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Beyond clean arteries
MADAM A's case was both tragic and heart-wrenching. She had perfectly clean heart arteries and yet had an enlarged and weakened heart. Her condition is termed as dilated cardiomyopathy (DCM) - a generic term used for heart conditions where the heart is swollen, has damaged heart muscles and decreased heart pumping function.
She was a middle-aged woman who was admitted to hospital for recent onset of shortness of breath and was found to have a swollen and severely weakened heart.
She was in the pink of health prior to the admission. During the hospitalisation, despite all possible measures, her condition continued to deteriorate and a biopsy of the heart muscle showed that there was such widespread destruction of the heart muscle cells that hardly any were visible.
Sadly, the relentless destruction of her heart muscle by uncontrollable inflammation and a fulminant viral infection eventually led to her demise.
Mr B had a similar condition except that he survived the initial assault and was left with a swollen and scarred heart. Given the widespread scarring, he had recurrent episodes of abnormal heart rhythm.
He was advised on the implantation of an automatic implantable cardioverter defibrillator (AICD) to "reset" his episodes of life-threatening heart rhythm to normal (defibrillation therapy). However, he wanted to wait till the next clinic visit to make a decision.
Unfortunately, his hesitation was to cost him dearly and he never made it to the next visit. Patients with DCM die from either a severely weakened heart pump resulting in heart failure as in Madam A's case or from sudden onset of a life-threatening heart rhythm as in Mr B's case.
Lady Luck smiled on Madam C. She had been admitted to hospital for heart failure last year and continued to have recurrent breathlessness, episodic low blood pressure and palpitations. She had DCM and, surprisingly, no assessment was performed to determine the presence of life-threatening abnormal heart rhythms.
When she was put on ambulatory continuous heart rhythm monitoring (Holter monitoring) a fortnight ago, she had multiple episodes of a life-threatening heart rhythm called ventricular tachycardia which can lead to sudden death. Whenever she had ventricular tachycardia, her blood pressure dropped. Fortunately, appropriate medication and the implantation of an AICD have reduced her risk of sudden death significantly.
Understanding the potential causes of DCM is important in preventing the onset of the disease. Familial genetic DCM runs in families and those with first degree relatives with DCM should be cognisant of the possibility of genetic transmission of the disease. Remember the common advice dished out by your family doctor when you have fever and symptoms of common cold - do not do vigorous exercise until you recover?
This advice is still sound as viral infection and inflammation are important causes of DCM. Current evidence suggests that an excessively vigorous immune response to a virus may have the unintended effect of unleashing such overwhelmingly destructive processes to overcome the virus that they cannot be controlled.
This can have spillover effects onto "normal" heart muscle cells, causing destruction of healthy cells. Destruction of heart muscle cells can also be caused by certain "aggressive" viruses that have a predilection for the heart muscle, resulting in its inflammation.
Other medical conditions that can cause DCM include excessive thyroid hormones (causing loss of weight, palpitations and hand tremors) or pregnancy-related cardiomyopathy. Lifestyle habits such as prolonged, excessive consumption of alcohol and the improper use of harmful drugs (such as cocaine and amphetamines) are preventable causes of DCM.
For those under chemotherapy for cancer, the use of certain agents such as doxorubicin, daunorubicin, cyclophosphamide and trastuzumab can impair heart pump function. Patients on these drugs need monitoring of the heart pump function to ensure that they do not end up having their cancer "cured" only to die of heart failure. The death rate for "bad" hearts with symptoms that affect daily activities can be as high as 50 per cent in the first year.
Getting a swollen and weak heart is bad news and DCM often carries a bad prognosis if untreated. The twin evils of DCM are poor heart pump and abnormal heart rhythms - both of which are potential harbingers of death. The outcomes for those with weak hearts and heart failure have gradually been improving. In heart failure studies, based on data from the placebo group (patients given a placebo instead of heart failure medication), for those who are symptomatic on mild exertion or at rest, about half will die by the end of the first year. For those heart failure patients with minimal symptoms, about one quarter will die by the end of one year.
