ on the eighth day of residence in Morococha. B. A moment later the unipolar limb leads show the iiP vector placed at +65O. C, Four days later, with the subject still in Morococha. the AP vector has returned to 0”.
496
PE%ALOZA,
ECHEVARRiA,
MARTICORENA,
AND
GAMBOA
Am. Heart J. October, 1958
P-R, QRS, and Q-1’ Intervals.-Slight variations of P-R and Q-T intervals No significant changes were related to the changes observed in the heart rate. of the QRS interval were found.
Fig. 3.-Subject 8. On the sixteenth day of residence in Morococha deviation can be noted. The T wave is negative from Lead V~R up to Lead an elevation and upward convexity in the same leads, and the transitional All these changes disappeared when the ward the left precordial leads. (E and F).
(D) left and backward SAT Va; the RS-T segment shows zone of QRS has shifted tosubject returned to sea level
P Wave.-No changes occurred immediately after the arrival at high altitude. Afterward, positional changes of the AP vector (Table II) and modifications of the P-wave direction in Leads III, aVr, and sometimes in Leads II and aVr,, were observed in some subjects. These changes were unstable, the variations occurring from one day to the next and even during the same observation (Fig. 2).
EARLY
ECG
CHANGES
AT
HIGH
ALTITI’DES
497
When the subjects returned to sea level, the AP vector and the direction of the P wave recovered their original characteristics; this occurred after 1 to 2 weeks. QRS Complex.-No variations were observed immediately after the subjects arrived at high altitude. Later, the following changes were observed in most cases: (1) The transitional zone shifted toward the left precordial leads (Table III). (2) The SAQRS vector shifted slightly to the right and backward.* (3)
Big. I.-Subject 7. On the eighth day of residence in Morococha (C) the T wave is negative from in extremity leads. The RS-T segment exhibits a slight Lea ,d V3a to Lead V4, and it shows low voltage these changes disappeared while and upward convexity in Leads V2, Va. and Vq. Afterward, El01 ration was still in Morococha (I> and E). Variations of the .&P vector and slight changes of the the subject also. QRS complex can be observed
high ward
*Only in one subject (Case altitudes. It is well known SAQRS deviation determines
4) was left AQRS deviation observed: -5O that when the AQRS vector is located between left AQRS shift on the frontal plane.
at sea level and -40’ at O0 and -90”. the back-
498
PE%ALOZA,
ECHEVARRiA,
MARTICORENA,
AND
Am. Heart J. October, 195X
GAMBOA
The S wave increased its voltage slightly in Leads I and aVL and in the left precordial leads. (4) The R wave increased its voltage slightly in Leads III 1 to 2 weeks after the and aVr (Figs. 3 and 4). These changes disappeared subjects returned to sea level. TABLE
IV.
CHANGES
1
SUBJECTS
IN THE
2
HORIZONTAL
3
OF SAT
PROJECTION
4
6
5 ~
Lima Morococha (16 days) Lima (16 days)
+20” +45” +30”
+60” +60” +60”
$55” $55” $55”
+40° +25” +40”
+SO” i-30” +55”
7*
8
i +.55” +20” +45”
*In this subject the greatest backward SAT deviation (-60°, and negative was observed on the eighth day of residence at Morococha. The ventricular became normal during the following 2 weeks of residence in this place.
