Influenza affects the heart in various ways. The influenza toxins may harm the heart muscle directly; generally, however, the toxic influence is limited to the cardiac nervous apparatus. Indirect influence is exerted upon the heart by the elevation of temperature, but more particularly by the affection of pulmonary circulation characteristic of influenza, viz., hyperemia of the lungs, capillary bronchitis, and pneumonia, processes which, in turn, acting partly mechanically by disturbance of the circulation and partly chemically by the increase of carbon dioxid in the blood, influence the heart and consequently the whole circulation.
' We will not here enter into any exhaustive discussion in what manner influenza and its pulmonary complications influence the heart, the circulation, and the composition of the blood. We will confine ourselves to a few important points.
The pulse rate corresponds, as a rule, to the height of the fever, but the degree of tachycardia is usually proportionately higher than the rise of temperature, a point which, in agreement with Drasche, Vester dahl, Sansom, and Bahrdt, I emphasized some time ago in opposition to some other observers. Especially in those cases of diffuse bronchitis and bronchiolitis with dyspnea and cyanosis there is regularly a very marked tachycardia, notwithstanding an afebrile or subfebrile course of the disease. Frequently the pulse shows a marked cardiac weakness, quite disproportionate to the slight fever which is revealed on the sphygmogram (Pribram, our lectures) by a marked dicrotism.
Bradycardia occurs in influenza more often than in any other acute infectious disease. Here again the neurotoxic character of influenza is manifested, for we cannot assign any other cause for this remarkable, often perfebrile, bradycardia, or for the afebrile tachycardia in simple uncomplicated influenza, than the influence of the toxin on the vagus or other centers which regulate the cardiac beat.
Influenzal bradycardia was mentioned by Rutty (1762), by Hod son (1800), in the recent pandemic by Stintzing, Strumpell, Hefforn, Barthelemy, Ruhemann, Ward, Farbstein, and by ourselves. In the garrison hospital of Munich, among 275 patients, 46 per cent, of them were found to have " a marked slowing of the pulse, frequently combined with irregularity, and lasting from ten to twelve days."
Bradycardia may be either absolute (a pulse of 48 to 60 with an afebrile or subfebrile course) or relative (pulse of 80 to 120, with high fever-from 39° to 41° C). It even occurs in severe influenza pneumonia, as Rankin and ourselves pointed out.
In one such case observed by us, which occurred in an individual twenty seven years old with influenza pneumonia, we found the following numeric relations between temperature and pulse rate: 40.7°: 106; 39.8°: 96; 40.1°: 92; 39.8°: 88; 39.3°: 94, etc.
Rutty (1762) well described this phenomenon: "But in general the pulse is not quick, and even when the feverish symptoms were very high, it was often observed to be not more quick than in health."
Huchard describes as a characteristic manifestation due to "disturbed cardiac innervation" (vagus weakness) the "pouls instable," in which condition the pulse rate is rapidly increased by an alteration of posture from the recumbent to the erect-an increase such as from 80 to 120 beats. This is an old, well known phenomenon occurring especially in convalescence from febrile diseases and in "weakened hearts."
There is another occasional anomaly of influenza which requires repeated careful counting of the pulse for its detection; it is very frequently present also in epidemic cerebrospinal meningitis. This is the allorrhythmia or poikilorhythmia, in which the pulse rate is variable, constantly changing within narrow limits, so that, for instance, in eight successive quarter minutes the following numbers was counted: 25, 24, 28, 28, 26, 25, 28, 26. Heubner also emphasizes the "marked variations in pulse rate" in influenza.
Allorrhythmia forms a transition to the graver forms of arhythmia, generally combined with tachycardia and seen sometimes in uncomplicated influenza, even in young individuals.
Angina pectoris or stenocardia was observed by several authors (Rohring, Pawinski, Ruhemann, Teissier, Sansom, Huchard, Duflocq), sometimes as a transitory phenomenon during the influenza attack, but more frequently as a persistent sequela, and often in strong individuals with sound hearts and in the prime of life.
In rare cases, even in uncomplicated influenza, alarming symptoms of cardiac weakness with attacks of syncope may occur in individuals who have previously had no heart trouble, either at the acme or at the end of the attack (Teissier, Drasche). Cases of sudden death due to "cardiac paralysis" occurred most frequently during the period of convalescence. They are mentioned in the epidemics of 1729, 1732, and 1755, and recently by Pribram, Drasche, Back, and Braubach, in the reports of the Swiss Board of Health and by ourselves.
Drasche says: "Influenza has often a veritably toxic influence on the hearts of otherwise healthy individuals. Occasional irregularity of the pulse, accompanied by remarkable frequency and smallness, is often the first sign of the malignant character of the disease, which not infrequently causes sudden death by cardiac paralysis."
To our own impressions of the effects of the pandemic we gave expression at the end of the epidemic as follows: "That influenza is frequently followed by serious, long continuing, and persistent functional disturbance of the heart of a neuropathic or myopathic origin is taught by a series of recent observations; we frequently saw vigorous people in the prime of life who, some weeks after recovery from an attack of influenza, complained of shortness of breath, attacks of angina pectoris, palpitation of the heart, and inconveniences, in whom, beyond an occasional marked tachycardia or arhythmocardia with smallness of the pulse, no other signs of cardiac affection could be found. In Cologne, after the pandemic, some notable cases of sudden cardiac failure occurred in persons who, convalescent from a more or less severe influenza, had again taken up their vocations. I think it not unlikely that this was due to the influenza from which they had just recovered."