Data from Framingham studies and the Mayo Clinic has shown that over the last decades, the death rates have gradually been decreasing for those with weak hearts. Based on data of about one decade ago, one-year death rates have declined to as low as about 21 per cent for men and 17 per cent for women. Similarly, five-year death rates have also declined to as low as about 50 per cent for men and about 45 per cent for women.
The right diagnosis
If you have shortness of breath on exertion, an ultrasound of the heart (echocardiogram) will help to establish whether there is swelling of the heart chambers and impairment of heart pump function. If they are present, before coming to the conclusion that the condition is DCM, it is essential to at least do a computed tomography scan of the hear
This scan can be performed safely as an outpatient procedure within seconds and has a virtually 100 per cent accuracy in excluding the presence of significant heart artery disease.
"Treatable" causes such as excessively high thyroid hormones, drug-induced causes and excessive alcohol can be confirmed by history and blood tests.
The best outcome
Getting the best prognosis means battling the twin evils of DCM and preventing the poor heart pump and abnormal heart rhythms from shortening the life span and impairing the quality of life. If the doctor confirms the diagnosis of DCM, it will be necessary to do Holter monitoring as in the case of Madam C to determine whether there is any evidence of life threatening heart rhythms.
This is often a cause of sudden death in DCM patients as in Mr B's case. The life threatening heart rhythm is usually ventricular tachycardia in which the electrical impulse is intermittently generated by the irritable and scarred heart muscle of the lower heart chambers rather than the pacemaker of the heart which is situated at the right upper heart chamber. Recurrent prolonged episodes of ventricular tachycardia can lead to the onset of ventricular fibrillation in which the heart "quivers" rather than contracts, leading to little or no blood being pumped from the heart chambers. This situation is also commonly known as cardiac arrest. Without immediate emergency treatment, death from ventricular fibrillation is certain.
While medication to control the heart rhythm may reduce the risk of sudden death, the current 2012 guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities by the American College of Cardiology Foundation, American Heart Association and the Heart Rhythm Society recommend the implantation of an AICD to reduce sudden death.
The AICD is a pacemaker which is able to detect life threatening heart rhythms and "reset" the heart rhythm by passing small electrical impulses through the heart muscle.
Treating the weakened heart pump means reducing stress on the heart such as treating any existing high blood pressure, avoiding excessive consumption of liquids and taking heart failure medication.
While serial measurements of the heart chamber sizes and the heart pump function by echocardiogram can provide objective assessment of response to treatment, a simpler way is to measure the blood B-type natriuretic peptide (brain natriuretic peptide or BNP).
BNP is a protein stored in the inactive form, pro-BNP, in the heart muscle cells. Pro-BNP is released into the blood when the heart chambers are subjected to increase in volume or when there is excessive pressure in the heart. Once pro-BNP is released into the blood, it is cleaved into a non-active longer segment (N-terminal segment or NT-proBNP) and a shorter active protein chain, BNP. Hence, serial measurements of either NT-proBNP or BNP are often used by physicians to gauge the response of heart failure patients to treatment.
Finally, do remember that your heart arteries can be as clean as a whistle but you may still get heart disease. Hence, if you have recent or progressive onset of shortness of breath, do get your heart checked.
- Dr Lim is medical director at the Singapore Heart, Stroke & Cancer Centre. He is a professor at Fudan University, Shanghai and vice-president of both the World Chinese Doctors Association and the World Federation of Chinese Cardiovascular Physicians. He is also founding editor of Heart Asia, a journal of the British Medical Journal Publishing Group
- This series is brought to you by Heart, Stroke and Cancer Centre. It is produced on alternate Saturdays.
- To read more of Dr Lim's previous health-related articles, visit: http://www.btinvest.com.sg/specials/shscc