+35” +lO” +25”
T wave up repoladzation
$45” - 60” +45” to Lead V4) process
RS-T Segment and T Wave.-Immediate changes after arrival at high altitudes were not noted. Afterward, in most cases the T wave showed an abnormal contour in the right precordial leads. Some few days later the T wave became negative and the RS-T segment showed a slight elevation and upward convexity in the same leads (Figs. 3 and 4). The forward SAT orientation decreased, not varying its frontal projection* (Table IV). When the SAT deviation was slight, the T wave was negative in Leads V 4R and VBs and sometimes in Lead Vi. On the other hand, when the SAT vector shifted to a backward position, negative T waves were observed in the right and medial precordial leads up to Lead Va (Figs. 3 and 4). In only one case was regression of the changes observed in the last 2 weeks of residence at high altitudes (Fig. 4). When the subjects returned to sea level the ventricular repolarization process became normal again in all cases in the course of 1 to 2 weeks. DISCUSSION
Heart Rate.-A rise in the heart rate was the first circulatory response produced by the ascent to high altitude. After the first week the heart rate decreased, but figures similar to those at sea level were not obtained. In a previous work an important decline in the heart rate was only observed after 30 to 60 days of residence at high altitudes, with bradycardia and sinus arrhythmia in some of cases. i The decline in the heart rate is probably related to the preponderance the vagal tone4 and to the development of more definitive mechanisms of adaptation, cardiopulmonary5 and hematite-8 in nature. Auricular Activation Process.-The variations observed in the mean direction of the auricular activation process are apparently related to a wandering pacemaker in the sinoatrial node, or to synchronous activity, in some periods, of the sinus node and the sinocoronary node. g The wandering pacemaker is probably determined by the modifications of the vagal tone. ation
*Only in Case on the frontal
8, the subject who showed the greatest plane observed: + 15’ at sea level and
backward SAT deviation, -30” at high altitudes.
was moderate
devl-
ieli%z“4”
EARLY
ECG
CHANGES
AT
HIGH
ALTITUDES
499
Ventricular Activation Process.-In a previous investigation important changes of the QRS complex were observed after 1 year of residence at high altitudes, and these changes were ascribed to two factors: (1) variations in the cardiac position, and (2) a moderate development of right ventricular hypertrophy, the latter being a consequence of pulmonary hypertension.’ In the native residents of high altitudes the QRS complex shows signs of right ventricular hypertrophy,lO and in the same subjects pulmonary hypertension has been proved6 and right ventricular hypertrophy verified anatomically.” When these subjects are brought to sea level the QRS changes regress slowly,i2 as occurs in some heart diseases after surgical treatment. In the present investigation the QRS changes are early and slight, and they promptly disappear when the subjects return to sea level. Therefore, it is probable that these changes are fundamentally related to variations in the cardiac position : clockwise rotation around the long axis of the heart with backward rotation of the apex. This change of the cardiac position would be determined in part by the hyperventilation observed at high altitudes,13 and in part by the subacute overloading of the right ventricle as a consequence of the modifications of the pulmonary circulation in an environment of anoxic anoxia.5J4-r’ The short time of residence at high altitudes is insufficient for determination in these subjects of the development of an incipient right ventricular hypertrophy. Nevertheless, on the basis of recent experimental data,2 this possibility cannot be discounted. Ventricular Recovery Process.LThe SAT deviation to the left, backward, and downward (upward in only one case), and the negative T waves in the right precordial leads, suggest the possibility of right ventricular ischemia,12 which would be related to subacute overloading of the right ventricle produced by the new conditions of the pulmonary circulation as a result of the anoxic anoxia.6J4-17 The changes in the T wave can be observed from the first days of residence at high altitude, and these changes are similar to those occurring in the residents when they lose their adaptation.‘O Therefore, it is probable that the changes observed in the present investigation indicate delayed or impaired adaptation to the high altitudes, The duration of these changes is quite variable: the Twave changes regress in less than a month in some subjects, while in others the changes persist after 1 year of residence. * This variable behavior would depend on a differing capacity for adaptation to the life at high altitudes. SUMMARY
1. Electrocardiographic observations were made in subjects taken from sea level to high altitudes, where they remained from 16 to 30 days. The first changes were observed a few hours after the arrival at high altitude, and the modifications were evident some days later. The changes disappeared 1 to 2 weeks after the subjects returned to sea level. 2. The following changes were observed: (a) variations of the AP vector, which are probably related to wandering pacemaker in the sinus node; (b) changes of the QRS complex, which are explained by variations in the cardiac position; and (c) modifications of the ventricular recovery process, which are prob-
500
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Am. Heart J. October, 1958
ably related to subacute overloading of the right ventricle and to right ventricular ischemia, as a consequence of the modifications of the pulmonary circulation in an environment of anoxic anoxia. REFERENCES
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